title: Grapes on steroids. Brassinosteroids are involved in grape berry ripening.
abstract: 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.
authors.affiliation: School of Plant Science, University of Tasmania, Hobart, Tasmania 7005, Australia.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Symons
authors.forename: Christopher
authors.initials: C
authors.lastname: Davies
authors.forename: Yuri
authors.initials: Y
authors.lastname: Shavrukov
authors.forename: Ian B
authors.initials: IB
authors.lastname: Dry
authors.forename: James B
authors.initials: JB
authors.lastname: Reid
authors.forename: Mark R
authors.initials: MR
authors.lastname: Thomas
mesh_terms: D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000033:anatomy & histology / Q000378:metabolism; D015398:Signal Transduction; D013256:Steroids / Q000378:metabolism / Q000502:physiology*; D014230:Triazoles / Q000378:metabolism; D027843:Vitis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism
chemical_list: D005875:Gibberellins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D013256:Steroids; D014230:Triazoles; C030737:indoleacetic acid; C007842:gibberellic acid; C412342:brassinazole