Rubisco small subunits of C₄ plants, Napier grass and guinea grass confer C₄-like catalytic properties on Rubisco in rice

Overexpression of Rubisco small subunit (RbcS) of C₄ plant, sorghum (sorghum bicolor) was shown to enhance the catalytic turnover rate (k_cat) of Rubisco in rice (Oryza sativa). In this study, the effects of other Rubisco small subunits of C₄ plants, Napier grass (Pennisetum purpureum) and guinea grass (Megathyrsus maximus) on kinetic properties of Rubisco in rice were studied. The expression levels of Napier grass RbcS (NgRbcS) and guinea grass RbcS (GgRbcS) proteins accounted for 41% and 45% of total RbcS, respectively in homozygous overexpression lines. The k_cat and K_m for CO₂ (Kc) of Rubisco were increased in all transgenic lines. Interestingly, the k_cat was markedly higher in NgRbcS homozygous line, whereas K_c was notably higher in GgRbcS homozygous line. Although its effects depend on species, these results suggest that the introduction of C₄ RbcS are effective approaches to alter the catalytic properties of Rubisco in rice.

GgRbcS: guinea grass RbcS; K_c: K_m for CO2; k_cat: catalytic turnover rate; NpRbcS: Napier grass RbcS; RbcL: Rubisco large subunit; RbcS: Rubisco small subunit; S_c/o: CO₂/O₂ specificity.