The promoter of an apple Ypr10 gene, encoding the major allergen Mal d 1, is stress- and pathogen-inducible

Mal d 1 protein, constituting the major apple allergen, was classified as pathogenesis-related protein 10 (PR-10) on the basis of sequence homologies, although its induction by pathogens or stress has not been demonstrated so far. Here we report the promoter activity of a member of the apple Ypr10 gene family and the inducibility of its gene product Mal d 1. The genomic clone and the promoter sequence of Ypr10*a from Malus domestica have been isolated and characterized. For gene regulation studies the promoter was translationally fused to the uidA reporter gene and expressed in stable transformed Nicotiana tabacum. A total of 1.25 kb of 5' regulating sequence turned out to be necessary to direct strong beta-glucuronidase (GUS) expression. Besides the already known occurrence of Mel d 1 in ripe fruits, Ypr10 genes were found to be highly expressed only in old leaves, but can be induced in young leaves by multiple stress factors. Application of abiotic stimuli, like salicylic acid and reduced glutathione significantly increased both, Ypr10*a-GUS activity in transgenic tobacco and transcriptional and translational expression of Mal d 1 in young apple leaves. Virus infection of the transformed tobacco plants strongly induced Ypr10*a-GUS transgene expression. After treatment with fungal elicitors a clear increase in GUS activity and Mal d 1 expression was observed in young tobacco and apple leaves, respectively. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.