Beyond the CO-FT regulatory module: E1 and PHYA emerge as players in photoperiodic regulation of flowering in legumes.
The legume family (Fabaceae) is the third largest in plants and includes several crop species that are able to fix nitrogen, promote soil health, and contribute to food security worldwide. Recent progress in legume genetics and genomics allowed the identification of photoperiod-dependent flowering loci, which were incorporated into specific signalling networks. Functional characterization of these regulators revealed new roles for known photoreceptors such as phytochrome A, and it also identified legume-specific B3 domain transcriptional factors (E1 and E1-like proteins). This suggests some diversification from the traditional CONSTANS-FLOWERING LOCUS T module present in other angiosperms. Although most of the findings discussed herein pertain to species from the two main legume clades, the Galegoids (e.g. alfalfa, clover, and pea) and the Phaseoloids (e.g. common bean, soybean, cowpea, and pigeon pea), research on flowering regulation in the basal Genistoid clade (e.g. lupins) will also be addressed. We propose that functional diversification of photoperiod-dependent flowering strategies in the different legume species could have contributed to their environmental adaptation and allowed their geographical expansion and success worldwide.