Laboratory of Crop Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.
Plant Physiol. 2011 Jul;156(3):1603-11. doi: 10.1104/pp.111.177030. Epub 2011 May 11.
Rubisco limits photosynthetic CO(2) fixation because of its low catalytic turnover rate (k(cat)) and competing oxygenase reaction. Previous attempts to improve the catalytic efficiency of Rubisco by genetic engineering have gained little progress. Here we demonstrate that the introduction of the small subunit (RbcS) of high k(cat) Rubisco from the C(4) plant sorghum (Sorghum bicolor) significantly enhances k(cat) of Rubisco in transgenic rice (Oryza sativa). Three independent transgenic lines expressed sorghum RbcS at a high level, accounting for 30%, 44%, and 79% of the total RbcS. Rubisco was likely present as a chimera of sorghum and rice RbcS, and showed 1.32- to 1.50-fold higher k(cat) than in nontransgenic rice. Rubisco from transgenic lines showed a higher K(m) for CO(2) and slightly lower specificity for CO(2) than nontransgenic controls. These results suggest that Rubisco in rice transformed with sorghum RbcS partially acquires the catalytic properties of sorghum Rubisco. Rubisco content in transgenic lines was significantly increased over wild-type levels but Rubisco activation was slightly decreased. The expression of sorghum RbcS did not affect CO(2) assimilation rates under a range of CO(2) partial pressures. The J(max)/V(cmax) ratio was significantly lower in transgenic line compared to the nontransgenic plants. These observations suggest that the capacity of electron transport is not sufficient to support the increased Rubisco capacity in transgenic rice. Although the photosynthetic rate was not enhanced, the strategy presented here opens the way to engineering Rubisco for improvement of photosynthesis and productivity in the future.
Rubisco 因其低催化周转率（k(cat)）和竞争加氧酶反应而限制光合作用 CO2 固定。先前通过遗传工程提高 Rubisco 催化效率的尝试进展甚微。在这里，我们证明了从 C4 植物高粱（Sorghum bicolor）引入具有高 k(cat)的 Rubisco 小亚基（RbcS）可显著提高转基因水稻（Oryza sativa）中 Rubisco 的 k(cat)。三个独立的转基因系高水平表达高粱 RbcS，占总 RbcS 的 30%、44%和 79%。Rubisco 可能是高粱和水稻 RbcS 的嵌合体，其 k(cat)比非转基因水稻高 1.32-1.50 倍。来自转基因系的 Rubisco 对 CO2 的 K(m)更高，对 CO2 的特异性略低。这些结果表明，用高粱 RbcS 转化的水稻 Rubisco 部分获得了高粱 Rubisco 的催化特性。与野生型相比，转基因系中的 Rubisco 含量显著增加，但 Rubisco 激活略有降低。在一系列 CO2 分压下，高粱 RbcS 的表达并不影响 CO2 同化速率。与非转基因植物相比，转基因系的 J(max)/V(cmax) 比值显著降低。这些观察结果表明，电子传递的能力不足以支持转基因水稻中 Rubisco 能力的增加。尽管光合速率没有提高，但这里提出的策略为未来通过工程改造 Rubisco 以提高光合作用和生产力开辟了道路。
