Molecular evolution of genes recruited into C4 photosynthesis

The C4 pathway is found in 62 lineages of land plants. We assess evidence for parallel versus convergent evolution of C4 photosynthesis from three approaches: (i) studies of specific genes and cis-elements controlling their expression; (ii) phylogenetic analyses of mRNAs and inferred amino acid sequences; and (iii) analysis of C3 and C4 genomes and transcriptomes. Evidence suggests that although convergent evolution is common, parallel evolution can underlie both changes to gene expression and amino acid sequence. cis-elements that direct cell specificity in C4 leaves are present in C3 orthologues of genes recruited into C4, probably facilitating this parallel evolution. From this, and genomic data, we propose that gene duplication followed by neofunctionalisation is not necessarily important in the evolution of C4 biochemistry.