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IN BRIEF

Three Arabidopsis GID1 Genes Encode Gibberellin Receptors with Overlapping Functions

neckardt{at}aspb.org

Arabidopsis contains a family of three genes (GID1a, GID1b, and GID1c) that encode putative gibberellin (GA) receptors. Griffiths et al. (pages 3399–3414) present a thorough genetic characterization of single, double, and triple gid1 mutants of Arabidopsis that provides strong evidence that the proteins encoded by all three genes are bona fide GA receptors. The triple gid1 mutant, which lacks all three receptors, is severely dwarfed and does not exhibit any of the known GA responses examined. Although the three GID1s were found to be largely functionally redundant, gene expression and mutant analysis showed that they likely have some degree of functional specificity. For example, in contrast with the triple mutant, all of the single and double mutants flowered at the same time as wild-type plants, indicating that the GID1 genes possess functionally redundant roles in promoting floral initiation in long-day photoperiods. However, some specificity was evident in their regulation of stem, filament, and silique elongation.

Additional experiments support the notion that GA responses are regulated by a complex network of interactions (at both gene transcript and protein levels) among GA-promoting components (GA biosynthetic enzymes and GA receptors) and GA signaling repressors (DELLA proteins). GA derepresses its signaling pathway by inducing degradation of the DELLA proteins via the ubiquitin-proteasome pathway. Griffiths et al.provide evidence from yeast two-hybrid and pull-down assays for GA-dependent direct interaction between GID1 and DELLA proteins via their N-terminal DELLA domain. In addition, three-hybrid assays showed that the GA-GID1 complex enhanced direct binding of the F-box protein SLY1 to the DELLA proteins. Therefore, upon binding to bioactive GA, GID1 appears to derepress the GA response pathway by binding to DELLA proteins and promoting their degradation via the SCF^SLY1-proteasome pathway. This work represents a significant contribution to the field of GA signaling.

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Severe defects in floral organ morphology of the gid1 triple mutant.

www.plantcell.org/cgi/doi/10.1105/tpc.107.181210

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Genetic Characterization and Functional Analysis of the GID1 Gibberellin Receptors in Arabidopsis

Jayne Griffiths, Kohji Murase, Ivo Rieu, Rodolfo Zentella, Zhong-Lin Zhang, Stephen J. Powers, Fan Gong, Andrew L. Phillips, Peter Hedden, Tai-ping Sun, and Stephen G. Thomas
Plant Cell 2006 18: 3399-3414. [Abstract] [Full Text]  

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