Biochemical approaches to C4 photosynthesis evolution studies: the case of malic enzymes decarboxylases

C₄ photosynthesis enables the capture of atmospheric CO₂ and its concentration at the site of RuBisCO, thus counteracting the negative effects of low atmospheric levels of CO₂ and high atmospheric levels of O₂ (21 %) on photosynthesis. The evolution of this complex syndrome was a multistep process. It did not occur by simply recruiting pre-exiting components of the pathway from C₃ ancestors which were already optimized for C₄ function. Rather it involved modifications in the kinetics and regulatory properties of pre-existing isoforms of non-photosynthetic enzymes in C₃ plants. Thus, biochemical studies aimed at elucidating the functional adaptations of these enzymes are central to the development of an integrative view of the C₄ mechanism. In the present review, the most important biochemical approaches that we currently use to understand the evolution of the C₄ isoforms of malic enzyme are summarized. It is expected that this information will help in the rational design of the best decarboxylation processes to provide CO₂ for RuBisCO in engineering C₃ species to perform C₄ photosynthesis.