Increased Rubisco content in transgenic rice transformed with "sense" rbcS gene

Abstract

Rice (Oryza sativa L.) plants were transformed with the rice rbcS cDNA under the control of its own promoter by Agrobacterium-mediated method. The primary transformants were screened for the ratio of Rubisco-N to leaf-N. In the progeny of the selected lines, the mRNA levels of rbcS and rbcL were increased from 2.1- to 2.8-fold and 1.2- to 1.9-fold, respectively. Rubisco content was significantly increased by 30% on a leaf area basis. The ratio of Rubisco-N to leaf-N was also increased by 10 to 20%. However, light-saturated photosynthesis was not enhanced even when the rate was measured at low [CO₂] where Rubisco becomes limiting for photosynthesis. We conclude that introduction of additional sense rbcS leads to overexpression of rbcS and that this overexpression slightly up-regulates the gene expression of rbcL at a transcript level and enhances the amount of Rubisco holoenzyme. However, overproduction of Rubisco protein does not improve photosynthesis.