Setaria viridis: A Model for C4 Photosynthesis

C-4 photosynthesis drives productivity in several major food crops and bioenergy grasses, including maize (Zea mays), sugarcane (Saccharum officinarum), sorghum (Sorghum bicolor), Miscanthus x giganteus, and switchgrass (Panicum virgatum). Gains in productivity associated with C-4 photosynthesis include improved water and nitrogen use efficiencies. Thus, engineering C-4 traits into C-3 crops is an attractive target for crop improvement. However, the lack of a small, rapid cycling genetic model system to study C-4 photosynthesis has limited progress in dissecting the regulatory networks underlying the C-4 syndrome. Setaria viridis is a member of the Panicoideae clade and is a close relative of several major feed, fuel, and bioenergy grasses. It is a true diploid with a relatively small genome of similar to 510 Mb. Its short stature, simple growth requirements, and rapid life cycle will greatly facilitate genetic studies of the C-4 grasses. Importantly, S. viridis uses an NADP-malic enzyme subtype C-4 photosynthetic system to fix carbon and therefore is a potentially powerful model system for dissecting C-4 photosynthesis. Here, we summarize some of the recent advances that promise greatly to accelerate the use of S. viridis as a genetic system. These include our recent successful efforts at regenerating plants from seed callus, establishing a transient transformation system, and developing stable transformation.