Arabidopsis PPC2 is crucial for growth at low CO2 by involvement in photorespiratory metabolism and integration of ABI5

Phosphoenolpyruvate carboxylase (PEPC) is a pivotal enzyme that plays a key role in photosynthetic CO2 fixation in C4. However, the function of C3 PEPCs and their roles at environmental CO2 changes are still limited. Here, we report the role of PPC2 in seedling growth at low CO2 by linking photorespiratory metabolism with primary metabolism and involvement of ABA and ABI5. Mutation of PPC2 caused seedling growth arrest, with reduced Fv/Fm, photosynthetic carbohydrates and ABA biosynthesis at low CO2. PPC2 is induced by low CO2 and the PEPC activity was greatly reduced in ppc2 leaves. Moreover, metabolic analyses showed the photorespiratory intermediates, glycine and serine, were greatly increased and primary metabolites were reduced. Application of sucrose, malate and ABA greatly rescued the growth arrest phenotype of ppc2. The expression of glycine/serine synthesis and metabolism related photorespiratory enzyme genes were decreased in ppc2 and regulated by ABI5 at low CO2 conditions. ppc2 and abi5 mature plants exhibited reduced A-Ci curves at relatively low CO2, which could be recovered by non-photorespiratory low oxygen conditions. ABI5 expression greatly rescued the growth arrest and A-Ci curves of ppc2 at low CO2. Our findings demonstrate the important role of C3 PEPCs in carbon fixation and metabolism.