Deletion of the 1 Gene Increases the Pathogenicity of and Reduces Its Tolerance to the Exogenous Toxic Substances Spermidine and Pyrimethanil.

During the infection of grapevine () by the fungus , the concentration of polyamines, which are toxic substances for the phytopathogen, increases in the grape. Nine NRPS genes have been identified in the genome of , yet the function of five of them remains unknown. For this reason, we have studied the expression of the 9 NRPS genes by RT-qPCR in a medium supplemented with sublethal concentrations of three polyamines (1,3-diaminopropane (1,3-DAP), spermidine (SPD), and spermine (SPM)). Our results show that the presence of polyamines in the culture medium triggered the overexpression of the 1 gene in the pathogen. Deleting 1 did not affect mycelial growth or adaptation to osmotic stress, and we show that its expression is not essential for the cycle of infection of the . However, mutating the 1 gene resulted in overexpression of the 6 gene, which encodes for the excretion of siderophores of the coprogen family. Moreover, gene deletion has reduced the tolerance of B05.10 to toxic substances such as the polyamine SPD and the fungicide pyrimethanil, and its virulence has increased. Our findings provide new insights into the function of the 1 gene and its involvement in the tolerance of against exogenous toxic compounds.