Machteld Mok
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Professor, Horticulture |
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Education
Ph.D. 1975, University of Wisconsin, MadisonResearch
Our research focuses on two areas: 1) Regulation of the metabolism of cytokinins, an important group of plant hormones; and 2) Genetic modification of plants using tissue culture and/or gene transfer techniques.Cytokinins are known to play a crucial role in plant development; however, the mechanisms controlling the levels of cytokinins in plant tissues are poorly understood. Our objectives are to identify and characterize enzymes and genes involved in cytokinin metabolism; to determine the expression of these genes during plant development; and eventually, to modify plant development by targeted changes in the expression of key genes. These studies have led to identification of a novel group of cytokinin metabolites (O-xylosyl derivatives of zeatin and dihydrozeatin), purification of four key enzymes involved in zeatin metabolism (an O-xylosyltransferase, O-glucosyltransferase, reductase, and cis-trans-isomerase), and isolation of genes encoding the O-glucosyltransferase and O-xylosyltransferase. Presently, we are further characterizing this gene family and determining their role in plant development. Isolation of additional genes is in progress.
Unconventional strategies are aimed at genetic improvement of horticultural plants. Past projects were centered on: interspecific gene transfer in beans using embryo rescue techniques, haploid production of lily by anther culture, regeneration of plants from pear rootstocks, and selection of somaclonal variants of quince with increased tolerance to low iron. Recent emphasis has been on expression of the yeast FRE genes, encoding Fe(III) reductases, in plants. The long-term goal of this research is to improve Fe utilization under low-Fe conditions. FRE1 and FRE2, placed under control of the 35S promoter, were used to transform tobacco. The transformed plants showed enhanced Fe(III) reduction in roots as well as shoots. Tests determining the responses of these plants to conditions where Fe availability is limiting indicated that FRE2 confers increased tolerance to low Fe availability.