Function of HRBs and interaction of HRB1 with PP7 in blue light-mediated stomatal opening

Intellectual Merit: Drought is one of the major environmental factors that limit crop yield. The stomatal pores of plant leaves, situated in the epidermis and surrounded by a pair of guard cells, allow CO2 uptake for photosynthesis and the loss of water through transpiration. Blue light regulates the stomatal aperture and the signals are perceived by the blue/UV A light-absorbing phototropins and cryptochromes. The signaling components that link the perception of blue light to the stomatal opening response are largely unknown, and hypersensitive to red and blue (hrb) mutants are of particular interest. The hrb mutants were initially isolated for their short hypocotyl phenotype under red and blue light. Interestingly, the blue light-induced stomatal opening response is also impaired in the hrb mutants, and the mutant plants are more resistant to dehydration and show reduced water loss and stomatal aperture. The strong stomatal phenotype of the hrb mutants may be due to impairment in both red and blue light signaling since red light often enhances blue light responses. The HRB1 gene has been molecularly cloned and encodes a nuclear ZZ-type zinc finger protein. HRB1 physically interacts with phosphatase 7 (or PP7), a nuclear serine/threonine phosphatase and a positive regulator of blue light signaling, through its ZZ-type zinc finger domain. The goal of this project is to understand the roles of HRBs in blue light regulation of stomatal aperture. How HRB1 functions within the phototropin and cryptochrome signaling pathways and the function of HRB1 in hrb2 and hrb3 backgrounds will be investigated. How HRB1 and PP7 interact in vivo and genetically and the nature of their interaction will also be thoroughly studied.

Broader Impacts: This research will provide excellent opportunities for undergraduates, graduate students, and postdoctoral fellows to gain significant research experiences, and most importantly, to develop their ability to critically analyze and solve scientific problems. A diverse group of undergraduates including African American and Hispanic students have conducted research in this lab in the past. Six of the 13 undergraduates are minorities from a campus-wide life science summer undergraduate research program. The students are recruited throughout the country, spend 10 weeks on the campus, participate in major research projects and a weekly seminar series, and present their research results to their peers and mentors at a concluding symposium. In specific aim I of this project, a specific training plan was outlined for the undergraduates, ranging from physiological, genetic, to molecular studies. On an even broader level, this project will open new possibilities to engineering stomatal activity and help plants to survive desiccation. The stomatal aperture is also regulated by other environmental cues such as drought in addition to blue light. Given that hrb plants may still respond to ABA, a well-known drought signal, these plants should enjoy the advantages of both constitutive and induced protection under water-limiting conditions.