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IN BRIEF

GA Signaling: Direct Targets of DELLA Proteins

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DELLA proteins are negative regulators of gibberellin (GA) signaling that act immediately downstream of the GA receptor. Binding of GA to its soluble receptor, GID1, causes binding of GID1-GA to DELLAs and leads to their degradation via the ubiquitin-proteasome pathway. DELLAs are nuclear localized and are hypothesized to function as transcriptional regulators, but little is known about their direct targets or even whether they bind DNA directly. Zentella et al. (pages 3037–3057) used microarray gene expression analysis to identify direct targets of DELLA proteins in Arabidopsis seedlings. The authors compared gene expression in the GA-deficient mutant ga1-3 in the presence and absence of GA treatment to identify early GA-regulated genes and examined downstream gene expression affected by induced expression of a dominant DELLA mutant protein in a dexamethasone-inducible system to identify DELLA-regulated genes. These experiments led to the identification of 14 early GA-responsive genes that are also early DELLA responsive. These included genes encoding GA biosynthesis components and GA receptors, ubiquitin E2/E3 enzymes, and putative transcription factors/regulators. Chromatin immunoprecipitation experiments provided evidence for in vivo association of DELLA proteins with promoters of eight of these genes. Surprisingly, the expression of all 14 genes was downregulated by GA and upregulated by DELLA. This suggests that DELLA proteins promote the expression of downstream negative components of GA signaling and provide a direct feedback mechanism for regulating GA homeostasis. DELLA may also mediate interaction between GA and ABA pathways because one of its targets (XERICO) regulates ABA metabolism.

View larger version (16K): [in this window] [in a new window] [as a PowerPoint slide]   DELLA inhibits GA-promoted processes by modulating both GA and ABA pathways.

www.plantcell.org/cgi/doi/10.1105/tpc.107.191010

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Global Analysis of DELLA Direct Targets in Early Gibberellin Signaling in Arabidopsis

Rodolfo Zentella, Zhong-Lin Zhang, Mehea Park, Stephen G. Thomas, Akira Endo, Kohji Murase, Christine M. Fleet, Yusuke Jikumaru, Eiji Nambara, Yuji Kamiya, and Tai-ping Sun
Plant Cell 2007 19: 3037-3057. [Abstract] [Full Text]  

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