Comparative physiological and metabolomic responses of four Brachypodium distachyon varieties contrasting in drought stress resistance

Brachypodium distachyon (Brachypodium) is not only a monocot grass species, but also a promising model organism of crop research. In this study, the drought resistance of four Brachypodium varieties was identified including drought stress-tolerant Bd1-1 and Bd21, drought stress-susceptible Bd3-1 and Bd18-1. Physiological assay showed that drought-tolerant varieties (Bd1-1 and Bd21) were more effective in maintenance of leaf water content, activation of catalase and peroxidase activities and accumulation of reduced glutathione, resulting in alleviated cell damage and lower reactive oxygen species level than drought-susceptible varieties (Bd3-1 and Bd18-1) in response to drought stress. In addition, 54 primary metabolites were differentially regulated among Brachypodium varieties and after drought stress treatment, indicating the complexity of Brachypodium response to drought stress. We also identified several commonly regulated metabolites especially some compatible solutes including proline and soluble sugars, which exhibited higher concentrations in the drought-tolerant varieties. Taken together, this study suggested that natural variation of Brachypodium varieties in response to drought stress might be connected with higher leaf water, enhanced accumulation of osmolyte and more effective antioxidant system, as well as the modulation of metabolic profiles under drought stress conditions.