The many and varied responses of different varieties and species of rice to a range of external stresses

Introduction: Drought and temperature fluctuations of increasing frequency and amplitude are both a consequence of accelerating climate change and a serious threat to global food security. Rice is one of the most important food crops in the world, and the productivity of rice crops is threatened by a number of different environmental stresses, including drought and temperature. For many years, we have been investigating the proteomic response of rice varieties and species with different genetic backgrounds, when exposed to a range of different abiotic stresses, including drought, salt, and high and low temperatures. Detailed quantitative proteomic analysis allows us to understand how the cells in rice plants respond at the molecular level to external stresses, and thus how the plants adapt.

Methods: Proteins from leaves and roots of young rice plants under control and stress conditions were extracted using trichloroacetic acid – acetone extraction and precipitation. Peptides were separated using reversed phase nanoflow liquid chromatography, and identified and quantified using high resolution mass spectrometry on a Q Exactive orbitrap, followed by peptide to spectrum matching using GPM, Sequest and MaxQuant. Physiological parameters relevant to specific experiments, including leaf water potential and plant growth rates, were measured for separate cohorts of control and stressed plants. Multiple Reaction Monitoring quantitative assays were also performed for confirmation of initial results, which also enabled more detailed analysis of protein expression changes in plants exposed to stress.

Preliminary data: This presentation will synthesise results from a number of different rice stress response studies performed in our laboratory in recent years. An overview will be presented, highlighting both similarities and differences in how different rice plants respond at the molecular level to different stresses, degrees of stress, or combinations of stresses.

In one study, for example, plants from 8 different rice varieties were subjected to drought stress and recovery; Nipponbare, Doongara, IAC1131, Mahsuri, Reiziq, MC05, MC06 and MC07. The data show different genotypes are able to cope with drought stress by adaptive changes in the major biological pathways. Between 20 to 40% of proteins significantly reduced in abundance in stress conditions were involved in photosynthesis, while, in contrast, proteins involved in proteolytic processing pathways were significantly increased in abundance. Many proteins were uniquely differentially expressed in specific genotypes, while 8 proteins were up-regulated in response to drought stress in all genotypes, including actin-depolymerizing factor 3 (ADF-3) and GSH-dependent dehydroascorbate reductase 1.
In a separate exemplar study, three different species of rice were exposed to drought stress: the Asian rice cultivar O. sativa cv. Nipponbare; the wild species Oryza australiensis; and the African cultivar Oryza glaberrima cv. CG14. These wild species are considered to contain rich untapped reservoirs of valuable genes. The 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, while this response was not observed in O. glaberrima. A majority of proteins increased in abundance in stress conditions in O. australiensis were associated with photosynthesis and carbohydrate biosynthesis.

Using the information obtained from these and numerous other studies will pave the way for development of rice varieties with higher drought stress tolerance, which is important for our future food security.

Novel Aspect: Comprehensive characterisation of molecular and physiological responses to abiotic stress across a broad range of rice varieties and species.