Evidence for orthologous S- Locus-Related I genes in several genera of Brassicaceae
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O R I GI N A L P A P E R
D.-T. Luu á S. Hugues á E. PasseleÁgue á P. Heizmann
Evidence for orthologous S- Locus-Related I genes in several genera of Brassicaceae
Received: 19 June 2000 / Accepted: 30 August 2000 / Published online: 18 October 2000 Ó Springer-Verlag 2000
Abstract In the Brassica genus, self-incompatibility (SI) is considered to be controlled by the combined action of several highly polymorphic genes located at the S-locus. These genes, including the S-Locus Gene (SLG), and the S-Receptor Kinase (SRK) are all members of the complex multigenic S-family. The S-Locus Related I gene (SLR1) is a member of the S-family, but is not involved in SI control since it is not linked to the S-locus and is essentially monomorphic. Here we con®rm or demonstrate the occurrence of SLR1 as highly diverged but not very polymorphic genes in several genera of the Brassicaceae family (Arabidopsis, Brassica, Hirschfeldia, Raphanus, Sinapis). They show similar expression patterns with respect to location (stigmatic papillae), developmental stage (before and during anthesis) and transcript size (1.6 kb). In addition, they are assumed to be involved in the same biological function (late pollen adhesion). These features suggest that the pollen adhesion function might have evolved towards self-pollen recognition through duplication of SLR1 and recruitment of a protein kinase gene. Key words Sporophytic self-incompatibility á Pollen adhesion á Molecular evolution
Communicated by A. Kondorosi P. Heizmann (&) Laboratoire de Biologie MicromoleÂculaire et Phytochimie, EA632, Universite Lyon I, 69632 Villeurbanne Cedex, France E-mail: [email protected] Tel.: +33-4-72432957 Fax: +33-4-72431426 D.-T. Luu á E. PasseleÁgue á P. Heizmann Laboratoire de Reproduction et DeÂveloppement des Plantes, UMR 5667 CNRS-INRA-ENSL-UCBL, 69643 Lyon Cedex 07, France S. Hugues Laboratoire de BiomeÂtrie et Biologie Evolutive, UMR CNRS 5558, Universite Lyon I, 69622 Villeurbanne Cedex, France
Introduction Self-incompatibility (SI), a barrier to sel®ng that acts before fertilisation, is the most widespread mechanism promoting outbreeding and maintaining genetic adaptability among angiosperm populations, since it has been estimated to occur in at least 50% of all species of ¯owering plants (De Nettancourt 1977). Whitehouse (1951) hypothesized that the sudden rise of the angiosperms during the Cretaceous, as attested by the fossil record, was essentially due to the reproductive advantage conferred on the angiosperms by the simultaneous acquisition of both hermaphrodism and homomorphic SI. Hermaphrodism allows any plant to mate with any other plant in a population (compared to only half of the population in the case of balanced sex separation). Homomorphic SI is closely associated with hermaphrodism, serving to prevent inbreeding and genetic depression in these populations. To explain the occurrence of self-fertile individuals (or populations) among SI species, Whitehouse (1951) proposed further that after a species had conquered its ecolog
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