Abiotic stress is a major limitation on agricultural productivity. Due to global climate change and rising temperatures, plants increasingly face the threat of heat stress, which has significant impacts on plant growth and crop yield. C4 plants are thought to have evolved under warm and dry conditions. The implementation of a carbon concentrating pathway, known as the C4 pathway, serves to alleviate the cost of photorespiration at moderately high temperatures. The accompanying benefits of the C4 pathway also include high water and nitrogen use efficiencies. There are over 60 independent lineages of C4 plants, accounting for about 3% of the total number of land vascular plant species. However, C4 plants contribute ~25% of the total terrestrial primary productivity, owing to their high photosynthetic efficiency.
Setaria viridis (also known as the “green foxtail”) is an emerging C4 model species for the C4 research community, due to its small stature, short lifespan and small diploid genome. It is the wild relative of Setaria italica (“foxtail millet”), a major staple species cultivated mainly in northern China. S. viridis is also phylogenetically closely related to maize and sorghum, making it an attractive model species for C4 monocot plants. This thesis presents a systematic analysis of the long-term heat stress response in S. viridis, with the aim of understanding its heat stress response at the physiological, anatomical, metabolic, transcriptional and proteomic level, in order to gain insights into its mechanisms of heat tolerance. Plants grown at 42 C for two weeks (as compared to 28 C) showed stunted growth, despite heat showing little impact on leaf area-based photosynthetic rates. Rates of dark respiration significantly increased in the heat-stressed plants. Major alterations in carbon and nitrogen metabolism were observed in the heat-stressed plants, represented by reduced amount of starch, accumulation of soluble sugars and increase in dry weight leaf total nitrogen content. The levels of major hormones were also measured. These were characterized by a dramatic increase in abscisic acid in the heat-stressed plants. Leaf transcriptomics, proteomics and metabolomics analyses were carried out for the control and heat-stressed plants, and the heat response of the corresponding genes (transcript and protein) were mapped onto each of the aforementioned metabolic pathways (photosynthesis, respiration, carbon/nitrogen metabolism and hormone synthesis and signaling pathways) to identify the underlying causes of the changes in metabolism.