A BIRCH GENE FAMILY ENCODING POLLEN ALLERGENS AND PATHOGENESIS-RELATED PROTEINS

Bet upsilon 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 spe cies. We have used a pollen Bet upsilon I cDNA clone and anti-Bet upsi lon I antibodies as probes to study the expression of Bet upsilon I ge nes in birch cell suspension cultures under different experimental con ditions. Induction of Bet upsilon I-related proteins was detected in i mmunoblots of cell extracts upon co-cultivation with microbial pathoge ns. Northern analysis revealed the rapid induction of Bet upsilon I tr anscripts in the presence of bacteria and fungi, but not by stress tre atments (heat shock, metal ions) or by chemical elicitors. RNase prote ction experiments showed that the pathogen-inducible RNAs did not corr espond to the pollen cDNA clone but most likely to the products of tra nscription of other members of the Bet upsilon I gene family, sharing high sequence homology with the pollen-specific gene within the 5'-hal f of the coding region. We conclude that the Bet upsilon I gene family of pollen allergens includes a subset of defense-related genes that a re transcriptionally activated in the presence of microbial pathogens.