Seed endophytic bacterium Bacillus velezensis and its lipopeptides acts as elicitors of defense responses against Fusarium verticillioides in maize seedlings

Abstract

Purpose: The potential of endophytic bacteria to improve plant health has been well-established. In maize plants, studies have reported the antagonistic activity of endophytic bacteria against various kinds of phytopathogenic strains; however, the effect of lipopeptide inoculation on germinated seedlings and its underlying defense responses remain unexplored. In this study, we examined the effects of seed endophytic bacterium Bacillus velezensis and its lipopeptides in improving plant defense against Fusarium verticillioides in maize seedlings.

Methods: In vitro germinated maize seedlings were treated with lipopeptides extracted from the B. velezensis, followed by inoculation with the phytopathogen Fusarium verticillioides. The lipopeptides were characterized using MALDI-TOF analysis and their effects on fungal colonization and defense gene expression were investigated. Polyphenol content was checked in the bacterium-ZMW8 as well as ZMW8 and Fusarium-inoculated seedlings through UHPLC.

Results: Lipopeptide treatment to the maize seedling’s roots resulted in enhanced protection from the fungus with significant improvement in all the growth parameters measured. Antifungal lipopeptides were identified as bacillomycin D and fengycin. Confocal microscopy images revealed the heavy colonization of fungus on the seed and root surface of non-lipopeptide-treated seedlings. Gene expression analysis revealed upregulation of various defense response genes including ZmPR-1, ZmPR-4, ZmSOD-2, ZmLOX, ZmPDF1.2, and ZmERF in the roots of bacteria and lipopeptides-treated maize seedlings. Targeted metabolite analysis through UHPLC revealed the accumulation of antifungal polyphenols including p-coumaric acid, kaempferol, dihydrokaempferol (DHK), and dihydroquercetin (DHQ).

Conclusions: The study highlights the potential of bacterial lipopeptides as elicitors of defense responses in maize seedlings against Fusarium infection.