背景回顾：Plants depend on the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) for CO2 fixation. 

提出问题：However, especially in C3 plants, photosynthetic yield is reduced by formation of 2-phosphoglycolate, a toxic oxygenation product of Rubisco, which needs to be recycled in a high-flux–demanding metabolic process called photorespiration. 

研究基础：Canonical photorespiration dissipates energy and causes carbon and nitrogen losses. Reducing photorespiration through carbon-concentrating mechanisms, such as C4 photosynthesis, or bypassing photorespiration through metabolic engineering is expected to improve plant growth and yield. 

研究思路：The β-hydroxyaspartate cycle (BHAC) is a recently described microbial pathway that converts glyoxylate, a metabolite of plant photorespiration, into oxaloacetate in a highly efficient carbon-, nitrogen-, and energy-conserving manner. 

研究结果：Here, we engineered a functional BHACin plant peroxisomes to create a photorespiratory bypass that is independent of 3-phosphoglycerate regeneration or decarboxylation of photorespiratory precursors. 

结论：While efficient oxaloacetate conversion in Arabidopsis thaliana still masks the full potential of the BHAC, nitrogen conservation and accumulation of signature C4 metabolites demonstrate the proof of principle, opening the door to engineering a photorespiration-dependent synthetic carbon–concentrating mechanism in C3 plants.

 摘 要 

植物依赖于核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）进行CO2的固定。但是，尤其在C3植物中，Rubisco产生的一种有毒氧化产物2-磷酸乙醇酸盐会导致光合产量降低，该物质需要在一种叫做光呼吸的高通量代谢过程中循环利用。典型的光呼吸会消耗能量，并导致碳和氮的损失。通过碳浓缩机制（如C4光合作用），减少光呼吸，或是通过代谢工程绕过光呼吸，有望提高植物的生长和产量。β-羟基天冬氨酸循环（BHAC）是近年来研究的一种微生物代谢途径，其以高效的碳、氮和节能的方式将植物光呼吸的代谢物乙醛酸转化为草酰乙酸。本文中，作者在植物的过氧化物酶体中设计了一个功能性的BHAC来创建一个光呼吸旁路，其不依赖于3-磷酸甘油酸的再生或光呼吸前体的脱羧。虽然拟南芥中草酰乙酸会被高效转化为其他代谢物，导致会低估BHAC的潜力，但氮的保存和C4代谢物的积累证明了该方法的可行性，为在C3植物中构建依赖光呼吸的合成碳富集机制打开了一个新的大门。