Isolation and characterization of genes differentially expressed during the interaction between apple fruit and Pencillium expansum

Differences in gene expression during the susceptible interaction between 'Golden Delicious' apple fruits and the fungus Penicillium expansum were investigated by differential display (DD) RTPCR. Partial cDNAs from 26 clones from both the fungus and the fruit were selected for nucleotide sequence determination and homology searches, and 20 were subsequently selected for further analyses. In a preliminary series of Northern blot analyses, 18 genes were confirmed as showing a higher expression level during the apple-fungus interaction than in control tissues. Southern analyses permitted an assignation of the fruit or fungal origin of each cDNA. Thirteen clones were derived from P. expansum and five from apple. A more detailed analysis of their expression patterns was conducted in an independent infection experiment confirming the differential expression for 12 of them. Among the differentially expressed genes were one fungal gene. encoding an unknown protein and two apple genes, homologous to a beta-glucosidase and a phosphatase 2C, respectively, that were exclusively expressed during the infection process. Several up-regulated P. expansum genes seem to mediate adaptive responses to the host environment.