Plant Biotechnol. J|将C4光合作用途径引入水稻C3作物中，有望实现水稻增产

将C4光合作用机制引入C3作物，除了潜在地提高氮和水的利用效率外，还提供了提高光合作用效率、生物量和产量的机会。

为了建立NADP-苹果酸酶型C4水稻的两细胞代谢原型，我们将其转化为水稻(Oryza sativa spp.)。粳稻品种Kitaake在细胞优先启动子的驱动下，构建了含有玉米碳酸酐酶、磷酸烯醇式丙酮酸(PEP)羧化酶、NADP-苹果酸脱氢酶、丙酮酸正磷酸二激酶和NADP-苹果酸酶编码区的单一结构。证实了5种转基因的基因表达、蛋白质积累和酶活性，并对蛋白质的胞间定位进行了分析。

13CO2标记表明，通过PEP羧化酶的光合通量增加了10倍，超过了离体测定的酶活性的增加，估计约占玉米光合通量的2%。

从苹果酸通过丙酮酸到PEP的通量仍然很低，这与转基因品系中观察到的低NADP-苹果酸酶活性是相称的。生理干扰很小，RNA测序显示转基因表达对其他与光合作用相关的内源水稻转录本没有实质性影响。

这些结果表明，到目前为止，随着C4蛋白水平的提高，在水稻中实现功能性的C4途径是可能的。

图：C4酶在水稻中的表达

Introduction of a C4 photosynthetic mechanism into C3 crops offers an opportunity to improve photosynthetic efficiency, biomass and yield in addition to potentially improving nitrogen and water use efficiency. To create a two-cell metabolic prototype for an NADP-malic enzyme type C4 rice, we transformed Oryza sativa spp. japonica cultivar Kitaake with a single construct containing the coding regions of carbonic anhydrase, phosphoenolpyruvate (PEP) carboxylase, NADP-malate dehydrogenase, pyruvate orthophosphate dikinase and NADP-malic enzyme from Zea mays, driven by cell-preferential promoters. Gene expression, protein accumulation and enzyme activity were confirmed for all five transgenes, and intercellular localization of proteins was analysed. 13CO2 labelling demonstrated a 10-fold increase in flux though PEP carboxylase, exceeding the increase in measured in vitro enzyme activity, and estimated to be about 2% of the maize photosynthetic flux. Flux from malate via pyruvate to PEP remained low, commensurate with the low NADP-malic enzyme activity observed in the transgenic lines. Physiological perturbations were minor and RNA sequencing revealed no substantive effects of transgene expression on other endogenous rice transcripts associated with photosynthesis. These results provide promise that, with enhanced levels of the C4 proteins introduced thus far, a functional C4 pathway is achievable in rice.

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