Vein patterning and evolution in C-4 plants

The C-4 photosynthetic pathway provides a platform to gain insight into the formation, regulation, and biological consequences of leaf vein pattern modification. This review examines the functional role of the vascular system in C-4 photosynthesis and the development of veins in C-3 and C-4 plants, highlighting the contribution of vasculature in the evolution of the C-4 pathway. With interest in developing C-3 plant crops into C-4 systems, it is essential to understand vascular patterning as a necessary element for C-4 functioning. Leaf venation in C-4 plants generally shows a higher vein density through a greater network complexity (more veins) compared with the ancestral C-3 condition. Thus, C-4 plants can provide a model that links the development of vein patterning with evolutionary selection pressures and molecular mechanisms (i.e., modifications of different components of vascular development). Numerous studies, including a comparative C-3 and C-4 Flaveria case study, highlight that the overall process of vein formation and patterning is complex, involving interactions between procambium and ground meristem during leaf ontogeny, and points to potential roles of changes in auxin production, transport, and perception.