Poster: Hormone synthesis & metabolism

Abs # 479: Understanding cytokinin N-glucosyltransferase metabolism using Arabidopsis mutants.

Presenter:	Auer, Carol , carol.auer@uconn.edu
Authors	Dwivedi, Somya  (A)   Auer, Carol  (A)
Affiliations:	(A): University of Connecticut

Cytokinin levels in plants are down-regulated through conjugation to sugars and/or degradation by cytokinin oxidase. One important pathway for irreversible inactivation of cytokinins is through N-glucosylation of the cytokinin purine ring at the N-7 or N-9 position. In contrast to cytokinin oxidase, almost nothing is known about the function, biochemistry or genetics of the N-glucosyltransferase (N-GT) enzyme pathway(s). The best evidence for N-GT pathways comes from cytokinin feeding studies. Arabidopsis studies showed that 48% of benzyladenine was converted to the N-9 conjugate and 10% to the N-7 conjugate, and analysis of endogenous cytokinins demonstrated the presence of N-7 and N-9 glucosides. Therefore, the N-GT enzyme(s) down-regulate the level of active cytokinins in Arabidopsis and mutants could identify genes involved in the N-GT pathway(s). At present, we are screening activation-tagged lines for N-GT over-expression mutants. A few cytokinin analogs (roscovitine, olomoucine) have been discovered which block activity of the N-GT enzymes. We have designed an in vitro screening process that selects activation-tagged plants resistant to roscovitine, suggesting over-expression of N-GT enzymes. At present, we are focusing on the mutant ror-1 (roscovitine resistant) which shows normal elongated hypocotyl growth when cultured on 2μM roscovitine in the dark. The ror-1 mutant is not resistant to the closely related compound olomoucine. Flowering time and overall phenotype are similar to wild type plants. Many additional experiments are being conducted to characterize hormone response, patterns of cytokinin metabolism and other aspects of ror-1 phenotype.