Molecular cloning of RBCS genes in Selaginella and the evolution of the rbcS gene family

Rubisco small subunits (RBCS) are encoded by a nuclear rbcS multigene family in higher plants and green algae. However, owing to the lack of rbcS sequences in lycophytes, the characteristics of rbcS genes in lycophytes is unclear. Recently, the complete genome sequence of the lycophyte Selaginella moellendorffii provided the first insight into the rbcS gene family in lycophytes. To understand further the characteristics of rbcS genes in other Selaginella, the full length of rbcS genes (rbcS1 and rbcS2) from two other Selaginella species were isolated. Both rbcS1 and rbcS2 genes shared more than 97% identity among three Selaginella species. RBCS proteins from Selaginella contained the Pfam RBCS domain F00101, which was a major domain of other plant RBCS proteins. To explore the evolution of the rbcS gene family across Selaginella and other plants, we identified and performed comparative analysis of the rbcS gene family among 16 model plants based on a genome-wide analysis. The results showed that (i) two rbcS genes were obtained in Selaginella, which is the second fewest number of rbcS genes among the 16 representative plants; (ii) an expansion of rbcS genes occurred in the moss Physcomitrella patens; (iii) only RBCS proteins from angiosperms contained the Pfam PF12338 domains, and (iv) a pattern of concerted evolution existed in the rbcS gene family. Our study provides new insights into the evolution of the rbcS gene family in Selaginella and other plants.