Molecular Mechanisms of CO2 Signal Transduction in Plants

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Plant leaves have thousands of microscopic adjustable pores in their leaf surface, called stomata. These stomatal pores in the surface of leaves open and close to regulate the necessary uptake of carbon dioxide into plants from the air. However, these stomatal pores also are the main pathway by which plants lose water, by evaporation. A typical plant loses 200 to 500 water molecules through these stomatal pores for every carbon atom that is absorbed (assimilated) by the plant for growth. The opening and closing of stomata is regulated by signals that include the concentration of carbon dioxide (CO2) in the air. The concentration of CO2 in the air is now 50% higher and rising, compared to only 150 years ago, meaning that plants could theoretically more efficiently take up CO2 from the air, while losing less water. However, important mechanisms and genes that mediate this agronomically relevant CO2 response of stomatal pore aperture regulation remain unknown. This project will characterize newly found key genes and proteins and define cellular networks through which elevated carbon dioxide controls the closing of stomatal pores and how low CO2 controls the opening of stomatal pores. This research can develop the knowledge necessary for the breeding of plants with improved growth properties and enhanced water use efficiency. The ability to manipulate the response of stomatal pores to carbon dioxide is important for unfavorable weather conditions, agricultural ground water depletion and droughts that are becoming more frequent in several of the major agricultural regions in the US as well as globally. The scientists will pursue an outreach program with research internships, professional preparation 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 ENLACE program and with Howard University. Project personnel will be active within community outreach work that brings science and innovation close to the public and the investigators will participate in a recently launched outreach program through presentations and discussions with underrepresented students at inner city high schools in San Diego.This project will use a combination of cell biological, biochemical, molecular genetic, mathematical modeling, genomic and systems biological approaches to identify new critical molecular components of the CO2 signaling network and characterize how this network operates to regulate stomatal pore apertures. The focus of this project is to identify how the CO2 stimulus is transmitted into the stomatal movement network, with these goals: (1) Biochemical mechanisms and network principles will be determined by which newly identified genes and the encoded proteins mediate early CO2 sensing and signal transduction. (2) New hypotheses will be investigated on how cell-to-cell signaling in leaves affects CO2 control of stomatal movements by combined computational modeling, genetics, metabolomics and molecular cell biology. (3) Newly isolated "chill" mutants that have cooler leaf temperatures and are defective in the dynamic CO2 response of grass stomata will be mapped and the underlying gene and protein of at least one rate-limiting gene will be isolated and its functions in stomatal movements of the specialized dumbbell-shaped guard cells of grasses will be determined.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.