Authors: Katharina Schiller, Andrea Bräutigam
Published: 2021-04-13
DOI: 10.1146/annurev-arplant-071720-104814
Source: Full article
Crassulacean acid metabolism (CAM) has evolved from a C3ground state to increase water use efficiency of photosynthesis. During CAM evolution, selective pressures altered the abundance and expression patterns of C3genes and their regulators to enable the trait. The circadian pattern of CO2fixation and the stomatal opening pattern observed in CAM can be explained largely with a regulatory architecture already present in C3plants. The metabolic CAM cycle relies on enzymes and transporters that exist in C3plants and requires tight regulatory control to avoid futile cycles between carboxylation and decarboxylation. Ecological observations and modeling point to mesophyll conductance as a major factor during CAM evolution. The present state of knowledge enables suggestions for genes for a minimal CAM cycle for proof-of-concept engineering, assuming altered regulation of starch synthesis and degradation are not critical elements of CAM photosynthesis and sufficient malic acid export from the vacuole is possible.