Post-translational regulation of the gamma-aminobutyrate (GABA) shunt in phosphorus-starved plants
Abstract
Inorganic phosphate (Pi) is an essential macronutrient for crop development, yet its limited availability in soil drives the overuse of unsustainable Pi fertilizers in agriculture. Plants respond to Pi deprivation through evolved adaptations that improve Pi acquisition and use, including changes in gene expression, enzyme regulation, and central metabolism. The gamma-aminobutyrate (GABA) shunt, a partial bypass of the Krebs cycle, is implicated in this metabolic reprogramming. Its first committed step is catalyzed by glutamate decarboxylase (GAD), a calcium-calmodulin-activated enzyme that produces GABA. Our lab previously reported that the root-specific GAD1 isozyme becomes hyperphosphorylated at conserved N-terminal serine residues following Pi resupply to Pi-starved (−Pi) Arabidopsis thaliana (Mehta et al., 2021). We also discovered that −Pi gad1 knockout mutants exhibit severely reduced growth and diminished GABA and Pi accumulation compared with −Pi wild-type (WT) plants (Benidickson et al., 2023). These findings suggest that GAD1 and the GABA shunt are important during Pi deprivation and that reversible phosphorylation may inhibit GAD1 activity following Pi resupply. My upcoming BSc Honours thesis (BIOL537) will investigate this regulation using gad1 plants complemented with phospho-mimetic or phospho-ablative GAD1 mutants. I hypothesize that if phosphorylation inhibits GAD1 in vivo, the GAD1 phospho-mimetic complemented plants will exhibit reduced GABA levels and impaired growth during Pi deprivation, similar to gad1 knockouts. Through my USRA research, I have identified several lines that contain the phospho-mimetic or phospho-ablative GAD1 transgene through PCR genotyping, some of which show evidence of root GAD1 polypeptide expression via anti-GAD1 immunoblotting. Viable lines will be grown in various (a)biotic stresses for phenotypic and molecular characterization of GAD1 phosphorylation in vivo. This work will advance our understanding of post-translational regulation of central plant metabolism during nutrient stress and may contribute to the development of Pi-use-efficient crops, supporting sustainable agriculture, food security, and environmental protection. Settings Supervisors: William Plaxton, Wayne Snedden References Benidickson, K. H., Raytek, L. M., Hoover, G. J., Flaherty, E. J., Shelp, B. J., Snedden, W. A., & Plaxton, W. C. (2023). Glutamate decarboxylase‐1 is essential for efficient acclimation of arabidopsis thaliana to nutritional phosphorus deprivation. New Phytologist, 240(6), 2372–2385. Mehta, D., Ghahremani, M., Pérez‐Fernández, M., Tan, M., Schläpfer, P., Plaxton, W. C., & Uhrig, R. G. (2021). Phosphate and phosphite have a differential impact on the proteome and phosphoproteome of arabidopsis suspension cell cultures. The Plant Journal, 105(4), 924–941.