Improving the thermal tolerance of photosynthesis in wheat

Wheat yields need to rise to meet growing demands due to population growth and changing diets. Additionally, the resilience of crop yields to climate change and rising temperatures needs to be improved. Inhibition of photosynthesis under sub-optimal environmental conditions decreases carbon fixation, reducing crop yields. Heat stress inhibits photosynthesis, in part due to a decrease in the activation state of Rubisco. Rubisco activase (Rca) is required to restore and maintain the catalytic activity of Rubisco. Rca has a relatively low temperature optimum; improving its thermal tolerance would maintain Rubisco activity and enhance photosynthesis at higher temperatures, with predicted positive impacts on grain yields under moderate heat stress. Two approaches were taken to improve the thermal tolerance of Rca in wheat. Firstly, natural variation in the thermal tolerance of Rca in wheat was investigated. Cultivars exhibiting differences in their photosynthetic performance were identified, but the complexity in breeding for increased thermal tolerance was highlighted, with both advantageous and disadvantageous characteristics being identified. The second approach was to introduce the more thermally stable Rca from cotton into wheat in an attempt to broaden the range of temperatures at which photosynthesis operates. Transgenic plants were produced but the cotton Rca protein was undetectable in the wheat lines investigated. Two genes encoding Rca in wheat were identified; one gene is alternatively spliced to produce α and β isoforms. Virus-Induced Gene Silencing of the Rca isoforms in wheat indicated that the Rca genes in wheat may be co-regulated. A non-radioactive activity assay was developed for use in Rubisco and Rca research, allowing high-throughput of samples and avoiding the difficulties some labs may have in completing radioactive assays. The information gained in this study will guide future approaches to optimise the thermal stability of Rca and generate temperature-resilient crops.