Functional complementation of pop2-3 T-DNA insertion mutant of Arabidopsis thaliana by overexpression of gamma-aminobutyric acid transaminase gene to reveals its role in complex pattern of leaf senescence

Abstract

Aim: Gamma-aminobutyric acid (GABA) is the chief inhibitory neurotransmitter in the mammalian central nervous system, and its important role is reducing the neuronal excitability throughout the nervous system. The GABA transaminase (GABA-T) enzyme catalyzes the transamination of GABA to form succinic semialdehyde using pyruvate as amino acid acceptor in GABA shunt pathway. The Arabidopsis thaliana GABA-T gene (pollen-pistil incompatibility 2 [POP2]; At3g22200) belongs to Class III pyridoxal-phosphate-dependent aminotransferase family. The full-length cDNA of the gene encodes a protein of 513 amino acids residues and located at chromosome 3. It could be demonstrated that the GABA-T is involved in the regulation of leaf senescence in A. thaliana. Materials and Methods: To ensure the role of GABA-T gene in leaf senescence, we have performed functional complementation using transformation of pPZP200GB-GABA-T construct into pop2-3 T-DNA insertion mutant (GABA-T knockout mutant) of A. thaliana (GABA-T complement plant) that the mutant plant reverts back to wild-type plant. We have measured and compared the physiological characteristics associated with senescence (chlorophyll content, ion leakage and lipid peroxidation) and quantified the GABA shunt components (GABA content, GABA-T, and glutamate decarboxylase activity) of the wild-type, pop2-3 mutant, and GABA-T complement plant of A. thaliana. Results: The result showed the low chlorophyll content, increased ion leakage, and higher level of lipid peroxidation in pop2-3 mutant than wild-type plant after 30 days in normal growth condition. GABA-T pop2-3 mutants act as signals that mediate early leaf senescence. GABA-T complement plant shared similar characteristics of senescence parameters with wild-type plants. Conclusion: These data concluded that GABA-T is involved in the regulation of leaf senescence in A. thaliana.