Petunia hybrida S-proteins: ribonuclease activity and the role of their glycan side chains in self-incompatibility |
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Authors: | W Broothaerts P Vanvinckenroye B Decock J Van Damme J C Vendrig |
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Institution: | (1) Laboratory of Plant Physiology, Katholieke Universiteit Leuven, Kard. Mercierlaan 92, B-3001 Heverlee, Belgium;(2) Rega Institute for Medical Research, K.U. Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium;(3) F.A. Janssens Memorial Laboratory of Genetics, K.U. Leuven, W. de Croylaan 42, B-3001 Heverlee, Belgium |
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Abstract: | Summary Self-incompatibility in flowering plants is controlled by the S-gene, encoding stylar S (allele-specific) glycoproteins. In addition to three previously characterized Petunia hybrida S-proteins, we identified by N-terminal sequence analysis another stylar S-protein, co-segregating with the S
b-allele. Purified S-proteins reveal biological activity, as is demonstrated for two of them by the allele-specific inhibition of pollen tube growth in vitro. Moreover, the four isolated S-proteins are ribonucleases (S-RNases). Specific activities vary from 30 (S1) to 1000 (S2) units per min per mg protein. We attempted to investigate the functionality of the carbohydrate portion of the S-RNases. Deglycosylation studies with the enzyme peptide-N-glycosidase F (PNGase F) reveals differences in the number of N-linked glycan chains present on the four S-RNases. Variability in the extent of glycosylation accounts for most of the molecular weight differences observed among these proteins. By amino acid sequencing, the positions of two of the three N-glycosylation sites on the S2-RNase could be located near the N-terminus. Enzymic removal of the glycan side chains has no effect on the RNase activity of native S-RNases. This suggests another role of the glycan moiety in the self-incompatibility mechanism. |
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Keywords: | Glycan chains Petunia hybrida Ribonuclease (RNase) Self-incompatibility S-(glyco)protein |
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