Requirement of γ-Aminobutyric Acid Chemotaxis for Virulence of <i>Pseudomonas syringae</i> pv. <i>tabaci</i> 6605

Abstract

γ-Aminobutyric acid (GABA) is a widely distributed non-proteinogenic amino acid that accumulates in plants under biotic and abiotic stress conditions. Recent studies suggested that GABA also functions as an intracellular signaling molecule in plants and in signals mediating interactions between plants and phytopathogenic bacteria. However, the molecular mechanisms underlying GABA responses to bacterial pathogens remain unknown. In the present study, a GABA receptor, named McpG, was conserved in the highly motile plant-pathogenic bacteria Pseudomonas syringae pv. tabaci 6605 (Pta6605). We generated a deletion mutant of McpG to further investigate its involvement in GABA chemotaxis using quantitative capillary and qualitative plate assays. The wild-type strain of Pta6605 was attracted to GABA, while the ΔmcpG mutant abolished chemotaxis to 10 mM GABA. However, ΔmcpG retained chemotaxis to proteinogenic amino acids and succinic semialdehyde, a structural analog of GABA. Furthermore, ΔmcpG was unable to effectively induce disease on host tobacco plants in three plant inoculation assays: flood, dip, and infiltration inoculations. These results revealed that the GABA sensing of Pta6605 is important for the interaction of Pta6605 with its host tobacco plant.

Identification of Aerotaxis Receptor Proteins Involved in Host Plant Infection by <i>Pseudomonas syringae</i> pv. <i>tabaci</i> 6605

“…The Pta 6605 chemotaxis system plays a significant role in virulence ( Tumewu et al , 2021b ). Furthermore, mutations in the mcp genes for γ-aminobutyric acid and amino acids had a prominent impact on Pta 6605 fitness in host plants ( Tumewu et al , 2020 ; 2021a ). To elucidate the role of aerotaxis on virulence by Pta 6605, a flood inoculation assay was performed.…”

“…To investigate the surface motility of aer mutant strains, motility assays were performed on semisolid agar medium as previously described ( Tumewu et al , 2020 ). Bacterial strains were cultured overnight in LB broth supplemented with 10‍ ‍mM MgCl 2 and resuspended in 10‍ ‍mM of MgSO 4 at an OD 600 of 0.1.…”

“…A quantitative chemotaxis assay was performed as described in our previous study ( Tumewu et al , 2020 ). To prepare bacterial cells, each strain was cultured in LB medium supplemented with 10‍ ‍mM MgCl 2 overnight.…”

“…The virulence of WT and mutant strains was analyzed using a flood inoculation method as described in our previous study ( Tumewu et al , 2020 ). Briefly, gas-sterilized tobacco seeds ( Nicotiana tabacum L. cv.…”

Vfr targets promoter of genes encoding methyl-accepting chemotaxis protein in Pseudomonas syringae pv. tabaci 6605

“…We also found the requirements of cheA2 and cheY2 of Pta 6605 in chemotaxis and virulence on host tobacco plant (unpublished results). Recently, it was reported that the defective mutant of chemoreceptor of amino acid, PscA in Pto DC3000 and chemoreceptor of γ-aminobutyric acid, McpG in Pta 6605 reduced virulence [ 16 , 17 ]. Furthermore, PscA and McpG are not only chemoreceptors but also regulator of virulence related traits.…”