Hydrophobic protein synthesized in the pod endocarp adheres to the seed surface

Soybean (Glycine max [L.] Merr.) hydrophobic protein (HPS) is an abundant s eed constituent and a potentially hazardous allergen that causes asthma in persons allergic to soybean dust. By analyzing surface extracts of soybean seeds with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and am ino-terminal microsequencing, we determined that large amounts of HPS are d eposited on the seed surface. The quantity of HPS present varies among soyb ean cultivars and is more prevalent on dull-seeded phenotypes. We have also isolated cDNA clones encoding HPS and determined that the preprotein is tr anslated with a membrane-spanning signal sequence and a short hydrophilic d omain. Southern analysis indicated that multiple copies of the HPS gene are present in the soybean genome, and that the HPS gene structure is polymorp hic among cultivars that differ in seed coat luster. The pattern of HPS gen e expression, determined by in situ hybridization and RNA analysis, shows t hat HPS is synthesized in the endocarp of the inner ovary wall and is depos ited on the seed surface during development. This study demonstrates that a seed dust allergen is associated with the seed luster phenotype in soybean and that compositional properties of the seed surface may be altered by ma nipulating gene expression in the ovary wall.