Roles of Alkaline Phosphatase PhoA in Algal Metabolic Regulation under Phosphorus-replete Conditions

Alkaline phosphatase (AP) in plants and algae is known to hydrolyze dissolved organophosphate (DOP) in order to obtain phosphorus when the preferred dissolved inorganic phosphorus (DIP) is present in limited supply. By conducting comparative analyses of physiologies and transcriptomes on a mutant of PhoA type AP (mPhoA) and wild type (WT) of the marine diatom Phaeodactylum tricornutum CCAP 1055/1 under P-replete and P-depleted conditions, we document other roles of this gene than DOP scavenging. PhoA mutation created by CRISPR/Cas9 diminished its DOP hydrolase activity but led to significant increases in cellular contents of pigment, carbon, and lipids, photosynthetic rate, growth rate, and the transcriptional levels of their corresponding metabolic pathways. All the results in concert indicate that besides P-nutrient scavenging under DIP deficiency, AP also functions, under the P-replete condition, to constrain pigment biosynthesis, photosynthesis, fatty acid biosynthesis, and cell division. These functions have important implications in maintaining metabolic homeostasis and preventing premature cell division.