Ectopic Expression of a Bacterial Thiamin Monophosphate Kinase Enhances Vitamin B1 Biosynthesis in Plants

In plants, thiamin monophosphate (TMP) synthesized in the vitamin B1 biosynthetic pathway is first converted to thiamin by a phosphatase, which is then pyrophosphorylated to the bioactive thiamin diphosphate (TDP). In contrast, bacteria use a TMP kinase encoded by ThiL to phosphorylate TMP to TDP directly. Ectopic expression of E. coli ThiL driven by an endosperm-specific GLUTELIN1 (GT1) promoter enhanced TDP biosynthesis in rice. Total vitamin B1 increased by approximately 25-30% in the polished and unpolished seeds of the pGT1:ThiL transgenic rice compared to the wild type. These results suggest that genetic engineering of a bacterial vitamin B1 biosynthetic gene downstream of TMP can enhance vitamin B1 production in rice.