Inhibition of jasmonate-mediated plant defences by the fungal metabolite higginsianin B.

Debora Gasperini,Despoina D Gianniou,Géraldine Le Goff,Ioannis P Trougakos,Jamal Ouazzani,Jean-Félix Dallery,Marlene Zimmer,Mohamed Suliman,Richard J O’Connell,Sandrine Pigné,Vivek Halder

doi:10.1093/jxb/eraa061

Abstract

Infection of Arabidopsis thaliana by the ascomycete fungus Colletotrichum higginsianum is characterized by an early symptomless biotrophic phase followed by a destructive necrotrophic phase. The fungal genome contains 77 secondary metabolism-related biosynthetic gene clusters, whose expression during the infection process is tightly regulated. Deleting CclA, a chromatin regulator involved in the repression of some biosynthetic gene clusters through H3K4 trimethylation, allowed overproduction of three families of terpenoids and isolation of 12 different molecules. These natural products were tested in combination with methyl jasmonate, an elicitor of jasmonate responses, for their capacity to alter defence gene induction in Arabidopsis. Higginsianin B inhibited methyl jasmonate-triggered expression of the defence reporter VSP1p:GUS, suggesting it may block bioactive jasmonoyl isoleucine (JA-Ile) synthesis or signalling in planta. Using the JA-Ile sensor Jas9-VENUS, we found that higginsianin B, but not three other structurally related molecules, suppressed JA-Ile signalling by preventing the degradation of JAZ proteins, the repressors of jasmonate responses. Higginsianin B likely blocks the 26S proteasome-dependent degradation of JAZ proteins because it inhibited chymotrypsin- and caspase-like protease activities. The inhibition of target degradation by higginsianin B also extended to auxin signalling, as higginsianin B treatment reduced auxin-dependent expression of DR5p:GUS. Overall, our data indicate that specific fungal secondary metabolites can act similarly to protein effectors to subvert plant immune and developmental responses.

Highlights

The perception of microbial plant aggressors is mediated turn activates a cascade of PAMP-triggered immune (PTI) by the recognition of pathogen-associated molecular pat- responses (Dodds and Rathjen, 2010)
Chemical genetics screens using transgenic Arabidopsis lines expressing suitable reporter genes are powerful tools to detect small molecules interfering with components of plant defence and hormone signalling (Meesters and Kombrink, 2014; Serrano et al, 2015).To search for such activities among C. higginsianum metabolites, we generated a small library of partially purified fractions (F1–F4) and one pure molecule, namely higginsianin B, isolated from liquid cultures of the C. higginsianum ΔcclA mutant (Dallery et al, 2019b)
Seedlings pre-treated with fraction F4 and higginsianin B showed a higher activation of PR1p:GUS compared with the dimethyl sulfoxide (DMSO) pre-treated control, these differences were not significant

Summary

Introduction

The perception of microbial plant aggressors is mediated turn activates a cascade of PAMP-triggered immune (PTI) by the recognition of pathogen-associated molecular pat- responses (Dodds and Rathjen, 2010). Infection of A. thaliana by C. higginsianum is characterized by an early symptomless biotrophic phase followed by a destructive necrotrophic phase (O’Connell et al, 2004).As with other hemibiotrophic pathogens, it is assumed that during the biotrophic phase the fungus manipulates living host cells to evade plant defences, while in the necrotrophic phase fungal toxins and degradative enzymes are secreted to kill host cells and mobilize nutrients (Collemare et al, 2019). We previously reported that C. higginsianum tightly regulates the expression of secondary metabolism biosynthetic gene clusters (BGCs) at different stages of the infection process (Dallery et al, 2017). Not including possible biosynthetic intermediates, up to 14 different secondary metabolites are potentially delivered to the first infected host cell, where they may contribute to establishing a biotrophic interaction with A. thaliana. We reported a ΔcclA mutant of C. higginsianum affected in the trimethylation of histone proteins at H3K4 residues, which overproduces 12 different metabolites belonging to three terpenoid families, including five new molecules (Dallery et al, 2019a, b)

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Conclusion