Comparison of proteomes of three species of rice from different ecological backgrounds in drought stress

Drought is a major hazard for world rice production. Substantial genetic variation in drought tolerance has been reported within rice ecotypes. Proteomic analysis provides insights into the expression of key genes by contrasting diverse germplasm that has been exposed to the steady-state drought. In this study, we analysed the proteome of leaves of three species of rice grown principally in Asia, Africa and Oceania. Commercial Asian cultivar (Oryza sativa; Nipponbare), Australian (Oryza australiensis), and African (Oryza glaberrima) rice plants were exposed to moderate drought stress and leaves from stressed and untreated control plants were harvested for protein extraction, followed by label-free quantitative shotgun proteomics analysis. 
Leaf water potential was measured in plants that were well-watered throughout or exposed to constant but moderate water deficits. Proteins were extracted from leaf tissue using trichloroacetic acid – acetone extraction and precipitation. In-solution digested peptides were separated and identified using nanoflow reversed-phase liquid chromatography – tandem orbitrap mass spectrometry on a Thermo Q-Exactive. Peptides and proteins were identified and quantified using MaxQuant.
Oryza australiensis is tolerant to variable water supply in nature and in our controlled experiments. However, this response was not observed in O. glaberrima which is also known as a stress tolerant species. Stress-responsive proteins were up-regulated in all three species, a number of which were unique to O. glaberrima. Interestingly, preliminary analysis has shown that the identified differentially expressed proteins were assigned to variant biochemical pathways showing the different strategies of each species to modulate molecular responses to overcome water stress.