Gibberellin metabolism in Vitis vinifera L. during bloom and fruit-set: functional characterization and evolution of grapevine gibberellin oxidases

Gibberellin are involved in the regulation of flowering and fruit-set in grapes (Vitis vinifera L.), although the molecular mechanisms intervening in this process are not completely known. Berry and bunch morphology are economically important traits in cultivated grapes, which are controlled with the aid of exogenous GA treatments especially at bloom and fruit-set, In this work we characterized the family of grapevine GA oxidase genes involved in biosynthesis and deactivation of bioactive GAs, by a combination of phylogenetic analysis, in-vitro activity tests and ectopic expression. We identified six putative GA 20-oxidases (GA20ox), three GA 3-oxidases (GA3ox) and eight GA 2-oxidases (GA2ox), the latter further distinct into five C19-GAox and three C20-GAox. Our phylogenetic analyses suggest a common origin of GAox acting on C19 GAs (GA3ox and C19-GA2ox). In vitro analysis with selected members of each group revealed that all GA3ox and GA20ox enzymes prefer substrates of the non-13-hydroxylation pathway. In addition, ectopic expression of four grapevine GA2ox in Arabidopsis thaliana confirmed their activity in vivo. In this work we showed that bioactive GA1 accumulates in the opening grapevine flowers, whereas at later developmental stages only GA4 is detected in the setting fruit. By studying the expression pattern of the grapevine GA oxidase genes in different organs, and at different stages of flowering and fruit-set we showed that the pool of bioactive GAs is controlled by a fine regulation of the abundance and localization of GA oxidases transcripts