IDENTIFICATION AND CHARACTERIZATION OF STYLAR GLYCOPROTEINS ASSOCIATED WITH SELF-INCOMPATIBILITY GENES OF JAPANESE PEAR, PYRUS-SEROTINA REHD

Japanese pear (Pyrus serotina Rehd.) exhibits gametophytic self-incomp atibility. Following our previous findings that basic ribonucleases in the styles of Japanese pear are associated with self-incompatibility genes (S-RNases), stylar proteins with high pl values were analyzed by two-dimensional gel electrophoresis further to characterize S-RNases. A group of basic proteins of about 30 kDa associated with self-incomp atibility genes were identified. These proteins contained sugar chains which reacted with concanavalin A and wheat germ agglutinin, and thus were designated as S-glycoproteins of Japanese pear. The fact that th e S-glycoprotein was expressed at a much lower level in a self-compati ble mutant than in the original variety suggested a role of S-glycopro teins in mediating self-incompatibility of Japanese pear. Immunoblot a nalysis indicated that S-glycoproteins are identical to previously ide ntified S-RNases. The S-glycoproteins were predominantly expressed in the style, in the ovary in trace amounts, and not in leaf, pollen or g erminated pollen. The N-terminal amino acid sequences of the S-glycopr oteins showed homology not only with each other but also with those of the S-allele-associated proteins from plants of the family Solanaceae at levels of about 30-50%.