[P004] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P02-236] Boric acid chemotaxis contributes to wound entry in the plant pathogen Pseudomonas amygdali pv. tabaci

○Akiko Hida¹, Kotaro Fujikawa¹, Takahisa Tajima¹ (1. Hiroshima University (Japan))

Keywords:

chemotaxis,boric acid,plant pathogen,Pseudmonas syringae,plant-derived compounds

Chemotaxis plays an important role in plant–microbe interactions by guiding bacteria toward host-derived chemical signals. In our previous work, boric acid was identified as a novel chemoattractant along with its specific receptor McpB in Ralstonia pseudosolanacearum. Because homologs of McpB appear to be conserved among plant pathogenic bacteria and boric acid is an essential micronutrient ubiquitously present in plants, chemotaxis toward boric acid is thought to contribute to plant infection; however, its functional importance has not been experimentally demonstrated. We hypothesized that boric acid may leak in a damage-dependent manner from plants and serve as a chemical cue marking entry sites for pathogenic bacteria, because boric acid is not commonly secreted from plants.Here, we used Pseudomonas amygdali pv. tabaci (Pta; formerly Pseudomonas syringae pv. tabaci), the causal agent of tobacco wildfire disease, as a model pathogen to test the hypothesis. In chemotaxis assays, wild-type Pta showed concentration-dependent chemotaxis toward boric acid, whereas deletion of the mcpB-homologous gene abolished this response, indicating that the McpB homolog also functions as a boric acid chemoreceptor in Pta, hereafter referred to as McpB. To confirm leakage of boric acid from the host plant, water drops placed on the surface of intact or wounded tobacco leaves were analyzed by ICP-MS. As a result, boron was detected at intact sites and increased markedly at wound sites, suggesting that boric acid is released from leaf wounds, because boron predominantly exists as boric acid in aqueous environments. Furthermore, bacterial entry assays using wild-type and mcpB mutant Pta strains revealed that McpB-mediated chemotaxis contributes to bacterial entry through leaf wounds.Collectively, these results suggest that boric acid released from wounds may serve as a damage-derived chemical cue that guides bacteria toward wounds, where they subsequently enter plant tissues during Pta infection. Since the leakage of boric acid is likely passive based on semiquantitative elemental analysis, and homologs of McpB are preferentially distributed among plant pathogenic bacteria, the boric acid-guided invasion mechanism identified in Pta may also operate in other plant pathogenic bacteria that possess McpB homologs. These findings provide new insight into how plant pathogenic bacteria utilize host-derived chemical cues to locate entry sites during infection and may inform strategies to interfere with early stages of plant infection.