Glutamate decarboxylase‐1 is essential for efficient acclimation of Arabidopsis thaliana to nutritional phosphorus deprivation

Abstract

Summary Glutamate decarboxylase (GAD) is a Ca2+‐calmodulin‐activated, cytosolic enzyme that produces γ‐aminobutyrate (GABA) as the committed step of the GABA shunt. This pathway bypasses the 2‐oxoglutarate to succinate reactions of the tricarboxylic acid (TCA) cycle. GABA also accumulates during many plant stresses. We tested the hypothesis that AtGAD1 (At5G17330) facilitates Arabidopsis acclimation to Pi deprivation. Quantitative RT‐PCR and immunoblotting revealed that AtGAD1 transcript and protein expression is primarily root‐specific, but inducible at lower levels in shoots of Pi‐deprived (−Pi) plants. Pi deprivation reduced levels of the 2‐oxoglutarate dehydrogenase (2‐OGDH) cofactor thiamine diphosphate (ThDP) in shoots and roots by > 50%. Growth of −Pi atgad1 T‐DNA mutants was significantly attenuated relative to wild‐type plants. This was accompanied by: (i) an > 60% increase in shoot and root GABA levels of −Pi wild‐type, but not atgad1 plants, and (ii) markedly elevated anthocyanin and reduced free and total Pi levels in leaves of −Pi atgad1 plants. Treatment with 10 mM GABA reversed the deleterious development of −Pi atgad1 plants. Our results indicate that AtGAD1 mediates GABA shunt upregulation during Pi deprivation. This bypass is hypothesized to circumvent ThDP‐limited 2‐OGDH activity to facilitate TCA cycle flux and respiration by −Pi Arabidopsis.

Parallel comparison reveals conservation and re-wiring of abiotic stress response networks across three plant species

“…The salvaged products can then be converted back into nucleotides, which could be particularly important during nutrient starvation (Chen and Thelen 2011). Glutamate dehydrogenase 3 ( GAD3 ), which catalyzes a reversible reaction that synthesizes or deaminates glutamate, may play a role in the control of nitrogen metabolism in leaf development (Marchi et al 2013), while the other members of the GAD family also facilitate acclimation of Arabidopsis to P starvation by GABA shunt upregulation (Benidickson et al 2023). Apart from the starvation response, in shorter photoperiod, all three species showed upregulation of a gene corresponding ATNTT2 , which shows necrotic lesions during shrefort photoperiod (Reinhold et al 2007).…”

Heterologous expression and purification of glutamate decarboxylase-1 from the model plantArabidopsis thaliana: characterization of the enzyme’sin vitrotruncation by thiol endopeptidase activity

“…Preliminary evidence of Raytek (2022) supports the hypothesis that differential phosphorylation inhibits the activity of native AtGAD1 following Pi resupply to Pi-starved Arabidopsis. Phenotypic analyses of atgad1 T-DNA insertional mutants demonstrated that AtGAD1 and the GABA shunt play important adaptive roles during Arabidopsis acclimation to Pi deprivation (Benidickson et al, 2023).…”

“…GAD catalyzes the irreversible decarboxylation of glutamate to γ-aminobutyrate (GABA) and CO 2 . This represents the first committed step of the GABA shunt, a pathway that bypasses the 2-oxoglutarate to succinate reactions of the tricarboxylic acid cycle, and that facilitates plant acclimation to various (a)biotic stresses (Benidickson et al, 2023; Bouché et al, 2003; Che-Othman et al, 2020; Joshi et al, 2019). GADs belong to the aspartate aminotransferase superfamily of pyridoxal-5’-P (PLP)-dependent enzymes (Rossignoli et al, 2018).…”

“…The genome of the model plant Arabidopsis thaliana encodes five closely related GAD isozymes. AtGAD1 (AT5G17330) is the most studied paralog, and is primarily expressed in roots (Benidickson et al, 2023; Bouché et al, 2004; Turano & Fang, 1998). Knockout of AtGAD1 in atgad1 T-DNA mutants decreases root GABA levels by up to 85% while compromising the ability of Arabidopsis to survive various stresses including salinity, excessive heat, or nutritional Pi deprivation (Benidickson et al, 2023; Mekonnen et al, 2016; Shelp, 1999; Su et al, 2019).…”