Ultrastructural observation and transcriptome analysis provide insights into mechanisms of Penicillium expansum invading apple wounds

Penicillium expansum is a pathogen causing enormous postharvest losses of fruits, especially apples. In this study, we first investigated the morphological changes of P. expansum within apple wounds during infectious process by microscopic observation. We found that conidia swelled and secreted potential hydrophobin in 4 h, germinated in 8 h, and finally formed conidiophores in 36 h, a critical control time point to prevent the second contamination of spores. We then compared the transcript accumulation of P. expansum in apple tissues and liquid culture at 12 h. In total, 3168 and 1318 up-regulated and down-regulated genes were identified. Among them, genes regarding the biosynthesis of substances such as ergosterol, organic acid, cell wall degrading enzymes, and patulin were induced in expression. Pathways were activated, including autophagy, the mitogen-activated protein kinase, and pectin degradation. Our findings provide insights into the lifestyle and the mechanisms of P. expansum invading apple fruits.

Automated summary

In this study, the morphological changes of Penicillium expansum within apple wounds during the infection process were investigated. The study revealed that conidia swelled and secreted potential hydrophobin in 4 h, germinated in 8 h, and formed conidiophores in 36 h. The transcript accumulation of P. expansum in apple tissues and liquid culture at 12 h was also compared, revealing the up-regulation and down-regulation of genes related to the biosynthesis of substances and activation of pathways.