几种光呼吸旁路已经被引入植物中，并被证明通过增加叶绿素二氧化碳浓度或优化能量平衡来改善光合作用。我们最近报道了工程GOC旁路可以提高水稻的光合作用和生产力。然而，由于结实率的不同，GOC植株的籽粒产量不稳定，在不同的栽培季节波动较大。
在本研究中，我们设计了一个由水稻乙醇酸氧化酶和大肠杆菌过氧化氢酶、乙醛酸碳寡酶和酒石酸半醛还原酶基因组成的人工光呼吸捷径(GCGT旁路)。GCGT旁路是由优化的叶绿体转运肽引导的，该转运肽以水稻叶绿体为靶标，将75%的乙醇酸代谢中的碳重新定向到Calvin循环，与天然光呼吸途径相同。转GCGT基因植株的生物量和产量显著增加，这主要归因于叶绿体CO2浓度的增加而增强了光合作用。
尽管生物产量和籽粒产量有所增加，但转GCGT基因植株的结实率降低了，这是以前报道的GOC植株的一种表型。综合转录学、生理生化分析表明，光合碳水化合物没有有效地运输到籽粒中，从而导致结实率下降。
综上所述，我们的结果表明，GCGT光呼吸捷径主要通过增加叶绿素CO2浓度来促进水稻的光合作用，从而获得更高的产量。
Several photorespiratory bypasses have been introduced into plants and shown to improve photosynthesis by increasing chloroplastic CO2 concentrations or optimizing energy balance. We recently reported that an engineered GOC bypass could increase photosynthesis and productivity in rice. However, grain yield of the GOC plants was unstable, fluctuating at the different cultivation seasons due to the varying seed setting rate. In this study, we designed a synthetic photorespiratory shortcut (the GCGT bypass) consisting of genes encoding Oryza sativa glycolate oxidase and Escherichia coli catalase, glyoxylate carboligase, and tartronic semialdehyde reductase. The GCGT bypass was guided by an optimized chloroplast transit peptide that targeted rice chloroplasts and redirected 75% of carbon from glycolate metabolism to the Calvin cycle, identical to the native photorespiration pathway. GCGT transgenic plants exhibited significantly increased biomass production and grain yield, which was mainly attributed to enhanced photosynthesis due to the increased chloroplastic CO2 concentration. Despite the increases in biomass production and grain yield, GCGT transgenic plants showed a reduced seed setting rate, a phenotype previously reported for the GOC plants. Integrative transcriptomic, physiological, and biochemical assays revealed that the photosynthetic carbohydrates were not transported to grains in an efficient manner, which then resulted in the decreased seed setting rate. Taken together, our results demonstrate that the GCGT photorespiratory shortcut confers higher yield by promoting photosynthesis in rice, mainly by increasing chloroplastic CO2 concentrations.
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