Identification of low-temperature-regulated genes in the fire blight pathogenErwinia amylovora
Genes involved in pathogenicity of several plant pathogens were shown to be induced at relatively cold temperatures. Loci from the fire blight pathogen Erwinia amylovora (Burrill) induced at 18 °C were identified using the miniTn5 transposon that contains the promoterless reporter gene gusA coding for β-glucuronidase (GUS). Certain mutants (2.7%) expressed GUS predominantly at 18 °C on minimal medium plates, indicating that the transposon had been inserted downstream of a putatively thermoregulated promoter. Those mutants were further screened with a quantitative GUS fluorometric assay. A total of 21 mutants were selected: 19 mutants had a transposon insertion in temperature-dependent genetic loci, with a 2.2- to 6.3-fold induction of gusA gene expression at 18 °C, and two mutants with impaired growth at 18 °C. Some of these genetic loci encoded (i) proteins implicated in flagella biosynthesis, biotin biosynthesis, multi-drug efflux, and type II secretion protein, and (ii) proteins of unknown function.Key words: fire blight, Erwinia amylovora, transposon mutagenesis, gene regulation, low temperature.