Identification and characterization of an L-fucose specific lectin GVSL involved in gamete recognition of Gracilaria vermiculophylla

The lectin-carbohydrate recognition system is especially important for red algae which female and male gametes are both non-motile. A sex-related lectin gene GvSL from Gracilaria vermiculophylla was cloned and expressed heterologously in Escherichia coli . ORF of GvSL was 684 bp in length and encoded a polypeptide of 228 amino acids with a deduced molecular weight of 25.8 kDa. Real -time PCR analysis showed that it up-regulated most in mature male gametophytes which was 15.4-fold and 21.94-fold higher than mature female gametophytes and immature male gametophytes respectively. The immunohistochemical staining also demonstrated that GvSL was mainly expressed in the spermatangium crypts of mature male gametophytes. Purified rGVSL showed significant agglutination of rabbit blood erythrocytes and only L-fucose showed the glycoinhibitory effect among the eight monosaccharides tested. The inhibitory tests further proved that GVSL and its complementary carbohydrate Lfucose composed a lectin-carbohydrate recognition system affecting the fertilization efficiency of G . vermiculophylla .