Résumé
VvTFL1A overexpression due to transposon insertion in its promoter region causes delayed flowering and production of a ramose cluster in the ‘Carignan’ RRM somatic variant (Fernandez et al. 2010). In order to analyze the possible contribution of this gene to cluster phenotypic variation in cultivated grapevine (Vitis vinifera L. subsp. sativa), we have characterized its nucleotide diversity and performed association analyses among detected sequence polymorphisms and VvTFL1A expression and cluster traits. We sequenced a total of 3489 bp of the VvTFL1A gene (corresponding to 2177 bp of promoter and 1312 bp of coding sequence) in a core collection designed to maximize phenotypic variation at 50 agromically relevant traits (Barnaud et al. 2006). Nucleotide polymorphisms were highly abundant in the promoter and intron sequences of the gene and some of them revealed significant associations (P <0.01) with flowering time, cluster width and density, berry weight and VvTFL1A expression. Using a multivariate regression method, we showed that two adjacent SNPs at the promoter region account for 56% of gene expression variation. Three other polymorphisms corresponding to INDELs in promoter and intron regions showed major effects on flowering time, berry weight, cluster density and cluster width. The results suggest that part of the trait variation associated to those polymorphisms could be functionally explained through variation in gene regulation or structural changes in the VvTFL1A protein. Since no trace of the transposon was detected in the VvTFL1A promoter in any of Vitis vinifera accessions of the core collection, the extreme phenotypic variation observed for flowering time and cluster size in the RRM somatic variant must correspond to a unique random insertion event.