Genomic Identification of the TOR Signaling Pathway as a Target of the Plant Alkaloid Antofine in the Phytopathogen Fusarium graminearum.

Christopher Mogg,Rajagopal Subramaniam,Johann Schernthaner,Christopher Bonner,Li Wang,Myron Smith,Darrell Desveaux,James W Kronstad

doi:10.1128/mbio.00792-19

Christopher Mogg, Rajagopal Subramaniam + Show 6 more

Open Access

https://doi.org/10.1128/mbio.00792-19

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Abstract

Antofine, a phenanthroindolizidine alkaloid, is a bioactive natural product isolated from milkweeds that exhibits numerous biological activities, including anticancer, antimicrobial, antiviral, and anti-inflammatory properties. However, the direct targets and mode of action of antofine have not been determined. In this report, we show that antofine displays antifungal properties against the phytopathogen Fusarium graminearum, the cause of Fusarium head blight disease (FHB). FHB does devastating damage to agriculture, causing billions of dollars in economic losses annually. We therefore sought to understand the mode of action of antofine in F. graminearum using insights from yeast chemical genomic screens. We used haploinsufficiency profiling (HIP) to identify putative targets of antofine in yeast and identified three candidate targets, two of which had homologs in F. graminearum The Fusarium homologues of two targets, glutamate dehydrogenase (FgGDH) and resistance to rapamycin deletion 2 (FgRRD2), can bind antofine. Of the two genes, only the Fgrrd2 knockout displayed a loss of virulence in wheat, indicating that RRD2 is an antivirulence target of antofine in F. graminearum Mechanistically, we demonstrate that antofine disrupts the interaction between FgRRD2 and FgTap42, which is part of the Tap42-phosphatase complex in the target of rapamycin (TOR) signaling pathway, a central regulator of cell growth in eukaryotes and a pathway of extensive study for controlling numerous pathologies.IMPORTANCEFusarium head blight caused by the fungal pathogen Fusarium graminearum is a devastating disease of cereal crops worldwide, with limited effective chemical treatments available. Here we show that the natural alkaloid compound antofine can inhibit fusarium head blight in wheat. Using yeast genomic screening, we identified the TOR pathway component RRD2 as a target of antofine that is also required for F. graminearum pathogenicity.

Highlights

Antofine, a phenanthroindolizidine alkaloid, is a bioactive natural product isolated from milkweeds that exhibits numerous biological activities, including anticancer, antimicrobial, antiviral, and anti-inflammatory properties
Antofine belongs to the phenanthroindolizidine class of alkaloids that are produced by relatives of the milkweed family (Apocynaceae subfamily Asclepiadoideae), which include Vincetoxicum spp., as well as members of the related genus Tylophora [1]
® mbio.asm.org 1 which stimulates angiogenesis through the action of protein kinase B or AKT/mTOR signaling pathways, is inhibited by antofine via an unknown mechanism [5]

Summary

Introduction

A phenanthroindolizidine alkaloid, is a bioactive natural product isolated from milkweeds that exhibits numerous biological activities, including anticancer, antimicrobial, antiviral, and anti-inflammatory properties. We show that binding of antofine to RRD2 leads to the disruption of the Tap42 phosphatase complex, providing a potential mechanism for disruption of the TOR signaling pathway. The suppression of F. graminearum germination and growth (as well as yeast growth [Fig. 1B]) was specific to antofine, and we used tylophorine as a biologically inactive negative control (Fig. 1A) [15].

Results

Conclusion