Catalyzes the production of trehalose from glucose-6-phosphate and UDP-alpha-D-glucose in a 2 step process. D-glucose 6-phosphate + UDP-alpha-D-glucose = alpha,alpha-trehalose 6-phosphate + H(+) + UDP Expressed in all development stages. No visible phenotype. In the N-terminal section; belongs to the glycosyltransferase 20 family. In the C-terminal section; belongs to the gob-1 trehalose phosphatase family.