Apoplastic proteomic reveals Colletotrichum fructicola effector CfXyn11A recognized by tobacco and suppressed by pear in the apoplast.

Colletotrichum fructicola is a hemibiotrophic fungal plant pathogen that transitions from biotrophic growth on living host tissue to necrotrophic tissue destruction. During the hemibiotrophic phase, numerous proteins are secreted into the apoplast, mediating host‒pathogen interactions. In this study, we employed apoplastic proteomics and RNA-seq to analyse the proteins secreted during the interaction between C. fructicola and pear. A secreted xylanase, CfXyn11A, was identified as a dual-function effector. In the nonhost Nicotiana benthamiana, it triggered immune responses, including reactive oxygen species production and programmed cell death. However, CfXyn11A evades detection in the host pear, enabling its role in cell wall degradation and nutrient acquisition. Genetic and biochemical assays confirmed that the immune-triggering function of CfXyn11A relies on its apoplastic localization and is independent of enzymatic activity. Additionally, we identified an aspartic protease-like protein, PbXIP1, in the pear apoplast, which binds CfXyn11A to suppress its enzymatic activity and virulence. This study highlights the role of apoplastic proteomics in elucidating the molecular mechanisms underlying plant immunity and pathogen virulence and emphasizes the contrasting outcomes of CfXyn11A in different host contexts. The findings provide new insights into the interplay between extracellular effectors and plant defense proteins during fungal infection.