C4 decarboxylases. Different solutions for the same biochemical problem, the provision of CO2 in the Bundle Sheath Cells

DRINCOVICH, MARÍA FABIANA; LARA, MARÍA VALERIA; MAURINO, VERÓNICA GRACIELA; ANDREO, CARLOS SANTIAGO

C4 Photosynthesis

Springer

Año: 2007; p. 1 - 1

The decarboxylation of C4 acids in the bundle sheath cells (BSCs) of C4-plants is a key step inthe photosynthetic process in this type of carbon assimilation. Depending on the particularsubtype of C4-species, this process can be mediated by different enzymes: NADP-malic enzyme(NADP-ME), NAD-malic enzyme (NAD-ME) and/or Phosphoenolpyruvate carboxykinase(PEPCK), and each enzyme has a different subcellular compartmentalization within the BSCs.Thus, the C4 subtype cycle mediated by each decarboxylase displays distinguishing features inleaf anatomy, biochemistry and physiology in various families having C4 species. In some casesamong C4 plants, the operation of more than one type of decarboxylating enzyme in the C4photosynthetic process has been assessed. During the last few years, remarkable advances havebeen made in the characterization of different isoforms of each C4 decarboxylase. In most cases,non-photosynthetic isoforms of the C4-decarboxylating enzymes involved in primary and/orsecondary metabolisms were characterized. These non-C4 isoforms were for sure the startingpoint for the evolution of the C4-specific decarboxylases, gaining characteristics that make themmore suitable to fulfill the requirements of the photosynthetic process. For each decarboxylatingenzyme, the analysis of phylogenetic relationships reveals several features of the molecularevolution of the C4 process which accomplished the same biochemical feature: generation ofCO2 around Rubisco in BSCs, preventing photorespiration and enhancing photosynthesis.