A <i>Fusarium sacchari</i> Glycoside Hydrolase 12 Protein <scp>FsEG1</scp> Is a Major Virulence Factor During Sugarcane Infection and Confers Resistance to Pokkah Boeng Disease via the <scp>HIGS</scp> Strategy

Pokkah Boeng disease (PBD), caused by Fusarium sacchari, has severely impacted the yield and quality of sugarcane, resulting in significant economic losses. However, the molecular interaction mechanisms between F. sacchari and sugarcane remain poorly understood. In this study, we identified the GH12 family protein FsEG1, secreted by F. sacchari, as a critical virulence factor. Further analysis demonstrates that the hydrolase activity of FsEG1 is essential for the full virulence of F. sacchari. The enhanced immune responses and cell death induced by FsEG1 in N. benthamiana depend on the recognition of oligosaccharide elicitors derived from the degradation of host cell walls by FsEG1, which are detected by membrane-localised receptors NbWAKs and NbCERK1, and this process also necessitates RAR1 and MAP3Kα to facilitate intracellular signal transduction. Consequently, FsEG1 activates DTI (DAMP-triggered immunity) rather than the conventional PTI. The stable transgenic sugarcane plants carrying the FsEG1 RNAi hairpin construct displayed high levels of resistance to F. sacchari and decreased FsEG1 expression, production of specific FsEG1 siRNA in transgenic HIGS sugarcane plants was confirmed by stem-loop qRT-PCR; at the same time, the stable transgenic sugarcane plants with ectopic expression of FsEG1 also showed enhanced PBD resistance with activated expression of defence-related genes. Overall, these findings establish a foundational basis for investigating the molecular mechanisms that govern the interactions between F. sacchari and sugarcane and offering valuable insights into enhancing sugarcane's resistance to PBD.