Diversity of for the Production of the Phytotoxic Metabolites (-)-Terremutin and ()-Mellein.

Two 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 ()-mellein, and it was the most aggressive on grapevine, triggering apoplexy. Similar symptoms were not induced by purified (-)-terremutin. The isolate Bourgogne S-116 (Np-B) produced 3-fold less (-)-terremutin and high amounts of ()-mellein, but it was less aggressive on grapevine than Np-Bt67. The UV9 mutant obtained from Np-B (NpB-UV9) no longer produced (-)-terremutin but overproduced ()-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 ()-mellein, nor (-)-terremutin biosynthetic genes, but likely involved in the control of (-)-terremutin biosynthesis. Grapevine immunity was disturbed upon challenge with these pathogens or purified 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 ()-mellein alone is essential for the pathogenicity of on grapevine, since isolate/mutant non-producing these toxins in vitro is pathogenic. However, these phytotoxins could play a quantitative role in the infection process.