CDNA CLONING AND CHARACTERIZATION OF 3 GENES IN THE BET-V-1 GENE FAMILY THAT ENCODE PATHOGENESIS-RELATED PROTEINS

Bet v 1 isoforms, the major pollen allergens of white birch (Betula verrucosa), show sequence homology to a class of pathogenesis-related (PR) proteins identified in several other plant species, We recently reported that Bet v 1-related mRNAs and proteins are induced by microbial pathogens in birch cell suspension cultures, which suggests that these pollen allergens and PR proteins are encoded by the same gene family, However, apart from the genes expressed in pollen, no other Bet v 1 clones have been characterized until now, Here we describe the isolation, by screening with a pollen Bet v 1 cDNA probe, of three full-length cDNA clones, Bet v 1-Sc1, Sr2 and Sc3, from a cDNA library prepared from cultured birch cells grown in the presence ofPseudomonas syringae, Sequence analysis indicated that these clones are highly homologous, but different from the genes encoding the pollen isoallergens. Northern blots and RNase protection experiments showed that the three genes are transcriptionally activated, with similar kinetics, in birch cells co-cultivated with bacteria or fungi, regardless of whether they were pathogenic for birch, Infection of leaves with the fungus Taphrina betulina, a natural pathogen of birch, also led to the coordinated activation of the Bet v 1-Sc genes, although infection with Fusarium solani did not, These results demonstrate that the Bet v 1 gene family of pollen allergens includes a subset of genes, different from those constitutively expressed in pollen, that are induced in somatic cells upon their interaction with microorganisms. The possible implications of these results fdr the function of Bet v 1 proteins in the defence reaction against pathogens, as well as for the incidence of Type I allergies, are discussed.