Poster: Hormones

Abs # 605: Genome level analysis of cytokinin regulation in Arabidopsis

Presenter:	Rashotte, Aaron M., rashotte@unc.edu
Authors	Rashotte, Aaron M. (A)   Morris, Veronica R.F. (A)   Carson, Susan D.B. (A)   To, Jennifer P.C. (A)   Kieber, Joseph J. (A)
Affiliations:	(A): University of North Carolina

The hormone cytokinin is an important regulator of plant growth and development, yet relatively few genes that mediate cytokinin responses have been identified. We conducted genome level analyses of Arabidopsis seedlings using Affymetrix ~8,300 element Arabidopsis GeneChips. This revealed at least thirty genes whose steady-state level of mRNA was elevated, and at least forty that were down-regulated at multiple time points following application of cytokinin. The cytokinin up-regulated genes include the type-A ARRs, which had previously been shown to be cytokinin primary response genes, cytokinin oxidase, which encodes an enzyme that degrades cytokinins, and several transcription factors. Cytokinin down-regulated genes include several peroxidases and kinases and an E3 ubiquitin ligase. We identified a potential cytokinin responsive element (CyRE) enriched in the upstream regions of the most consistently cytokinin-up regulated genes. This element is highly similar to the optimal DNA binding sites for ARR1/ARR2, type-B ARRs that have been implicated in the transcriptional elevation of the type-A ARRs. Additionally, analyses of cytokinin receptor mutants revealed large-scale changes in gene expression, including down-regulation of the type-A ARRs and several meristem and cell cycle genes, such as CycD3. However, mutations in CRE1 had relatively little effect on gene induction in response to exogenous cytokinin, suggesting functional redundancy among the cytokinin receptors.