A Fungal Cysteine‐Rich Protein <i>Ss</i> SCP Activates Immune Responses and Confers Broad‐Spectrum Disease Resistance in Tomato

Plant immune systems recognise pathogen-derived molecular patterns to activate defence responses, yet the mechanisms underlying fungal pattern recognition in crops remain largely unclear. Here, we characterise the cysteine-rich secretory protein SsSCP from the broad-host-range fungal pathogen Sclerotinia sclerotiorum as a potent elicitor of immune responses in tomato (Solanum lycopersicum). Using an optimised Escherichia coli expression system, we successfully produced bioactive SsSCP and demonstrated its ability to induce hallmark immune responses, including reactive oxygen species (ROS) bursts and extensive transcriptional reprogramming. Time-course transcriptomic analysis after SsSCP treatment revealed the rapid activation of defence pathways coupled with suppression of photosynthetic processes. While tomato lacks orthologs of the Arabidopsis SsSCP receptor AtRLP30, we identified a candidate receptor that may mediate SsSCP recognition in tomato. SsSCP activates immune responses independent of the EDS1-PAD4 module in Nicotiana benthamiana. Remarkably, transgenic expression of AtRLP30 in tomato conferred resistance against both bacterial (Pseudomonas syringae) and fungal (S. sclerotiorum and Botrytis cinerea) pathogens without compromising plant growth. Exogenous SsSCP application similarly enhanced disease resistance, with protection levels matching those of AtRLP30-expressing lines. Our findings reveal both conserved and species-specific aspects of SsSCP recognition while establishing its potential as a sustainable crop protection strategy. This research advances our understanding of fungal pattern recognition in crops and provides new tools for plant immunity research and disease control.