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First published online December 16, 2005; 10.1104/pp.105.070706 Plant Physiology 140:150-158 (2006) © 2006 American Society of Plant Biologists Grapes on Steroids. Brassinosteroids Are Involved in Grape Berry Ripening1School of Plant Science, University of Tasmania, Hobart, Tasmania 7005, Australia (G.M.S., J.B.R.); and Commonwealth Scientific and Industrial Research Organization, Plant Industry and Cooperative Research Centre for Viticulture, Glen Osmond, South Australia 5064, Australia (C.D., Y.S., I.B.D., M.R.T.)
Fruit ripening is a unique plant developmental process with direct implications for our food supply, nutrition, and health. In contrast to climacteric fruit, where ethylene is pivotal, the hormonal control of ripening in nonclimacteric fruit, such as grape (Vitis vinifera), is poorly understood. Brassinosteroids (BRs) are steroidal hormones, essential for normal plant growth and development but not previously implicated in the ripening of nonclimacteric fruit. Here we show that increases in endogenous BR levels, but not indole-3-acetic acid (IAA) or GA levels, are associated with ripening in grapes. Putative grape homologs of genes encoding BR biosynthesis enzymes (BRASSINOSTEROID-6-OXIDASE and DWARF1) and the BR receptor (BRASSINOSTEROID INSENSITIVE 1) were isolated, and the function of the grape BRASSINOSTEROID-6-OXIDASE gene was confirmed by transgenic complementation of the tomato (Lycopersicon esculentum) extreme dwarf (dx/dx) mutant. Expression analysis of these genes during berry development revealed transcript accumulation patterns that were consistent with a dramatic increase in endogenous BR levels observed at the onset of fruit ripening. Furthermore, we show that application of BRs to grape berries significantly promoted ripening, while brassinazole, an inhibitor of BR biosynthesis, significantly delayed fruit ripening. These results provide evidence that changes in endogenous BR levels influence this key developmental process. This may provide a significant insight into the mechanism controlling ripening in grapes, which has direct implications for the logistics of grape production and down-stream processing.
1 This work was supported by the Cooperative Research Centre for Viticulture, the Grape and Wine Research and Development Corporation, and the Australian Research Council. 2 These authors contributed equally to the paper. 3 Present address: Australian Centre for Plant Functional Genomics, PMB1, Glen Osmond, South Australia 5064, Australia. 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: Mark R. Thomas (mark.r.thomas{at}csiro.au). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070706. * Corresponding author; e-mail jim.reid{at}utas.edu.au; fax 61–3–62262698. Received August 31, 2005; returned for revision October 23, 2005; accepted November 1, 2005. Related articles in Plant Physiol.:
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