BBMB Research Seminars
October 9, 2008
Alice Harmon
Department of Botany
University of Florida
"Substrates of CDPKs in Arabidopsis and Soybean"
1414 Molecular Biology Buidling
4:10 p.m.
Biosketch
Professor Alice Harmon received her B.S. in Chemistry from the University of Florida in 1970 and Ph.D. in Biochemistry from the University of Georgia in 1984. She joined the Department of Botany at the University of Florida in 1989. Dr. Harmon's research focuses on calcium-dependent protein kinases, which she co-discovered. These protein kinases are involved in plant growth and development and in responses to the environment stress. The kinases are able to sense changes in the cellular concentrations of calcium that result from perception of developmental cues or stress signals. The increased level of calcium activates the kinase activity, which in turn brings about changes in cellular physiology. Dr Harmon's current research projects focus on the roles of calcium-dependent protein kinase in the regulation of sulfur metabolism in soybean in response to stress and in biogenesis of oil-storage bodies of seeds. Dr. Harmon's research has been funded by grants from the National Science Foundation and the United States Department of Agriculture Competitive Grants Program. She has published over 40 papers and received grant funding totaling over $4 million. Dr. Harmon teaches a graduate level course in plant metabolism, an advanced undergraduate biochemistry course, and introductory biology. She served as Graduate Coordinator for her department for eight years.
Abstract
Substrates of calcium-dependent protein kinases Calcium-dependent protein kinases (CDPKs) transduce micromolar calcium signals via binding of Ca2+ to their C-terminal calmodulin-like domains. To identify targets of CDPK signaling, we have used a variety of approaches. In soybean, the substrate serine acetyltransferase2;1 was discovered by interaction cloning. This enzyme, which catalyzes the first step in cysteine synthesis, is phosphorylated in vivo in response to oxidative stress.
Phosphorylation of SAT2;1 prevents feedback inhibition by cysteine, and thus may play a role in protection against reactive oxygen species. Screening of a yeast-two hybrid library with Arabidopsis CPKs 4 and 11 yielded several substrates including Di19-1, a drought stress-induced protein. Di19-1 is phosphorylated within its nuclear localization signal. Testing of synthetic peptide libraries containing 650 peptides based on known Arabidopsis phosphoproteins, yielded 110 substrates. Phosphorylation of at least 20 of these sites in vivo has been confirmed. This work not only identified new CDPK substrates, but also demonstrated both overlap and specificity for substrates of CDPK family members.
Selected Publications
Harper, J.F., Bretton, G. and A.C. Harmon, 2004, Decoding Ca2+ signals through plant protein kinases, Annu. Rev. Plant Biol. 55:263-288
Liu, F., B.-C. Yoo, J.-Y. Lee, W. Pan, and A.C. Harmon 2006, Calcium-regulated phosphorylation of soybean serine acetyltransferase in response to oxidative stress, J. Biol. Chem. 281:27405-27415
Rodriguez Milla, M.A., Uno, Y., Chang, I.-F. Townsend, J., Maher, E.A., Quilici, D., Cushman, J.C. (2006) A novel yeast two-hybrid approach to identify CDPK substrates: Characterization of the interaction between
AtCPK11 and AtDi19, a nuclear zinc finger protein. FEBS Lett. 580: 904-911
