Journal of Experimental Botany

JXB Advance Access originally published online on May 12, 2006
Journal of Experimental Botany 2006 57(8):1769-1776; doi:10.1093/jxb/erj184

This Article Abstract FREE Full Text (PDF) All Versions of this Article: 57/8/1769    most recent erj184v1 E-letters: Submit a response Alert me when this article is cited Alert me when E-letters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (10) Request Permissions Disclaimer Google Scholar Articles by Pauly, N. Articles by Puppo, A. Search for Related Content PubMed PubMed Citation Articles by Pauly, N. Articles by Puppo, A. Agricola Articles by Pauly, N. Articles by Puppo, A. Social Bookmarking          What's this?

© The Author [2006]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Reactive oxygen and nitrogen species and glutathione: key players in the legume–Rhizobium symbiosis

Nicolas Pauly, Chiara Pucciariello, Karine Mandon, Gilles Innocenti, Alexandre Jamet, Emmanuel Baudouin, Didier Hérouart, Pierre Frendo and Alain Puppo^*

Interactions Plantes–Microorganismes et Santé Végétale, UMR CNRS 6192/INRA 1064/Université de Nice-Sophia Antipolis, 400, route des Chappes, BP 167, F-06903 Sophia-Antipolis, France

^*To whom correspondence should be addressed. E-mail: puppo{at}unice.fr

Received 27 January 2006; Accepted 7 March 2006

	Abstract

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
Several reactive oxygen and nitrogen species (ROS/RNS) are continuously produced in plants as by-products of aerobic metabolism or in response to stresses. Depending on the nature of the ROS and RNS, some of them are highly toxic and rapidly detoxified by various cellular enzymatic and non-enzymatic mechanisms. Whereas plants have many mechanisms with which to combat increased ROS/RNS levels produced during stress conditions, under other circumstances plants appear to generate ROS/RNS as signalling molecules to control various processes encompassing the whole lifespan of the plant such as normal growth and development stages. This review aims to summarize recent studies highlighting the involvement of ROS/RNS, as well as the low molecular weight thiols, glutathione and homoglutathione, during the symbiosis between rhizobia and leguminous plants. This compatible interaction initiated by a molecular dialogue between the plant and bacterial partners, leads to the formation of a novel root organ capable of fixing atmospheric nitrogen under nitrogen-limiting conditions. On the one hand, ROS/RNS detection during the symbiotic process highlights the similarity of the early response to infection by pathogenic and symbiotic bacteria, addressing the question as to which mechanism rhizobia use to counteract the plant defence response. Moreover, there is increasing evidence that ROS are needed to establish the symbiosis fully. On the other hand, GSH synthesis appears to be essential for proper development of the root nodules during the symbiotic interaction. Elucidating the mechanisms that control ROS/RNS signalling during symbiosis could therefore contribute in defining a powerful strategy to enhance the efficiency of the symbiotic interaction.

Key words: Glutathione, homoglutathione, Medicago truncatula–Sinorhizobium meliloti symbiosis, nitrogen fixation, reactive nitrogen species, reactive oxygen species

	Introduction

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
Reactive oxygen and nitrogen species (ROS/RNS) have been characterized as key actors in the response of plants to both biotic and abiotic stresses (for reviews, see Apel and Hirt, 2004; Delledonne, 2005). Initially, these species were only regarded as damaging to cells. Indeed, ROS and RNS are involved in degenerative processes associated with senescence and cell death. More recently, ROS and RNS species emerged as ubiquitous signalling molecules participating in the recognition of and the response to stress factors. For a signalling molecule to be effective, it needs to be produced quickly and efficiently on demand, to induce defined effects within the cell, and to be removed rapidly and effectively when no longer required. This is the case of ROS and RNS, which appear to be mainly generated by enzymes; hence, their rates and subcellular sites of production may be under metabolic control (Matamoros et al., 2003; Neill et al., 2003). It is now obvious that their role is not restricted to the stress response, but can encompass the whole lifespan of the plant, including normal growth and development stages. Moreover, ROS/RNS bioactivity is largely dependent upon their turnover, which not only includes ROS/RNS production, but also their detoxification. ROS/RNS detoxification relies on the antioxidant defence (AD), which involves enzymatic activities (catalases, superoxide dismutases, peroxidases) and antioxidant molecules (glutathione, GSH, ascorbate). Together with ROS/RNS production, AD is actively regulated in the response to environmental cues and plant development. Taken together, ROS/RNS and AD contribute to the redox balance, the modulation of which is probably crucial for physiological regulation.

The symbiosis between legumes and rhizobia is a complex process relying on finely tuned infectious and developmental events. The initial step of the symbiotic interaction is a chemical cross-talk between the plant and the bacterial partners leading to the production of bacterial nodulation factors (NF) upon sensing of the flavonoids present in root exudates. NF not only participate in bacterial infection, but also trigger the initiation of a specific developmental programme ending in the formation of a new organ, the nodule (for a review see Oldroyd et al., 2005). Nodule formation is assured by the dedifferentiation and division of root cortical cells and nodules are subsequently colonized by the bacteria released from the infection threads formed upon infection. During the last few years, significant progress has been made in understanding nod factor transduction pathways. In particular, several NF receptor candidates have been identified (Spaink, 2004). Moreover, a series of genes involved in signalling processes acting downstream of NF perception have been characterized (for a review, see Geurts et al., 2005; Stacey et al., 2006). Nevertheless, how those elements integrate to form the complex signalling network regulating symbiotic interaction is still unknown.

There is increasing evidence that ROS, RNS and/or GSH play an important role in legume–rhizobia symbiosis (Hérouart et al., 2002). As for plant–pathogen interactions, they may be important actors in the initial interaction between the two partners, which leads to the recognition of the bacteria as a partner or as a foe. Indeed, 90% of the infection threads initially formed abort in Medicago. Such abortion is achieved by a hypersensitive-like response, a well-known ROS- and RNS-regulated process during plant pathogenesis (Vasse et al., 1993; Penmetsa and Cook, 1997). The cell mitotic cycle is also tightly regulated by the cell redox balance (Vernoux et al., 2000). Therefore, nodule organogenesis may be deeply dependent on the cellular redox conditions. More generally, nodulation efficiency is highly dependent on plant fitness (Oldroyd et al., 2001), which may be modulated by ROS and RNS formation and the antioxidant content. This is important when considering that the active nodule metabolism involved in the nitrogen fixation may itself provoke the formation of ROS, which will impair nodule functioning (Puppo et al., 2005).

In this framework, current knowledge on where, when, and how ROS, RNS, and GSH participate in symbiosis regulation is summarized, and new fields are suggested for future investigations.

	Reactive oxygen species

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
ROS, which are formed in numerous cellular processes, were first described as deleterious, as they can provoke cellular damage (Halliwell and Gutteridge, 1986). It is now largely admitted that they can play a signalling role in various cellular mechanisms (Neill et al., 2002). It has been demonstrated that ROS are key players in the plant's defence system against pathogens (‘oxidative burst’; for a review see Apel and Hirt, 2004), and also in fundamental processes such as cellular growth (Foreman et al., 2003), stomatal closure (Pei et al., 2000), and in the regulation of gene expression (Neill et al., 2002; Vranova et al., 2002).

More recently, the involvement of ROS in the establishment of the legume–Rhizobium symbiosis has also been underlined, supporting the hypothesis that symbiosis and pathogeny are variations on a common theme (Baron and Zambryski, 1995). However, the situation differs according to the infection time-course. In the early stages of the symbiotic interaction, the oxidation of nitro blue tetrazolium (NBT) can be detected in infection threads, indicating that is produced during the infection process (Santos et al., 2001; Ramu et al., 2002). Moreover, this production was not observed when M. truncatula plants were inoculated with a S. meliloti nodD1ABC mutant that was unable to produce Nod factors, suggesting that they have a role in the oxidative burst (Ramu et al., 2002). By contrast, in the very early stages of the symbiotic interaction, the production of H₂O₂ appears to be inhibited by the Nod factors (Shaw and Long, 2003); in the same way, a S. meliloti nodC^– mutant, defective in Nod factor biosynthesis, showed an increase in H₂O₂ accumulation (Bueno et al., 2001). Moreover, the compatible interaction between M. sativa and S. meliloti is linked, at least in part, with an increase in antioxidant defence (particularly catalase and lipoxygenase) during the preinfection period (up to 12 h) (Bueno et al., 2001). Simultaneous treatment of an alfalfa suspension culture with yeast elicitors and S. meliloti lipopolysaccharides (LPS) was unable to induce an alkalinization of the culture medium or an oxidative burst that is systematically observed when the cells are treated with yeast elicitors alone (Albus et al., 2001). Thus, S. meliloti LPS released from the bacterial surface might function as a specific signal molecule, promoting the symbiotic interaction and suppressing a pathogenic response in the host plant, alfalfa (Albus et al., 2001).

In the later stages of the nodulation process, ROS (H₂O₂, ) can be observed in infected cells of young nodules, revealing the prolonged production of these radicals during nodule development. H₂O₂ production was detected in ultrathin sections of mature 6-week-old nodules as an electron-dense precipitate stained with cerium chloride (Santos et al., 2001; Rubio et al., 2004). Extensive cerium labelling was observed in the cell walls of infected cells and in some infection threads all around bacteria. In functioning nodules, leghaemoglobin autoxidation appears to be an important source of ROS. To avoid any deleterious effect, nitrogen-fixing nodules are fitted with a very efficient antioxidant defence (Matamoros et al., 2003). Moreover, a strong cerium precipitate can also be observed around peribacteroid and bacteroid membranes of senescent infected cells, strongly suggesting that H₂O₂ is involved in the senescence process (Alesandrini et al., 2003; Rubio et al., 2004).

However, it should be noted that ROS have not been detected in the micro-organisms progressing within the threads, suggesting that the rhizobia have an efficient antioxidant defence (Santos et al., 2001; Rubio et al., 2004). To detoxify ROS, symbiotic bacteria display a multiple enzymatic antioxidant defence that is required for the development and the functioning of symbiosis. S. meliloti possesses two superoxide dismutases that convert to O₂ and H₂O₂ (Santos et al., 2000; Hérouart et al., 2002) and three haem b-containing catalases, which are able to scavenge H₂O₂ (Hérouart et al., 1996; Ardissone et al., 2004). Two catalases are monofunctional hydroperoxidases and are regulated mainly at the transcriptional level: in the presence of H₂O₂ or in low-phosphate conditions for KatA or in the presence of paraquat (a superoxide-generating compound) and in response to environmental stresses such as heat, osmotic and ethanol shocks for KatC (Sigaud et al., 1999; Yuan et al., 2005). The H₂O₂-dependent expression of katA involves the redox-sensitive transcriptional regulator OxyR (Jamet et al., 2005), while the PhoB response regulator controls the katA transcription at a second promoter in phosphate-starved cells (Yuan et al., 2005). By contrast, KatB is a bifunctional catalase-peroxidase constitutively expressed in free-living cells, such as in planta (Jamet et al., 2003). In addition to these well-characterized enzymes, S. meliloti genome analysis suggests that this bacterium contains three alkyl hydroperoxide reductases, at least one of which is encoded by an ahpC-like gene and might use H₂O₂ in addition to alkyl hydroperoxide as a substrate (Seaver and Imlay, 2001). Other non-enzymatic scavengers such as glutathione (see below) or other enzymatic systems might account for the antioxidant machinery of rhizobia. For example, chloroperoxidase is secreted after exposure to H₂O₂ or organic hydroperoxides in S. meliloti (Barloy-Hubler et al., 2004) and a microaerobiosis-induced 2-cys peroxiredoxin (PrxS) expressed during the symbiotic interaction has been characterized in R. etli (Dombrecht et al., 2005). Moreover, it has recently been demonstrated that the levels of peroxiredoxins are decreased during nodule development and are redox regulated during nodule senescence (Groten et al., 2006).

The whole antioxidant defence is essential for optimal nodule development and maintenance. The three catalases are differentially expressed during nodule formation. The katB gene is expressed during all steps of symbiosis, whereas katC expression is only detectable in the infection threads, at the early stage of infection, and in the infection zone of the mature nodule (Jamet et al., 2003). The katA expression is restricted to the fixation zone of the mature nodule, despite a clear production of H₂O₂ around bacteria inside the infection threads (Jamet et al., 2005; Yuan et al., 2005). The presence of KatB and KatA in the bacteroid is probably related to high internal H₂O₂ generation as a consequence of the high aerobic metabolism required to produce the ATP necessary to sustain nitrogenase activity. Whereas a single mutation in one catalase gene of S. meliloti does not lead to any phenotype, a feature also observed for katG mutant strains of R. etli (Vargas Mdel et al., 2003) and B. japonicum (Panek and O'Brian, 2004), the double katB/katC and katA/katC mutants of S. meliloti are strongly impaired in nodule formation and in nitrogen-fixation activity, respectively (Jamet et al., 2003). Interestingly, the nodule formed by the katB/katC double mutant contains many infection threads. However, the bacteria are released into plant cells without peribacteroid membranes, preventing differentiation into bacteroids and leading to bacteria that directly undergo senescence. The nodules induced with the katA/katC mutant strain display a very thin fixation zone. In fact, the bacteria are correctly released from the infection threads, but the newly differentiated bacteroids rapidly become senescent. The impact of ROS production on the microsymbiont was also shown by Dombrecht et al. (2005) in the case of R. etli–Phaseolus vulgaris symbiosis, where a katG/prxS double mutant exhibited a significant reduction in nitrogen fixation.

ROS production might also have a signalling role during symbiosis. Indeed, a S. meliloti mutant overexpressing the constitutive catalase, KatB, which exhibits the highest affinity for H₂O₂ among the three catalases (Ardissone et al., 2004), was constructed in this laboratory. The katB⁺⁺ resulting strain was able to degrade H₂O₂ very rapidly and displayed an intracellular H₂O₂ concentration below that of the wild-type strain (A Jamet et al., unpublished data). In planta, the mutant displayed a delayed nodulation phenotype, Nod^d, associated with cytological modifications which are currently under investigation. These last results clearly indicate that the presence of H₂O₂ is essential for optimal symbiosis development. It still remains to define more precisely the role of H₂O₂ in the infection thread development including bacterial proliferation.

An open question concerns the enzymes responsible for enhanced ROS formation during infection and nodule organogenesis, which have not been identified yet. The superoxide radicals are formed in the infection threads (Santos et al., 2001) possibly by a membrane-bound NADPH oxidase, as observed in activated neutrophils. Indeed, inhibition of the oxidative burst with DPI (a specific suicide inhibitor of the NADPH oxidase) corroborates this hypothesis (Ramu et al., 2002; Shaw and Long, 2003; Rubio et al., 2004). Moreover, other possible sources for H₂O₂ are cell wall peroxidases, germin-like oxalate oxidases, and diamine oxidases (Wisniewski et al., 2000).

In conclusion, these data clearly show that ROS accumulation is observed during the infection process and during the degeneration of the symbiotic association. It is, however, important to note that in the first hours of the infection, the production of ROS is inhibited. This clearly indicates the complexity of the process. Moreover, as ROS are produced by the plant partner, it would also be of interest to analyse the consequences of modifying plant ROS-scavenging or ROS-producing activities on the symbiotic capacities. Furthermore, the availability of the complete sequence of the S. meliloti genome and of large collections of Medicago truncatula ESTs, as well as microarray chips for both partners, will provide the opportunity to identify target genes regulated by ROS during symbiosis in both partners.

	Reactive nitrogen species

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
Together with ROS, RNS, and in particular nitric oxide (NO), are now considered as major components of oxidative burst and redox state regulation. Indeed, NO has been shown to be a ubiquitous signalling molecule in plants, controlling physiological processes as diverse as flowering, iron homeostasis, drought response, or resistance against pathogens (for review see Neill et al., 2003). Several studies have also illustrated the major role of NO as a signal in controlling primary and adventitious root organogenesis, a developmental process which shares common features with nodule formation (Pagnussat et al., 2002; Correa-Aragunde et al., 2004). Recent advances point out that it may also be involved in legume–rhizobia symbiotic interactions.

Several studies have reported direct or indirect evidence for the production of NO during plant–symbiont interactions. Data from Shimoda et al. (2005) suggest that a rapid and transient NO production, detected with the permeant NO-sensitive probe 4,5 diaminofluorescein diacetate, occurs in Lotus japonicus roots inoculated with Mesorhizobium loti (Shimoda et al., 2005). Using the same approach, such production was not observed during M. truncatula–S. meliloti interaction. The NO production in L. japonicus may reflect a specificity of this symbiotic model. Whereas the presence of NO during the early stages of symbiosis remains puzzling, its production in mature nodules has been clearly shown. A direct detection of NO using the DAF-2DA probe has been performed by confocal microscopy in M. truncatula/S. meliloti nodules (E Baudouin et al., unpublished data). The NO production, which can be impaired with the NO scavenger carboxyPTIO, is localized in the bacteroid-containing cells of the fixing zone. These data corroborate previous studies on soybean nodules, in which the presence of NO^• complexed with leghaemoglobin (Lb), a haemoprotein ensuring the oxygen flux to the bacteroids, had been detected in soybean nodules using Electron Paramagnetic Resonance (Mathieu et al., 1998).

Several mechanisms by which NO could be produced during plant/rhizobia interactions have been proposed. The bacterial denitrification pathway could be a first candidate. Indeed, rhizobia being denitrifying bacteria can generate NO as an intermediate of the reduction of to N₂. Mesa et al. (2004) showed that Bradyrhizobium japonicum denitrification genes are expressed in the nodule fixation zone (Mesa et al., 2004). Nevertheless, using S. meliloti mutants of the denitrification pathway, it was observed that NO accumulation was not modified in nodules, which makes the participation of the denitrification process to NO production in nodules unlikely (E Baudouin et al., unpublished data). NO could also be produced by the plant partner. Recent studies have identified plant NO synthases, which can generate NO from L-arginine (Guo et al., 2003). In this respect, Cueto et al. (1996) reported the presence of NO synthase activity in the fixation zone of lupin nodules, which was impaired by the mammalian NOS inhibitor N(G)-monomethyl-L-arginine (Cueto et al., 1996). This compound also inhibited NO production observed in Medicago truncatula nodules, further implicating a NO synthase-like enzyme in NO production during symbiosis (E Baudouin et al., unpublished results). A gene encoding a putative NO synthase in M. truncatula has recently been isolated in this laboratory and its study during the symbiotic interaction is in progress (N Pauly, unpublished results). In addition to NO synthases, nitrate reductases also participate to NO production in plants. In this view, the induction of a nitrate reductase independently of nitrate in L. japonicus nodules has been reported and it would be interesting to analyse its possible involvement in NO production (Kato et al., 2003). Future studies will have to clarify whether and when these putative NO generating systems operate during symbiosis.

The question of the possible role of NO in nodules is raised. As NO has been shown to inhibit nitrogenase (Trinchant and Rigaud, 1982; Kanayama et al., 1990), its steady-state concentration should be kept low at the bacteroid level. This is also true for the RNS peroxynitrite which is formed by the combination of NO with oxygen superoxide. In this context, the presence of large amounts of the O₂ carrier leghaemoglobin, which has a high affinity for NO and can act as a NO scavenger (Herold and Puppo, 2005), may modulate NO bioactivity. This may also be a function of non-symbiotic haemoglobins, which scavenge NO in plants (Romero-Puertas et al., 2004) and which are rapidly induced upon symbiotic infection and accumulate in fixing nodules (Shimoda et al., 2005; Vieweg et al., 2005). It has recently been shown that haemoglobin overexpression in alfalfa roots efficiently prevented the inhibition of aconitase, a NO-sensitive enzyme, by exogenous and endogenous NO generation (Igamberdiev et al., 2005).The low level of free NO could function in signalling processes in nodules, where it may participate in the low oxygen response of the fixing cells. In this way, Mesa et al. (2003) showed that, in B. japonicum, NO can regulate specific transcription factors such as NnrR which control denitrification gene expression. This activation would involve the FixLJ pathway, which is activated by low oxygen concentrations and can readily fix NO (David et al., 1988; McGongile et al., 2000). Moreover, a series of genes related to the plant response to hypoxia was recently isolated in a screen for M. truncatula genes induced upon NO treatment (M De Stefano, unpublished data). As these hypoxia-related genes are also regulated in fixing L. japonicus nodules (Colebatch et al., 2004), this may extend the hypothesis of NO regulating the low oxygen response to both symbiotic partners. The availability of symbiotic partners, modified for NO production or scavenging, will open new opportunities to unravel the molecular mechanisms regulated by NO during symbiotic interactions.

	Glutathione

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
One of the major antioxidant molecules in eukaryotes is GSH, a low-molecular mass thiol implicated in antioxidant defence mainly through the ascorbate/GSH cycle. It plays a crucial role in plant defence against abiotic and biotic stresses and is also involved in heavy metal tolerance and xenobiotic detoxification. The presence of homoglutathione (-glutamylcysteine-ß-alanine; hGSH), a homologue of GSH, is one of the characteristics of leguminous plants (Frendo et al., 1999; Matamoros et al., 1999; Moran et al., 2000).

The importance of GSH and hGSH during the first steps of symbiosis between M. truncatula and S. meliloti has been examined. Using both buthionine sulphoximine (BSO), a specific inhibitor of GSH and hGSH synthesis, and transgenic roots expressing GSH synthetase and hGSH synthetase in an antisense orientation, the deficiency in GSH and hGSH synthesis appeared to inhibit the formation of the root nodules (Frendo et al., 2005). This inhibition was not correlated to a modification in the number of infection events or to a change in the expression of the Rhizobium Induced Peroxidase rip1, indicating that the low level of GSH or hGSH did not alter the first steps of the infection process. By contrast, a strong diminution in the number of nascent nodules and in the expression of the early nodulin genes, Mtenod12 and Mtenod40, was observed in GSH and hGSH-depleted plants suggesting that GSH is involved in the nodule meristem formation. Thus, GSH and hGSH appear to be essential for the proper development of the root nodules resulting from the symbiotic interaction (Frendo et al., 2005).

The genes regulated by GSH/hGSH need to be identified in order to understand the role of GSH/hGSH in nodule formation. For this purpose, a transcript profiling analysis in M. truncatula plants inoculated with S. meliloti was performed using a cDNA-Amplified Fragment Length Polymorphism (AFLP) protocol. The effect of GSH depletion by BSO was studied to investigate whether there are patterns of gene regulation that require GSH. A collection of 306 gene tags regulated at different time points during the first 4 d of the nodulation process was obtained. Of these, 91 gene tags classifiable in two clusters corresponding, respectively, to up-regulated and down-regulated genes, showed GSH-dependent expression changes. Sequence analysis and functional characterization of these gene tags which is currently being undertaken will lead to a better understanding of the role of GSH/hGSH in nodule formation (C Pucciariello et al., unpublished data).

Nodules have a strong capacity to produce ROS due to their high respiration rates, the strong reducing conditions required to reduce N₂, and the leghaemoglobin autoxidation process (Becana et al., 2000; Hérouart et al., 2002). Moreover, although this may not be true in all symbiotic systems (Groten et al., 2005), ROS have been shown to accumulate during nodule senescence (Becana and Klucas, 1992; Alesandrini et al., 2003). In this framework, the GSH/hGSH pool may have an important antioxidant role in nitrogen-fixing nodules. These organs have a high thiol content with an active glutathione-ascorbate cycle (Dalton et al., 1986; Groten et al., 2005). However, legume root nodules are characterized by an early senescence. During senescence of nodules, GSH and hGSH are found to decline (Evans et al., 1999; Matamoros et al., 2003; Groten et al., 2005). Indeed, ageing causes a 50% decrease in hGSH in soybean and pea nodules and an 82% decrease in GSH in pea nodules (Evans et al., 1999; Matamoros et al., 2003; Groten et al., 2005) with a concomitant accumulation of catalytic Fe and oxidation of thiols, lipids, proteins, and DNA (Evans et al., 1999). Moreover, this age-related decline in thiol content can be observed in mature nodules where Matamoros et al. (1999) reported the senescent zones of pea nodules having 50% less GSH and 25% less hGSH than the meristematic and infected zones. Finally, there is a strong correlation between the N-fixation capacity and the nodule GSH content (Groten et al., 2005). Taken together these data strongly suggest a key involvement of thiols in the N₂-fixation efficiency. This is consistent with recent data indicating that antioxidants such as thioredoxin are essential to lower reactive oxygen species levels during nodule development (Lee et al., 2005).

Studies have shown that both thiols (GSH and hGSH) are especially abundant in the meristematic and infected zones of P. sativum nodules (Matamoros et al., 1999). The high concentration of thiols in nodules (Frendo et al., 1999; Matamoros et al., 1999), along with the finding that concentration of thiol peptides are 3–4-fold higher in effective than in ineffective nodules (Dalton et al., 1993) strongly suggest that part of GSH and hGSH may be synthesized by the microsymbiont. Thus, it has been tested whether part of the GSH present in the nodule may be synthesized by the bacteria and whether the bacterial GSH pool may modify the nodulation and nitrogen-fixation processes. In silico analysis of the bacterial genome was performed to find -glutamylcysteine synthetase (ECS) and glutathione synthetase (GSHS), the genes involved in GSH synthesis. Then, ECS- and GSHS-defective mutant strains (SmgshA and SmgshB, respectively) derived from wild-type S. meliloti Rm1021 were constructed. The SmgshA mutant strain, which is unable to synthesize GSH due to a gene disruption in gshA, encoding the enzyme for the first step in the biosynthesis of GSH, was unable to grow under non-stress conditions, precluding any nodulation. By contrast, SmgshB was able to grow, indicating that -glutamylcysteine, the dipeptide intermediate, can substitute for GSH under non-stress conditions. However, the SmgshB strain showed a delayed-nodulation phenotype coupled with a 75% reduction in the nitrogen fixation capacity. This phenotype was linked to abnormal nodule development with an early senescence process. Both the SmgshA and SmgshB mutant strains exhibited higher catalase activity than the wild-type S. meliloti strain, suggesting that both mutant strains are under oxidative stress. Taken together, these results show that the bacterial GSH pool plays a critical role in the growth of S. meliloti and during its interaction with the plant partner (Harrison et al., 2005).

	Conclusion

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
The recent data reviewed in this article point to possible new functions for ROS, RNS, and GSH during legume–rhizobia interactions. These overcome the deleterious and protective roles classically associated with such compounds in nodules. In particular, it is now obvious that key steps in the symbiotic process, such as infection thread development or nodule formation, are deeply impaired by the modulation of ROS or GSH content. Recent advances also underline that the relationship between redox-related molecules and symbiosis is much more subtle than first envisaged. For instance, H₂O₂, the production of which is inhibited during the very early steps of legume-rhizobia interactions, is subsequently produced in infection threads. Moreover, if bacterial strains with impaired capacity to detoxify H₂O₂ have deficiencies in their symbiotic capacities, bacterial strains with enhanced detoxification potential will also show symbiotic defects. Therefore, the outcome of ROS/GSH/RNS production during symbiosis would be a matter of where, when, and to what level they accumulate. Moreover, as these molecules interact and finally influence the cellular redox state, it has to be discovered whether ROS/GSH/RNS regulate the symbiotic process through a modulation of the redox state or, instead, act as signalling molecules on their own.

A major step towards an understanding of the mechanisms regulated by ROS/GSH/RNS during symbiosis relies on the identification of their molecular targets. Strategies are currently being developed that rely on cDNA-AFLP and microarray technologies to isolate and analyse H₂O₂, GSH, and NO targets. Together with the use of symbiotic partners modified in ROS/GSH/RNS production, the study of these targets will provide information on the nature of the processes regulated by such molecules during symbiosis. It will also give an opportunity to investigate how ROS/GSH/RNS production overlaps with the regulation of specific genes at particular stages of the symbiotic process. Finally, it will give clues on whether and how ROS/GSH/RNS cross-talk during symbiosis. As ROS/GSH/RNS not only modify gene expression, but also impact plant physiology through post-translational modification of protein targets, future prospects will be aimed at comparing glutathionylated and nitrosylated protein patterns during symbiosis. The identification of differentially modified proteins will provide clues to the early targets of ROS/GSH/RNS sensing and signalling. Taken together, these data should show how ROS/GSH/RNS participate in the symbiotic process at the molecular level. Legume–rhizobia symbiosis is a remarkable model for infectious and developmental processes and their integration, and this information will be of general interest for the plant biologists.

	Abbreviations

 
ROS, reactive oxygen species; RNS, reactive nitrogen species; GSH, glutathione; hGSH, homoglutathione; AD, antioxidant defence.

	References

Top Abstract Introduction Reactive oxygen species Reactive nitrogen species Glutathione Conclusion References

 
Albus U, Baier R, Holst O, Puhler A, Niehaus K. (2001) Suppression of an elicitor-induced oxidative burst reaction in Medicago sativa cell cultures by Sinorhizobium meliloti lipopolysaccharides. New Phytologist 151:597–606.[CrossRef][Web of Science]

Alesandrini F, Mathis R, Van de Sype G, Hérouart D, Puppo A. (2003) Possible roles of a cysteine protease and hydrogen peroxide in soybean nodule development and senescence. New Phytologist 158:131–138.[CrossRef][Web of Science]

Apel K and Hirt H. (2004) Reactive oxygen species: metabolism, oxidative stress, and signal transduction. Annual Review of Plant Biology 55:373–399.[CrossRef][Medline]

Ardissone S, Frendo P, Laurenti E, Jantschko W, Obinger C, Puppo A, Ferrari RP. (2004) Purification and physical-chemical characterization of the three hydroperoxidases from the symbiotic bacterium Sinorhizobium meliloti. Biochemistry 43:12692–12699.[CrossRef][Medline]

Barloy-Hubler F, Cheron A, Hellegouarch A, Galibert F. (2004) Smc01944, a secreted peroxidase induced by oxidative stresses in Sinorhizobium meliloti 1021. Microbiology 150:657–664.[Abstract/Free Full Text]

Baron C and Zambryski PC. (1995) The plant response in pathogenesis, symbiosis, and wounding: variations on a common theme? Annual Review of Genetics 29:107–129.[CrossRef][Web of Science][Medline]

Becana M, Dalton DA, Moran JF, Iturbe-Ormaetxe I, Matamoros MA, Rubio MC. (2000) Reactive oxygen species and antioxidants in legume nodules. Physiologia Plantarum 109:372–381.[CrossRef]

Becana M and Klucas RV. (1992) Transition metals in legume root nodules. Iron dependent free radical production increases during nodule senescence. Proceedings of the National Academy of Sciences, USA 87:7295–7299.

Bueno P, Soto MJ, Rodriguez-Rosales MP, Sanjuan J, Olivares J, Donaire JP. (2001) Time-course of lipoxygenase, antioxidant enzyme activities and H₂O₂ accumulation during early stages of Rhizobium–legume symbiosis. New Phytologist 152:91–96.[CrossRef][Web of Science]

Colebatch G, Desbrosses G, Ott T, Krusell L, Montanari O, Kloska S, Kopka J, Udvardi MK. (2004) Global changes in transcription orchestrate metabolic differentiation during symbiotic nitrogen fixation in Lotus japonicus. The Plant Journal 39:487–512.[CrossRef][Web of Science][Medline]

Correa-Aragunde N, Graziano M, Lamattina L. (2004) Nitric oxide plays a central role in determining lateral root development in tomato. Planta 218:900–905.[CrossRef][Web of Science][Medline]

Cueto M, Hernandez-Perera O, Martin R, Bentura ML, Rodrigo J, Lamas S, Golvano MP. (1996) Presence of nitric oxide synthase activity in roots and nodules of Lupinus albus. FEBS Letters 398:159–164.[CrossRef][Web of Science][Medline]

Dalton DA, Langeberg L, Treneman NC. (1993) Correlations between the ascorbate-glutathione pathway and effectiveness in legume root nodules. Physiologia Plantarum 84:365–370.[CrossRef]

Dalton DA, Russell SA, Hanus FJ, Pascoe GA, Evan HJ. (1986) Enzymatic reactions of ascorbate and glutathione that prevent peroxide damage in soybean root nodules. Proceedings of the National Academy of Sciences, USA 83:3811–3815.[Abstract/Free Full Text]

David M, Daveran ML, Batut J, Dedieu A, Domergue O, Ghai J, Hertig C, Boistard P, Kahn D. (1988) Cascade regulation of nif gene expression in Rhizobium meliloti. Cell 54:671–683.[CrossRef][Web of Science][Medline]

Delledonne M. (2005) NO news is good news for plants. Current Opinion in Plant Biology 8:390–396.[CrossRef][Web of Science][Medline]

Dombrecht B, Heusdens C, Beullens S, Verreth C, Mulkers E, Proost P, Vanderleyden J, Michiels J. (2005) Defence of Rhizobium etli bacteroids against oxidative stress involves a complexly regulated atypical 2-Cys peroxiredoxin. Molecular Microbiology 55:1207–1221.[CrossRef][Web of Science][Medline]

Evans PJ, Gallesi D, Mathieu C, Hernandez MJ, de Felipe M, Halliwell B, Puppo A. (1999) Oxidative stress occurs during soybean nodule senescence. Planta 208:73–79.[CrossRef][Web of Science]

Foreman J, Demidchik V, Bothwell JH, et al. (2003) Reactive oxygen species produced by NADPH oxidase regulate plant cell growth. Nature 422:442–446.[CrossRef][Medline]

Frendo P, Gallesi D, Turnbull R, Van de Sype G, Hérouart D, Puppo A. (1999) Localisation of glutathione and homoglutathione in Medicago truncatula is correlated to a differential expression of genes involved in their synthesis. The Plant Journal 17:215–219.[CrossRef][Web of Science]

Frendo P, Harrison J, Norman C, Hernandez Jimenez MJ, Van de Sype G, Gilabert A, Puppo A. (2005) Glutathione and homoglutathione play a critical role in the nodulation process of Medicago truncatula. Molecular Plant–Microbe Interactions 18:254–259.[CrossRef]

Geurts R, Fedorova E, Bisseling T. (2005) Nod factor signaling genes and their function in the early stages of Rhizobium infection. Current Opinion in Plant Biology 8:346–352.[CrossRef][Web of Science][Medline]

Groten K, Dutilleul C, van Heerden PD, Vanacker H, Bernard S, Finkemeier I, Dietz KJ, Foyer CH. (2006) Redox regulation of peroxiredoxin and proteinases by ascorbate and thiols during pea root nodule senescence. FEBS Letters 580:1269–1276.[CrossRef][Web of Science][Medline]

Groten K, Vanacker H, Dutilleul C, Bastian F, Bernard S, Carzaniga R, Foyer CH. (2005) The roles of redox processes in pea nodule development and senescence. Plant, Cell and Environment 28:1293–1304.[CrossRef]

Guo FQ, Okamoto M, Crawford NM. (2003) Identification of a plant nitric oxide synthase gene involved in hormonal signaling. Science 302:100–103.[Abstract/Free Full Text]

Halliwell B and Gutteridge JM. (1986) Oxygen free radicals and iron in relation to biology and medicine: some problems and concepts. Archives of Biochemistry and Biophysics 246:501–514.[CrossRef][Web of Science][Medline]

Harrison J, Jamet A, Muglia CI, Van de Sype G, Aguilar OM, Puppo A, Frendo P. (2005) Glutathione plays a fundamental role in growth and symbiotic capacity of Sinorhizobium meliloti. Journal of Bacteriology 187:168–174.[Abstract/Free Full Text]

Herold S and Puppo A. (2005) Oxyleghemoglobin scavenges nitrogen monoxide and peroxynitrite: a possible role in functioning nodules? Journal of Biological Inorganic Chemistry 10:935–945.[CrossRef][Medline]

Hérouart D, Baudouin E, Frendo P, Harrison J, Santos R, Jamet A, Van de Sype G, Touati D, Puppo A. (2002) Reactive oxygen species, nitric oxide and glutathione: a key role in the establishment of the legume: Rhizobium symbiosis. Plant Physiology and Biochemistry 40:619–624.[CrossRef][Web of Science]

Hérouart D, Sigaud S, Moreau S, Frendo P, Touati D, Puppo A. (1996) Cloning and characterization of the katA gene of Rhizobium meliloti encoding a hydrogen peroxide-inducible catalase. Journal of Bacteriology 178:6802–6809.[Abstract/Free Full Text]

Igamberdiev AU, Stoimenova M, Seregelyes C, Hill RD. (2005) Class-1 haemoglobin and antioxidant metabolism in alfalfa roots. Planta 223:1041–1046.

Jamet A, Kiss E, Batut J, Puppo A, Hérouart D. (2005) The katA catalase gene is regulated by OxyR in both free-living and symbiotic Sinorhizobium meliloti. Journal of Bacteriology 187:376–381.[Abstract/Free Full Text]

Jamet A, Sigaud S, Van de Sype G, Puppo A, Hérouart D. (2003) Expression of the bacterial catalase genes during Sinorhizobium meliloti–Medicago sativa symbiosis and their crucial role during the infection process. Molecular Plant–Microbe Interactions 16:217–225.

Kanayama Y, Watanabe I, Yamamoto Y. (1990) Inhibition of nitrogen fixation in soybean plants supplied with nitrate. I. Nitrite accumulation and formation of nitrosylleghemoglobin in nodules. Plant Cell Physiology 31:341–346.[Abstract/Free Full Text]

Kato K, Okamura Y, Kanahama K, Kanayama Y. (2003) Nitrate-independent expression of plant nitrate reductase in Lotus japonicus root nodules. Journal of Experimental Botany 54:1685–1690.[Abstract/Free Full Text]

Lee MY, Shin KH, Kim YK, et al. (2005) Induction of thioredoxin is required for nodule development to reduce reactive oxygen species levels in soybean roots. Plant Physiology 139:1881–1889.[Abstract/Free Full Text]

Matamoros MA, Dalton DA, Ramos J, Clemente MR, Rubio MC, Becana M. (2003) Biochemistry and molecular biology of antioxidants in the rhizobia–legume symbiosis. Plant Physiology 133:499–509.[Free Full Text]

Matamoros MA, Moran JF, Iturbe-Ormaetxe I, Rubio MC, Becana M. (1999) Glutathione and homoglutathione synthesis in legume root nodules. Plant Physiology 121:879–888.[Abstract/Free Full Text]

Mathieu C, Moreau S, Frendo P, Puppo A, Davies MJ. (1998) Direct detection of radicals in intact soybean nodules: presence of nitric oxide leghaemoglobin complexes. Free Radicals in Biology and Medicine 24:1242–1249.

McGongile B, Keeler SJ, Lau SMC, Koeppe MJ, O'Keefe DP. (2000) A genomics approach to the comprehensive analysis of the glutathione S-transferase gene family in soybean and maize. Plant Physiology 124:1105–1120.[Abstract/Free Full Text]

Mesa S, Alche Jd J, Bedmar E, Delgado MJ. (2004) Expression of nir, nor, and nos denitrification genes from Bradyrhizobium japonicum in soybean root nodules. Physiologia Plantarum 120:205–211.[CrossRef][Medline]

Mesa S, Bedmar EJ, Chanfon A, Hennecke H, Fischer HM. (2003) Bradyrhizobium japonicum NnrR, a denitrification regulator, expands the FixLJ-FixK2 regulatory cascade. Journal of Bacteriology 185:3978–3982.[Abstract/Free Full Text]

Moran JF, Iturbe-Ormaetxe I, Matamoros MA, Rubio MC, Clemente MR, Brewin NJ, Becana M. (2000) Glutathione and homoglutathione synthetases of legumes nodules. Cloning, expression, and subcellular localization. Plant Physiology 124:879–888.

Neill SJ, Desikan R, Clarke A, Hurst RD, Hancock JT. (2002) Hydrogen peroxide and nitric oxide as signalling molecules in plants. Journal of Experimental Botany 53:1237–1247.[Abstract/Free Full Text]

Neill SJ, Desikan R, Hancock JT. (2003) Nitric oxide signalling in plants. New Phytologist 159:11–35.[CrossRef][Web of Science]

Oldroyd GE, Harrison MJ, Udvardi M. (2005) Peace talks and trade deals. Keys to long-term harmony in legume–microbe symbioses. Plant Physiology 137:1205–1210.[Free Full Text]

Oldroyd GED, Engstrom EM, Long SR. (2001) Ethylene inhibits the nod factor signal transduction pathway of Medicago truncatula. The Plant Cell 13:1835–1849.[Abstract/Free Full Text]

Pagnussat GC, Simontacchi M, Puntarulo S, Lamattina L. (2002) Nitric oxide is required for root organogenesis. Plant Physiology 129:954–956.[Free Full Text]

Panek HR and O'Brian MR. (2004) KatG is the primary detoxifier of hydrogen peroxide produced by aerobic metabolism in Bradyrhizobium japonicum. Journal of Bacteriology 186:7874–7880.[Abstract/Free Full Text]

Pei ZM, Murata Y, Benning G, Thomine S, Klusener B, Allen GJ, Grill E, Schroeder JI. (2000) Calcium channels activated by hydrogen peroxide mediate abscisic acid signalling in guard cells. Nature 406:731–734.[CrossRef][Medline]

Penmetsa RV and Cook DR. (1997) A legume ethylene-insensitive mutant hyperinfected by its rhizobial symbiont. Science 275:527–530.[Abstract/Free Full Text]

Puppo A, Groten K, Bastian F, Carzaniga R, Soussi M, Lucas MM, de Felipe MR, Harrison J, Vanacker H, Foyer CH. (2005) Legume nodule senescence: roles for redox and hormone signalling in the orchestration of the natural aging process. New Phytologist 165:683–701.[CrossRef][Web of Science][Medline]

Ramu SK, Peng HM, Cook DR. (2002) Nod factor induction of reactive oxygen species production is correlated with expression of the early nodulin gene rip1 in Medicago truncatula. Molecular Plant–Microbe Interactions 15:522–528.

Romero-Puertas MC, Perazzolli M, Zago ED, Delledonne M. (2004) Nitric oxide signalling functions in plant–pathogen interactions. Cell Microbiology 6:795–803.

Rubio MC, James EK, Clemente MR, Bucciarelli B, Fedorova M, Vance CP, Becana M. (2004) Localization of superoxide dismutases and hydrogen peroxide in legume root nodules. Molecular Plant–Microbe Interactions 17:1294–1305.[CrossRef]

Santos R, Hérouart D, Puppo A, Touati D. (2000) Critical protective role of bacterial superoxide dismutase in Rhizobium–legume symbiosis. Molecular Microbiology 38:750–759.[CrossRef][Web of Science][Medline]

Santos R, Hérouart D, Sigaud S, Touati D, Puppo A. (2001) Oxidative burst in alfalfa–Sinorhizobium meliloti symbiotic interaction. Molecular Plant–Microbe Interactions 14:86–89.

Seaver LC and Imlay JA. (2001) Alkyl hydroperoxide reductase is the primary scavenger of endogenous hydrogen peroxide in Escherichia coli. Journal of Bacteriology 183:7173–7181.[Abstract/Free Full Text]

Shaw SL and Long SR. (2003) Nod factor inhibition of reactive oxygen efflux in a host legume. Plant Physiology 132:2196–2204.[Abstract/Free Full Text]

Shimoda Y, Nagata M, Suzuki A, Abe M, Sato S, Kato T, Tabata S, Higashi S, Uchiumi T. (2005) Symbiotic rhizobium and nitric oxide induce gene expression of non-symbiotic haemoglobin in Lotus japonicus. Plant Cell Physiology 46:99–107.[Abstract/Free Full Text]

Sigaud S, Becquet V, Frendo P, Puppo A, Hérouart D. (1999) Differential regulation of two divergent Sinorhizobium meliloti genes for HPII-like catalases during free-living growth and protective role of both catalases during symbiosis. Journal of Bacteriology 181:2634–2639.[Abstract/Free Full Text]

Spaink HP. (2004) Specific recognition of bacteria by plant LysM domain receptor kinases. Trends in Microbiology 12:201–204.[CrossRef][Web of Science][Medline]

Stacey G, Libault M, Brechenmacher L, Wan J, May GD. (2006) Genetics and functional genomics of legume nodulation. Current Opinion in Plant Biology 9:1–12.[CrossRef][Web of Science]

Trinchant JC and Rigaud J. (1982) Nitrite and nitric oxide as inhibitors of nitrogenase from soybean bacteroids. Applied Environmental Microbiology 44:1385–1388.[Abstract/Free Full Text]

Vargas Mdel C, Encarnacion S, Davalos A, Reyes-Perez A, Mora Y, Garcia-de los Santos A, Brom S, Mora J. (2003) Only one catalase, katG, is detectable in Rhizobium etli, and is encoded along with the regulator OxyR on a plasmid replicon. Microbiology 149:1165–1176.[Abstract/Free Full Text]

Vasse J, de Billy F, Truchet G. (1993) Abortion of infection during the Rhizobium meliloti–alfalfa symbiotic interaction is accompagnied by a hypersensitive reaction. The Plant Journal 4:555–566.[CrossRef][Web of Science]

Vernoux T, Wilson RC, Seeley KA, et al. (2000) The ROOT MERISTEMLESS1/CADMIUM SENSITIVE2 gene defines a glutathione-dependent pathway involved in initiation and maintenance of cell division during post-embryonic root development. The Plant Cell 12:97–110.[Abstract/Free Full Text]

Vieweg MF, Hohnjec N, Kuster H. (2005) Two genes encoding different truncated haemoglobins are regulated during root nodule and arbuscular mycorrhiza symbioses of Medicago truncatula. Planta 220:757–766.[CrossRef][Web of Science][Medline]

Vranova E, Inzé D, Van Breusegem F. (2002) Signal transduction during oxidative stress. Journal of Experimental Botany 53:1227–1236.[Abstract/Free Full Text]

Wisniewski JP, Rathbun EA, Knox JP, Brewin NJ. (2000) Involvement of diamine oxidase and peroxidase in insolubilization of the extracellular matrix: implications for pea nodule initiation by Rhizobium leguminosarum. Molecular Plant–Microbe Interactions 13:413–420.

Yuan ZC, Zaheer R, Finan TM. (2005) Phosphate limitation induces catalase expression in Sinorhizobium meliloti, Pseudomonas aeruginosa, and Agrobacterium tumefaciens. Molecular Microbiology 58:877–894.[CrossRef][Web of Science][Medline]

CiteULike    Connotea    Del.icio.us    What's this?

This article has been cited by other articles:

				S. Mesa, L. Reutimann, H.-M. Fischer, and H. Hennecke Posttranslational control of transcription factor FixK2, a key regulator for the Bradyrhizobium japonicum-soybean symbiosis PNAS, December 22, 2009; 106(51): 21860 - 21865. [Abstract] [Full Text] [PDF]

				J. Prell, J. P. White, A. Bourdes, S. Bunnewell, R. J. Bongaerts, and P. S. Poole Legumes regulate Rhizobium bacteroid development and persistence by the supply of branched-chain amino acids PNAS, July 28, 2009; 106(30): 12477 - 12482. [Abstract] [Full Text] [PDF]

				X.-H. Gao, M. Bedhomme, D. Veyel, M. Zaffagnini, and S. D. Lemaire Methods for Analysis of Protein Glutathionylation and their Application to Photosynthetic Organisms Mol Plant, March 1, 2009; 2(2): 218 - 235. [Abstract] [Full Text] [PDF]

				S. Haaning, S. Radutoiu, S. V. Hoffmann, J. Dittmer, L. Giehm, D. E. Otzen, and J. Stougaard An Unusual Intrinsically Disordered Protein from the Model Legume Lotus japonicus Stabilizes Proteins in Vitro J. Biol. Chem., November 7, 2008; 283(45): 31142 - 31152. [Abstract] [Full Text] [PDF]

				Z.-C. Yuan, P. Liu, P. Saenkham, K. Kerr, and E. W. Nester Transcriptome Profiling and Functional Analysis of Agrobacterium tumefaciens Reveals a General Conserved Response to Acidic Conditions (pH 5.5) and a Complex Acid-Mediated Signaling Involved in Agrobacterium-Plant Interactions J. Bacteriol., January 15, 2008; 190(2): 494 - 507. [Abstract] [Full Text] [PDF]

				A. Lindemann, A. Moser, G. Pessi, F. Hauser, M. Friberg, H. Hennecke, and H.-M. Fischer New Target Genes Controlled by the Bradyrhizobium japonicum Two-Component Regulatory System RegSR J. Bacteriol., December 15, 2007; 189(24): 8928 - 8943. [Abstract] [Full Text] [PDF]

				W. Capoen, J. Den Herder, S. Rombauts, J. De Gussem, A. De Keyser, M. Holsters, and S. Goormachtig Comparative Transcriptome Analysis Reveals Common and Specific Tags for Root Hair and Crack-Entry Invasion in Sesbania rostrata Plant Physiology, August 1, 2007; 144(4): 1878 - 1889. [Abstract] [Full Text] [PDF]

				J.-P. Combier, T. Vernie, F. de Billy, F. El Yahyaoui, R. Mathis, and P. Gamas The MtMMPL1 Early Nodulin Is a Novel Member of the Matrix Metalloendoproteinase Family with a Role in Medicago truncatula Infection by Sinorhizobium meliloti Plant Physiology, June 1, 2007; 144(2): 703 - 716. [Abstract] [Full Text] [PDF]

				S. Peleg-Grossman, H. Volpin, and A. Levine Root hair curling and Rhizobium infection in Medicago truncatula are mediated by phosphatidylinositide-regulated endocytosis and reactive oxygen species J. Exp. Bot., May 1, 2007; 58(7): 1637 - 1649. [Abstract] [Full Text] [PDF]

This Article Abstract FREE Full Text (PDF) All Versions of this Article: 57/8/1769    most recent erj184v1 E-letters: Submit a response Alert me when this article is cited Alert me when E-letters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Archive Download to citation manager Search for citing articles in: ISI Web of Science (10) Request Permissions Disclaimer Google Scholar Articles by Pauly, N. Articles by Puppo, A. Search for Related Content PubMed PubMed Citation Articles by Pauly, N. Articles by Puppo, A. Agricola Articles by Pauly, N. Articles by Puppo, A. Social Bookmarking          What's this?

Online ISSN 1460-2431 - Print ISSN 0022-0957

Copyright © 2005 Society for Experimental Biology

Oxford Journals Oxford University Press

• Site Map
• Privacy Policy
• Frequently Asked Questions

Other Oxford University Press sites: Oxford University Press Oxford Journals China Oxford Journals Japan American National Biography Booksellers' Information Service Children's Fiction and Poetry Children's Reference Corporate & Special Sales Dictionaries Dictionary of National Biography Digital Reference English Language Teaching Higher Education Textbooks Humanities International Education Unit Law Medicine Music Online Products Oxford English Dictionary Reference Rights and Permissions Science School Books Social Sciences Very Short Introductions World's Classics