Poor Evidence for C4 Photosynthesis in the Wheat Grain

Abstract

Research on C₄ photosynthesis has seen a revival in recent years, leading to a Nature Scientific Reports article announcing the discovery of C₄ photosynthesis in grains of the C₃ plant wheat (Triticum aestivum; Rangan et al., 2016). The authors indicate the presence of C₄ cycle enzymes, which they interpret as evidence for the existence of a C4-type carbon-concentrating mechanism in the wheat pericarp. “Extraordinary claims require extraordinary evidence,” however, and the evidence presented in this case is based entirely on transcriptome data of the entire wheat grain, with a notable absence of biochemical or physiological support, or the exact location of expression. One needs to consider the wider context of C₄ photosynthesis, and this challenges the interpretation provided by Rangan et al. (2016).