High level expression of C4 photosynthesis enzymes in transgenic rice

Abstract

In C4 plants, the C4 photosynthetic pathway confers a number of advantages, including enhanced photosynthetic capacity and high nitrogen and water use efficiencies. It has long been anticipated that the transfer of C4 trait to C3 plants could improve the photosynthetic performance of C3 plants. The recent progress in molecular engineering enabled us to express C4 enzymes at high levels and in desired locations in the leaves of C3 plants. Phosphoenolpyruvate carboxylase (PEPC) and pyruvate, orthophosphate dikinase (PPDK) can be expressed at high levels in rice leaves by introduction of the intact maize C4-specific genes. In transgenic rice plants carrying the intact maize gene, the level of transcript per copy of the maize gene in the leaves was comparable to that in maize, and the maize gene was expressed in an organ-specific manner as in maize, suggesting that the maize C4-specific genes for PEPC and PPDK behave in a quantitatively and qualitatively similar way in both maize and transgenic rice plants. NADP-malic enzyme (NADP-ME) can be expressed at high levels in rice leaves by introduction of cDNA for the maize C4-specific NADP-ME fused to the rice Cab promoter. Although high level expression of a single C4 enzyme did not improve photosynthetic performance of rice plant, we observed changes in some traits of rice plants, probably through enhancement of housekeeping functions of the endogenous C4 enzymes.