Function of Basic Helix-Loop-Helix Transcription Factors in Specifying Stomatal Cell Fate

University Of Washington, Seattle WA

Investigators

Abstract

The productivity of land plants relies on the proper development and function of stomata, which are microscopic valves on the plant surface. Stomata regulate the movement of gases between plants and the atmosphere. Molecules of carbon dioxide (a greenhouse gas) enter the plant through the stomata and are converted into carbohydrates by photosynthesis. Oxygen, a byproduct of photosynthesis, is then released from plants to the atmosphere through the stomata. In addition, water loss through open stomata, a process known as transpiration, promotes water movement from the roots and supports plant growth, while closure of stomata prevents plants from wilting. During plant development, stomata are formed through a series of differentiation events, where activation of "master regulatory" transcription factors with a basic helix-loop-helix (bHLH) motif play a pivotal role. Three bHLH proteins, SPEECHLESS, MUTE, and FAMA, act as a switch for three consecutive steps of stomatal cell differentiation, and two other bHLH proteins, SCREAM (SCRM)/ICE1 and SCRM2, act as their partners through the formation of heterodimers. The activity of the SCREAM factors determines the fate of the plant epidermis: the complete absence of SCREAMs eliminates stomatal cell lineages, while gain-of-function of SCRM/ICE1 results in plants that are covered with stomata. This research project will uncover the function and regulation of SCRM/ICE1 and its paralog in specifying stomatal cell fate, and investigate how SCRM/ICE1 influence stomatal-specific bHLH proteins. Biochemical mechanisms that inhibit their action will be investigated, and novel factors that regulate their activity and function will be isolated using a sensitive genetic screen. SCRM/ICE1 has a dual role in freezing tolerance and stomatal differentiation, and the mechanism of the dual function will be explored. The broader impacts of this project include the training of young female scientists (a starting postdoctoral fellow and a graduate student) and an undergraduate student, who will have excellent opportunities to obtain broad training in plant developmental biology, molecular genetics, biochemistry, and cell imaging. Additional undergraduate researchers will also be trained through independent research for credit. They will be mentored directly by the PI to formulate scientific hypotheses, interpret their results, and present their findings within the laboratory as well as in a public setting. A part of this project will be incorporated into the Introductory Biology classroom (with an enrollment of greater than 200 students) and into practical laboratory experiences for college sophomores and juniors. Outreach lectures will be initiated to emphasize the connections between plant stomata and human life, and to encourage young female scientists to advance in their career paths.