S14 - Session O6 - Antifungal natural products targeting the Unfolded Protein Response (UPR) as an alternative to crop protection

Authors: Thomas Charpentier *, Anne-Marie Le-Ray Richomme , Guillaume Viault, Nelly Bataillé-Simoneau, Thomas Guillemette, Pascal Richomme

The Unfolded Protein Response (UPR) is essential in the control of Endoplasmic Reticulum (ER) protein folding and maturation for eukaryotes. As far as phytopathogens are concerned, the UPR is also an important pathway associated with antifungal resistance. Indeed, UPR depletion in Alternaria brassicicola mutants shows a complete loss of virulence as well as a high sensitivity to phytoalexins. Therefore, the UPR pathway appear as an interesting target for the development of new antifungals. In fungi, the UPR signal pathway is only mediated by transmembrane protein IRE1. Its activation due to a reticulum stress allows to restore protein homeostasis through mRNA HAC1 splicing. Our search for inhibitors targeting IRE1 started with the implementation of a screening test using genetically modified Saccharomyces cerevisiae as a reporter system for IRE1 activity. Testing 77 naturals products (terpenoids, alkaloids and polyphenols) led us to identify 7 potential inhibitors ("hits") of IRE1. Inhibition of HAC1 mRNA splicing by the best of them was then confirmed by RT-PCR. Antifungal activity was finally monitored in planta on cabbage leaves infected by A. brassicicola or Botrytis cinerea . At subtoxic levels, a disease regression was clearly shown for both filamentous fungi. The screening test was also evaluated during bioguided fractionation of complex plant extracts whereas pharmacomodulation studies on hits were undergone through molecular modelling and (semi)synthesis.