Biological Sciences

Yunde Zhao Associate Professor Section of Cell and Developmental Biology, UCSD e-mail: yzhao@biomail.ucsd.edu Lab Homepage: Zhao Lab

    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.

    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.