UC San Diego

Plants respond to elevated CO2 concentrations with stomatal closure, which increases intrinsic water use efficiency. CO2-induced stomatal closing also reduces the evaporative cooling ability of leaves, which may increase susceptibility to heat stress. Since the onset of the Industrial Revolution, global atmospheric CO2 concentrations have rapidly increased, reaching levels of approximately 420ppm. For this reason, it is crucial to understand the response of cereal crops to CO¬2 in order to potentially engineer enhanced water use efficiency and/or mitigate potential crop yield penalties as a result of climate change. In the grass model Brachypodium distachyon, novel components of the CO2 signaling pathway are being investigated through the analysis of chill mutant lines identified in a forward genetic screen of over 1000 individual EMS mutagenized lines. These chill lines display reduced sensitivity to shifts in CO2 compared to the wildtype Bd21-3, and characterization analyses of the most promising lines suggest specificity of the mutant to the CO2 signaling pathway. Candidate mutations have been identified in mutant lines chill15 and chill1 through the use of techniques in genetics, molecular biology, and bioinformatics. In chill15, candidate mutations in genes were investigated through the sequencing of impactful mutations identified by Bulk Segregant Analysis of the Bd21-3xchill15 F2 generation. In chill1, candidate genes have been analyzed through the creation and characterization of CRISPR lines to determine the gene responsible for the chill1 phenotype.