Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum
Journal
Molecular Plant Pathology
Journal Volume
17
Journal Issue
4
Pages
553
Date Issued
2016-05-01
Author(s)
Wang, Keke
Remigi, Philippe
Anisimova, Maria
Lonjon, Fabien
Kars, Ilona
Kajava, Andrey
Li, Chien Hui
Vailleau, Fabienne
Genin, Stéphane
Peeters, Nemo
Abstract
© 2016 BSPP AND JOHN WILEY & SONS LTD. The soil-borne pathogen Ralstonia solanacearum causes bacterial wilt in a broad range of plants. The main virulence determinants of R.solanacearum are the type III secretion system (T3SS) and its associated type III effectors (T3Es), translocated into the host cells. Of the conserved T3Es among R.solanacearum strains, the Fbox protein RipG7 is required for R.solanacearum pathogenesis on Medicago truncatula. In this work, we describe the natural ripG7 variability existing in the R.solanacearum species complex. We show that eight representative ripG7 orthologues have different contributions to pathogenicity on M.truncatula: only ripG7 from Asian or African strains can complement the absence of ripG7 in GMI1000 (Asian reference strain). Nonetheless, RipG7 proteins from American and Indonesian strains can still interact with M.truncatulaSKP1-like/MSKa protein, essential for the function of RipG7 in virulence. This indicates that the absence of complementation is most likely a result of the variability in the leucine-rich repeat (LRR) domain of RipG7. We identified 11 sites under positive selection in the LRR domains of RipG7. By studying the functional impact of these 11 sites, we show the contribution of five positively selected sites for the function of RipG7 CMR15 in M.truncatula colonization. This work reveals the genetic and functional variation of the essential core T3E RipG7 from R.solanacearum. This analysis is the first of its kind on an essential disease-controlling T3E, and sheds light on the co-evolutionary arms race between the bacterium and its hosts.
Subjects
LRR | Medicago truncatula | Positive selection | Ralstonia solanacearum | Type III effector | Virulence function
Type
journal article