Self-Incompatibility in Brassica: The Nature and Role of Female Glycoproteins
The roles played by stigmatic glycoproteins in the self-incompatibility (SI) mechanism in Brassica oleracea have been investigated. In a physiological study, the suppression of protein synthesis was demonstrated to overcome SI, but also affect a number of other pollination-related events, such as regulated hydration of the pollen grain. Interestingly, inhibition of glycosylation appears to affect SI alone, leaving other processes to proceed normally. When stigmatic glycoproteins are used in bioassays, it is clear that they can regulate pollen tube growth in accordance with the S (incompatibility) genes present. However, the multiplicity of glycoproteins possessed by each genotype, and their presence in quantity indicates that they are unlikely to be simple intercellular signals. Database searches involving concensus sequences from the family of stigmatic glycoproteins have revealed strong homologies with domains in several classes of animal proteins, principally the von Willebrand factor and type VI collagen. These polypeptides, which are also heavily glycosylated, are held to be involved in protein-protein interactions and extracellular matrix formation — processes which may also be involved in the initial stages of pollination. Detailed modelling of these sequences indicate that, despite small differences in amino acid composition, these domains are strikingly similar in their three dimensional molecular architecture.
KeywordsPollen Tube Pollen Tube Growth Brassica Oleracea Extracellular Matrix Formation Pollen Hydration
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- Anderson, M.A., Cornish, E.L., Mau, S.L., Williams, E.G., Hoggart, R., Atkinson, A., Bonig, I., Gregor, B., Simpson, R., Roche,P.J., Haley, J.D., Penscaow, J.D., Niall, H.D., Tredegar, G.W., Cochlan, J.P., Crawford, R.J. and Clarke, A.E. 1986. Cloning of a cDNA for a stylar glycoprotein associated with the expression of self-incompatibility in Nicotiana alata. Nature 321, 38–44.CrossRefGoogle Scholar
- Chu, M.L., Pan, T.C., Conway, D., Kuo, H.J., Glanville, R.W., Timpl, R., Mann, K. and Deutzmann, R. 1989. Sequence analysis of x 1 (VI) and x 2 (VI) chains of human type VI collagen reveals internal triplication of globular domains similar to the A domains of von Willebrand factor and two x 2 (VI) chain variants that differ in carboxy terminus. EMBO J. 8, 1939–46.PubMedGoogle Scholar
- Crabbe, M.J.C. and Appleyard, J. 1989. Desk-top Molecular Modeller Version 1.2. Oxford University Press (Oxford, UK).Google Scholar
- Dickinson, H.G. 1990. Self-incompatibility in flowering plants. Bioessays (in the press).Google Scholar
- Dickinson, H.G. and Lewis, D. 1975. Interaction between the pollen grain coating and the stigmatic surface during compatible and incompatible intraspecific pollinations in Raphanus. In: The biology of the male gamete, eds J.G. Duckett and P.A. Racey. Biol. J. Linn. Soc. Suppl. I, pp. 165–175.Google Scholar
- Elleman, C.J., Sarker, R.H., Aivalakis, G., Slade, H. and Dickinson, H.G. 1989. Molecular physiology of the pollen-stigma interaction in Brassica. In: Plant Reproduction: from floral induction to pollination, E. Lord and G. Bernier eds. Am. Soc. Pl. Physiol. Symp. Ser. 1, 136–145.Google Scholar
- Lewis, D. 1965. A protein dimer hypothesis on incompatibility. In: Genetics Today, ed. S.J. Geerts. Proc. XI Int. Congress Genet. 1963, pp. 657–663. Pergamon (Oxford, UK).Google Scholar
- Trick, M., Larsen, K. and Flavell, R.B. 1990. A basis for S-allele specificity suggested by closely-related S-allele sequences. In the press.Google Scholar
- Whitehouse, H.L.K. 1950. Multiple allelomorph incompatibility of pollen and tyle in the evolution of the angiosperms. Ann. Bot. N.S. 14: 198–216.Google Scholar