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 ve rrucosa), show sequence homology to a class of pathogenesis-related (P R) proteins identified in several other plant species, We recently rep orted that Bet v 1-related mRNAs and proteins are induced by microbial pathogens in birch cell suspension cultures, which suggests that thes e 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 isolati on, by screening with a pollen Bet v 1 cDNA probe, of three full-lengt h 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. Northe rn 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 be tulina, a natural pathogen of birch, also led to the coordinated activ ation 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 po llen allergens includes a subset of genes, different from those consti tutively expressed in pollen, that are induced in somatic cells upon t heir interaction with microorganisms. The possible implications of the se results fdr the function of Bet v 1 proteins in the defence reactio n against pathogens, as well as for the incidence of Type I allergies, are discussed.