Kre6 (yeast 1,6-ß-transglycosylase) homolog, PhTGS, is essential for ß-glucan synthesis in the haptophyte Pleurochrysis haptonemofera.

ABSTRACT

Haptophytes synthesize unique ß-glucans containing more ß-1,6-linkages than ß-1,3 linkages, as a storage polysaccharide. To understand the mechanism of the synthesis, we investigated the roles of Kre6 (yeast 1,6-ß-transglycosylase) homologs, PhTGS, in the haptophyte Pleurochrysis haptonemofera. RNAi of PhTGS repressed ß-glucan accumulation and simultaneously induced lipid production, suggesting that PhTGS is involved in ß-glucan synthesis and that the knockdown leads to the alteration of the carbon metabolic flow. PhTGS was expressed more in light, where ß-glucan was actively produced by photosynthesis, than in the dark. The crude extract of E. coli expressing PhKre6 demonstrated its activity to incorporate 14C-UDP-glucose into ß-glucan of P. haptonemofera. These findings suggest that PhTGS functions in storage ß-glucan synthesis specifically in light, probably by producing the ß-1,6-branch.