Molecular Mechanisms of Stomatal CO2 Signal Transduction in Plants

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Plant leaves have a very large number of tiny pores, named stomata, that regulate water loss while providing the pathway for carbon dioxide (CO2) to enter leaves. CO2 is a vital plant nutrient, and is required for plant growth and crop production. However, a typical plant loses between 150 and 500 water molecules through these stomatal pores for every carbon atom that is absorbed from CO2 for nutrition and growth. The opening and closing of these stomatal “breathing” pores in leaves is regulated by the concentration of CO2 inside leaves. Since the concentration of CO2 in the air is now 50% higher than it was 150 years ago, plants could more easily take up CO2 from the air while losing less water. Yet important mechanisms and genes that enable this agriculturally important CO2 response of stomatal pore regulation are unknown. This research will identify proteins and genes of a recently discovered CO2 sensor in order to determine cellular signaling mechanisms through which carbon dioxide controls plant water loss and CO2 intake. The ability to improve the response of stomatal pores to carbon dioxide is important for unfavorable weather conditions, agricultural ground water availability, and droughts that are becoming more frequent in several of the major agricultural regions in the US. Project personnel will prepare graduate students for professional careers and further conduct an outreach program with scientific training internships and professional preparation of students and mentoring with the public Preuss School for disadvantaged high school students in San Diego County, as well as training and professional preparation of visiting underrepresented summer research interns with UC San Diego’s STARS and ENLACE program. The researchers will be active with community outreach work that brings science and innovation close to the public. The PI will also conduct outreach through presentations and discussions with students and K-12 teachers in San Diego. Atmospheric CO2 is predicted to double during this century and the ensuing concentration rise in CO2 rise will reduce stomatal conductance of plants globally, which will have severe effects on gas exchange, leaf heat stress, plant water use efficiency, and plant robustness, but can also benefit plant growth. A network of signal transduction mechanisms senses and transduces CO2 changes to regulate stomatal movements for optimization of CO2 influx, water loss and plant growth under diverse conditions. In recent research these researchers have identified a major CO2/bicarbonate sensor consisting of a complex of a Raf-like kinase (HT1) and a MAP kinase (MPK12 & MPK4). Major questions and new hypotheses have arisen from this advance as to the unknown cellular locations and protein properties of the recently discovered reversible MPK12/4 – HT1 CO2/bicarbonate sensor, the molecular nature of unknown protein phosphatases that are predicted to be required to “shut off” this CO2 sensing core, and a gap in molecular and cellular mechanisms linking this proposed CO2 sensing core to downstream guard cell signaling mechanisms. Moreover, no forward genetics stomatal CO¬2-specific response screen in grasses has been reported, despite the agronomic important of grasses. New hypotheses will be directly investigated based on the team’s recent discoveries. This project will leverage interdisciplinary cell biological, molecular genetic, biophysical, biochemical and genomic approaches to identify new critical molecular components of the CO2 signaling network and characterize how this network operates to regulate stomatal pore apertures, plant transpiration and CO2 influx. This award is funded by the Cellular Dynamics and Function Cluster of the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.