Identification and Application of the Heptad Repeat Domain in the <scp>CPR5</scp> Protein for Enhancing Plant Immunity

Plant resistance to pathogens can be significantly enhanced through genetic modification, thereby reducing the reliance on chemical pesticides. CONSTITUTIVE EXPRESSER OF PATHOGENESIS-RELATED GENES 5 (CPR5) serves as a key negative regulator of plant immunity. Here we explored the functional domains of the CPR5 protein with the goal of dampening its activity to bolster plant immunity. Using hexapeptide asparagine-alanine-alanine-isoleucine-arginine-serine (NAAIRS) linker-scanning analysis, we identified a heptad repeat domain (HRD) in the middle region of the CPR5 protein, which is highly conserved across the plant kingdom. The HRD is predicted to form an α-helix structure and acts as an interface for CPR5 dimerization. Intriguingly, overexpression of the HRD in Arabidopsis wild-type plants resulted in a phenotype similar to the cpr5 mutant and led to an enhancement of plant immunity, indicating that the introduced HRDs disrupt the native CPR5 dimers, thereby relieving the suppression of plant immunity. Furthermore, expression of the HRD under the control of a pathogen-inducible promoter significantly improved the resistance of cotton plants to Verticillium dahliae, a destructive wilt pathogen affecting cotton production worldwide. These findings suggest that downregulating CPR5 activity by the pathogen-inducible expression of its HRD could be a promising approach for strengthening plant immunity.