Enhancing Fruit Resistance against Fungal Pathogens Using a Pathogen-Associated Molecular Pattern PdEIX

Fruit is an essential part of the human diet, and postharvest fungal diseases are the major cause of fruit postharvest losses worldwide. Pathogen-associated molecular patterns (PAMPs) are important elicitors from microbes, and the recognition between microbial PAMPs and plant receptors leads to PAMP-triggered immunity. Here, we identified a PAMP, PdEIX, that is an important protein elicitor with plant immunity-inducing activity, from the citrus green mold pathogen Penicillium digitatum. PdEIX showed an apoplastic location similar to that of known PAMPs, and plant receptor-like protein NbEIX2, receptor-like kinase BAK1, and other signaling components of plant immunity were required for PdEIX-triggered plant cell death in the model plant Nicotiana benthamiana. Moreover, PdEIX triggered a series of immune responses in citrus fruit and enhanced the resistance of citrus and other fruit against fungal pathogens. Our results indicate that application of a microbial PAMP as the plant immunity inducer is an effective strategy for controlling postharvest fungal diseases of fruit.