JXB Advance Access originally published online on January 8, 2007
Journal of Experimental Botany 2007 58(3):555-568; doi:10.1093/jxb/erl230
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RESEARCH PAPER |
Differential distribution of the lipoxygenase pathway enzymes within potato chloroplasts
Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Campus de Cantoblanco, Universidad Autónoma de Madrid, Carretera de Colmenar Viejo km 15,500. 28049 Madrid, Spain
* Present address and to whom correspondence should be sent. Institute of Agrobiotechnology, Centre for Research and Technology, 6th Km Charilaou-Thermi Rd., 570 01 Thermi, Thessaloniki, Greece. E-mail: mfarmaki{at}certh.gr
The lipoxygenase pathway is responsible for the production of oxylipins, which are important compounds for plant defence responses. Jasmonic acid, the final product of the allene oxide synthase/allene oxide cyclase branch of the pathway, regulates wound-induced gene expression. In contrast, C6 aliphatic aldehydes produced via an alternative branch catalysed by hydroperoxide lyase, are themselves toxic to pests and pathogens. Current evidence on the subcellular localization of the lipoxygenase pathway is conflicting, and the regulation of metabolic channelling between the two branches of the pathway is largely unknown. It is shown here that while a 13-lipoxygenase (LOX H3), allene oxide synthase and allene oxide cyclase proteins accumulate upon wounding in potato, a second 13-lipoxygenase (LOX H1) and hydroperoxide lyase are present at constant levels in both non-wounded and wounded tissues. Wound-induced accumulation of the jasmonic acid biosynthetic enzymes may thus commit the lipoxygenase pathway to jasmonic acid production in damaged plants. It is shown that all enzymes of the lipoxygenase pathway differentially localize within chloroplasts, and are largely found associated to thylakoid membranes. This differential localization is consistently observed using confocal microscopy of GFP-tagged proteins, chloroplast fractionation, and western blotting, and immunodetection by electron microscopy. While LOX H1 and LOX H3 are localized both in stroma and thylakoids, both allene oxide synthase and hydroperoxide lyase protein localize almost exclusively to thylakoids and are strongly bound to membranes. Allene oxide cyclase is weakly associated with the thylakoid membrane and is also detected in the stroma. Moreover, allene oxide synthase and hydroperoxide lyase are differentially distributed in thylakoids, with hydroperoxide lyase localized almost exclusively to the stromal part, thus closely resembling the localization pattern of LOX H1. It is suggested that, in addition to their differential expression pattern, this segregation underlies the regulation of metabolic fluxes through the alternative branches of the lipoxygenase pathway.
Key words: Allene oxide cyclase, allene oxide synthase, hydroperoxide lyase, lipoxygenase, oxylipins, stroma, thylakoid
Present address: Instituto de la Grasa, Consejo Superior de Investigaciones Científicas, Avenida Padre García Tejero 4, 41012 Sevilla, Spain.
Present address: Bayer BioScience NV, Technologiepark 38, B-9052 Gent, Belgium.
Present address: Instituto de Biología Molecular y Celular de Plantas. Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas. 46022 Valencia, Spain.
Database accession: Allene oxide cyclase cDNA, GenBank accession number AY135641; allene oxide synthase 2 cDNA, GenBank accession number AY135640.
Received 17 July 2006; Revised 26 September 2006 Accepted 13 October 2006
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