Characterization in apple leaves of two subclasses of PR-10 transcripts inducible by acibenzolar-S-methyl, a functional analogue of salicylic acid

This study is focusing on the identification of PR-10 genes expressed in leaves of Malus domestica L, cv. Golden Delicious treated with acibenzolar-S-methyl (ASM), a functional analogue of salicylic acid. The complete sequence of four cDNAs (named AP1 to AP4) was determined and the corresponding genes were grouped into two subclasses: APa including AP1 and AP4, and APb regrouping AP2 and AP3. The nucleotide sequence of AP2 Plus upstream regulating sequences was found nearly identical to the previously described gene 1'pr10*Md.a. By contrast, members of the APa subclass were considered as yet undescribed apple PR-10 genes. Results of gene expression show that the transcripts of the AN subclass strongly accumulated from 20 up to 120 h after ASM application in treated leaves and systemically in Upper untreated leaves 120 h after ASM treatment. Significantly lower levels of induction were recorded with transcripts of the APb subclass. Using immunoblot analysis, two polypeptides of 17 and 18 kDa, respectively, were detected in leaves 48 h after ASM application. Immunodetcction performed on leaf sections allowed the localization of proteins in the Palisade parenchyma and the vascular tissues. The results su cst that the apple PR-10 genes, in particular those of the APa subclass, which arc strongly inducible by ASM, could play a role in local and systemic defences. (C) 2001 Academic Press.