Comparative proteomic analysis of the fungal pathogen Neoscytalidium dimidiatum infection in the pitaya

The pathogenic fungus Neoscytalidium dimidiatum (Nd) is the causal agent of pitaya canker and causes significant yield losses. The mechanism by which Nd invades pitaya stems remains largely unknown. Here, quantitative proteomic analysis was employed to investigate pitaya immune responses against Nd infection. A total of 2766 proteins including 244 differentially expressed proteins (DEPs) were identified during infection. Nearly half of the upregulated proteins were predicted to be located in the chloroplast and mitochondrion, implying that these organelles are most affected by fungal infection. Bioinformatics analysis indicated that the DEPs were associated with photosynthesis, phytohormone activity, reactive oxygen species (ROS) homeostasis, and pathogenic defense responses. Notably, the phytohormones auxin and abscisic acid were accumulated for defense against Nd invasion. qRT-PCR validation showed that the mRNA expression levels of auxin binding protein (ABP), auxin response 4 protein (ARP4), and aspartic protease 2 (ASP2) were not consistent with the protein variation, suggesting that these proteins were regulated post-transcriptionally. Additionally, DEPs associated with ROS metabolism changed markedly, indicating that ROS homeostasis in pitaya is important for defense against Nd invasion. In summary, the results revealed the involvement of many essential proteins in the response to Nd infection and provide a basis for studying other biotic stresses of pitaya.