Kinetic variation in grass phosphoenolpyruvate carboxylases provides opportunity to enhance C4 photosynthetic efficiency. (5th February 2021)

• Record Type: Journal Article
• Authors: DiMario, Robert J.; Kophs, Ashley N.; Pathare, Varsha S.; Schnable, James C.; Cousins, Asaph B.
• Is Part Of: Plant journal. Volume 105:Number 6(2021)
• Page Start: 1677
• Page End: 1688
• Publication Date: 2021-02-05
• Subjects: C4 photosynthesis -- phosphoenolpyruvate carboxylase -- plant biochemistry -- plant biology; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.15141
• Languages: English
• ISSNs: 0960-7412

Abstract

SUMMARY: The high rates of photosynthesis and the carbon‐concentrating mechanism (CCM) in C4 plants are initiated by the enzyme phosphoenolpyruvate (PEP) carboxylase (PEPC). The flow of inorganic carbon into the CCM of C4 plants is driven by PEPC's affinity for bicarbonate ( K HCO3 ), which can be rate limiting when atmospheric CO2 availability is restricted due to low stomatal conductance. We hypothesize that natural variation in K HCO3 across C4 plants is driven by specific amino acid substitutions to impact rates of C4 photosynthesis under environments such as drought that restrict stomatal conductance. To test this hypothesis, we measured K HCO3 from 20 C4 grasses to compare kinetic properties with specific amino acid substitutions. There was nearly a twofold range in K HCO3 across these C4 grasses (24.3 ± 1.5 to 46.3 ± 2.4 μm ), which significantly impacts modeled rates of C4 photosynthesis. Additionally, molecular engineering of a low‐HCO3 − affinity PEPC identified key domains that confer variation in K HCO3 . This study advances our understanding of PEPC kinetics and builds the foundation for engineering increased‐HCO3 − affinity and C4 photosynthetic efficiency in important C4 crops. Significance Statement: Phosphoenolpyruvate carboxylase (PEPC) is an essential enzyme involved in C4 photosynthesis and our research determined significant variability in the binding affinity for bicarbonate ( K HCO3 ) among 20 PEPC isozymes from C4 grasses. Additionally, we identified the region of the PEPC enzyme that is responsible for this variability in K HCO3, which builds the foundation for engineering a kinetically enhanced PEPC to increase photosynthesis and production in C4 crops to meet the demands of the growing population.