Comparative Genome Analysis of Flowering Genes in Legume Crops

The regulation of the seasonal timing of flowering is a major goal of plant breeding to produce novel varieties that are better adapted to local environmental changes. As the model plant Arabidopsis thaliana has the best-characterized information of the molecular regulation of flowering time, a set of about 200 genes of Arabidopsis, involved in the control of flowering time, were used as a reference to identify orthologous (or homologous) counterparts of these genes in three legume species, Lotus Japonicus, Medicago truncalula, and Glycine max. A large portion of the flowering genes of Arabidopsis was represented in the legume species. A total of 96, 98, and 304 homologues of flowering genes were identified in L. Japonicus, M. truncalula, and G. max, respectively. Most of these genes were categorized into six different flowering pathways including photoperiod, vernalization, gibberellins, and autonomous pathways, flowering pathway integrators (FPI) and floral meristem identity. A lot of key genes including three FPI genes, FT, SOC1, and LFY were conserved in the legumes, while the missing of CO, FRI, FLC and FD in the legume genomes was observed. Eighteen genes were found to be conserved as a single copy in all three legume species, including GI, VRN2, COP1, and TSF. In addition, chromosomal distribution of paralog-rich genes showed major forces of evolution process of flowering genes are different in the legume species; whole genome duplication for soybean, tandem duplication for M. truncalula, and etopic duplication of L. Japonicus. High divergence among the members of large gene families, mostly transcription factors, indicates accumulation of gene copy and their divergence is one of evolutionary adaptation to environmental changes. Identification of the missing elements in flowering regulatory networks and functional analysis of conserved genes for different flowering behaviors in the legume species provide new insights into flowering pathways.