The crucial roles of mitochondria in supporting C<sub>4</sub> photosynthesis
Yuzhen Fan, Shinichi Asao, Robert T. Furbank, Susanne von Caemmerer, David A. Day, Guillaume Tcherkez, Tammy L. Sage, Rowan F. Sage, Owen K. Atkin
Abstract
Summary C 4 photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C 3 photosynthesis. We explore how evolution of the three classical biochemical types of C 4 photosynthesis (NADP‐ME, NAD‐ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C 4 NAD‐ME and PCK types play a direct role in decarboxylation of metabolites for C 4 photosynthesis. Mitochondria in C 4 PCK type also provide ATP for C 4 metabolism, although this role for ATP provision is not seen in NAD‐ME type. Such involvement has increased mitochondrial abundance/size and associated enzymatic capacity, led to changes in mitochondrial location and ultrastructure, and altered the role of mitochondria in cellular carbon metabolism in the NAD‐ME and PCK types. By contrast, these changes in mitochondrial properties are absent in the C 4 NADP‐ME type and C 3 leaves, where mitochondria play no direct role in photosynthesis. From an eco‐physiological perspective, rates of leaf respiration in darkness vary considerably among C 4 species but does not differ systematically among the three C 4 types. This review outlines further mitochondrial research in key areas central to the engineering of the C 4 pathway into C 3 plants and to the understanding of variation in rates of C 4 dark respiration.