Yunde Zhao
e-mail: yzhao@biomail.ucsd.edu |
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The goal of our research is to elucidate the mechanisms by which the plant hormone auxin regulates plant growth and development. Although auxin has been studied for over a century, the biochemical mechanisms that govern auxin-regulated processes have remained elusive. One of the major obstacles in auxin research has been a lack of knowledge of the details of the various auxin biosynthetic pathways. In order to help bridge this gap, our efforts had initially been focused on auxin biosynthesis; however, results from these studies have enabled us to investigate auxin-mediated signal transduction from a completely different perspective. Research in our laboratory is multidisciplinary, in that it draws on techniques rooted in classical genetics, chemical genetics, biochemistry, physiology, molecular biology, and bioinformatics. We currently use Arabidopsis as the model system.
We have identified and characterized an auxin overproducing Arabidopsis mutant named yucca (Zhao et al. (2001), Science 291, 306-309). This mutant displays typical auxin-mediated phenotypes, namely, light grown yucca has long hypocotyls and epinastic cotyledons, whereas dark grown yucca has short hypocotyls and lacks an apical hook. The protein encoded by YUCCA is a flavin-containing monooxygenase that catalyzes the N-hydroxylation of tryptamine, a key step in tryptophan dependent auxin biosynthesis. Based on the detailed characterization of yucca phenotypes, we have been able to carry out a genetic screen for yucca-like mutants that should enable us to identify new components in both the auxin biosynthesis and signal transduction pathways. We have also initiated a genetic screen for mutants that can suppress yucca phenotypes. The cloning and characterization of the mutants already identified by these screens is one of our current priorities. In addition, we have undertaken the biochemical characterization of YUCCA and its associated proteins.
We have also initiated a chemical genetics
approach to elucidate gene functions in Arabidopsis, with
the initial focus on genes that are involved in auxin homeostasis
and signal transduction. We have identified a small molecule sirtinol
that constitutively activates auxin signal transduction. Analysis
of sirtinol resistant mutants led to the discovery of a key auxin
signaling component SIR1 (Zhao et al. (2003), Science 301,
1107-1110). We are currently characterizing other sirtinol resistant
mutants and analyzing the biochemical mechanisms of SIR1.
Cheng, Y., Dai, X., and Zhao, Y. (2006). Auxin biosynthesis by the YUCCA flavin monooxygenases controls the formation of floral organs and vascular tissues in Arabidopsis. Genes and Development 20 (13): 1790-1799.
Dai, X., Hayashi, K., Nozaki, H. Cheng, Y., and Zhao, Y. (2005). Genetic and chemical analyses of the action mechanisms of sirtinol in Arabidopsis. PNAS 102: 3129-3134.
Cheng, Y., Dai, X. and Zhao, Y. (2004). AtCAND1, A HEAT-Repeat Protein That Participates in Auxin Signaling in Arabidopsis. Plant Physiol. 135: 1020-1026.
Zhao, Y., Dai, X., Blackwell, H.E., Schreiber, S.L., and Chory, J. (2003). Chemical genetics identifies SIR1, a missing link in auxin signaling in Arabidopssis. Science 301: 1107-1110.
Zhao, Y., Hull, A. K., Gupta, N., Goss, K.A., Alonso, J., Ecker, J. R., Normanly, J., Chory, J., and Celenza, J. L. (2002). Trp-dependent auxin biosynthesis in Arabidopsis: involvement of cytochrome P450s CYP79B2 and CYP79B3. Genes & Development, 16: 3100-3112.
Zhao, Y. and Chory, J (2001). A link between the light and gibberellin signaling cascades. Development Cell 1: 315-316.
Zhao, Y., Christensen, S. K., Fankhauser, C., Cashman, J. R., Cohen, J. D., Weigel, D., and Chory, J (2001). A Role for Flavin monooxygenase-like enzymes in auxin biosynthesis. Science 291: 306-309.
Yunde Zhao received his Ph.D. in biochemistry from the University of Michigan and his postdoctoral training in plant genetics at the Salk Institute, where he was a Howard Hughes Medical Institute Fellow of the Life Sciences Research Foundation.
