Role of the arginyl-glycyl-aspartic motif in the action of Ptr ToxA produced by Pyrenophora tritici-repentis.
A fundamental problem of plant science is to understand the biochemical basis of plant/pathogen interactions. The foliar disease tan spot of wheat (Triticum aestivum), caused by Pyrenophora tritici-repentis, involves Ptr ToxA, a proteinaceous host-selective toxin that causes host cell death. The fungal gene ToxA encodes a 17.2-kD pre-pro-protein that is processed to produce the mature 13.2-kD toxin. Amino acids 140 to 142 of the pre-pro-protein form an arginyl-glycyl-aspartic (RGD) sequence, a motif involved in the binding of some animal proteins and pathogens to transmembrane receptor proteins called integrins. Integrin-like proteins have been identified in plants recently, but their role in plant biology is unclear. Our model for Ptr ToxA action predicts that toxin interacts with a putative host receptor through the RGD motif. Mutant clones of a ToxA cDNA, created by polymerase chain reaction such that the RGD in the pro-toxin was changed to arginyl-alanyl-aspartic or to arginyl-glycyl-glutamic, were expressed in Escherichia coli. Extracts containing mutated forms of toxin failed to cause host cell death, but extracts from E. coli expressing both a wild-type pro-protein cDNA and a control mutation away from RGD were active in cell death development. In competition experiments, 2 mM RGD tripeptide reduced the level of electrolyte leakage from wheat leaves by 63% when co-infiltrated with purified Ptr ToxA (15 microg mL(-1)) obtained from the fungus, but the control peptide arginyl-glycyl-glutamyl-serine provided no protection. These experiments indicate that the RGD motif of Ptr ToxA is involved with toxin action, possibly by interacting with a putative integrin-like receptor in the host.
Meinhardt
Steven W
SW
Department of Biochemistry, North Dakota State University, Fargo 58105, USA. steven.meinhardt@ndsu.nodak.edu
Cheng
Weijun
W
Kwon
Chil Y
CY
Donohue
Christine M
CM
Rasmussen
Jack B
JB
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004573:Electrolytes / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D009183:Mycotoxins / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D009842:Oligopeptides / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014908:Triticum / Q000166:cytology / Q000187:drug effects*
D018076:DNA, Complementary; D004573:Electrolytes; D005656:Fungal Proteins; D009183:Mycotoxins; D009842:Oligopeptides; C105776:TOXA protein, Pyrenophora tritici-repentis; C047981:arginyl-glycyl-aspartic acid