Fig. 2

Mode of action of Fusarium graminearum-secreted pathogenicity factors and FHB resistance and susceptibility genes in wheat during F. graminearum-wheat interaction. F. graminearum secretes cell wall-degrading enzymes (CWDEs) such as polygalacturonases and xylanases to degrade wheat cell walls. The apoplastic effector (AE) FGL1 suppresses callose deposition. F. graminearum exo-1,5-a-L-arabinanase Arb93B and the putative catalase-peroxidase KatG2 and FCA7 contribute to fungal virulence by suppressing host ROS generation. The orphan secreted protein Osp24 in F. graminearum functions as a cytoplasmic effector targeting host defense-related TaSnRK1α for degradation and is important for pathogenicity. The sRNA effector Fg-sRNA1 contributes to virulence by silencing wheat defense-related TaCEBiP. Fungal toxin DON inhibits protein biosynthesis by binding to the ribosome. DON also affects programmed cell death (PCD) of plant cells in a concentration-dependent manner. The fungal toxin Fusaoctaxin A changes the subcellular localization of chloroplasts in the coleoptile cells and prevents callose accumulation in plasmodesmata during pathogen infection, facilitating the cell-to-cell invasion of F. graminearum in wheat tissues. To combat F. graminearum, the DON response wheat orphan and defense-related protein TaFROG competes with Osp24 to interact with TaSnRK1α, preventing TaSnRK1α degradation mediated by the ubiquitin-26S proteasome system. TaFROG also interacts with the FHB resistance-related NAC-like transcription factor TaNACL-D1. Wheat FHB resistance genes Fhb1–Fhb7 and pattern-triggered immunity (PTI) components, such as TaLRRK-6D and TaWAK2A-800, confer resistance to FHB. Fhb7 encodes a glutathione S-transferase which detoxifies multiple trichothecene mycotoxins, whereas the wheat ethylene receptor gene EIN2, the 9-lipoxygenase-coding gene TaLpx-1, the stearoyl-acyl carrier protein fatty acid desaturase gene TaSSI2, the auxin receptor gene TaTIR1, and the DON-induced transcription factor gene TaNFXL1 contribute to wheat susceptibility to FHB