Proteome response of Elymus elongatum to severe water stress and recovery.

Tall wheatgrass (Elymus elongatum Host) is a drought-tolerant, cool-season forage grass native to Iran. A proteomic approach has been applied 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 d. The leaf samples were taken in triplicate from both stressed/rewatered plants and continuously watered controls at five times: (i) 75% FC, (ii) 50% FC, (iii) 25% FC, (iv) 3 d after rewatering, and (v) 14 d after rewatering. Changes in the 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% compared with 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, 58 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 severe drought. The fifty-eight 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 belonging to these two groups were analysed by liquid chromatography tandem mass spectrometry leading to the identification of 11 of them, including the oxygen-evolving enhancer protein 2, abscisic acid- and stress-inducible protein, several oxidative stress tolerance enzymes, two small heat shock proteins, and Rubisco breakdown. The 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 plants tolerate erratic rainfall in semi-arid regions.