Gibberellins metabolism in Vitis vinifera at flowering and fruit set

Gibberellin treatment allows to control bunch architecture and berry size in grapevine. Applications of gibberellic acid (GA3) at bloom result in reduced fruit set, which in turn produces bunches that are less dense, better aerated and, thus, less prone to fungal attack. This treatment is currently applied to wine cultivars with thick bunches such those belonging to the Pinot family, where fruit set and yield reductions remain moderate and are compensated by harvesting of healthier grapes. In this work we studied the accumulation of the active endogenous gibberellins (GA1 and GA4) in inflorescences and setting fruits. We also identified and characterized the family of grapevine gibberellin oxidases, in order to understand how the active gibberellin pool is maintained. Grapevine gibberellin oxidases were expressed as recombinant protein to study their activity in vitro, whereas overexpression in Arabidopsis thaliana confirmed their activity in vivo. We show that the pool of active GA4 and GA1 is controlled by a fine regulation of the diverse gibberellin oxidases at the level of transcript abundance and tissue-specific expression as well as enzymatic activity and substrate specificity. Acknowledgments: post-doc project MagiaVitis funded by Autonomous Province of Trento