Meeting in the Middle: Lessons and Opportunities from Studying C-C Intermediates.

The discovery of C-C intermediate species nearly 50 years ago opened up a new avenue for studying the evolution of photosynthetic pathways. Intermediate species exhibit anatomical, biochemical, and physiological traits that range from C to C. A key feature of C-C intermediates that utilize C photosynthesis is the improvement in photosynthetic efficiency compared with C species. Although the recruitment of some core enzymes is shared across lineages, there is significant variability in gene expression patterns, consistent with models that suggest numerous evolutionary paths from C to C photosynthesis. Despite the many evolutionary trajectories, the recruitment of glycine decarboxylase for C photosynthesis is likely required. As technologies enable high-throughput genotyping and phenotyping, the discovery of new C-C intermediates species will enrich comparisons between evolutionary lineages. The investigation of C-C intermediate species will enhance our understanding of photosynthetic mechanisms and evolutionary processes and will potentially aid in crop improvement.