Phosphoenolpyruvate carboxylase (PEPC) plays a pivotal role in the photosynthetic CO₂ fixation of C₄ plants. However, the functions of PEPCs in C₃ plants are less well characterized, particularly in relation to low atmospheric CO₂ levels. Of the four genes encoding PEPC in Arabidopsis, PPC2 is considered as the major leaf PEPC gene. Here we show that the ppc2 mutants suffered a growth arrest when transferred to low atmospheric CO₂ conditions, together with decreases in the maximum efficiency of PSII (F_v/F_m) and lower levels of leaf abscisic acid (ABA) and carbohydrates. The application of sucrose, malate, or ABA greatly rescued the growth of ppc2 lines under low CO₂ conditions. Metabolite profiling analysis revealed that the levels of glycine and serine were increased in ppc2 leaves, while the abundance of photosynthetic metabolites was decreased under these conditions. The transcript levels of encoding enzymes involved in glycine or serine metabolism was decreased in ppc2 in an ABI5-dependent manner. Like the ppc2 mutants, abi5-1 mutants had lower photosynthetic rates and F_v/F_m compared with the wild type under photorespiratory conditions (i.e. low CO₂ availability). However, the growth of these mutants was similar to that of the wild type under non-photorespiratory (low O₂) conditions. The constitutive expression of ABI5 prevented the growth arrest of ppc2 lines under low CO₂ conditions. These findings demonstrate that PPC2 plays an important role in the acclimation of Arabidopsis plants to low CO₂ availability by linking photorespiratory metabolism to primary metabolism, and that this is mediated, at least in part, through ABA- and ABI5-dependent processes.

中文翻译：

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脱落酸、ABI5 和 PPC2 在植物适应低 CO2 中的作用。

_{磷酸烯醇丙酮酸羧化酶(PEPC)在C 4}植物的光合CO ₂固定中起关键作用。然而，PEPCs 在 C ₃植物中的功能还没有得到很好的表征，特别是在低大气 CO ₂水平方面。在拟南芥中编码PEPC的四个基因中，PPC2被认为是主要的叶PEPC基因。在这里，我们表明ppc2突变体在转移到低大气 CO ₂条件时会出现生长停滞，同时 PSII 的最大效率降低 ( F _v / F _m) 和较低水平的叶脱落酸 (ABA) 和碳水化合物。蔗糖、苹果酸盐或ABA的应用极大地挽救了低CO ₂条件下ppc2系的生长。代谢物谱分析表明，在这些条件下， ppc2叶中甘氨酸和丝氨酸的含量增加，而光合代谢物的丰度降低。参与甘氨酸或丝氨酸代谢的编码酶的转录水平在ppc2中以 ABI5 依赖性方式降低。与ppc2突变体一样，abi5-1突变体具有较低的光合速率和F _v / F _m与光呼吸条件下的野生型相比（即 CO ₂可用性低）。然而，这些突变体的生长与非光呼吸（低 O ₂）条件下的野生型相似。ABI5的组成型表达阻止了ppc2系在低CO ₂条件下的生长停滞。这些发现表明，PPC2 通过将光呼吸代谢与初级代谢联系起来，在拟南芥植物适应低 CO ₂可用性方面发挥重要作用，并且这至少部分是通过 ABA 和 ABI5 依赖性过程介导的。