An endoglucanase from Erwinia amylovora induces broad-spectrum immune response in plants

The phytopathogen endoglucanases play vital roles in pathogenesis, likely due to their capacity in deconstructing plant cell wall. While acting as virulence factors, some endoglucanases can also be recognized by the plant immune system and activate plant defense responses against possible pathogens. However, many of these enzymes and their roles in inducing plant defense responses are not characterized, especially those from Erwinia amylovora. In this study we cloned a putative glycoside hydrolase family 8 (GH8) endoglucanase (EaCel8) from E. amylovora. The enzymatic properties of EaCel8 and its induction of plant immune responses were comprehensively investigated. The biochemical characterization of the recombinant EaCel8 showed high activity towards barley β-glucan and lower activity on carboxymethyl cellulose. EaCel8 was active within a broad range of pH and temperature, and it hydrolyzed barley β-glucan mainly to mixed-linked glucan (MLG) oligosaccharides with a degree of polymerization ≥3. Interestingly, EaCel8 triggered immune responses in Arabidopsis thaliana, rice, soybean, and pepper, and pretreating tobacco and rice with the purified recombinant EaCel8 significantly enhanced the disease resistance of these plants against Rhizoctonia solani. These findings deepen our mechanistic understanding of plant pathogen derived cell wall degrading enzymes, and the novel GH8 endoglucanase EaCel8 has the potential to be developed as a plant immune inducer.