Abstract: Strain H1, isolated from rotten citrus wounds in our laboratory, was identified as Penicillium expansum and was found to be able to produce citrinin (CIT). In this study, the possible mechanisms underlying citrus infection by P. expansum were investigated by measurement of cell wall degrading-enzymes and transcriptome analysis. The results showed that P. expansum H1 could produce polygalacturonase, pectin methylgalacturonase, endo-1,4-β-D-glucanase and β-glucosidase in both modified Marcus medium and infected citrus tissues. Meanwhile, the expression levels of all genes related to the infection were up-regulated, such as those related to cell wall degrading-enzymes, CIT production, the pH changes of the host, antioxidative stress response and effector factors. The results indicated that cell wall-degrading enzymes, CIT, pH, and antioxidant enzymes all play vital roles in citrus infection by P. expansum H1.

Key words: Penicillium expansum, citrus, infection, enzyme activity, transcriptome