Alkaline phosphatase promoter as an efficient driving element for exogenic recombinant in the marine diatom Phaeodactylum tricornutum

A highly inducible promoter capable of actively expressing exogenous genes in diatoms is critical to further improving the utility of this organism as a low-cost platform for industrial applications. In this study, the functional promoter of alkaline phosphatase gene in Phaeodactylum tricornutum (PtAPase) was used to develop a novel vector. The pPhAP1-EGFP vector containing the putative promoter region of PtAPase (pPhAP1) with EGFP (enhanced green fluorescent protein) open reading frame attached to downstream side. Transgenic diatom clones containing the introduced pPhAP1-EGFP vector did not express EGFP fluorescent at high phosphate concentration, and exhibit growth curves similar to that of wild type strain. EGFP fluorescent was induced and actively expressed when ambient phosphate concentration was decreased to 3.6 μM or lower. The endogenous alkaline phosphatase activity had the same expression pattern, indicating that the pPhAP1 possessed uncompromised regulatory capability. In terms of the quantity of EGFP generated by expression vectors, the yield of pPhAP1-EGFP was 9.3 to 10.5 times greater than those of other diatom vectors. These results suggested that pPhAP1 is an outstanding expression vector for diatoms with desirable characteristics of no interference with algal growth, easily tunable conditions for gene induction, and high yield of recombinant proteins.