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是负责光合作用CO ₂固定的关键酶。以前，我们通过在水稻中过表达高粱C ₄型Rubisco小亚基（RbcS）成功提高Rubisco的催化速率（k _cat）。这些Rubisco以高粱RbcS和大米RbcS的嵌合体形式存在。在这项研究中，我们将水稻RbcS的RNAi构建体引入了高粱RbcS过表达株系（SS10）。获得的双转基因品系iSS4和iSS5主要表达高粱RbcS，并分别积累了非转基因水稻（WT）的Rubisco含量的35％和20％。加氧酶在这些双转基因品系表现出较高的ķ_猫和ķ_米为CO 比WT和SS10高₂。此外，iSS4在高CO ₂条件下显示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条件下改善光合性能的有用性。