My main interest is in understanding how extracellular signals are perceived by plant cells to produce cellular responses. Intercellular signaling is important throughout plant growth and development, but the molecular mechanisms and components of many cellular interactions are still poorly understood. These studies have been hindered by the difficulty in manipulating plant cells with their surrounding cell wall. The results of forward genetic screens have not identified many components, especially receptors, of plant signaling pathways. Our studies are carried out using Arabidopsis thaliana because of the availability of genetic and genomics tools. For example, we have learned from the results of the Arabidopsis sequencing project that this plant genome differs in important ways from the animal and fungal genomes that have been sequenced so far. Gene families are significantly larger in the plant genomes, implying there is greater overlapping function between members of these gene families.
One type of receptor used by plant cells to perceive signals is called a receptor kinase; these are composed of an extracellular domain, a transmembrane domain, and a cytoplasmic kinase domain. Two known ligands for receptor kinases include steroids and small peptides. Receptor kinases are the largest gene family within the Arabidopsis genome (420 genes), and little is known about the function of more than 400 of these genes. To learn more about these genes, we are involved in a project to identify insertion mutants in as many receptor kinase genes as possible (http://plantsp.sdsc.edu). These insertion or knockout mutants will help us determine function even with partial redundancy by allowing us to make selected double and multiple mutants. Morphological analyses of phenotypes of single and multiple mutant strains will define the signaling events involving these specific receptor kinases.
One of our goals is to define the signal transduction pathway for the plant steroid hormone brassinosteroids. Brassinosterods are required for cell expansion, and mutations in genes required for brassinosteroid biosynthesis or signaling have a characteristic dwarf phenotype. A receptor kinase known as BRI1 (brassinosteroid insensitive-1, for the insensitive response of bri1 mutants to the plant steroid hormone brassinosteroids) has been demonstrated to be a plasma-membrane receptor for brassinosteroids. We are using the genetic tools available in Arabidopsis to identify additional components of the signaling pathway that initiates with perception at the plasma membrane and ends with changes in transcription and reorganization of the cytoskeleton.
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Lallie, D.J., E. Brooks, F.E. Tax, and E.L. Dolan. 2007. Sowing the seeds of dialogue: Public engagement through platn science. The Plant Cell (in press).
Nodine, M., R. Yadegari, and F.E. Tax. 2007. RPK1 and TOAD2 are two receptor-like kinases redundantly required for Arabidopsis embryonic pattern formation. Developmental Cell 12: 943-956.
Morillo, S.A., and F.E. Tax. 2006. Functional analysis of receptor-like kinases in monocots and dicots. Current Opinion in Plant Biology 9: 460-469 .
Tax F.E., and A. Durbak. 2006. Meristems in the movies: live imaging as a tool for decoding intercellular signaling in shoot apical meristems. The Plant Cell 18: 1331-1337.
Kim, G.-T., S. Fujioka, T. Kozuka, F.E. Tax, S. Takatsuto, S. Yoshida, and H. Tsukaya. 2005. CYP90C1 and CYP90D1 are involved in different steps in the biosynthesis pathway of brassinosteroids in Arabidopsis thaliana. Plant Journal 41: 710-721.
Dievart, A., M. Dalal, F.E. Tax, A.D. Lacey, A. Huttly, J. Li, and S.E. Clark. 2003. CLAVATA1 dominant-negative alleles reveal functional overlap between multiple receptor kinases that regulate meristem and organ development. The Plant Cell 15: 1198-1211.
Choe, S., R.J. Schmitz, S. Fujioka, S. Takatsuto, M.O. Lee, Y. Yoshida, K.A. Feldmann, and F.E. Tax. 2002. Arabidopsis brassinosteroid-insensitive dwarf12 mutants are semidominant and defective in a glycogen synthase kinase 3beta-like kinase. Plant Physiology 130: 1506-1515.
Zhao, J., P. Peng, R.J. Schmitz, A.D. Decker, F.E. Tax, and J. Li. 2002. Two putative BIN2 substrates are nuclear components of brassinosteroid signaling. Plant Physiology 130: 1221-1229.
Li, J., J. Wen, K.A. Lease, J.T. Doke, F.E. Tax, and J.C. Walker. 2002. BAK1, an Arabidopsis LRR receptor-like protein kinase, interacts with BRI1 and modulates brassinosteroid signaling. Cell 110: 213-222.
Tax, F.E., and D. Vernon. 2001. T-DNA associated duplication/translocations in Arabidopsis: implications for mutant analysis, reverse genetics and genomics resources. Plant Physiology 126: 1527-1538.
Li, J., K. Lease, F.E. Tax, and J.C. Walker. 2001. BRS1, a serine carboxypeptidase, is a regulator of BRI1 signaling in Arabidopsis thaliana. Proceedings of the National Academy of Sciences US.A. 98: 5916-5921.
