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JXB Advance Access published online on April 8, 2009
Journal of Experimental Botany, doi:10.1093/jxb/erp072
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Over-expression of a tomato N-acetyl-L-glutamate synthase gene (SlNAGS1) in Arabidopsis thaliana results in high ornithine levels and increased tolerance in salt and drought stresses

Mary S. Kalamaki, Dimitris Alexandrou, Diamanto Lazari, Georgios Merkouropoulos *, Vasileios Fotopoulos {dagger}, Irene Pateraki {ddagger}, Alexandros Aggelis $, Armando Carrillo-López §, Maria J. Rubio-Cabetas % and Angelos K. Kanellis

Group of Biotechnology of Pharmaceutical Plants, Laboratory of Pharmacognosy, Division of Pharmacognosy-Pharmacology, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece

To whom correspondence should be addressed: E-mail: kanellis{at}pharm.auth.gr

A single copy of the N-acetyl-L-glutamate synthase gene (SlNAGS1) has been isolated from tomato. The deduced amino acid sequence consists of 604 amino acids and shows a high level of similarity to the predicted Arabidopsis NAGS1 and NAGS2 proteins. Furthermore, the N-terminus ArgB domain and the C-terminus ArgA domain found in SlNAGS1 are similar to the structural arrangements that have been reported for other predicted NAGS proteins. SlNAGS1 was expressed at high levels in all aerial organs, and at basic levels in seeds, whereas it was not detected at all in roots. SlNAGS1 transcript accumulation was noticed transiently in tomato fruit at the red-fruit stage. In addition, an increase of SlNAGS1 transcripts was detected in mature green tomato fruit within the first hour of exposure to low oxygen concentrations. Transgenic Arabidopsis plants have been generated expressing the SlNAGS1 gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Three homozygous transgenic lines expressing the transgene (lines 1-7, 3-8, and 6-5) were evaluated further. All three transgenic lines showed a significant accumulation of ornithine in the leaves with line 3-8 exhibiting the highest concentration. The same lines demonstrated higher germination ability compared to wild-type (WT) plants when subjected to 250 mM NaCl. Similarly, mature plants of all three transgenic lines displayed a higher tolerance to salt and drought stress compared to WT plants. Under most experimental conditions, transgenic line 3-8 performed best, while the responses obtained from lines 1-7 and 6-5 depended on the applied stimulus. To our knowledge, this is the first plant NAGS gene to be isolated, characterized, and genetically modified.

Key words: Arabidopsis thaliana, arginine biosynthesis, citrulline, drought tolerance, N-acetyl-L-glutamate synthase, ornithine, salt stress, seed germination, transgenic plants

* Present address: Institute of Agrobiotechnology, 6th Km Charilaou-Thermi Road,Thermi, Thessaloniki, Greece

{dagger} Present address: Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology, PC 3036, Limassol, Cyprus

{ddagger} Present address: Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain

$ Present address: Larisa University Hospital, School of Medicine, University of Thessaly, Larisa, Greece

§ Present address: Universidad Autonoma de Sinaloa, Mexico

% Present address: Unidad de Fruticultura, Centro de Investigacion y Tecnologia Agroalimentaria, Avda Montañana, 930, 50059, Zaragoza, Spain

Received 5 December 2008; Revised 11 February 2009 Accepted 19 February 2009


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