Comparative analysis of Glycine BBX gene family reveals lineage-specific evolution and expansion

BBX genes are associated with photomorphogenesis, hormone response and seed gemination. Although, BBX gene family is reported in G. max, little is known about its classification and expansion. Similarly, no information is available for the BBX gene family in its closest relative Glycine soja (Siebold & Zucc.). With extensive genome diversity, G. soja can be used as an effective genetic reservoir for introgressing important agronomic traits in G. max. In the present study, we carried out a comprehensive comparative genome-wide analysis of BBX gene family in G. max and G. soja, to identify their evolutionary relationship and origin in plant lineage. Our results show an ancient BBX gene family expansion through segmental duplication, further suggesting, that the GmBBX members are the out-paralogs. These genes show lineage-specific evolution and expansion in the ancestral Glycine genome supported by the incidences of microsynteny between G. max and G. soja. The two genomes also showed interesting evidence of conserved linkages which might be due to their common ancestor descendance, with minimum horizontal expansion in G. max after its split from G. soja. Our study suggests that the BBX gene family diverged before the split of G. max and G. soja. As the two genomes share several regions of synteny, the paralogous members in G. max could have been a result of segmental duplications.