New insights into the evolution of host specificity of three Penicillium species and the pathogenicity of P. Italicum involving the infection of Valencia orange (Citrus sinensis)

Blue and green molds, the common phenotypes of post-harvest diseases in fruits, are mainly caused by Penicillium fungal species, including P. italicum, P. digitatum, and P. expansum. We sequenced and assembled the genome of a P. italicum strain, which contains 31,034,623 bp with 361 scaffolds and 627 contigs. The mechanisms underlying the evolution of host specificity among the analyzed Penicillium species were associated with the expansion of protein families, genome restructuring, horizontal gene transfer, and positive selection pressure. A dual-transcriptome analysis following the infection of Valencia orange (Citrus sinensis) by P. italicum resulted in the annotation of 9,307 P. italicum genes and 24,591 Valencia orange genes. The pathogenicity of P. italicum may be due to the activation of effectors, including 51 small secreted cysteine-rich proteins, 110 carbohydrate-active enzymes, and 12 G protein-coupled receptors. Additionally, 211 metabolites related to the interactions between P. italicum and Valencia orange were identified by gas chromatography-time of flight mass spectrography, three of which were further confirmed by ultra-high performance liquid chromatography triple quadrupole mass spectrometry. A metabolomics analysis indicated that P. italicum pathogenicity is associated with the sphingolipid and salicylic acid signaling pathways. Moreover, a correlation analysis between the metabolite contents and gene expression levels suggested that P. italicum induces carbohydrate metabolism in Valencia orange fruits as part of its infection strategy. This study provides useful information regarding the genomic determinants that drive the evolution of host specificity in Penicillium species and clarifies the host-plant specificity during the infection of Valencia orange by P. italicum. IMPORTANCE: P. italicum GL_Gan1, a local strain in Guangzhou, China, was sequenced. Comparison of the genome of P. italicum GL_Gan1 with other pathogenic Penicillium species, P. digitatum and P. expansum, revealed that the expansion of protein families, genome restructuring, HGT, and positive selection pressure were related to the host range expansion of the analyzed Penicillium species. Moreover, gene gains or losses might be associated with the speciation of these Penicillium species. In addition, the molecular basis of host-plant specificity during the infection of Valencia orange (Citrus sinensis) by P. italicum was also elucidated by transcriptomic and metabolomics analysis. The data presented herein may be useful for further elucidating the molecular basis of the evolution of host specificity of Penicillium species and for illustrating the host-plant specificity during the infection of Valencia orange by P. italicum.