Quaternized chitosan oligomers as novel elicitors inducing protection against B. cinerea in Arabidopsis

Chitosan oligomers prepared from enzyme hydrolysis of chitosan have for many years been recognized as potent elicitors of plant innate immunity, but their efficacy is limited by the degree of polymerization and the degree of acetylation. In this study, we presented a new type of chitosan oligomers (COS), with the name of quaternized chitosan oligomers (QCOS) that were prepared by reacting COS with glycidyltrimethylammonium chloride and overcome these problems. First, QCOS clearly induced hydrogen peroxide accumulation and callose deposition in Arabidopsis seedlings. Second, we found that PAD3 expression was significantly upregulated more than 5-fold by QCOS as compared to COS. Further, PAD3 expression activated by QCOS was required for inducing Arabidopsis resistance to the necrotrophic fungus Botrytis cinerea, independent of salicylic acid signaling. These results demonstrate that quaternized modifications of COS possess better elicitor properties than the original COS and that QCOS stimulate plant protection against B. cinerea attack in Arabidopsis. Importantly, our work provides a novel and valuable strategy for enhancing elicitor activities of other types of oligosaccharides for plant innate immunity.