Gibberellin metabolism in grapevine during bloom and fruit-set

Gibberellin treatment allows controlling bunch architecture and berry size in grapevine (Vitis vinifera L.). Application of gibberellic acid (GA3) at bloom results 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 as those of 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 in grapevine. In order to understand how the pool of active gibberellins is maintained in grapevine, we identified and characterized the family of gibberellin oxidases (GA 20-oxidases, GA 3-oxidases and GA 2-oxidases). Grapevine gibberellin oxidases were expressed as recombinant protein to study their activity in vitro. The ectopic expression of GA 2-oxidases in Arabidopsis thaliana confirmed their activity in vivo