Reprogramming virulence networks to attack resistant hosts?

The infectious capacities of bacteria rely on the establishment of finely regulated virulence programs. In an experimental evolutionary study of the plant pathogen Ralstonia solanacearum, Rekha Gopalan-Nair and her colleagues from the LIPME "Pathogenicity of Ralstonia and its Adaptation to its Environment" team were able to show that a convergent reprogramming of regulatory networks allowed this bacterium to infect a usually resistant tomato. After a series of successive passages of the GMI1000 strain of R. solanaceaum on the tomato Hawaii 7996 —usually resistant, the authors of this paper observed the appearance of variants of the bacterium able to overcome the quantitative resistance carried by Hawaii 7996. Genomic and transcriptomic analyses established that this was not a circumvention of resistance but rather a global and convergent reprogramming of bacterial gene expression, involving in particular 4 regulatory genes among which are hrpB and efpR that control the virulence of R. solanacearum. Transcriptomic data suggest that epigenetic modifications may also regulate some of the components of these regulatory networks.