Terrestrial photosynthesis is largely the result of the Embryophytes, while aquatic photosynthesis is performed by a huge phylogenetic diversity of algae whose biochemical properties are poorly known. We compared the redox-regulation of phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a wide range of algal groups under standard conditions. Redox-regulation of PRK was greatest in chlorophytes and least in a red alga and the chromalveolates. The lack of regulation was linked to amino-acid insertions or deletions between two regulatory cysteine residues. Regulation of GAPDH appeared not to be related just to the different forms of this enzyme, GapA, GapB and GapC1, because marine and freshwater diatoms both possess GapC1 but are differently regulated. The regulation patterns varied with algal phylogeny and addition of CP12, a protein forming a complex with PRK and GAPDH, from Chlamydomonas reinhardtii showed that PRK and GAPDH from Plantae responded differently to that from chromalveolates. These patterns were used to produce a phylogenetic tree in which cryptophytes and haptophytes, at the base of the chromalveolates, formed a distinct clade. A second clade comprised only chromalveolates. Interestingly, a third clade comprised a mixture of Plantae, an Excavate and three chromalveolates. The chromalveolates comprised a marine diatom and two chromalveolates (a xanthophyte and eustigmatophyte) that are distinguished from the rest of this supergroup by low content of chlorophyll c and lack of fucoxanthin. This study highlights the importance of understanding the different regulation patterns in the ecology of these algae
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