Identification of OsGGR2, a second geranylgeranyl reductase involved in α-tocopherol synthesis in rice

Tocopherol (Toc) and tocotrienol (T3) are abundant in rice bran. Geranylgeranyl reductase (GGR) is an essential enzyme for Toc production that catalyzes the reduction of geranylgeranyl pyrophosphate and geranylgeranyl-chlorophyll. However, we found that a rice mutant line with inactivated Os02g0744900 (OsGGR1/LYL1/OsChl P) gene produces Toc, suggesting that rice plants may carry another enzyme with GGR activity. Using an RNA-mediated interference technique, we demonstrated that the Os01g0265000 ("OsGGR2") gene product has GGR activity. This result supports the existence of two GGR genes (OsGGR1 and OsGGR2) in rice, in contrast to Arabidopsis thaliana (thale cress) and cyanobacterium Synechocystis that each have only one GGR gene. We also produced rice callus with inactivated OsGGR1 and OsGGR2 that produced T3 but not Toc. Such rice callus could be used as a resource for production of pure T3 for nutraceutical applications.