Abstract
Cell wall-degrading enzymes are viewed as extracellular virulence factors. However, their potential to act as immune elicitors and interact with intracellular immune receptors remains poorly defined. Here, we demonstrate that six conserved glycoside hydrolase 7 (GH7) family proteins from the fungal pathogen Verticillium dahliae have dual roles in virulence and immune activation. Deletion of each GH7 gene significantly impaired virulence without affecting fungal growth. The secretion of each GH7 protein was confirmed using yeast invertase and triphenyltetrazolium chloride assays. Live-cell imaging revealed that all GH7 proteins translocate into plant cells and localize to the cytoplasm, where they triggered canonical immune responses, including hypersensitive cell death, reactive oxygen species burst, and callose deposition, independent of their enzymatic activity. Genetic disruption of Nicotiana benthamiana Suppressor of G2 allele of Skp1 (SGT1) and Non-race specific Disease Resistance 1 (NDR1), but not Enhanced Disease Susceptibility 1 (EDS1), compromised GH7-triggered cell death, indicating that GH7-triggered cell death partially depends on a classical NLR-mediated signalling pathway. Thus, GH7s act as both virulence factors and unconventional intracellular effectors that activate effector-triggered immunity via the SGT1-NDR1 pathway. This reveals how fungal metabolic enzymes evolve effector-like properties and offers new insight into host-pathogen coevolution.