Novel clues on abiotic stress tolerance emerge from embryo proteome analyses of rice varieties with contrasting stress adaptation

Cereal embryos sustain severe water deficit at the final stage of seed maturation. The molecular mechanisms underlying the acquisition of desiccation tolerance in seed embryos are similar to those displayed during water deficit in vegetative tissues. The genetic variation among six rice genotypes adapted to diverse environmental conditions was analysed at the proteome level to get further clues on the mechanisms leading to water-stress tolerance. MS analysis allowed the identification of 28 proteins involved in stress tolerance (late embryogenesis abundant proteins), nutrient reservoir activity, among other proteins implicated in diverse cellular processes potentially related to the stress response (e.g., mitochondrial import translocase). Hierarchical clustering and multidimensional scaling analyses revealed a close relationship between the stress-sensitive genotypes, whereas the stress-tolerant varieties were more distantly related. Besides qualitative and significant quantitative changes in embryo proteins across the distinct varieties, we also found differences at post-translational level. The results indicated that late embryogenesis abundant Rab21 was more strongly phosphorylated in the embryos of the sensitive varieties than in the embryos of the tolerant ones. We propose that the differences found in the phosphorylation status of Rab21 are related to stress tolerance.