Comparative RNA-seq analysis of citrus fruit in response to infection with three major postharvest fungi

Green mold, blue mold and sour rot caused by Penicillium digitatum, Penicillium italicum and Geotrichum citri-aurantii infections, respectively, are major fungal diseases of citrus fruit. The above-mentioned diseases present a great threat to fruit quality, it is very important to clarify the pathogenicity mechanisms of the pathogens and the resistance mechanism of the host, but the mechanisms remain largely unknown. In this study, RNA sequencing was employed to analyze the gene expression of citrus fruit to P. digitatum, P. italicum and G. citri-aurantii on a genome-wide scale. The results suggest that a total of 4,520, 4785 and 4683 genes of citrus fruit were differentially expressed (P-value < 0.05, ︱Log2 fold change︱≥1) in response to P. digitatum, P. italicum and G. citri-aurantii, respectively. These differentially expressed genes are involved in a variety of stress responses, such as host innate immunity, synthesis of secondary metabolites and hormone-related pathways, etc. Remarkably, the host reactions under different pathogen infections are similar, and the establishment of citrus fruit systemic resistance in response to P. digitatum, P. italicum and G. citri-aurantii is salicylic acid-reliant. Overall, our study presents a genome-wide analysis of the similarities and differences in citrus fruit responses to common fungal pathogens, which is not only beneficial for a better understanding of host-pathogen interactions but also for the development of novel measures for the prevention of common fungal diseases.