EXPRESSION OF BET-V-1, THE MAJOR BIRCH POLLEN ALLERGEN, DURING ANTHER DEVELOPMENT - AN IN-SITU HYBRIDIZATION STUDY

Bet v 1 proteins, a group of isoforms that constitute the major pollen allergen of the white birch (Betula verrucosa), are encoded by a complex multigene family which also includes a subset of genes transcriptionally activated in cell suspension cultures in the presence of microbial pathogens. We have investigated the temporal and spatial expression patterns of Bet v 1 genes during development of male birch inflorescences. Western and Northern analysis indicated that the expression of Bet v 1 isoallergens is regulated at the transcriptional level and activated only during the late phases of anther maturation, so that high levels of these proteins accumulate in mature pollen. In situ hybridization experiments, carried out with sections of male inflorescences isolated at defined developmental stages, showed that Bet v 1 genes are specifically expressed in late bicellular and mature pollen, but no transcripts were detected in sporophytic anther tissues of any developmental stage. These data suggest a possible role of Bet v 1 proteins during pollen germination on the stigma, protecting the female reproductive tissues from infection by pathogens.