Phosphoenolpyruvate Carboxylase in Arabidopsis Leaves Plays a Crucial Role in Carbon and Nitrogen Metabolism

Abstract

Phosphoenolpyruvate carboxylase (PEPC) is a crucial enzyme that catalyzes an irreversible primary metabolic reaction in plants. Previous studies have used transgenic plants expressing ectopic PEPC forms with diminished feedback inhibition to examine the role of PEPC in carbon and nitrogen metabolism. To date, the in vivo role of PEPC in carbon and nitrogen metabolism has not been analyzed in plants. In this study, we examined the role of PEPC in plants, demonstrating that PPC1 and PPC2 were highly expressed genes encoding PEPC in Arabidopsis (Arabidopsis thaliana) leaves and that PPC1 and PPC2 accounted for approximately 93% of total PEPC activity in the leaves. A double mutant, ppc1/ppc2, was constructed that exhibited a severe growth-arrest phenotype. The ppc1/ppc2 mutant accumulated more starch and sucrose than wild-type plants when seedlings were grown under normal conditions. Physiological and metabolic analysis revealed that decreased PEPC activity in the ppc1/ppc2 mutant greatly reduced the synthesis of malate and citrate and severely suppressed ammonium assimilation. Furthermore, nitrate levels in the ppc1/ppc2 mutant were significantly lower than those in wild-type plants due to the suppression of ammonium assimilation. Interestingly, starch and sucrose accumulation could be prevented and nitrate levels could be maintained by supplying the ppc1/ppc2 mutant with exogenous malate and glutamate, suggesting that low nitrogen status resulted in the alteration of carbon metabolism and prompted the accumulation of starch and sucrose in the ppc1/ppc2 mutant. Our results demonstrate that PEPC in leaves plays a crucial role in modulating the balance of carbon and nitrogen metabolism in Arabidopsis.

The Cytoplasmic Carbonic Anhydrases βCA2 and βCA4 Are Required for Optimal Plant Growth at Low CO2

“…Since 50% of the Asp in the plant is made as a result of PEPC activity (Melzer and O'Leary, 1987), we hypothesize that the loss of bCA2 and bCA4 lowers PEPC activity in the double mutant. Our results are consistent with the amino acid concentrations seen in PEPC knockout plants (Shi et al, 2015) and support the hypothesis that CA activity is required for optimal PEPC activity in the cytoplasm. The CO 2 compensation points were generated by finding the slope of the initial linear portion of the assimilation/inorganic carbon curve and solving for the x intercept.…”

“…8). In a previous study of a knockout of two PEPCs, a similar profile of low levels of Asp and high levels of Gly and Ser was found (Shi et al, 2015). Like the bca2bca4 double mutant (Fig.…”

“…Like the bca2bca4 double mutant (Fig. 6), the PEPC double mutant showed reduced growth and chlorosis (Shi et al, 2015).…”

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

“…The concurrent decrease of photoassimilate and demand for metabolites that occur during the cessation of growth also impacts the citric acid cycle that mediates between photosynthesis, respiration, and protein synthesis. The citric acid cycle generates NADH to fuel ATP synthesis via mitochondrial electron transport, as well as amino acid precursors (Shi et al, 2015). In C3 plants, the enzyme phosphoenolpyruvate carboxylase (PEPC) converts phosphoenolpyruvate to oxaloacetic acid in order to supplement the flow of metabolites to the citric acid cycle and thus controls the regulation of respiration and photosynthate partitioning (O'Leary et al, 2011).…”

Suppression of Chloroplastic Alkenal/One Oxidoreductase Represses the Carbon Catabolic Pathway in Arabidopsis Leaves during Night

“…PEPC activity greatly affects carbon and nitrogen metabolism. For example, an Arabidopsis knockout mutant of PEPC showed growth retardation (Shi et al, 2015). Furthermore, the decrease of PEPC activity in plants caused a decrease in starch degradation during the night period (Häusler et al, 1999;Shi et al, 2015).…”