Future Research into C₄ Biology [Editorial]

Abstract

The year 2016 marks the 50th anniversary of putting forward the idea of C₄ photosynthesis (Hatch and Slack 1966). During the early investigative years, considerable emphasis was placed on studying the biochemistry of C₄ photosynthesis (Hatch 1999), which revealed how the C₄ photosynthetic pathway functions as a CO₂ pump to concentrate CO₂ to the Calvin– Benson cycle. The high CO₂ concentration around ribulose-1, 5- bisphosphate carboxylase/oxygenase (Rubisco) causes suppression of the oxygenation reaction of Rubisco, which results in a lowering of photorespiration. In most C₄ plants, the C₄ cycle is distributed between two types of photosynthetic cells: the mesophyll (M) cells and bundle sheath (BS) cells. BS cells surround the vascular tissues and M cells encircle the cylinders of the BS cells. Both of these distinct photosynthetic cell types contain numerous well-developed chloroplasts, and the leaf anatomy, which is characterized by two concentric rings of photosynthetic cells surrounding a vascular bundle, is termed Kranz anatomy. Most of today’s crops are C₃ plants which do not possess the C₄ pathway. In these crops, photorespiration decreases the net CO₂ assimilation. Despite recent progress stimulated by technological innovations in molecular biology, such as next-generation sequencing, the C₄ Rice Project, which aims at establishing a C₄ cycle in rice plants, further serves as the driving force to advance knowledge of C₄ plant biology (von Caemmerer et al. 2012). In this Special Focus Issue, the current leading ideas and future prospects of C₄ photosynthetic research are discussed.