The alternative sigma factor HrpL negatively modulates the flagellar system in the phytopathogenic bacterium Erwinia amylovora under hrp-inducing conditions

Sophie Cesbron (1) , J Pierre Paulin (1) , Michel Tharaud (1) , Marie Anne M. A. Barny (2) , Marie-Noelle Brisset (1)

1 Unité de recherche Pathologie végétale et phytobactériologie
2 PaVé - Pathologie Végétale

In this work we present evidence of an opposite regulation in the phytopathogenic bacteria Erwinia amylovora between the virulence-associated Type III secretion system (TTSS) and the flagellar system. Using loss-of-function mutants we show that motility enhanced the virulence of wild-type bacteria relative to a nonmotile mutant when sprayed on apple seedlings with unwounded leaves. Then we demonstrated through analyses of motility, flagellin export and visualization of flagellar filament that HrpL, the positive key regulator of the TTSS, also down-regulates the flagellar system. Such a dual regulation mediated by an alternative sigma factor of the TTSS appears to be a level of regulation between virulence and motility not yet described among Proteobacteria.

Mots clés: SIGMA FACTOR; TYPE III SECRETION SYSTEM; FLAGELLIN; FIRE BLIGHT

Mots clés: INVERSE REGULATION; MALOIDEAE

Domaines: Microbiologie et Parasitologie

Sophie Cesbron, J Pierre Paulin, Michel Tharaud, Marie Anne M. A. Barny, Marie-Noelle Brisset. The alternative sigma factor HrpL negatively modulates the flagellar system in the phytopathogenic bacterium Erwinia amylovora under hrp-inducing conditions. FEMS Microbiology Letters, 2006, 257 (2), pp.221-227. ⟨10.1111/j.1574-6968.2006.00172.x⟩. ⟨hal-02659389⟩