Regulation of Cytokinin Metabolic Genes

Oregon State University, Corvallis OR

Investigators

Abstract

Cytokinins are plant hormones mediating cell division and differentiation. The most prevalent naturally occurring cytokinin is zeatin, a compound with high biological activity. Various zeatin metabolites are found in plant tissues, some of which are active, others not; therefore, it is important to understand how zeatin metabolism is regulated. The long-term goal of the project is to isolate genetic elements exerting such controls. Studies of zeatin metabolism in seeds of beans led to the identification of four zeatin-specific enzymes, zeatin O-glucosyltransferase, O-xylosyltransferase, reductase and cis-trans isomerase. Gene cloning was initiated with the O-glycosyltransferases, and a family of genes has now been identified in beans and soybean. The sequences of the genes are very similar but encode enzymes with distinct affinity to different cytokinins and sugar donors. Since O-glycosylated zeatin occurs widely in plant tissues and functions as a reversible storage form of cytokinin (via hydrolysis) and as metabolites resistant to enzymatic breakdown, the activity of these genes is likely to have significant impact on the level of active cytokinins. Therefore, these genes are important targets for further molecular and physiological studies. The proposed work will seek to isolate other members of the gene family and determine their expression. The influence of cytokinin O-glycosylation on plant growth will be investigated by generating transgenic plants harboring selected members of the cloned genes. In addition, amino acid sequences on the enzymes critical to recognizing specific substrates will be determined by constructing hybrid genes. The proposed work will define the properties and the effects of a set of cytokinin-specific genes governing a metabolic process ubiquitous in plants. These genes are potential targets for genetic modification and crop improvement.