Drought is a serious threat to global food security. The Asian rice cultivar O. sativa cv. Nipponbare is a domesticated sativa cultivar with a low level of drought-tolerance. The wild species O. australiensis and the cultivated O. glaberrima are considered to contain rich untapped reservoirs of valuable genes which have great potential for use in successful marker assisted breeding approaches. In this study, we analysed the proteome of leaves of three species of rice grown principally in Asia, Africa and Oceania. Plants were exposed to drought stress, and leaves from stressed and untreated control ones were harvested for protein extraction, followed by label-free quantitative shotgun proteomics
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. Our results showed no significant difference in water potential of O. australiensis leaves under drought stress, which indicates it is able to retain more water in leaf cells under drought conditions. However, this response was not observed in O. glaberrima which is also known as a stress tolerant species. Our analysis has shown that the identified differentially expressed proteins were assigned to various biochemical pathways, illustrating the different strategies of each species to modulate molecular responses to overcome water stress. A majority of proteins increased in abundance in stress conditions in Oryza australiensis were associated with photosynthesis and carbohydrate biosynthesis. Proteins participating in leaf starch biosynthesis in O. australiensis can be used in selective breeding to supplement the bio-engineering of improved photosynthetic efficiency, thus potentially contributing to improved crop yield in cultivated rice.