Effects of suppression of chloroplast phosphoglycerate kinase on photosynthesis in rice

As chloroplast phosphoglycerate kinase (cpPGK) is one of the enzymes which has the highest capacity among the Calvin-Benson cycle enzymes, it has not been regarded as a determinant for photosynthetic capacity. However, it was reported that the rate of CO₂ assimilation decreased under high irradiance and normal [CO₂] levels in the Arabidopsis cpPGK-knockdown mutant, implying that cpPGK has a control over photosynthetic capacity at a normal [CO₂] level. In the present study, the contribution of cpPGK to photosynthetic capacity was evaluated in transgenic rice plants with decreased amounts of cpPGK protein under high irradiance and various [CO₂] levels. The gene encoding cpPGK was suppressed using RNA interference techniques. Two lines of transgenic plants, Pi3 and Pi5, in which the amount of cpPGK protein decreased to 21% and 76% of that in wild-type plants, respectively, were obtained. However, there was no substantial difference in the rates of CO₂ assimilation between wild-type and transgenic plants. The rates of CO₂ assimilation decreased only slightly at elevated [CO₂] levels in the transgenic line Pi3 and did not differ between wild-type plants and the transgenic line Pi5, irrespective of [CO₂] level. These results clearly indicate that cpPGK does not have a strong control over photosynthetic capacity at various [CO₂] levels in rice.