Abstract
The catalytic turnover rate (kcat) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in C4 plants is higher than that in C3 plants. Transgenic rice plants that overexpress sorghum C4 Rubisco small subunit (SbRbcS) were produced and three independent transgenic rice lines expressing 30, 44 and 79% SbRbcS in total RbcS were used for analyses of kinetic properties of Rubisco. The kcat of Rubisco in transgenic rice was 1.3-1.5 fold higher than that in non-transgenic rice. Also, Rubisco in transgenic rice showed 1.3 fold higher Km (CO2) than that in non-transgenic rice. Interestingly, the extent of increase in kcat or Km (CO2) was similar among three transgenic lines expressing different levels of SbRbcS. In BN-PAGE, sorghum Rubisco showed slightly lower apparent MW compared with rice Rubisco. The expression of SbRbcS in transgenic rice caused a shift of apparent MW of Rubisco from the level of rice to sorghum Rubisco depending on the expression levels of SbRbcS. These results suggest that partial incorporation of SbRbcS induces some conformational changes in rice Rubisco and this leads to an enhancement of kcat of Rubisco.
