Diversity of Neofusicoccum parvum for the production of the phytotoxic metabolites (-)-terremutin and (R)-mellein

Two Neofusicoccum parvum fungal isolates and a UV mutant were characterized for their phytotoxin production in-vitro, their pathogenicity on grapevine, and their genome sequenced. The isolate Np-Bt67 produced high level of (-)-terremutin, but almost no (R)-mellein, suspected due to genetic polymorphism, and it was the most aggressive on grapevine, triggering apoplexy. However, similar symptoms were not induced by purified (-)-terremutin. The isolate Bourgogne S-116 (Np-B) produced 3-fold less (-)-terremutin and high amounts of (R)-mellein, but it was less aggressive on grapevine than Np-Bt67. The UV9 mutant obtained from Np-B (NpB-UV9) failed producing (-)-terremutin, but overproduced (R)-mellein by 2.5-fold and it was as pathogenic as its parent. NpB-UV9 differed from its parent by simple mutations in two genes (transcription factor, regulatory protein), not located neither near (R)-mellein, nor (-)-terremutin biosynthetic genes, but likely involved in the control of (-)-terremutin biosynthesis. Grapevine immunity was also disturbed upon challenge with pathogens or phytotoxins, leading to an upregulation of SA-dependent defenses, while (-)-terremutin interfered with host JA/ET-dependent defenses. Our results suggest that neither (-)-terremutin, nor (R)-mellein alone, are essential for the pathogenicity of N. parvum on grapevine, since non-producing isolate/mutant are pathogenic. However, these phytotoxins could play a quantitative role in the infection process.