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David Mok
Emeritus Professor, Horticulture
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RESEARCH:
Research interests include 1) Genetic regulation of cytokinin metabolism, and 2) genetic controls of embryo development and gene transfer in food legumes.
1) Cytokinins are plant hormones mediating cell division and differentiation. Appropriate levels of cytokinins are required for programmed development. Biosynthesis, metabolism, transport and perception can all affect the level of active cytokinins. The long-term goal of the project is to identify and characterize genes important to cytokinin biology. The project is focused on the metabolism of zeatin, the most prevalent naturally occurring cytokinin. Three groups of enzymes, O-glycosyltransferase (O-glucosyl- and O-xylosyl-), reductase and cis-trans isomerase have been identified. Gene families encoding zeatin O-glucosyltransferases and O-xylosyltransferases have been cloned (from Phaseolus. lunatus, P. vulgaris, Glycine max, Zea mays, Oryza sativa and Arabidopsis.). Some aspects of these genes have been characterized and their effects on plant development explored in model plants, tobacco and Arabidopsis as well as maize and soybean. The regulation of gene expression, modeling of protein structure and the growth function of these genes are being examined. In addition, we are in the process of cloning genes encoding zeatin reductase and isomerase.
2) Research on introgression between Phaseolus species led to the discovery of species-dependent developmental arrest at specific stages of hybrid embryos. RFLP analyses are used to identify genomic constitutions conditioning abnormal embryo development and to study the phenomena of gametic and zygotic selection. Skewed distribution of parental phenotypes in later generations of interspecific hybrids was influenced by the cytoplasm favoring nuclear markers originating from the same parental species.