Abstract
A salicylate-inducible PR-10 gene subclass from apple, designated as APa, was characterized. The APa genes were shown to be highly induced in leaves by abiotic stimuli (ethephon, wounding), as well as by inoculation with a virulent or an avirulent strain of Venturia inaequalis. The up-regulation of APa transcripts occurred earlier in the compatible situation than in the incompatible one, but at higher levels in the latter case. At the protein level, a PR-10 polypeptide band (18 kDa) was detected in both interactions, whereas an additional band (17 kDa) was markedly revealed only after infection with the avirulent strain. Immunodetection of PR-10 proteins on leaf prints indicated their vascular localization and an intensification of the signal in the incompatible condition. Overexpression of APa gene products after infection with the avirulent strain was concomitant with the occurrence of resistance symptoms. For two genes of the APa subclass ( Ypr10 ∗Md.b and Ypr10 ∗Md.d ), specific patterns of expression were observed: both Ypr10 ∗Md.b and Ypr10 ∗Md.d were transcriptionally activated by ethephon or following inoculation with the avirulent strain of V. inaequalis, whereas after treatment with a salicylate analogue, only Ypr10 ∗Md.d was induced. This suggests that at least a defense pathway involving ethylene is activated in the incompatible situation.
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