UC San Diego

With atmospheric CO2 levels steadily increasing, it is important for humans to understand how plants utilize CO2 and release O2 in the air we breathe. Several CO2 signaling components have been characterized, but there are still many unknown components of the CO2 signaling pathway. This thesis characterizes candidate mutant plants from a comprehensive artificial microRNA (amiRNA) forward genetic screen designed to isolate putative mutants involved in CO2 signaling. Each mutant carried an amiRNA specifically designed to downregulate a few genes in Arabidopsis thaliana. 39 putative mutants were isolated and confirmed at the T3 generation. This project aims to elucidate the role of these genes in CO2-mediated stomatal responses and stomatal development. Gas exchange assays under defined changes in CO2 concentrations were performed to quantify the stomatal conductance and kinetic responses of the candidates. Stomatal density assays were performed to quantify the number of stomata of the candidates. The database ePlant and a Python script were utilized to determine potential interactions between the targeted amiRNA loci and known CO2-mediated stomatal signaling components. The results highlight 15 candidate mutants with unique responses to imposed shifts in CO2 concentration and varying stomatal densities compared to HsMYO (wild-type control) plants. 6 of the putative mutants show an inhibited response to defined changes in CO2 concentration or are affected in stomatal development and warrant further investigation. The 6 putative mutants have been retransformed in wild-type plants and will be examined to verify the robustness of the mutant phenotypes seen in this thesis.