Plants have many small openings or pores (termed stomata) on the surface of their leaves, by means of which plants control the exchange of gases with the atmosphere. It is through the stomata that plants also lose water vapor; over 95% of plant water loss occurs by transpiration from stomatal pores. Stomatal pores are formed by a pair of guard cells that (by changing shape) control the size of the pore and thereby simultaneously control the rate of water loss from the leaf and the diffusion into the leaf of carbon dioxide from the atmosphere needed for photosynthesis and ultimately growth. There are large changes in the levels of carbon dioxide in the leaves of plants during the day, caused by photosynthesis and respiration. In the longer term, atmospheric carbon dioxide levels are increasing; presently they are 40% higher than before the industrial revolution and are predicted to double during this century. This project will identify and characterize the mechanisms by which plants sense the level of carbon dioxide and use this 1) to regulate the size of the stomatal apertures and 2) to control the number of stomatal pores that form during leaf development. The role of the stomatal pores in simultaneously controlling carbon dioxide exchange and the loss of water from the plant place them in a role central to the response of plants to the continuing increase in atmospheric carbon dioxide and changing patterns of temperature, drought and their associated stresses. However, relatively little is known about the cellular, molecular, genetic and biophysical signaling mechanisms that mediate carbon dioxide control of stomatal function. Identification of the molecular network that controls stomatal aperture and development and understanding physiological function will help predict the effects of rising atmospheric carbon dioxide levels on plants and can contribute to future engineering of crop plants to help avoid heat stress of leaves and enhance their efficiency of water use. In addition to training of graduate students and postdoctoral fellows, the project will provide opportunities for public outreach and research experiences for students from disadvantaged groups underrepresented in science and technology from the Preuss Charter School in San Diego.

A network of signal transduction mechanisms sense and transduce changes in carbon dioxide concentrations to regulate both stomatal movements and stomatal development in plants, thereby optimizing carbon dioxide influx, water loss, heat avoidance and plant growth under stress. Achieving a mechanistic molecular biophysical understanding of how the carbon dioxide stimulus is transmitted into the stomatal conductance regulation network is the long-term goal of this research. Robust carbon dioxide signaling mutants have been identified and their mechanisms of action characterized. However, the predicted intracellular bicarbonate sensors remain unknown. Furthermore, recent advances in this project have shown a key role of carbonic anhydrases in the repression of stomatal development by elevated carbon dioxide levels, leading to a model for carbon dioxide input into the stomatal development machinery. This project will investigate new working hypotheses by identifying bicarbonate sensing and signaling mechanisms in guard cells that function in carbon dioxide-induced stomatal closing. Functional multi-component reconstitution of carbon dioxide/bicarbonate signaling using heterologous expression systems will be used to identify the bicarbonate-activated proteins that mediate the carbon dioxide/bicarbonate response. The project will address the function of photosynthesis in guard cells for carbon dioxide control of stomatal movements and the functions of guard/mesophyll cell starch metabolism in carbon dioxide control of stomatal movements. The functions of the newly identified CRSP protease and CRSP homologs identified in a systems level cell wall proteome analysis will be characterized, and a mathematical model and model-driven experiments will be used to identify new mechanisms that function in carbon dioxide regulation of stomatal development. The carbon dioxide regulation of stomatal conductance will also be investigated using a genomic scale new artificial microRNA library recently developed in the laboratory.

Agency
National Science Foundation (NSF)
Institute
Division of Molecular and Cellular Biosciences (MCB)
Application #
1414339
Program Officer
Gregory W. Warr
Project Start
Project End
Budget Start
2014-07-01
Budget End
2016-06-30
Support Year
Fiscal Year
2014
Total Cost
$400,000
Indirect Cost
Name
University of California San Diego
Department
Type
DUNS #
City
La Jolla
State
CA
Country
United States
Zip Code
92093