ABSTRACT

Rubisco is the key enzyme responsible for photosynthetic CO₂ fixation. Previously, we succeeded to increase the catalytic rate (k_cat) of Rubisco by the overexpression of sorghum C₄-type Rubisco small subunit (RbcS) in rice. These Rubisco are present as a chimera of sorghum RbcS and rice RbcS. In this study, we introduced an RNAi construct for rice RbcS into a sorghum RbcS overexpression line (SS10). Obtained double-transgenic lines iSS4 and iSS5 dominantly expressed sorghum RbcS and accumulated 35% and 20% of Rubisco content of non-transgenic rice (WT), respectively. Rubisco in these double-transgenic lines showed higher k_cat and K_m for CO₂ than WT and SS10. Moreover, iSS4 showed higher photosynthetic nitrogen use efficiency under high CO₂ conditions. These results demonstrate the usefulness of C₄-type RbcS to improve photosynthetic performance under elevated CO₂ conditions.

摘要

Rubisco 是负责光合 CO ₂固定的关键酶。此前，我们通过在水稻中过表达高粱 C ₄型 Rub​​isco 小亚基 (RbcS) ，成功提高了Rubisco的催化率 ( k _cat ) 。这些 Rubisco 以高粱 RbcS 和水稻 RbcS 的嵌合体形式存在。在这项研究中，我们将水稻RbcS的 RNAi 构建体引入高粱 RbcS 过表达系 (SS10)。获得双转基因系 iSS4 和 iSS5 显性表达高粱 RbcS，分别积累了非转基因水稻（WT）Rubisco 含量的 35% 和 20%。这些双转基因品系中的 Rubisco对 CO显示出更高的k _cat和K _m2比 WT 和 SS10。此外，iSS4 在高CO ₂条件下表现出更高的光合氮利用效率。这些结果证明了 C ₄型 RbcS 在提高 CO ₂条件下提高光合性能的有用性。