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DEVELOPMENT AND HORMONE ACTION

Genetic and Molecular Regulation by DELLA Proteins of Trichome Development in Arabidopsis^1,[W],[OA]

Centre for Novel Agricultural Products, Department of Biology, University of York, York YO10 5YW, United Kingdom (Y.G., P.B.); Department of Biological Sciences and Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117543 (H.Y.); and Functional Genomics Laboratory, Institute of Molecular and Cell Biology, Protesos, Singapore 138673 (J.P.)

Gibberellins (GA) are known to influence phase change in Arabidopsis (Arabidopsis thaliana) as well as the development of trichomes, which are faithful epidermal markers of shoot maturation. They modulate these developmental programs in part by antagonizing DELLA repressors of growth, GIBBERELLIC ACID INSENSITIVE (GAI) and REPRESSOR OF ga1-3 (RGA). In this study, we have probed the relative roles played by RGA, GAI, and two homologs, RGA-LIKE1 (RGL1) and RGL2, in these processes and investigated molecular mechanisms through which they influence epidermal differentiation. We found that the DELLAs act collectively to regulate trichome initiation on all aerial organs and that the onset of their activity is accompanied by the repression of most genes known to regulate trichome production. These effects are consistent with the results of genetic analysis, which conclusively place theses genes downstream of the DELLAs. We find that repression of trichome regulatory genes is rapid, but involves an indirect, rather than a direct, molecular mechanism, which requires de novo protein synthesis. DELLA activity also influences postinitiation events and we show that GAI is a major repressor of trichome branching, a role in which it is antagonized by RGL1 and RGL2. Finally, we report that, in contrast to most other effects, the repression by GA applications of flower trichome initiation is not dependent on RGA, GAI, RGL1, or RGL2. In summary, our data show that DELLA proteins are central to trichome development in Arabidopsis and that their effect can be largely explained by their transcriptional influence on trichome initiation activators.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Pierre Broun (pierre.broun{at}rdto.nestle.com).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.104794

^* Corresponding author; e-mail pierre.broun{at}rdto.nestle.com.

Received June 27, 2007; accepted August 8, 2007; published August 17, 2007.