Understanding the Genetic Basis of C₄ Kranz Anatomy with a View to Engineering C₃ Crops

One of the most remarkable examples of convergent evolution is the transition from C 3 to C 4 photosynthesis, an event that occurred on over 60 independent occasions. The evolution of C 4 is particularly noteworthy because of the complexity of the developmental and metabolic changes that took place. In most cases, compartmentalized metabolic reactions were facilitated by the development of a distinct leaf anatomy known as Kranz. C 4 Kranz anatomy differs from ancestral C 3 anatomy with respect to vein spacing patterns across the leaf, cell-type specification around veins, and cell-specific organelle function. Here we review our current understanding of how Kranz anatomy evolved and how it develops, with a focus on studies that are dissecting the underlying genetic mechanisms. This research field has gained prominence in recent years because understanding the genetic regulation of Kranz may enable the C 3 -to-C 4 transition to be engineered, an endeavor that would significantly enhance crop productivity.