Fungal Weapon Hijacks Wheat Ethylene Signals to Blunt Crop Defenses

A tiny protein with no known functional domains is turning out to be one of the most cunning weapons deployed against wheat. Researchers studying Fusarium crown rot, a destructive disease of wheat caused by the soil-borne fungus Fusarium pseudograminearum, have identified a secreted effector called FpECIR that slips into plant cells and sabotages a key branch of the crop’s immune system. The study, published in the journal Stress Biology, reveals for the first time that a fungal effector can directly manipulate a PLATZ transcription factor in wheat, dampening ethylene signaling and leaving the plant far more vulnerable to infection. The finding not only explains a previously hidden layer of fungal virulence but also points to a promising new target for breeding disease-resistant wheat varieties.

Fusarium crown rot is a serious threat to wheat production worldwide. The disease was first identified in Henan province of China in 2011, and surveys conducted between 2013 and 2016 showed it was widespread throughout the HuangHuai wheat-growing region, which encompasses seven of China’s most important wheat-producing provinces. Beyond the direct yield losses, F. pseudograminearum produces deoxynivalenol and other mycotoxins during infection, contaminating grain and derived products and posing risks to human and animal health. Because wheat supplies roughly 40 percent of total caloric and protein intake for a large share of the global population, and China alone accounts for about 17 percent of world production, understanding how this pathogen outmaneuvers host defenses carries enormous agricultural weight.

The newly characterized effector, named FpECIR for F. pseudograminearum Effector Containing two Internal Repeats, is a small protein of 150 amino acids encoded by a 453-base-pair open reading frame. Bioinformatic analysis predicted a 17-amino-acid signal peptide but no transmembrane helices and no known conserved functional domains. What stood out were two internal repeat regions, designated IR1 and IR2, embedded within the sequence. Homologs of FpECIR are found mainly in other fungi, including plant pathogens, animal pathogens, and biocontrol species, but are absent from several well-studied phytopathogens such as Magnaporthe oryzae, Sclerotinia sclerotiorum, Botrytis cinerea, Ustilago maydis, and Puccinia striiformis, suggesting the gene family has undergone functional diversification during evolution.

Expression profiling showed that FpECIR is strongly induced during infection. Quantitative reverse transcription PCR revealed that transcript levels in infected wheat coleoptiles rose more than tenfold compared with those in fungal hyphae, peaking across a time course spanning 3 to 48 hours post inoculation. Functional validation using the YTK12 yeast secretion system confirmed that the predicted signal peptide genuinely drives secretion. Most strikingly, when the researchers fused FpECIR to mCherry with a nuclear localization signal and infected wheat seedlings with the transformed strain, red fluorescence appeared inside the nuclei of wheat cells at the infection sites, providing direct evidence that the effector is translocated into host cells and operates as a cytoplasmic effector.

To probe its immunosuppressive activity, the team transiently expressed FpECIR in Nicotiana benthamiana, a widely used plant immunity model. INF1, a well-known elicitin from the potato late blight pathogen, normally triggers a robust programmed cell death response in these leaves. When FpECIR, with or without its signal peptide, was expressed 24 hours before INF1 infiltration, the cell death response was markedly suppressed, while GFP controls had no such effect. Subcellular localization experiments showed that FpECIR-GFP accumulated in both the nucleus and cytoplasm. Critically, when the researchers added a nuclear export signal to force the protein out of the nucleus, the mutant lost its ability to block INF1-triggered cell death, indicating that nuclear localization is essential for the effector’s function.

The internal repeats proved equally indispensable. AlphaFold v3 structural modeling showed that the N-terminal region (residues 18 to 67) and the C-terminal region (residues 68 to 150) adopt strikingly similar three-dimensional conformations, each containing one internal repeat. Yet when each half was expressed separately in N. benthamiana, neither FpECIR-N nor FpECIR-C could suppress INF1-induced cell death. The full-length sequence, it turns out, is required for activity, and the N-terminal internal repeat is the most conserved feature among homologs. This structural logic became even more important when the team mapped exactly where the effector binds its host target.

That target emerged from yeast two-hybrid screening of a cDNA library built from wheat coleoptiles infected with F. pseudograminearum. Five independent screens using FpECIR as bait yielded fourteen candidate interactors, three of which encoded a putative wheat AT-rich sequence- and zinc-binding protein, a member of the PLATZ transcription factor family designated TaPLATZ2B. The interaction was confirmed through multiple independent approaches: yeast two-hybrid assays, GST pull-down experiments with purified recombinant proteins, confocal microscopy showing colocalization in plant nuclei, and co-immunoprecipitation from N. benthamiana leaves co-expressing tagged versions of both proteins. PLATZ factors are known regulators of plant growth, development, and stress responses, and a close relative, TaPLATZ5, had already been implicated in wheat defense against powdery mildew.

Structural prediction of the FpECIR-TaPLATZ2B complex identified a specific binding interface: residues 29 to 35 of FpECIR were predicted to form hydrogen bonds with complementary residues of TaPLATZ2B, including Glu29 with Ser92, Asp30 with Ser93, Cys33 with Tyr115 and Ile116, and Ala35 with Thr114. When the researchers deleted residues 29 to 35, the mutant protein lost the ability to interact with TaPLATZ2B in yeast two-hybrid, pull-down, and co-immunoprecipitation assays, and it also failed to suppress INF1-triggered cell death. Corresponding mutations in TaPLATZ2B confirmed the predicted contact sites from the host side. These experiments pinpoint a seven-residue stretch as the functional heart of the effector and validate the reliability of the AlphaFold-based interaction model.

The functional consequences for wheat were dramatic. Barley stripe mosaic virus-mediated gene silencing of TaPLATZ2B and its alleles reduced their expression by roughly 30 to 60 percent and made wheat plants visibly thinner and weaker, while also rendering them significantly more susceptible to F. pseudograminearum, with longer lesions following inoculation. Conversely, deleting the FpECIR gene from the fungus slowed its growth but, more importantly, sharply reduced its virulence on wheat coleoptiles, producing milder symptoms and shorter lesion lengths than the wild-type strain. RNA sequencing of wheat coleoptiles infected with the deletion mutant revealed 2,539 upregulated and 1,276 downregulated genes, with defense response prominently enriched among the upregulated terms and hormone signaling pathways highlighted by KEGG analysis, consistent with the effector actively suppressing immune responses during normal infection.

The mechanism converged on ethylene signaling. Quantitative PCR showed that FpECIR suppresses the expression of TaPLATZ2B and of ethylene signaling genes including TaERF1, TaPR3, and TaWRKY53, all of which were upregulated in plants infected with the deletion mutant. Electrophoretic mobility shift assays demonstrated that TaPLATZ2B directly binds a 42-base-pair probe from the promoter region of the ethylene response factor gene TaERF020L, and that adding FpECIR protein to the reaction significantly weakened this binding. When wheat seedlings were treated with aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, they developed more severe disease symptoms and longer lesions after fungal inoculation, and the expression of ethylene-related defense genes dropped. Together, these results sketch a complete molecular model: FpECIR enters wheat cells, represses TaPLATZ2B both at the transcript level and at the level of DNA binding, and thereby throttles an ethylene-dependent defense program. Because silencing TaPLATZ genes also impairs normal wheat development, the study suggests that TaPLATZ2B sits at a regulatory node coordinating both disease resistance and growth, a combination that could make it a powerful target for breeding wheat that resists crown rot without sacrificing yield.

Subject of Research: How the fungal effector FpECIR suppresses wheat immunity by targeting the TaPLATZ2B transcription factor and ethylene signaling during Fusarium crown rot infection

Article Title: Effector FpECIR from Fusarium pseudograminearum targets wheat ethylene signaling pathway to suppress plant immunity

Article References: Effector FpECIR from Fusarium pseudograminearum targets wheat ethylene signaling pathway to suppress plant immunity. (n.d.). https://doi.org/10.1007/s44154-026-00311-7

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00311-7

Keywords: Fusarium pseudograminearum, Fusarium crown rot, FpECIR, effector protein, wheat immunity, TaPLATZ2B, ethylene signaling, plant pathology, transcription factor, gene silencing, AlphaFold, disease resistance