A MICROARRAY APPROACH TO ANALYSE TRANSCRIPTIONAL CHANGES IN APPLE AFTER INFECTION BY ERWINIA AMYLOVORA

A microarray enriched in E. amylovora-induced and defence ESTs of apple (768) was created in order to compare transcriptional responses of two apple genotypes, MM106 and Evereste, susceptible and resistant to fire blight, respectively, after infection by a wild-type virulent strain of E. amylovora or one of its non-virulent TTSS-deficient mutant. Hybridization of chips revealed tens genes significantly and specifically induced or repressed by TTSS effectors in at least one of the two genotypes. Expression of genes encoding PR proteins and enzymes of the phenylpropanoid pathway confirmed previous data from our laboratory: TTSS effectors induced PR proteins in both genotypes and repressed genes of the phenylpropanoid pathway especially in the susceptible MM106. In addition, it was found that genes involved in photosynthesis showed the most differential responses between genotypes, with a strong and early activation by TTSS effectors in the resistant Evereste and by contrast an absence of activation or even a repression in the susceptible MM106. Some ESTs showed also a noteworthy differential modulation according to the genotype; however, their functions remain to be determined.