Ralstonia solanacearum requires F-box-like domain-containing type III effectors to promote disease on several host plants.
The phytopathogenic bacterium Ralstonia solanacearum encodes a family of seven type III secretion system (T3SS) effectors that contain both a leucine-rich repeat and an F-box domain. This structure is reminiscent of a class of typical eukaryotic proteins called F-box proteins. The latter, together with Skp1 and Cullin1 subunits, constitute the SCF-type E3 ubiquitin ligase complex and control specific protein ubiquitinylation. In the eukaryotic cell, depending on the nature of the polyubiquitin chain, the ubiquitin-tagged proteins either see their properties modified or are doomed for degradation by the 26S proteasome. This pathway is essential to many developmental processes in plants, ranging from hormone signaling and flower development to stress responses. Here, we show that these previously undescribed T3SS effectors are putative bacterial F-box proteins capable of interacting with a subset of the 19 different Arabidopsis Skp1-like proteins like bona fide Arabidopsis F-box proteins. A R. solanacearum strain in which all of the seven GALA effector genes have been deleted or mutated was no longer pathogenic on Arabidopsis and less virulent on tomato. Furthermore, we found that GALA7 is a host-specificity factor, required for disease on Medicago truncatula plants. Our results indicate that the GALA T3SS effectors are essential to R. solanacearum to control disease. Because the F-box domain is essential to the virulence function of GALA7, we hypothesize that these effectors act by hijacking their host SCF-type E3 ubiquitin ligases to interfere with their host ubiquitin/proteasome pathway to promote disease.
Angot
Aurélie
A
Laboratoire des Interactions Plantes Microorganismes, Institut National de la Recherche Agronomique-Centre National de la Recherche Scientifique, BP52627, 31326 Castanet-Tolosan, France.
Peeters
Nemo
N
Lechner
Esther
E
Vailleau
Fabienne
F
Baud
Catherine
C
Gentzbittel
Laurent
L
Sartorel
Elodie
E
Genschik
Pascal
P
Boucher
Christian
C
Genin
Stéphane
S
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044783:F-Box Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D018551:Solanum lycopersicum / Q000382:microbiology*; D046913:Medicago truncatula / Q000382:microbiology*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D043368:Ralstonia solanacearum / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D014774:Virulence
C120363:ASK1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D044783:F-Box Proteins; C484058:ASK2 protein, Arabidopsis; D044843:SKP Cullin F-Box Protein Ligases