THE PLANT CELL, Vol 6, Issue 8 1145-1155, Copyright © 1994 by American Society of Plant Biologists
Identification of the 100-kD Victorin Binding Protein from Oats
T. J. Wolpert, D. A. Navarre, D. L. Moore and V. Macko
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331-2902
The fungus Cochliobolus victoriae, the causal agent of victoria blight of
oats, produces the host-specific toxin victorin. Sensitivity of oats to
victorin, and thus susceptibility to the fungus, is controlled by a single
dominant gene. This gene is believed to also confer resistance to the crown
rust pathogen Puccinia coronata. In the case of victoria blight, the gene
has been hypothesized to condition susceptibility by encoding a toxin
receptor. A 100-kD victorin binding protein (VBP) has been identified; it
binds radiolabeled victorin derivatives in a ligand-specific manner and in
a genotype-specific manner in vivo. The VBP may function as a toxin
receptor. In vitro translation coupled with indirect immunoprecipitation
was used to identify the mRNA for the 100-kD VBP, and fractionated mRNAs
were used to prepare cDNA libraries enriched in the relative abundance of
cDNA for the 100-kD VBP. A 3.4-kb cDNA clone was isolated that, when
subjected to a 400-bp 5[prime] deletion, was capable of directing the
synthesis of a protein in Escherichia coli, which reacted to an antibody
specific for the 100-kD VBP. Peptide mapping, by limited proteotysis,
indicated that the protein directed by the cDNA is the 100-kD VBP.
Nucleotide sequence analysis of the cDNA revealed extensive homology to a
previously cloned cDNA for the P protein component of the multienzyme
complex glycine decarboxylase. Glycine decarboxylase is a nuclear-encoded,
mitochondrial enzyme complex. Protein gel blot analysis indicated that the
100-kD VBP copurifies with mitochondria. Based on analysis of in vitro
translation products, nucleotide sequence homology, mitochondrial
localization, and the widespread species distribution of the 100-kD VBP, we
concluded that the 100-kD VBP is the P protein component of glycine
decarboxylase.
