Wheat pathogen Zymoseptoria tritici N-myristoyltransferase inhibitors: on-target antifungal activity and an unusual metabolic defense mechanism.

Roman O Fedoryshchak,Jo Mattocks,Benjamin Strutton,Cory A Ocasio,Edward W Tate,Andrew J Corran

doi:10.1039/d0cb00020e

Abstract

Zymoseptoria tritici is the causative agent of Septoria tritici blotch (STB), which costs billions of dollars annually to major wheat-producing countries in terms of both fungicide use and crop loss. Agricultural pathogenic fungi have acquired resistance to most commercially available fungicide classes, and the rate of discovery and development of new fungicides has stalled, demanding new approaches and insights. Here we investigate a potential mechanism of targeting an important wheat pathogen Z. tritici via inhibition of N-myristoyltransferase (NMT). We characterize Z. tritici NMT biochemically for the first time, profile the in vivo Z. tritici myristoylated proteome and identify and validate the first Z. tritici NMT inhibitors. Proteomic investigation of the downstream effects of NMT inhibition identified an unusual and novel mechanism of defense against chemical toxicity in Z. tritici through the application of comparative bioinformatics to deconvolute function from the previously largely unannotated Z. tritici proteome. Research into novel fungicidal modes-of-action is essential to satisfy an urgent unmet need for novel fungicide targets, and we anticipate that this study will serve as a useful proteomics and bioinformatics resource for researchers studying Z. tritici.

Highlights

Fungicides play an important role in maintaining crop yields in wheat cultivation
As the peptide substrate we used an octapeptide derived from the N-terminus of F9X1I2 (Z. tritici predicted homolog of ADP-ribosylation factor 1, ARF1), which we hypothesized would be natively myristoylated in vivo
Most inhibitors in our set displayed at least some activity, with several highly potent examples identified in the low nanomolar IC50 range (Fig. 1B and C; inhibitor structures and full assay data are provided in Table S1, Electronic supplementary information (ESI)†)

Summary

Introduction

Populations of Z. tritici have acquired field resistance against two of the four mainstream antifungal classes: firstly, methyl benzimidazole carbamates (MBC)[6] and later the quinone outside inhibitors (QoI).[7,8] Of the remaining classes, demethylase inhibitors (DMI) often display decreased performance in the field due to reduced sensitivity of Z. tritici,[9] whilst the latest succinate dehydrogenase inhibitors (SDHI) have been effective to date. It may be possible to genetically engineer crop protection against STB,[2] the most relied upon strategy remains development of new antifungals. N-myristoyltransferase (NMT) is a well-characterized, druggable, and essential enzyme which was widely pursued as an antifungal target for human disease in the 1990s and early 2000s. NMT inhibition is effective in targeting a range of pathogens including parasites from Plasmodium, 68 | RSC Chem.

Methods

Results

Conclusion