title: A salt-inducible chloroplastic monodehydroascorbate reductase from halophyte Avicennia marina confers salt stress tolerance on transgenic plants.
abstract: Plant growth and productivity are adversely affected by various abiotic stress factors. In our previous study, we used Avicennia marina, a halophytic mangrove, as a model plant system for isolating genes functioning in salt stress tolerance. A large scale random EST sequencing from a salt stressed leaf tissue cDNA library of one month old A. marina plants resulted in identification of a clone showing maximum homology to Monodehydroascorbate reductase (Am-MDAR). MDAR plays a key role in regeneration of ascorbate from monodehydroascorbate for ROS scavenging. In this paper, we report the cellular localization and the ability to confer salt stress tolerance in transgenic tobacco of this salt inducible Am-MDAR. A transit peptide at the N-terminal region of Am-MDAR suggested that it encodes a chloroplastic isoform. The chloroplastic localization was confirmed by stable transformation and expression of the Am-MDAR-GFP fusion protein in tobacco. Transgenic tobacco plants overexpressing Am-MDAR survived better under conditions of salt stress compared to untransformed control plants. Assays of enzymes involved in ascorbate-glutathione cycle revealed an enhanced activity of MDAR and ascorbate peroxidase whereas the activity of dehyroascorbate reductase was reduced under salt stressed and unstressed conditions in Am-MDAR transgenic lines. The transgenic lines showed an enhanced redox state of ascorbate and reduced levels of malondialdehyde indicating its enhanced tolerance to oxidative stress. The results of our studies could be used as a starting point for genetic engineering of economically important plants tolerant to salt stress.
authors.affiliation: Oilseeds Research Station, Tamil Nadu Agricultural University, Tindivanam 604 002, India.
authors.forename: Kumaresan
authors.initials: K
authors.lastname: Kavitha
authors.forename: Suja
authors.initials: S
authors.lastname: George
authors.forename: Gayatri
authors.initials: G
authors.lastname: Venkataraman
authors.forename: Ajay
authors.initials: A
authors.lastname: Parida
mesh_terms: D032407:Avicennia / Q000201:enzymology*; D002736:Chloroplasts / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D009247:NADH, NADPH Oxidoreductases / Q000187:drug effects / Q000235:genetics*; D030821:Plants, Genetically Modified; D055049:Salt Tolerance / Q000502:physiology*; D055051:Salt-Tolerant Plants; D012965:Sodium Chloride / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects*
chemical_list: D012965:Sodium Chloride; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH)