Cloning and heterologous expression of a UDP-sugar-producing pyrophosphorylase gene from the harmful alga Phaeocystis globosa (Prymnesiophyceae) and its possible function in colony formation

Abstract

Massive Phaeocystis globosa blooms have caused serious damage to coastal Chinese marine ecosystems. Previous studies have shown that colony formation, a unique phenotypic characteristic of P. globosa, is accompanied by the up-regulation of USP (Uridine-diphosphate sugar pyrophosphorylase) genes. UDP-sugar-producing pyrophosphorylases are important enzymes involved in glucose metabolism. In this study, a novel UDPase protein, PgUSP, was identified in P. globosa that comprised a uridine binding motif and a pyrophosphorylase consensus motif. PgUSP encodes a novel polypeptide that localizes within the nucleus of cells. Moreover, exopolysaccharide production increased when PgUSP was transformed into Escherichia coli for over expression analysis. Further, we observed that the number and sizes of P. globosa colonies were significantly larger in cultures treated with cell-free filtrates of the diatom Chaetoceros affinis, while PgUSP expression was significantly up-regulated compared to that of the control without filtrate addition. These results indicate that expression of PgUSP can promote exopolysaccharide production and thus play an important role in P. globosa colony formation.