Getting closer: vein density in C4 leaves

C-4 grasses are major contributors to the world's food supply. Their highly efficient method of carbon fixation is a unique adaptation that combines close vein spacing and distinct photosynthetic cell types. Despite its importance, the molecular genetic basis of C-4 leaf development is still poorly understood. Here we summarize current knowledge of leaf venation and review recent progress in understanding molecular and genetic regulation of vascular patterning events in C-4 plants. Evidence points to the interplay of auxin, brassinosteroids, SHORTROOT/SCARECROW and INDETERMINATE DOMAIN transcription factors. Identification and functional characterization of candidate regulators acting early in vascular development will be essential for further progress in understanding the precise regulation of these processes.