Minor millets as model system to study C4 photosynthesis - A review.

C₄ photosynthesis is the primary mode of carbon capture and drives productivity in several major food crops and bio- energy grasses. Gains in productivity associated with C₄ photosynthesis include improved water and nitrogen use efficiencies. Within grasses rice and brachypodium are used as model species. Since these two crops are using C₃ photosynthesis for their growth and development, it cannot be used as model for to study C₄ photosynthesis. In order to characterize the evolutionary innovations and to provide genomic insight into crop improvement for the many important crop species, a new genomic and genetic model species is required. Minor millets have small diploid genomes, shorter life cycles, self pollination and prolific seed production. Due to these characteristics it gains importance over major C₄ species which lack all of these traits. Within Minor millets, Setaria italica and Setaria viridis are used as model systems since these crops fulfils all the traits responsible to be a model species. Importantly, Setaria species uses NADP-Malic enzyme subtype C₄ photosynthetic system to fix carbon and therefore is a potential powerful model system for dissecting C₄ photosynthesis. C₄ grasses have a shorter distance between longitudinal veins in the leaves than C₃ grasses. The C₄ grasses have denser transverse and small longitudinal veins than the C₃ grasses. It indicates that C₄ grasses have a structurally superior photosynthate translocation and water distribution system by developing denser networks of small longitudinal and transverse veins. Setaria has high vein density and kranz anatomy that helps to concentrate CO₂ in the bundle sheath cells. This minimizes photorespiration thereby prevents the loss of energy. [ABSTRACT FROM AUTHOR]