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Poster

Session: Session 2 Presenting Authors at Posters (Odds)

P-031 - Spatiotemporal dissection of camalexin functions in plant-bacterial interactions

Wednesday, July 16, 2025
13:30 - 15:15  
Location: Confex Hall 3
Spatial & temporal resolution of the interaction interface
Phytoalexins are secondary antimicrobial compounds that are rapidly accumulated de novo upon pathogen attacks. However, compared to their well-known functions against fungi and oomycetes, their roles against bacteria remained obscure as exemplified by camalexin (CM), the major phytoalexin in Arabidopsis, whose synthesis is mediated by PHYTOALEXIN DEFICIENT 3 (PAD3). In order to clarify the roles of CM in bacterial infections, we focused on Arabidopsis-Pseudomonas syringae pv. tomato DC3000 (Pst) interactions. First, we revealed that CM suppressed Pstgrowth in vitro in a nutrient-dependent manner. Pst growth in planta was also reduced when co-infiltrated with CM, as well as pad3-1 plants exhibited enhanced Pst growth in our assay, indicating the inhibitory effect of CM on Pst growth. We found that the promoter of PAD3 (pPAD3) was strongly up-regulated in the area surrounding the Pst-inoculated sites. This apparent suppression of the p<em>PAD3 activity within the infiltrated area occurred in a Type III Secretion System (T3SS)-dependent manner, suggesting the importance of CM as a generic barrier against bacterial pathogens. Our further dissection using mass spectrometry imaging techniques revealed that CM spatial distribution mostly overlapped with the pPAD3 active area, suggesting the pPAD3 reporter is a good marker reflecting the actual CA accumulation. These results indicated that Pst pathogenicity is achieved, at least, through the T3SS-mediated suppression of CM accumulation.