Rice as a cereal crop species is a remarkable part of the staple diet for half of the world’s population and is grown in every continent apart from Antarctica. Stresses are often unfavorable for rice growth. Abiotic stress is the primary cause of crop loss worldwide, reducing average yield for most major crops by more than 50%. Reduced rice crop productivity is mostly attributed to various abiotic stresses, which are a major area of concern when we are faced with increasing food requirements. Salt, drought and temperature stresses are major environmental abiotic factors all of which negatively influence the yield of crops, limit plant productivity and threaten our food security. Elucidating the various mechanisms of plant response to stress, and their roles in acquired stress tolerance, is thus of great practical important. Plants respond to multiple abiotic stresses differently from individual stresses, activating a specific program of gene and protein regulation relating to the exact stress. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing the susceptibility to other abiotic stresses. In this project, we are examining the combined effects of drought, temperature and salt stress at different time points.
We have investigated the proteomic response to multiple abiotic stresses in two varieties of rice (IAC1131 and Nipponbare) during their vegetative growing stage. The stress treatment was a combination of reducing the soil water content to 50% field capacity, with NaCl concentration increased to 50mM and temperature of 33/18 ºC for 2 and 4 days. Proteins were identified and quantified using TMT labeling, following protein extraction from 3-week leaf tissues combined with trypsin in-solution digestion. Peptides were separated and identified using a Q Exactive Orbitrap mass spectrometer coupled to an Easy-nLC 1000 nano-flow HPLC system. Proteome Discoverer v2.1 software was used to process raw files generated by Xcalibur software. Peptide to spectrum matching was performed using FASTA files of protein sequences from Oryza sativa. Relative quantitation of proteins was achieved by pairwise comparison of normalized TMT reporter ion intensities using TMTPrepPro. Deferentially expressed proteins in both genotypes under stress conditions were observed, with a greater number of proteins increase in abundance rather than decreased. Heat shock proteins and late embryogenesis abundant proteins were two of the most significantly altered protein groups, while hypothetical proteins with no specific function were also found to be deferentially expressed in response to stress.