The tomato resistance protein Bs4 is a predicted non-nuclear TIR-NB-LRR protein that mediates defense responses to severely truncated derivatives of AvrBs4 and overexpressed AvrBs3.
The Lycopersicon esculentum Bs4 resistance (R) gene specifies recognition of Xanthomonas campestris pv. vesicatoria (Xcv) strains that express the cognate AvrBs4 avirulence protein. Bs4 was isolated by positional cloning and is predicted to encode a nucleotide-binding leucine-rich repeat (NB-LRR) protein that is homologous to tobacco N and potato Y-1 resistance proteins. Xcv infection tests demonstrate that Bs4 confers perception of AvrBs4 but not the 97% identical AvrBs3 protein. However, when delivered via Agrobacterium T-DNA transfer, both, avrBs4 and avrBs3 trigger a Bs4-dependent hypersensitive response, indicating that naturally occurring AvrBs3-homologues provide a unique experimental platform for molecular dissection of recognition specificity. Transcript studies revealed intron retention in Bs4 transcripts. Yet, an intron-deprived Bs4 derivative still mediates AvrBs4 detection, suggesting that the identified splice variants are not crucial to resistance. The L. pennellii bs4 allele, which is >98% identical to L. esculentum Bs4, has a Bs4-like exon-intron structure with exception of a splice polymorphism in intron 2 that causes truncation of the predicted bs4 protein. To test if the receptor-ligand model is a valid molecular description of Bs4-mediated AvrBs4 perception, we conducted yeast two-hybrid studies. However, a direct interaction was not observed. Defense signaling of the Bs4-governed reaction was studied in Nicotiana benthamiana by virus-induced gene silencing and showed that Bs4-mediated resistance is EDS1- and SGT1-dependent.
Schornack
Sebastian
S
Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, D-06120 Halle (Saale), Germany.
Ballvora
Agim
A
Gürlebeck
Doreen
D
Peart
Jack
J
Baulcombe
David
D
Ganal
Martin
M
Baker
Barbara
B
Bonas
Ulla
U
Lahaye
Thomas
T
D016960:Agrobacterium tumefaciens / Q000235:genetics; D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D007113:Immunity, Innate / Q000235:genetics; D000090263:Leucine-Rich Repeat Proteins; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D008969:Molecular Sequence Data; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D000071336:Transcription Activator-Like Effectors
C434207:AvrBs4 protein, Xanthomonas campestris; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D000090263:Leucine-Rich Repeat Proteins; C089425:N protein, Nicotiana glutinosa; D010940:Plant Proteins; D011506:Proteins; D000071336:Transcription Activator-Like Effectors; C073876:avrBs3-2 protein, Xanthomonas campestris