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POSTERS: Late Breaking II

P-642 - Not Just a Cycle: Structural and functional characterization of CsgabP and its role in GABA metabolism and citrus defense response to Huanglongbing

Tuesday, August 5, 2025
10:15 AM - 11:00 AM HST
Location: Exhibit Hall 3

    Presenting author(s)

  • YN

    Yasser Nehela, PhD (he/him/his)

    Postdoctoral Researcher
    Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850
    Lake Alfred, Florida, United States

    • Author(s)

  • NK

    Nabil Killiny

    University of Florida
    Gainesville, Florida, United States

Abstract Text: The connection between the TCA cycle and γ-aminobutyric acid (GABA) shunt in citrus is poorly understood. We used multi-omics approaches to structurally and functionally characterize the GABA permease (CsgabP) from Citrus sinensis and to investigate its role in GABA metabolism and response to ‘Candidatus Liberibacter asiaticus’, the causal agent of Huanglongbing (HLB), and its vector, Diaphorina citri. The citrus genome encodes two putative CsgabP proteins (CsgabP-1 [521 aa] and CsgabP-2 [419 aa]) that are highly homologous to the bidirectional amino acid transporter 1 (BAT 1; 516 aa) from Arabidopsis thaliana (AtgabP), as well as BAT 1 proteins from other plant species. CsgabPs are hydrophobic integral transmembrane transporter proteins that depend on 9-12 transmembrane segments. Protein-protein interaction networks suggested that CsgabPs interact with 10 GABA shunt-associated proteins. The 3D structures of both CsgabPs were predicted and confirmed using AlphaFold as monomers with 100% coverage. Molecular docking showed that GABA interacts through two conventional hydrogen bonds with residues Tyr-255 and Thr-256 of CsgabP-1 and three hydrogen bonds with Tyr-260, Ser-263, and Thr-267 of CsgabP-2. Targeted metabolomics showed that GABA levels were increased within ‘Ca. L. asiaticus’-infected and D. citri-infested leaves. Likewise, the expression of CsgabP was positively correlated with GABA accumulation in HLB-affected citrus plants. These findings likely clarify the molecular and functional connection between the GABA shunt and the TCA cycle in non-model plants.