GROUP-I ALLERGENS OF GRASS-POLLEN AS CELL WALL-LOOSENING AGENTS

Group I allergens are the major allergens of grass pollen, but their b iological function is unknown. These proteins are shown here to be str ucturally related to expansins, which are able to induce extension (cr eep) of plant cell walls. Extracts of maize pollen possess potent expa nsin-like activity, as measured in wall extension and wall stress-rela xation assays, This activity is selective for grass cell walls and is, at least partly, due to the action of maize group I allergens, We pro pose that group I allergens facilitate invasion of the pollen tube int o the maternal tissues by loosening the cell walls of the grass stigma and style. Additionally, the presence of related mRNAs in vegetative tissues of rice, Arabidopsis, and soybean implies that allergen homolo gs may function to loosen walls in growing vegetative tissues as well.