Research focuses on how the environmental stimuli of light and gravity alter patterns of growth and development in plants. Molecular approaches are used to characterize proteins that are critically involved in coupling light and gravity stimuli to morphogenic changes in plants. Studies of light-induced signal transduction has led us to a focus on potential signaling proteins that function primarily or partially in the nucleus. Proteins recently characterized include annexins and apyrases (= NTPase), both of which belong to a family of related proteins. Proteins in both of these families also function in the cell walls of plants. The effects of light on the abundance of mRNAs that encode certain apyrases and annexins have been documented. The phenotypes of transgenic Arabidopsis plants that ectopically express the sense or antisense versions of the genes encoding certain apyrases and annexins have been characterized. Antibodies to most of these proteins have been raised to help immunolocalize them and quantitate their expression. Most of the proteins carry out their nuclear and cell wall functions in partnership with other proteins. To help define these binding partners the yeast two-hybrid system and co-IP methods are being employed. Investigations of the molecular biology of these proteins should help to clarify how they function in plant photomorphogenesis.
Apyrase studies are currently being focused on the ability of certain apyrases to increase the nutrient uptake and seed yield of certain valuable crop plants. Identifying the signaling steps that link increased expression of apyrases to increased production of seeds would be an important contribution to addressing food security issues facing future generations. Both apyrases and annexins play significant roles in mediating the gravity response of plants, and both do so by modulating the asymmetric uptake of calcium into the plant cells that is induced by gravity. For gravitational studies, a single-cell model system has been developed, germinating spores of Ceratopteris richardii, in which gravity orients the direction of nuclear migration and subsequent polarization of spores while they are still single cells. The utility of this system for defining the genes needed for gravity responsiveness is being investigated. Both a Shuttle experiment (STS-93, July 1999) and parabolic flight experiments, which rapidly generate both hyper-g and micro-g forces on cells, have been completed, and these studies have allowed the identification of genes that are differentially expressed in microgravity and an examination of the role of these genes in mediating the gravity response.