You Lei, Zhang Jumei, Li Long, Xiao Chuanlei, Feng Xinhua, Chen Shaoping, Guo Liang, Hu Honghong
National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, China.
J Exp Bot. 2020 Jul 6;71(14):4093-4108. doi: 10.1093/jxb/eraa148.
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 (Fv/Fm) 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 Fv/Fm 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.
磷酸烯醇式丙酮酸羧化酶（PEPC）在C4植物的光合二氧化碳固定过程中起着关键作用。然而，PEPC在C3植物中的功能尚未得到充分表征，特别是在低大气二氧化碳水平方面。在拟南芥中编码PEPC的四个基因中，PPC2被认为是主要的叶片PEPC基因。在这里，我们表明，ppc2突变体在转移到低大气二氧化碳条件下时生长停滞，同时PSII的最大效率（Fv/Fm）降低，叶片脱落酸（ABA）和碳水化合物水平降低。蔗糖、苹果酸或ABA的施用极大地挽救了ppc2品系在低二氧化碳条件下的生长。代谢物谱分析表明，ppc2叶片中甘氨酸和丝氨酸水平升高，而在这些条件下光合代谢物的丰度降低。ppc2中参与甘氨酸或丝氨酸代谢的编码酶的转录水平以ABI5依赖的方式降低。与ppc2突变体一样，在光呼吸条件下（即低二氧化碳可用性），abi5-1突变体与野生型相比具有较低的光合速率和Fv/Fm。然而，在非光呼吸（低氧）条件下，这些突变体的生长与野生型相似。ABI5的组成型表达阻止了ppc2品系在低二氧化碳条件下的生长停滞。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二氧化碳可用性方面发挥重要作用，并且这至少部分是通过ABA和ABI5依赖的过程介导的。
