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CAM photosynthesis: the acid test
Author(s) -
Winter Klaus,
Smith J. Andrew C.
Publication year - 2022
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.17790
Subject(s) - crassulacean acid metabolism , photosynthesis , malic acid , biology , carbon fixation , nocturnal , botany , metabolic pathway , glycolysis , carbohydrate metabolism , metabolism , biochemistry , ecology , citric acid
Summary There is currently considerable interest in the prospects for bioengineering crassulacean acid metabolism (CAM) photosynthesis – or key elements associated with it, such as increased water‐use efficiency – into C 3 plants. Resolving how CAM photosynthesis evolved from the ancestral C 3 pathway could provide valuable insights into the targets for such bioengineering efforts. It has been proposed that the ability to accumulate organic acids at night may be common among C 3 plants, and that the transition to CAM might simply require enhancement of pre‐existing fluxes, without the need for changes in circadian or diurnal regulation. We show, in a survey encompassing 40 families of vascular plants, that nocturnal acidification is a feature entirely restricted to CAM species. Although many C 3 species can synthesize malate during the light period, we argue that the switch to night‐time malic acid accumulation requires a fundamental metabolic reprogramming that couples glycolytic breakdown of storage carbohydrate to the process of net dark CO 2 fixation. This central element of the CAM pathway, even when expressed at a low level, represents a biochemical capability not seen in C 3 plants, and so is better regarded as a discrete evolutionary innovation than as part of a metabolic continuum between C 3 and CAM.