Conserved glycoside hydrolase 12 proteins from kiwifruit soft rot pathogens trigger distinct immune signaling pathways in the non-host Nicotiana benthamiana and host kiwifruit

Abstract

Glycoside hydrolase family 12 proteins are broadly distributed effectors in fungi and oomycete. Over the past decade, several microbial GH12 proteins have been identified as both virulence factors and microbe-associated molecular patterns (MAMPs). However, the function and mechanism of GH12 proteins from postharvest pathogens are largely unknown. Here, we identified that four domain-conserved GH12 proteins from kiwifruit soft rot pathogens induce cell death and activate pattern-triggered immunity (PTI) in the non-host N. benthamiana. The four soft rot-associated GH12 proteins are highly upregulated during pathogen colonization, and their virulence functions rely on hydrolase activity. Remarkably, transient overexpressing the four GH12s in kiwifruit enhances resistance to rot pathogens without inducing host cell death. Transcriptome analysis revealed that soft rot-associated GH12s activate a subset of immune-associated genes involved in multiple signal transduction and metabolic pathways, including JA and ET signaling, Ca2+ sensing, antioxidant defense, and phenylpropanoid metabolism. Biochemical results indicate that soft rot-associated GH12s regulate kiwifruit resistance by enhancing antioxidant capacity and activate defense systems. Our findings demonstrate that pathogen-derived GH12 proteins activate kiwifruit immune response in a non-necrotic manner. Overall, we reported a novel founding that soft rot-associated GH12s employ distinct immune regulatory modes in N. benthamiana and kiwifruit.