Poster: Hormones

Abs # 596: Cytokinin oxidase gene expression in Zea mays is localized to the vasculature, and is induced by cytokinins, abscisic acid, and abiotic stress

Presenter:	Brugière, Norbert , norbert.brugiere@pioneer.com
Authors	Brugière, Norbert  (A)   Jiao, Shuping  (A)   Hantke, Sabine  (A)   Zinselmeier, Chris  (A)   Roessler, Jeff  (B)   Niu, Xiaomu  (A)   Jones, Robert J.  (B)   Habben, Jeffrey E.  (A)
Affiliations:	(A): Pioneer Hi-Bred International Inc., Agronomic Traits, 7250 N.W. 62nd Avenue, Johnston, IA, 50131 (B): University of Minnesota, Department of Agronomy and Plant Genetics, 411 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108

Cytokinins are hormones that play an essential role in plant growth and development. The irreversible degradation of cytokinins, catalyzed by cytokinin oxidase, is an important mechanism by which plants modulate their cytokinin levels. Cytokinin oxidase has been well-characterized biochemically, but its regulation at the molecular level is not well understood. We characterized the expression and regulation of the Ckx1 gene encoding a cytokinin oxidase from maize. We found that the gene is expressed in a developmental manner in the kernel, which correlates with cytokinin oxidase activity. In situ hybridization and transgenic expression of a transcriptional fusion of the Ckx1 promoter to the E. coli b-glucuronidase reporter gene (GUS) revealed that the gene is expressed in the vascular bundles of kernels, seedlings roots and coleoptiles. We show that Ckx1 gene expression is inducible in various organs by cytokinins but not auxins. Ckx1 is also induced in the kernel under abiotic stress. We hypothesize that under non-stress conditions cytokinin oxidase in maize plays a role in controlling growth and development via regulation of cytokinin levels transiting in the xylem. In addition, we suggest that under environmental stress conditions cytokinin oxidase gene induction results in a decrease of cytokinins levels, which slows down cell division and organ development.