Functional assignment to positively selected sites in the core type III effector RipG7 from Ralstonia solanacearum

• Published in: Molecular plant pathology Vol. 17; no. 4; pp. 553 - 564
• Main Authors: Wang, Keke, Remigi, Philippe, Anisimova, Maria, Lonjon, Fabien, Kars, Ilona, Kajava, Andrey, Li, Chien-Hui, Cheng, Chiu-Ping, Vailleau, Fabienne, Genin, Stéphane, Peeters, Nemo
• Format: Journal Article
• Language: English
• Published: England Blackwell Science in collaboration with the British Society of Plant Pathology 01-05-2016; Blackwell Publishing Ltd; John Wiley & Sons, Inc
• Subjects: Amino Acid Sequence; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacterial Secretion Systems; Genetic Complementation Test; LRR; Medicago truncatula; Medicago truncatula - microbiology; Models, Molecular; Mutagenesis, Site-Directed; Mutation - genetics; Pathogens; Phylogeny; Plant Diseases - microbiology; positive selection; Ralstonia solanacearum; Ralstonia solanacearum - growth & development; Ralstonia solanacearum - metabolism; Ralstonia solanacearum - pathogenicity; Selection, Genetic; Sequence Homology, Amino Acid; type III effector; Virulence; virulence function; Medicago truncatula; virulence function; positive selection; Ralstonia solanacearum; LRR; type III effector
• ISSN: 1464-6722; 1364-3703
• DOI: 10.1111/mpp.12302

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. truncatula SKP1‐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 RipG7CMR₁₅ 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.