Abstract

In a common bean plant exhibiting determinate growth, the terminal shoot meristem switches from a vegetative to reproductive state, resulting in a terminal inflorescence. Contrary to this, indeterminate growth habit results in a terminal meristem that remains vegetative where it further regulates the production of lateral vegetative and reproductive growth. In the last century, breeders have selected determinate growth habit, in combination with photoperiod insensitivity, to obtain varieties with a shorter flowering period, earlier maturation and ease of mechanized harvest. Previous work has identified TFL1 as a gene controlling determinate growth habit in Arabidopsis thaliana. In this work, we have validated that the Phaseolus vulgaris candidate gene, PvTFL1y, is the functional homolog of TFL1 using three independent lines of evidence. First, in a population of ~1,500 plants, PvTFL1y was found to co-segregate with the phenotypic locus for determinate growth habit (fin) on chromosome 01. Second, using quantitative PCR, we found that two unique haplotypes associated with determinacy at the PvTFL1y locus, a 4.1-kb retrotransposon and a splice-site mutation, cause mRNA abundance to decrease 20-133 fold, consistent with the recessive nature of fin. Finally, using a functional complementation approach, through Agrobacterium-mediated transformation of determinate Arabidopsis, we rescued tfl1-1 mutants with the wild-type PvTFL1y gene. Together, these three lines of evidence lead to the conclusion that PvTFL1y is the functional homolog of the Arabidopsis gene, TFL1, and is the gene responsible for naturally occurring variation for determinacy in common bean. Further work exploring the different haplotypes at the PvTFL1y locus may lead to improved plant architecture and phenology of common bean cultivars.