Flagellin-derived peptide flg22 from non-pathogenic Pseudomonas fragi Sneb1990 triggers plant immunity and reduces Meloidogyne incognita infestation

Biological control is widely recognized for its environmental benefits and has gained increasing attention. The peptide flg22 derived from biocontrol bacteria Pseudomonas fragi Sneb1990 (flg22Pf) exhibits significant efficacy against Meloidogyne incognita, but its mechanism is still unknown. In this study, we cloned the full-length flagellin gene from P. fragi Sneb1990 and found that it shares 32.02% sequence identity with the flagellin from non-pathogenic Pseudomonas syringae pv. tomato DC3000 (Pst DC300). Compared to flg22 derived from Pst DC3000 (flg22Ps), flg22Pf contains an amino acid substitution at position 19. Growth inhibition assays in Arabidopsis seedlings confirmed that flg22Pf activates immunity in an FLS2-dependent manner. The Nicotiana benthamiana leaf inoculation experiments indicated that flg22Pf significantly induces the expression of immune-related genes PTI5 and WRKY7, thereby enhancing resistance against Pst DC3000 infection. Furthermore, tomato treatment with flg22Pf promoted H2O2 production, ROS accumulation, callose deposition, and lignin accumulation. Consequently, this induction of defense responses resulted in suppressed nematode infestation. Collectively, our results reveal that flg22Pf from P. fragi Sneb1990 elicits a multi-layered immune response similar to flg22Ps, leading to an enhanced early immune response in tomato against M. incognita infestation. This study provides a novel plant immune-based strategy for sustainable M. incognita control.