Abstract
Phosphorus is an essential element for life, serving as an integral component of nucleic acids, lipids and a diverse range of other metabolites. Concentrations of bioavailable phosphorus are low in many aquatic environments. Microalgae, including diatoms, apply physiological and molecular strategies such as phosphorus scavenging or recycling as well as adjusting cell growth in order to adapt to limiting phosphorus concentrations. Such strategies also involve adjustments of the carbon metabolism. Here, we review the effect of phosphorus limitation on carbon metabolism in diatoms. Two transcriptome studies are analysed in detail, supplemented by other transcriptome, proteome and metabolite data, to gain an overview of different pathways and their responses. Phosphorus, nitrogen and silicon limitation responses are compared, and similarities and differences discussed. We use the current knowledge to propose a suggestive model for the carbon flow in phosphorus-replete and phosphorus-limited diatom cells.This article is part of the themed issue ‘The peculiar carbon metabolism in diatoms’.
Highlights
Phosphorus (P) is an essential element for all living organisms
[26] P. tricornutum [28] and S. costatum [31], respectively, were compared in order to gain an overview of the transcript level responses of the different carbon metabolism pathways to P limitation
The P limitation-induced expression of PLCs and PLDs observed in both P. tricornutum and T. pseudonana indicates that phospholipid degradation may contribute significantly to TAG accumulation during early stages of P limitation, until phospholipids become depleted
Summary
Phosphorus (P) is an essential element for all living organisms. It is a component of the backbone of DNA and RNA, and is central in the transmission of chemical energy through adenosine triphosphate (ATP). From T. pseudonana [26] P. tricornutum [28] and S. costatum [31], respectively, were compared in order to gain an overview of the transcript level responses of the different carbon metabolism pathways to P limitation. The oxidative pentose phosphate pathway (OPPP) in diatoms appears to be cytosolic, in contrast to plants, where most steps of the pathway take place in the chloroplast [37,50] In both T. pseudonana and P. tricornutum this pathway is induced at the transcript level by P limitation [26,28,30]. TAG biosynthesis is located in the endoplasmic reticulum, where fatty acyl-CoA molecules are serially attached to glycerol-3-phosphate [76] The enzymes of this pathway, termed the Kennedy pathway, are unregulated at transcript level in T. pseudonana and show diverging responses in P. tricornutum under P limitation. The P limitation-induced expression of PLCs and PLDs observed in both P. tricornutum and T. pseudonana indicates that phospholipid degradation may contribute significantly to TAG accumulation during early stages of P limitation, until phospholipids become depleted
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