Functions and Interactions of the Arabidopsis phyB/D/E Phytochromes

Montana State University, Bozeman MT

Investigators

Abstract

Plants sense the environmental light cues that control their physiological and developmental processes through the activities of specific photoreceptor molecules. Three basic types of plant photoreceptors have been identified: the red/far-red (R/FR) light sensing phytochromes and the blue light sensing cryptochromes and phototropins. All of these receptors are found in multiple forms in plants and this proposal explores the functions and interactions of members of the R/FR-activated phytochrome family. Phytochromes are known to regulate diverse responses throughout the plant growth cycle, including seed germination, seedling de-etiolation, leaf expansion and stem elongation, shade-avoidance, and flowering time. These responses contribute to a large number of ecologically and agriculturally important plant traits; hence, an understanding of the molecular mechanism of phytochrome signaling is likely to have application across many areas of integrative plant biology. Phytochromes are soluble chromoproteins that exhibit R/FR-photoreversible conformational changes and biological activities. The model plant Arabidopsis contains five different phytochromes, phyA through phyE. Among these, phyA is abundant in dark-grown plant tissue, is strongly down-regulated by light, and regulates responses to prolonged FR and very low fluence R. The phyB-phyE phytochromes are lower in abundance, less light-labile, and function together to regulate plant responses to prolonged R light and the ratio of R to FR. The overall goals of this proposal are to achieve a better understanding of the individual functions of the phyB-phyE phytochromes, the genetic and physical interactions between these photoreceptors, and the molecular mechanisms through which they control cellular signaling pathways. The first objective is to use chimeric phyB/D apoproteins to identify regions of phyB and phyD that have diverged to yield their disparate sensing/signaling activities and to investigate how this divergence has affected their mechanisms. The second objective is to further elucidate the recently discovered binding interactions among the phyB-phyE phytochromes. The third objective is to assess the role of phyD and its physical and genetic interactions with phyB in regulation of floral organ elongation and fertility. The fourth objective is to isolate mutations in phyB that interfere with dimerization and to use these mutations to evaluate the importance of quaternary structure to phytochrome photochemistry and biological function. Challenges in science education facing Montana State University and other universities in predominantly rural areas include geographical and cultural isolation of rural students, notably minority and women students, limited access to role models and mentoring relationships, and lack of opportunities to participate in enrichment programs. The goals of this proposal are to provide improved access for undergraduate and graduate students to individual research experiences, interaction with the broader national and international scientific community, participation in scientific meetings and discussions, and enhanced classroom/laboratory resources.