Gene expression analyses on Dickeya solani strains of diverse virulence levels unveil important pathogenicity factors for this species

Dickeya solani causes soft rot and blackleg mainly on potato crops. High pathogenicity of this species results from efficient production of plant cell wall-degrading enzymes, especially pectate lyases, potent root colonization, and fast vascular movement. Despite genomic homogeneity, variations in virulence-related phenotypes suggest differences in the gene expression patterns between diverse strains. Therefore, the methylomes and transcriptomes of two strains (virulent IFB0099 and low virulent IFB0223), differing in tissue maceration capacity and virulence factors production, have been studied. Methylation analysis revealed no significant differences. However, the analysis of transcriptomes, studied under both non-induced and induced by polygalacturonic acid conditions (in order to mimic diverse stages of plant infection process), unveiled higher expression of pectate lyases (pelD, pelE, pelL), pectin esterase (pemA), proteases (prtE, prtD) and Vfm-associated quorum-sensing genes (vfmC, vfmD, vfmE) in IFB0099 strain compared to IFB0223. Additionally, the genes related to the secretion system II (T2SS) (gspJ, nipE) displayed higher induction of expression in IFB0099. Furthermore, IFB0099 showed more elevated expression of genes involved in flagella formation, which coincides with enhanced motility and pathogenicity of this strain compared to IFB0223. To sum up, differential expression analysis of genes important for the virulence of D. solani indicated candidate genes, which might be crucial for the pathogenicity of this species.