A rice small GTPase, OsRab6a, is involved in the regulation of grain yield and iron nutrition in response to CO2 enrichment.

Despite extensive studies on the effects of elevated atmospheric CO2 concentrations ([CO2]) on rice, the molecular players and signaling events underlying adaptation of rice plants to elevated [CO2] remains largely elusive. Here, we report that the OsRab6a gene encoding a small GTPase is involved in the regulation of rice growth, seed yield and iron (Fe) accumulation in response to elevated [CO2] using wild-type and transgenic rice plants of OsRab6a-overexpressing and OsRab6a-RNAi. No differences in growth and grain yield among wild-type and the transgenic plants were detected under ambient [CO2] conditions. When growing in elevated [CO2] conditions, growth and grain yield of wild-type and OsRab6a-overexpression rice plants were enhanced, with the OsRab6a-overexpression rice plants exhibiting higher growth and yield than their wild-type counterparts. In contrast, there were no effects of elevated [CO2] on growth and grain yield of OsRab6a-RNAi plants. Photosynthetic rates of both WT and OsRab6a-overexpressing plants were stimulated by elevated [CO2], with the magnitude of increase being higher in OsRab6a overexpression. Fe concentrations in vegetative tissues and grains of wild-type and transgenic rice plants were reduced by elevated [CO2], and the magnitude of decrease was lower in overexpression than that of wild-type and RNAi plants. The genes associated with Fe acquisition Fe in OsRab6a-overexpressing lines exhibited greater expression than those in WT and OsRab6a-RNAi plants under elevated [CO2]. By analyzing data with the Dunnett's multiple comparison test, our results suggest that OsRab6a is an important molecular regulator underlying rice adaptation to elevated [CO2] by regulating photosynthesis and Fe accumulation.