UC San Diego

Overview: The global atmospheric CO2 concentration is rising and in 2013 it surpassed 400 parts per million for the first time in human history. Plants can sense CO2 concentrations in leaves and adapt transpiration accordingly. Ultimately, plants control gas exchange by opening and closing stomatal pores, which are highly responsive to changes in CO2 concentration, and CO2-mediated regulation of stomatal conductance has profound effects on plants. Among several signals that regulate stomatal movements, the stress hormone Abscisic Acid (ABA) plays a critical role in plant responses to abiotic stresses such as drought. The molecular signaling mechanisms and network principles by which CO2 and ABA control plant gas exchange were investigated. Three unbiased forward genetic screens were pursued and, after screening over 10,000 artificial microRNA lines and over 1,000 EMS mutagenized Brachypodium lines, partially ABA or CO2 insensitive lines were isolated and are currently being characterized.

Major Goal: Due to the rising atmospheric CO2 concentration, CO2 control of gas exchange in plants will have profound effects on global water-transpiration, plant water use efficiency, leaf heat stress and optimal stomatal conductance of plants, including crops. Elevated CO2 concentrations in leaves cause stomatal closure, whereas reduced CO2 concentrations result in stomatal opening. However, little is known about the molecular signal transduction mechanisms that mediate CO2-induced stomatal movements, especially in grasses. Besides, the stress hormone ABA plays a key role in drought-induced stomatal closure, and the molecular pathways of CO2 and ABA converge, fine tuning stomatal movements in plants. My main goal was to identify and characterize new genes/proteins that play a role in CO2 and ABA signaling in plants, further elucidating these complex molecular pathways.

Specific Goals: Three extensive forward genetic screens were pursued: 1- over 10,000 amiRNA lines were screened for ABA sensitivity, leading to the isolation of partially insensitive lines, 2- over 10,000 amiRNA lines were screened for low [CO2] sensitivity, leading to the isolation and characterization of lines and 3- over 1,000 EMS mutagenized Brachypodium lines were screened, leading to the isolation of two [CO2]-insensitive lines. As some of these finding have already been published (Hauser and Ceciliato et al., 2018 Journal of Experimental Botany), the other most relevant lines are being further investigated.