Shared characteristics underpinning C4 leaf maturation derived from analysis of multiple C3 and C4 species of Flaveria.

Most terrestrial plants use C photosynthesis to fix carbon. In multiple plant lineages a modified system known as C photosynthesis has evolved. To better understand the molecular patterns associated with induction of C photosynthesis, the genus Flaveria that contains C and C species was used. A base to tip maturation gradient of leaf anatomy was defined, and RNA sequencing was undertaken along this gradient for two C and two C Flaveria species. Key C traits including vein density, mesophyll and bundle sheath cross-sectional area, chloroplast ultrastructure, and abundance of transcripts encoding proteins of C photosynthesis were quantified. Candidate genes underlying each of these C characteristics were identified. Principal components analysis indicated that leaf maturation and the photosynthetic pathway were responsible for the greatest amount of variation in transcript abundance. Photosynthesis genes were over-represented for a prolonged period in the C species. Through comparison with publicly available data sets, we identify a small number of transcriptional regulators that have been up-regulated in diverse C species. The analysis identifies similar patterns of expression in independent C lineages and so indicates that the complex C pathway is associated with parallel as well as convergent evolution.