Cleome, a genus closely related to Arabidopsis, contains species spanning a developmental progression from C3 to C4 photosynthesism

C-4 photosynthesis involves alterations to leaf development, cell biology and biochemistry. Different lineages of C-4 plants use varying mechanisms to generate the C-4 pathway. Although the biochemistry of C-4 photosynthesis was described around 20 years ago, the phylogenetic distance between Arabidopsis and the traditional C-4 models has not facilitated the transfer of knowledge from Arabidopsis research to understanding C-4 systems. We show that Cleome, a genus closely related to Arabidopsis, contains species spanning a developmental progression from C-3 to C-4 photosynthesis. The majority of species we assessed are C-3 plants but have increased venation in leaves. Three C-3 species have both increased venation and enlarged bundle sheath cells, and there is also a tendency to accumulate proteins and transcripts needed for C-4 photosynthesis. Cleome gynandra shows all the characteristics needed for efficient C-4 photosynthesis, including alterations to leaf biochemistry, cell biology and development, and belongs to the NAD-dependent malic enzyme subtype. Combined with its phylogenetic proximity to Arabidopsis, the developmental progression from C-3 to C-4 photosynthesis within the genus provides a potentially excellent new model to increase our understanding of C-4 photosynthesis, and provide insights into its evolution.