Pathogen-Associated Molecular Pattern (PAMP)-Induced Peptide LcPIP1 Derived from Litchi Promotes the Resistance of Litchi Fruit against Litchi Downy Blight Caused by <i>Peronophythora litchii</i>

Litchi downy blight is a postharvest disease caused by Peronophythora litchii, causing yield loss and postharvest deterioration. The role of native plant peptides in fruit responses to fungal infections has seldom been reported. Here, we identified LcprePIP1 encoding a precursor of pathogen-associated molecular pattern (PAMP)-induced secreted peptide (LcPIP1) and characterized gene expression during P. litchii infection. Synthetic LcPIP1 application improved litchi fruit resistance to P. litchii by enhancing ATP, anthocyanin, and lignin accumulation as well as defense response. Furthermore, LcPIP1 treatment enhanced immunity responses by increasing cytosolic Ca 2+ as well as reactive oxygen species accumulation and triggering mitogen-activated protein kinase signaling. We highlighted the crucial role of LcWRKY34 in LcPIP1-induced disease resistance by activating the LcprePIP1 expression. Transcriptomic and metabolomic analyses found that LcPIP1 regulated defense-related gene expression and metabolite accumulation. Overall, for the first time, our findings provided novel insights into the vital role of LcPIP1 in eliciting fruit defense responses.