Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/31/2005
Publication Date: N/A
Interpretive Summary: A gene that encodes an enzyme that glycosylates zeatin was isolated from beans and homologs were later isolated from corn, rice and Arabidopsis. The enzymes from monocots preferred cis-zeatin and o-topolin as substrates and the enzymes from dicots preferred trans-zeatin and m-topolin as substrates. Molecular modeling was used to determine regions that were important in determining substrate specificity in these enzymes and in cytokinin receptors.
Technical Abstract: Cytokinins occur as free bases, nucleoside, nucleotides, N-glucosides, O-glucosides, and O-xylosides. Zeatin O-glycosylation genes and enzymes were isolated and characterized. The first genes were cloned from Phaseolus and subsequently, homologs were identified in other species including maize, rice, Arabidopsis. The enzymes from dicots and monocots obtained thus far prefer zeatin and cis-zeatin respectively as substrate. Interestingly, topolins are also substrates of these enzymes, with parallel preference for m-topolin and trans-zeatin, and for o-topolin and cis-zeatin. Based on enzyme/substrate interactions and receptor assays, similarities are evident between cytokinin-binding sites on the enzymes and receptors. Cytokinin O-glycosyltransferases display sugar donor preference, recognizing UDP-glucose, UDP-xylose, or both. Sequence comparisons, nucleotide exchanges, and enzyme modeling have pinpointed regions of importance to substrate binding. Transgenic experiments with tobacco and maize indicated that effects of increasing zeatin O-glucosylation are partly species-specific.