FadP affects the virulence of Ralstonia pseudosolanacearum by altering nitrogen metabolism processes and reducing motility, cellulase, and extracellular polysaccharide production

Abstract

Ralstonia pseudosolanacearum, the causative agent of bacterial wilt disease, is a significant pathogen of economically-important agricultural crops. FadP is a transcriptional regulator of fatty acid degradation; however, its function remains unknown in R. pseudosolanacearum. Herein, a R. pseudosolanacearum fadP deletion mutant (ΔfadP) was constructed to examine the role of FadP. Compared with wild-type strain Tm1401 and fadP complementation strain R-ΔfadP, ΔfadP showed reduced motility and cellulase and extracellular polysaccharide production, along with decreased resistance to tetracycline and virulence on tomato plants. Further, the mutant strain induced only a weak hypersensitive response in tobacco plants. To further understand the underlying virulence mechanisms, RNA-Seq technology was used to compare the transcriptomes of the wild-type and mutant strains. Analysis revealed 848 differentially-expressed genes, amongst which 505 were up-regulated and 343 were down-regulated in ΔfadP. Both flagella and chemotaxis genes were up-regulated, while genes coding for extracellular hydrolytic enzymes, cytochrome c oxidase, and carbon and nitrogen metabolism proteins were down-regulated. Two-step reverse-transcription polymerase chain reaction analysis targeting 13 genes confirmed that the expression of egl, rsl, pehC, pme, cspD3, narH, norB, ccoP, tek, and xpsR was significantly decreased. Our results suggest that FadP affects the virulence of R. pseudosolanacearum by altering nitrogen metabolism processes, reducing bacterial motility and extracellular polysaccharide and cellulase production, and affecting protein-carbohydrate interactions involved in host recognition, attachment, and invasion.