Graduate Student University of Florida Gainesville, Florida
Body of Abstract: Domestication of crops led to the accumulation of favorable alleles controlling desirable traits like larger seeds, as it occurred in the common bean, Phaseolus vulgaris. Phylogenetic analyses have demonstrated that this species was domesticated independently and almost simultaneously in the Mesoamerican and Andean regions. Our lab has determined that domestication in these two regions lead to significant increases in seed size, seed cell size and number, and relative content of starch to the detriment of protein. Analysis of an Andean RI family (wild x landrace) has shown high broad sense heritabilities for seed size, starch content, and protein content indicating a significant amount of genetic control. Subsequent analysis identified QTL with apparent pleiotropic effects for seed weight, protein, and starch content. One of these QTL regions on Chrom6 contained a potential candidate gene homologous to the A. thalianaAtSWEET15 (Sugars Will Eventually be Exported Transporter 15) which we named PvSWEET15. Evidence supporting the domestication-QTL candidacy of this gene include qRT-PCR data showing a 2.5-increase in expression level during seed development of the domesticated over the wild allele, and a signature of selection detected through the cross-population composite likelihood ratio of 150 genome sequences. Comparative analysis between the Andean wild and landrace accessions revealed several SNPs and five deletions in the PvSWEET15 landrace promoter and one in its terminal exon. To assess the impact of these variants on the seed phenotype, we have performed comparative complementation assays between landrace and wild PvSWEET15 allelic sequences using an A. thaliana triple KO mutant (sweet 11/12/15). Due to overlapping redundancies single mutants are not phenotypically distinguishable from wild type and double mutants display intermediate seed phenotypes. The tests comprise Pv allelic promoters driving the expression of the AtSWEET15 CDS and the wild type At promoter driving the expression of the Pv allelic CDS.