A rust‐fungus Nudix hydrolase effector decaps mRNAin vitro and interferes with plant immune pathways

Abstract

To infect plants, pathogenic fungi secrete small proteins called effectors. Here, we describe the catalytic activity and potential virulence function of the Nudix hydrolase effector AvrM14 from the flax rust fungus (Melampsora lini).We completed extensive in vitro assays to characterise the enzymatic activity of the AvrM14 effector. Additionally, we used in planta transient expression of wild-type and catalytically dead AvrM14 versions followed by biochemical assays, phenotypic analysis and RNA sequencing to unravel how the catalytic activity of AvrM14 impacts plant immunity.AvrM14 is an extremely selective enzyme capable of removing the protective 5 0 cap from mRNA transcripts in vitro. Homodimerisation of AvrM14 promoted biologically relevant mRNA cap cleavage in vitro and this activity was conserved in related effectors from other Melampsora spp. In planta expression of wild-type AvrM14, but not the catalytically dead version, suppressed immune-related reactive oxygen species production, altered the abundance of some circadian-rhythm-associated mRNA transcripts and reduced the hypersensitive cell-death response triggered by the flax disease resistance protein M1.To date, the decapping of host mRNA as a virulence strategy has not been described beyond viruses. Our results indicate that some fungal pathogens produce Nudix hydrolase effectors with in vitro mRNA-decapping activity capable of interfering with plant immunity.

Plant pathogenic fungi hijack phosphate starvation signaling with conserved enzymatic effectors

“…2G). Conversely, AvrM14, a sequence-unrelated mRNA decapping Nudix hydrolase effector from the fungus Melampsora lini (30), does not hydrolyze 5-PP-InsP5 (fig S5D).…”

“…2G). Conversely, AvrM14, a sequence-unrelated mRNA decapping Nudix hydrolase effector from the fungus Melampsora lini ( 30 ), does not hydrolyze 5-PP-InsP 5 (fig S5D). All Nudix effectors used throughout this study were purified to homogeneity prior to in vitro characterization (fig.…”

NADases as weapons for both plant pathogens and their hosts

“…3′-NADP + was previously only reported as a synthetic inhibitor of NAD + -dependent enzymes ( 23 ). A NUDIX hydrolase virulence protein called AvrM14 from a fungal plant pathogen can interfere with host NAD + -capping of mRNA, potentially to posttranscriptionally regulate gene expression ( 24 ). The other NADase families discovered by Hulin et al.…”

Manipulation of plant immunity via an mRNA decapping pathogen effector

“…While many studies have identified and characterised a diverse array of molecular functions for such effectors, few have focussed on putative enzymatic activities as these are often not predicted from sequence or structure. A new paper published in this issue of New Phytologist by McCombe et al (2023; pp. 222-239), provides novel insight into the Nudix hydrolase effector AvrM14 from the flax rust fungus (Melampsora lini).…”

“…A new paper published in this issue of New Phytologist by McCombe et al . (2023; pp. 222–239), provides novel insight into the Nudix hydrolase effector AvrM14 from the flax rust fungus ( Melampsora lini ).…”