Temperature-responsive genetic loci in pectinolytic plant pathogenic Dickeya solani

Fifty-four Dickeya solani thermoregulated genes were identified using Tn5 transposon mutagenesis with an inducible gusA reporter system; 45 genes were up-regulated at 37 degrees C, whereas nine were up-regulated at 18 degrees C. The relative level of gene up-regulation ranged from 2-1200 and 5-650 U/mg total proteins at 18 and 37 degrees C, respectively. Among the temperature-regulated loci, genes coding for proteins involved in fundamental bacterial metabolism, membrane-related proteins and pathogenicity-corresponding factors and several hypothetical unknown proteins were found. The mutants were tested for their pathogenicity in planta and for features known to be important for D. solani virulence viz. production of pectinolytic enzymes, cellulases, proteases, siderophores and auxins as well as for motility and the ability to form a biofilm. Eight Tn5 mutants, four up-regulated at high and four up-regulated at low temperature, expressed visible phenotypes including the decreased ability to cause symptoms on potato tubers and chicory leaves, impairment in phospholipase production and/or deficiency in biofilm formation. The implications of environmental temperature on the ability of D. solani to cause disease symptoms in potato are discussed.