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RNA-seq, the measurement of steady-state RNA levels by next generation sequencing, has enabled quantitative transcriptome analyses of complex traits in many species without requiring the parallel sequencing of their genomes. The complex trait of C 4 photosynthesis, which increases photosynthetic efficiency via a biochemical pump that concentrates CO 2 around RubisCO, has evolved convergently multiple times. Due to these interesting properties, C 4 photosynthesis has been analyzed in a series of comparative RNA-seq projects. These projects compared both species with and without the C 4 trait and different tissues or organs within a C 4 plant. The RNA-seq studies were evaluated by comparing to earlier single gene studies. The studies confirmed the marked changes expected for C 4 signature genes, but also revealed numerous new players in C 4 metabolism showing that the C 4 cycle is more complex than previously thought, and suggesting modes of integration into the underlying C 3 metabolism. [ABSTRACT FROM AUTHOR]

C4 photosynthesis represents the most productive modes of photosynthesis in land plants and some of the most productive crops on the planet, such as maize and sugarcane, and many ecologically important native plants use this type of photosynthesis. Despite its ecological and economic importance, the genetic basis of C4 photosynthesis remains largely unknown. Even many fundamental aspects of C4 biochemistry, such as the molecular identity of solute transporters, and many aspects of C4 plant leaf development, such as the Kranz anatomy, are currently not understood. Here, we review recent progress in gaining a mechanistic understanding of the complex C4 trait through comparative evolutionary analyses of C3 and C4 species. [Copyright &y& Elsevier]