R. Nissinen et al., CLAVIBACTER-MICHIGANENSIS SUBSP SEPEDONICUS ELICITS A HYPERSENSITIVE RESPONSE IN TOBACCO AND SECRETES HYPERSENSITIVE RESPONSE-INDUCING PROTEIN(S), Phytopathology, 87(7), 1997, pp. 678-684
Strains of Clavibacter michiganensis subsp. sepedonicus, causal agent
of bacterial ring rot of potato, showed marked differences in virulenc
e on host plants. When infiltrated into tobacco leaves, virulent strai
ns caused a rapid localized necrotic response (within 24 to 48 h) char
acteristic of the hypersensitive response (HR), whereas nonpathogenic
strains did not. Concentrated cell-free culture supernatants (CCS) fro
m virulent strains caused a necrotic reaction on tobacco, whereas CCS
from nonpathogenic strains did not. The necrosis-inducing activity was
heat stable and protease sensitive. Inhibitors of eukaryotic metaboli
sm suppressed the necrotic reaction of tobacco to CCS. No necrotic res
ponse was observed when host plants were infiltrated with either cells
or CCS from virulent strains. HR-inducing protein(s) from a virulent
strain separated from the majority of other proteins on DEAE cellulose
at 250 to 300 mM NaCl. Ammonium sulfate-precipitated proteins from a
virulent strain produced a necrotic reaction at a total protein concen
tration of 18 mu g/ml, whereas those from a nonpathogenic strain did n
ot, even at a concentration of 180 mu g/ml. We conclude that virulent
strains of C. michiganensis subsp. sepedonicus elicit a typical HR in
tobacco and secrete proteinaceous elicitor(s) of the nonhost HR.