Shared characteristics underpinning C ₄ leaf maturation derived from analysis of multiple C ₃ and C ₄ species of Flaveria

Abstract

We identify transcription factors that show conserved patterns of expression in multiple C ₄ species, both within the Flaveria genus and also in more distantly related C ₄ plants.

Abstract

Most terrestrial plants use C ₃ photosynthesis to fix carbon. In multiple plant lineages a modified system known as C ₄ photosynthesis has evolved. To better understand the molecular patterns associated with induction of C ₄ photosynthesis, the genus Flaveria that contains C ₃ and C ₄ 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 ₃ and two C ₄ Flaveria species. Key C ₄ traits including vein density, mesophyll and bundle sheath cross-sectional area, chloroplast ultrastructure, and abundance of transcripts encoding proteins of C ₄ photosynthesis were quantified. Candidate genes underlying each of these C ₄ 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 ₄ species. Through comparison with publicly available data sets, we identify a small number of transcriptional regulators that have been up-regulated in diverse C ₄ species. The analysis identifies similar patterns of expression in independent C ₄ lineages and so indicates that the complex C ₄ pathway is associated with parallel as well as convergent evolution.