Overexpression of rice aquaporin OsPIP1;2 improves yield by enhancing mesophyll CO(2) conductance and phloem sucrose transport

Aquaporins are involved in CO(2) transport from the leaf intercellular air space to the chloroplast, which contributes to CO(2) assimilation. However, the mechanism of CO(2) transport by rice (Oryza sativa L.) aquaporins is unknown. Here, we investigated the function of the aquaporin OsPIP1;2 in CO(2) diffusion-associated photosynthesis and phloem sucrose transport. Moreover, the grain yield of rice lines overexpressing OsPIP1;2 was determined. OsPIP1;2 was localized to the plasma membrane and the relative expression of OsPIP1;2 was approximately 5-fold higher in leaves in the presence of an elevated CO(2) concentration. Overexpression of OsPIP1;2 increased mesophyll conductance by approximately 150% compared with wild-type (WT) rice. The OsPIP1;2-overexpressing lines had higher biomass than the WT, possibly due to increased phloem sucrose transport. In addition, the grain yield of OsPIP1;2-overexpressing lines was approximately 25% higher than that of the WT in three-season field experiments, due to the increased numbers of effective tillers and spikelets per panicle. Our results suggest that OsPIP1;2 modulates rice growth and grain yield by facilitating leaf CO(2) diffusion, which increases both the net CO(2) assimilation rate and sucrose transport.