PdCP1 from Penicillium digitatum Acts as a Protein Elicitor to Control Postharvest Decay and Preserve Quality in Citrus Fruit

Citrus fruits are susceptible to infection by Penicillium digitatum, causing significant economic loss. Exploring eco-friendly control strategies is therefore critical. Here, we identified and heterologously expressed a novel secreted protein, PdCP1, from P. digitatum and characterized it as a proteinaceous elicitor. Exogenous application of PdCP1 to citrus fruit significantly inhibited lesion development without direct antifungal activity, effectively preserving postharvest quality. PdCP1 triggered a series of defense responses, including reactive oxygen species bursts, callose deposition, and upregulation of pattern-triggered immunity genes. Furthermore, it enhanced the activity and transcript levels of key defense enzymes, upregulated the expression of critical genes in salicylic acid and jasmonic acid signaling pathways, and elevated endogenous hormone levels. PdCP1-induced resistance was also effective in other fruits tested against fungal pathogens. These findings demonstrated that PdCP1 acts as a potent protein elicitor, providing a novel and sustainable strategy for controlling postharvest decay via an induced resistance.