Analysis of differential metabolites of sunflower induced by virulent Verticillium dahlia V33 and hypovirulent Gibellulopsis nigrescens Vn-1

Abstract

Verticillium wilt is a widespread soil-borne vascular disease of crops. Hypovirulent strains of pathogens show potential in providing cross-protection against Verticillium wilt. To identify metabolites associated with the induction of resistance, gas chromatography–mass spectrometry-based metabolomic technology was used to screen for differential metabolites induced by virulent (Verticillium dahlia V33) and hypovirulent (Gibellulopsis nigrescens Vn-1) pathogen strains in sunflower (Helianthus annuus) roots. Forty-eight differential metabolites were detected in the comparison between Vn-1 and V33 inoculation treatments. Among these differential metabolites, the accumulation of 17 secondary metabolites was significantly higher in response to Vn-1 inoculation compared with that after V33 inoculation. We selected nine differential metabolites for further analyses. Pyruvate, phenethylamine and 2-phenylbutyric acid inhibited infection of Nicotiana benthamiana leaves by Botrytis cinerea and Phythophthora infestans. Pyruvate, phenethylamine and 2-phenylbutyric acid induced H2O2 burst at 24 hours post-spray (hps) treatment of N. benthamiana leaves with these organic acids. Quantitative RT-PCR analysis revealed that pyruvate, phenethylamine and 2-phenylbutyric acid significantly enhanced the expression of pathogenesis-related genes at 24 hps, including PR1, NPR1 and PDF1.2. In addition, the activities of peroxidase, catalase, polyphenol oxidase and superoxide dismutase were increased. These results indicated that many metabolites were differentially induced by hypovirulent and virulent pathogen strains and were involved in resistance of sunflower against Verticillium wilt. Pyruvate, 2-phenylbutyric acid and phenethylamine show potential for induction of plant resistance to pathogen infection.