Phylogenetically-based variation in the regulation of the Calvin cycle enzymes, phosphoribulokinase and glyceraldehyde-3-phosphate dehydrogenase, in algae

Abstract

Aquatic photosynthesis is responsible for about half of the global production and is undertaken by a huge phylogenetic diversity of algae that are poorly studied. The diversity of redox-regulation of phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was investigated in a wide range of algal groups under standard conditions. Redox-regulation of PRK was greatest in chlorophytes, low or absent in a red alga and most chromalveolates, and linked to the number of amino acids between two regulatory cysteine residues. GAPDH regulation was not strongly-related to the different forms of this enzyme and was less variable than for PRK. Addition of recombinant CP12, a protein that forms a complex with PRK and GAPDH, to crude extracts inhibited GAPDH and PRK inversely in the Plantae, but in most chromalveolates had little effect on GAPDH and inhibited or stimulated PRK depending on the species. Patterns of enzyme regulation 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. A third clade comprised a mixture of Plantae, an excavate and three chromalveolates: a marine diatom and two others (a xanthophyte and eustigmatophyte) that are distinguished by a low content of chlorophyll c and a lack of fucoxanthin. Regulation of both enzymes was greater in freshwater than in marine taxa, possibly because most freshwaters are more dynamic than oceans. This work highlights the importance of understanding enzyme regulation in diverse algae if their ecology and productivity is to be understood.

Do Red and Green Make Brown?: Perspectives on Plastid Acquisitions within Chromalveolates

“…In parallel, it will be essential to gain a better understanding of the physiological properties of different endosymbiont lineages, including whether the red chloroplast lineage mitigates CO 2 and nutrient limitation and whether the retention of specific green genes confers enhanced selective fitness on chromalveolates. This could include comparative studies, such as investigation of the kinetic properties of homologous enzymes from different endosymbiont lineages (6,66) or identification of genes that are differentially expressed in particular species under stress conditions using deep-sequencing approaches (53,67). If these features can be linked to observed changes in phytoplankton community structure following environmental perturbation (31,44,69), the evolutionary diversity of algae may be placed into a functional context.…”

“…For example, the green alga-derived chromalveolate isoform of phosphoribulokinase has unusually low activity in all of the taxa studied (66,97). This is significant in that chromalveolates lack CP12, a circadian regulator of PRK found in both red and green algae (39,66), and in the absence of the negative regulator, the lower-activity isoform may have been selected over a higher-activity, red orthologue. Conversely, individuals that retained the higher-specificity red isoform of RubisCO may have been selectively advantaged over others that lost this gene early during endosymbiosis.…”

“…One possibility is that a complex endosymbiotic heritage equipped early chromalveolates with an enlarged gene pool of endogenous green-and red-derived genes so that they were more able to expand into niches previously occupied by green algae in what has elsewhere been termed the "shopping bag model" of algal evolution (38,59). For example, the green alga-derived chromalveolate isoform of phosphoribulokinase has unusually low activity in all of the taxa studied (66,97). This is significant in that chromalveolates lack CP12, a circadian regulator of PRK found in both red and green algae (39,66), and in the absence of the negative regulator, the lower-activity isoform may have been selected over a higher-activity, red orthologue.…”

Regulation of glyceraldehyde-3-phosphate dehydrogenase in the eustigmatophytePseudocharaciopsis ovalisis intermediate between a chlorophyte and a diatom

“…Enzyme regulation in higher plants and green algae has been extensively studied and shown to act via a range of factors including pH, metabolite concentration, redox and proteinprotein interactions (Gontero et al, 2006). Much less is known for chromalveolates (Michels et al, 2005;Boggetto et al, 2007;Erales et al, 2008;Maberly et al, 2010) and we present here for the first time a detailed study of GAPDH regulation in a eustigmatophyte.…”

“…The isoforms of GAPDH, such as GapA and GapC1, that do not possess regulatory cysteine residues may still be redox-regulated by interacting with other proteins (Boggetto et al, 2007;Erales et al, 2008;Maberly et al, 2010). Specifically, GAPDH can form a supramolecular complex with PRK via an intrinsically disordered protein of 8.5 kDa called CP12 (Pohlmeyer et al, 1996).…”