Identification and characterization of Flowering Locus D in Indian bean [Lablab purpureus (L.) Sweet].

Background: The transition from vegetative to floral development is a critical process regulated by a variety of complex internal and external factors. This study aims to characterize the Flowering Locus D (FLD) gene in relation to the floral induction pathway and examine its expression profiles under different photoperiodic conditions in Indian bean (Lablab purpureus (L.) Sweet).

Methods: The LprFLD gene was PCR-amplified and sequenced using gene-specific primers for both photosensitive (GNIB-22, GP-189) and photoinsensitive (GNIB-21) varieties of Indian bean. Exon prediction, phylogenetic analysis, and in silico domain prediction were performed, followed by gene expression analysis using qRT-PCR for contrasting phenotypes.

Results: The complete LprFLD gene sequence was characterized, containing five exons and showing significant similarity to GmFLD and VuFLD. Phylogenetic analysis of FLD homologs from 27 taxa revealed the closest evolutionary relationships among members of the Phaseoleae tribe, including Lablab purpureus, Vignaumbellata, Vigna angularis, Vignaradiata, Vigna unguiculata, Phaseolus vulgaris, Glycine max, Glycinesoja, and Cajanus cajan. In silico domain prediction identified two conserved domains, SWIRM and amino oxidase, in the FLD homologs of Indian bean, soybean, cowpea, Arabidopsis and rice. Gene expression analysis showed that the relative expression of LprFLD in trifoliate leaves corresponded with flowering in both photosensitive and photoinsensitive genotypes under long-day conditions. Overall, the expression level of LprFLD was lower in trifoliate leaves and shoot tips.

Conclusion: This is the first report on the characterization of the LprFLD locus in Indian bean. Phylogenetic analysis confirmed its close evolutionary relationship with other Phaseoleae species. qRT-PCR results suggest that the elevated expression of LprFLD in trifoliate leaves coincides with flowering time in both photosensitive and photoinsensitive genotypes under long-day conditions, indicating that other loci may also regulate floral transition under varying photoperiods in Indian bean.