Endosperm-specific expression of a yeast thiamin transporter enhances vitamin B1 content in white rice

Vitamin B1 is a vital cofactor in cellular metabolism, but must be obtained through the diet in humans. Polished (white) rice, a dietary staple for much of the global population, contains very low levels of vitamin B1, which contributes to widespread thiamin deficiency in regions that rely heavily on rice. To address this issue, we engineered rice to express the Saccharomyces cerevisiae thiamin transporter gene THI7 under the control of the endosperm-specific GLUTELIN1 (GT1) promoter. We found that endosperm-specific expression of yeast THI7 significantly increased thiamin levels by up to 24% in unpolished and 26% in polished seeds in transgenic rice lines with moderate to high THI7 expression. This increase was specific to free thiamin, with no change in thiamin monophosphate or thiamin diphosphate, consistent with the known transporter activity of THI7. Importantly, the transgenic plants displayed normal phenotypes under field conditions. Our findings demonstrate that endosperm-targeted expression of a heterologous thiamin transporter is an effective strategy for enhancing vitamin B1 content in rice grains, offering a new approach for biofortification that complements metabolic engineering of biosynthetic pathways.