Table1_Kre6 (yeast 1,6-β-transglycosylase) homolog, PhTGS, is essential for β-glucan synthesis in the haptophyte Pleurochrysis haptonemofera.XLSX

Haptophytes synthesize unique β-glucans containing more β-1,6-linkages than β-1,3 linkages, as a storage polysaccharide. To understand the mechanism of the synthesis, we investigated the roles of Kre6 (yeast 1,6-β-transglycosylase) homologs, PhTGS, in the haptophyte Pleurochrysis haptonemofera. RNAi of PhTGS repressed β-glucan accumulation and simultaneously induced lipid production, suggesting that PhTGS is involved in β-glucan synthesis and that the knockdown leads to the alteration of the carbon metabolic flow. PhTGS was expressed more in light, where β-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 β-glucan of P. haptonemofera. These findings suggest that PhTGS functions in storage β-glucan synthesis specifically in light, probably by producing the β-1,6-branch.浮游植物合成独特的β-葡聚糖，其中β-1,6-糖苷键的数量多于β-1,3-糖苷键，用作储存的多糖。为了探究其合成机制，本研究探讨了酵母中的1,6-β-转糖基化酶Kre6同源物PhTGS在浮游植物Pleurochrysis haptonemofera中的作用。PhTGS的RNA干扰抑制了β-葡聚糖的积累，并同步促进了脂质的生产，表明PhTGS参与β-葡聚糖的合成，且其敲低导致碳代谢途径的改道。PhTGS在光照条件下表达更为丰富，此时通过光合作用积极产生β-葡聚糖，而在黑暗条件下则相对较少。表达PhKre6的E. coli的粗提物显示了其将14C-UDP-葡萄糖整合进P. haptonemofera的β-葡聚糖中的活性。这些发现表明，PhTGS在光照条件下特异地参与储存型β-葡聚糖的合成，可能通过产生β-1,6分支来实现。