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

B-box or BBX gene family is a set of zinc-finger transcription factor family that regulates plant developmental characteristics like seed gemination, photomorphogenesis, hormone regulations, flowering and senescence. Although BBX gene family is reported in Glycine max, little is known about its members' classification and family 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 its wild progenitor, G. soja, to identify their evolutionary relationship and origin in plant lineage. Our results show an ancient BBX gene family expansion in the Glycine genome, through segmental duplication, suggesting that the G. max BBX members are the out-paralogs. These genes also 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, and that the Glycine genome harbored 55-60 BBX genes.