Haplotype diversity of VvTFL1A gene and association with cluster traits ingrapevine (V. vinifera)

BACKGROUND: Interaction between TERMINAL FLOWER 1 (TFL1) and LEAFY(LFY) seem to determine the inflorescence architecture inArabidopsis. In a parallel way, overexpression of VvTFL1A, agrapevine TFL1 homolog, causes delayed flowering and production of aramose cluster in the reiterated reproductive meristem (RRM) somatic variant ofcultivar Carignan. To analyze the possible contribution of this gene to clusterphenotypic variation in a diversity panel of cultivated grapevine (Vitisvinifera L. subsp. vinifera) its nucleotide diversity wascharacterized and association analyses among detected sequence polymorphisms andphenology and cluster traits was carried out. RESULTS: A total of 3.6 kb of the VvTFL1A gene, including its promoter, wassequenced in a core collection of 140 individuals designed to maximize phenotypicvariation at agronomical relevant traits. Nucleotide variation forVvTFL1A within this collection was higher in the promoter and intronsequences than in the exon regions; where few polymorphisms were located inagreement with a high conservation of coding sequence. Characterization of theVvTFL1A haplotype network identified three major haplogroups,consistent with the geographic origins and the use of the cultivars that couldcorrespond to three major ancestral alleles or evolutionary branches, based on theexistence of mutations in linkage disequilibrium. Genetic association studies withcluster traits revealed the presence of major INDEL polymorphisms, explaining 16%,13% and 25% of flowering time, cluster width and berry weight, respectively, andalso structuring the three haplogroups. CONCLUSIONS: At least three major VvTFL1A haplogroups are present in cultivatedgrapevines, which are defined by the presence of three main polymorphism LD blocksand associated to characteristic phenotypic values for flowering time, clusterwidth and berry size. Phenotypic differences between haplogroups are consistentwith differences observed between Eastern and Western grapevine cultivars andcould result from the use of different genetic pools in the domestication processas well as different selection pressures on the development of table and winecultivars, respectively. Altogether, these results are coherent with previousclassifications of grapevine phenotypic diversity mainly based on cluster andberry morphotypes as well as with recent results on the structure of geneticdiversity in cultivated grapevine.