A birch gene family encoding pollen allergens and pathogenesis-related proteins

Bet v I, the major pollen allergen of birch (Betula verrucosa), shows high sequence homology to a family of pathogenesis-related (PR) proteins that have recently been identified in several other plant species. We have used a pollen Bet v I cDNA clone and anti-Bet v I antibodies as probes to study the expression of Bet v I genes in birch cell suspension cultures under different experimental conditions. Induction of Bet v I-related proteins was detected in immunoblots of cell extracts upon co-cultivation with microbial pathogens. Northern analysis revealed the rapid induction of Bet v I transcripts in the presence of bacteria and fungi, but not by stress treatments (heat shock, metal ions) or by chemical elicitors. RNase protection experiments showed that the pathogen-inducible RNAs did not correspond to the pollen cDNA clone but most likely to the products of transcription of other members of the Bet v I gene family, sharing high sequence homology with the pollen-specific gene within the 5'-half of the coding region. We conclude that the Bet v I gene family of pollen allergens includes a subset of defense-related genes that are transcriptionally activated in the presence of microbial pathogens.