Identification of candidate genes for drought tolerance in Elymus elongatum

Tall wheatgrass (Elymus elongatum Host) is a drought tolerant, cool-season forage grass native to Iran. We have applied a proteomic approach to identify mechanisms of drought responsiveness and tolerance in plants undergoing vegetative stage drought stress and then recovery after rewatering. Uniformed clones were reproduced from a parent plant collected from Brojen (central region of Iran). Clones were grown in pots and drought was initiated by withholding water for 16 days. The Leaf samples were collected in triplicate from both stressed/re-watered plants and continuously watered controls at four times: (a) 75% FC, (b) 50% FC, (c) 25% FC, (d) 3 days after rewatering, and (e) 14 days after rewatering. Changes in proteome pattern of shoots were studied using two dimensional gel electrophoresis. Following the 16 d water stress, both shoot dry weight and leaf width decreased up to 67% compare to the well-watered plants whereas proline content increased up to 20 fold. Leaf relative water contents (RWC) also declined from 85% to 24%. Out of about 600 protein spots detected on any given two dimensional gel, 67 protein spots were reproducibly and significantly changed during drought stress and recovery. Only one protein (abscisic acid- and stress-inducible protein) showed significant changes in expression and position in response to the severe drought treatment . The sixty-seven responsive proteins were categorized in six clusters including two groups of proteins specifically up- and down-regulated in response to severe drought stress. Eighteen proteins belong to these two groups were analyzed by liquid chromatography tandem mass spectrometry leading to identification of eleven of them including oxygen evolving enhancer protein 2, abscisic acid- and stress-inducible protein, several oxidative stress tolerance enzymes, two small heat shock proteins and rubisco breakdown. Our results suggest that E. elongatum may tolerate severe drought stress by accumulating proline and several proteins related to drought stress tolerance. Recovery after rewatering might be another mechanism by which plant tolerates erratic rainfall in semi-arid regions.