The bacterial lipopeptide iturins induce V erticillium dahliae cell death by affecting fungal signalling pathways and mediate plant defence responses involved in pathogen‐associated molecular pattern‐triggered immunity

Abstract

Summary V erticillium wilt in cotton caused by V erticillium dahliae is one of the most serious plant diseases worldwide. Because no known fungicides or cotton cultivars provide sufficient protection against this pathogen, V . dahliae causes major crop yield losses. Here, an isolated cotton endophytic bacterium, designated B acillus amyloliquefaciens 41 B ‐1, exhibited greater than 50% biocontrol efficacy against V . dahliae in cotton plants under greenhouse conditions. Through high‐performance liquid chromatography and mass analysis of the filtrate, we found that the antifungal compounds present in the strain 41 B ‐1 culture filtrate were a series of isoforms of iturins. The purified iturins suppressed V . dahliae microsclerotial germination in the absence or presence of cotton. Treatment with the iturins induced reactive oxygen species bursts, H og1 mitogen‐activated protein kinase (MAPK) activation and defects in cell wall integrity. The oxidative stress response and high‐osmolarity glycerol pathway contribute to iturins resistance in V . dahliae . In contrast, the S lt2 MAPK pathway may be involved in iturins sensitivity in this fungus. In addition to antagonism, iturins could induce plant defence responses as activators and mediate pathogen‐associated molecular pattern‐triggered immunity. These findings suggest that iturins may affect fungal signalling pathways and mediate plant defence responses against V . dahliae .

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