title: Self/non-self recognition mechanisms in sexual reproduction: new insight into the self-incompatibility system shared by flowering plants and hermaphroditic animals.
abstract: Sexual reproduction is an essential process for generating a genetic variety in the next generation. However, most flowering plants and hermaphroditic animals potentially allow self-fertilization. Approximately 60% of angiosperms possess a self-incompatibility (SI) system to avoid inbreeding. The SI system functions at a process of interaction between pollen (or pollen tube) and the pistil. These SI-responsible factors (S-determinants) in pollen and the pistil are encoded by highly polymorphic multiallelic genes in the S-locus, which are tightly linked making a single haplotype. Different taxonomic families utilize different types of S-determinant proteins. In contrast to the plant system, the mechanisms of SI in simultaneously hermaphroditic animals are largely unknown. Among them, promising candidates for SI in ascidians (primitive chordates) were recently identified. The SI system in the ascidian Cionaintestinalis was found to be very similar to those in flowering plants: The products of sperm- and egg-side multiallelic SI genes, which are tight linked and highly polymorphic, appear to be responsible for the SI system as revealed by genetic analysis. These findings led us to speculate that the SI systems in plants and animals evolved in a manner of convergent evolution. Here, we review the current understanding of the molecular mechanisms of the SI system in flowering plants, particularly Brassicacea, and in ascidians from the viewpoint of common mechanisms shared by plants and animals.
authors.affiliation: Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, Sugashima, Toba 517-0004, Japan. Electronic address: hsawada@bio.nagoya-u.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sawada
authors.affiliation: Sesoko Station, University of the Ryukus, Sesoko, Motobu, Okinawa 905-0227, Japan.
authors.forename: Masaya
authors.initials: M
authors.lastname: Morita
authors.affiliation: Graduate School of Bioscience, Nara Institute of Science and Technology, Nara 158-8501, Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Iwano
mesh_terms: D000818:Animals; D002938:Ciona intestinalis / Q000235:genetics / Q000502:physiology; D005260:Female; D057850:Hermaphroditic Organisms / Q000235:genetics / Q000502:physiology*; D019684:Magnoliopsida / Q000235:genetics / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D012098:Reproduction / Q000235:genetics / Q000502:physiology; D060436:Self-Incompatibility in Flowering Plants / Q000235:genetics / Q000502:physiology*; D014561:Urochordata / Q000235:genetics / Q000502:physiology
keywords: Animal; Fertilization; Plant; Self-incompatibility; Self/non-self recognition