Poster: Photosynthesis

Abs # 339: Co-overproduction of C4-specific NADP-malate dehydrogenase and C4-specific NADP-malic enzyme in transgenic rice

Presenter:	Lee, Kwang-hong , khlee@affrc.go.jp
Authors	Lee, Kwang-hong  (A)   Tsuchida, Hiroko  (A)   Fukayama, Hiroshi  (A)   Miyao, Mitsue  (A)
Affiliations:	(A): National Institute of Agrobiological Sciences, Japan

We have previously demonstrated that overproduction of the maize C4-specific NADP-malic enzyme (NADP-ME) inside the chloroplast leads to enhanced photoinhibition of photosynthesis of rice plant (Tsuchida et al. (2001) Plant Cell Physiol 42:138-145). This detrimental effect results from massive import of malate into, and accumulation of NADPH inside the chloroplast in the light by the action of the maize enzyme, and it seems to be mitigated by simultaneous overproduction of NADP-malate dehydrogenase (NADP-MDH), which converts oxaloacetate to malate consuming one molecule of NADPH, inside the chloroplast. To examine this hypothesis, we have produced transgenic rice plants overproducing the sorghum C4-specific NADP-MDH alone or together with the maize C4-specific NADP-ME. Expression of a full-length cDNA for the sorghum NADP-MDH under the control of the rice Cab promoter resulted in accumulation of the enzyme protein in the leaves at levels up to 1-2% of total leaf soluble protein. The two enzymes were co-overproduced by introducing a gene construct containing full-length cDNAs for the sorghum NADP-MDH and the maize NADP-ME, each of which was fused to the rice Cab promoter. The enzyme proteins were successfully overproduced in transgenic rice leaves at levels easily detectable by Coomassie-blue stain after SDS-PAGE. Susceptibility to photoinhibition of these transgenic rice plants is now being investigated.