Unsuspected functions of alkaline phosphatase PhoD in the diatom Phaeodactylum tricornutum

Abstract

Alkaline phosphatase (AP) in algae is known as the indicator of phosphorus nutrient (P) starvation and an enzyme to hydrolyze dissolved organic phosphorus (DOP) as an alternative source of P when the primary source of P, dissolved inorganic phosphate, DIP, is limited in the marine environment. Here, we document the roles of an intracellular PhoD type AP gene in the diatom Phaeodactylum tricornutum other than DOP scavenging when P supply is abundant. CRISPR-mediated mutation of PhoD_45757 resulted in increased lipid content, pigment content, photosynthetic efficiency, and oxygen evolution. Meanwhile, PhoD_45757 mutation also altered physiological and transcriptomic performance under different P conditions. Mutant strains grown in the P-replete medium exhibited significantly lower growth rates than the wild type, apparently by inhibiting G1 phase in the cell cycle, and higher phosphate uptake rate, accompanied by increased particulate P and RNA contents per cell. In addition, mPhoD cells increased in cellular carbon (including lipid) and nitrogen contents, and reprogrammed their metabolic response to changes in the nutrient condition. Our physiological and transcriptomic results reveal the roles of a PhoD in pigment synthesis and photosynthesis, lipid accumulation, cell cycle regulation, and nutrient homeostasis in a diatom when DOP scavenging is not required.