Exploring the evolutionary differences of SBP-box genes targeted by miR156 and miR529 in plants.

The combinatorial control of one target by multiple miRNAs brings big challenges to elucidate its precise evolutionary mechanism. Squamosa promoter binding protein-like (SBP) gene family exhibits the different regulatory patterns, in which some members are only regulated by miR156 and others by miR156 and miR529. Here, we explored the different evolutionary patterns and rates between miR156 targets and miR529 ones in three species (moss, rice, and maize). Our work found that the miR529 targets were members of miR156 target dataset, indicative of cooperative control. Further phylogenetic analyses as well as gene structure features demonstrated that miR529 targets derived from a monophyletic branch of miR156 targets which evolved into two independent branches duo to the ancient gene duplication. Moreover, inspection of evolutionary rate parameters (d(N)/d(S), d(N) and d(S)) for miR156 targets and miR529 ones revealed they were under different selection strength. MiR529 targets were more constraint by strong purifying selection and evolved conservatively with a slow rate. By contrast, miR156 targets evolved more rapidly and experienced more relaxed purifying selection, which may contribute to their functional diversification. Our results will enhance the understanding of different evolutionary fates of SBP-box genes regulated by the different numbers of miRNA families before functional studies.