Self-incompatibility in plants

1. Self-incompatibility in plants Gametophytic self-incompatibility inhibits pollen tube growth using different mechanisms Seiji Takayama & Akira Isogai Ann. Rev. Plant Biol. (2005) 56: 467-489 Noni Franklin-Tong & F. Chris H. Franklin TRENDS in Plant Science (2003) 8: 598-605

2. self-incompatibility very important in the evolution of flowering plants ~70% of plants are hermaphroditic SI appears to have evolved independently at least 21 times SI has also been independently lost in numerous lineages, due to human or environmental selection pressures

3. the S-locus in dicots, self-incompatibility maps to a single genetic locus (grasses have 2 unlinked loci!) molecular dissection of the S-locus in several plant species has shown that: the S-locus consists of multiple, tightly-linked genes, encoding male and female compatibility determinants divergent mechanisms of self-incompatibility are encoded by the S-loci of different plant species

4. SPOROPHYTIC (SSI) outcome of the interaction between the pollen tube and the style is determined by the genotype of the sporophyte (diploid tissue) S-locus products are synthesized before completion of meiosis growth of the pollen tube arrests at the surface of the stigma GAMETOPHYTIC (GSI) outcome of the interaction between the pollen tube and the style is determined by the genotype of the pollen (gamete) S-locus products are synthesized after completion of meiosis growth of the pollen tube arrests in the style

5. Apocynaceae Rubiaceae Convolvulaceae Solanaceae ASTERIDS Scrophularaceae Bignoniaceae GAMETOPHYTIC Oleaceae SPOROPHYTIC Campanulaceae Asteraceae MIXED Ericaceae Sasifragaceae Geraniaceae Malvaceae Brassicaceae ROSIDS Fabaceae RANUNCULIDAE Rosaceae Begoniaceae MAGNOLID DICOTS Betulaceae Fagaceae Papaveraceae

6. brassicaceae: SSI, ♂-determinant is a pollen ligand; ♀-determinant is a receptor kinase papaveraceae: GSI; ♀-determinant induces a calcium-dependent signaling network; ♂-determinant is not yet identified solanaceae: GSI; ♀-determinant is a ribonuclease, ♂-determinant is an F-box protein www.ogrod.uj.edu.pl

7. brassicaceae: SSI, ♂-determinant is a pollen ligand; ♀-determinant is a receptor kinase • SLG (S-locus glycoproteins): identified immunologically as an S-haplotype-specific antigen; SLG is not sufficient (or necessary) for SI response, but enhances the activity of SRK • SRK (S-locus receptor kinase): identified by sequencing S-locus; high similarity to SLG • SP11/SCR (S-locus protein 11/S-locus cysteine-rich): identified though cloning and sequencing of the S-locus region and polymorphic gene identification using differential display; induces incompatible reactions in stigma papilla cells (SP11/SCR of matching S-locus haplotype induced autophosphorylation of SRK in stigma plasma membrane) • ARC1 (Armadillo repeat-containing 1): identified through protein interaction with SRK, proposed to promote the degradation of stigmatic proteins promoting pollen germination/growth • MLPK (M-locus protein kinase): positive mediator of SI signaling, loss of function leads to self-compatibility www.ogrod.uj.edu.pl

9. SP11/SCR induces incompatible reactions in stigma papilla cells S6S6 stigmas (A) and S2S2 stigmas (B) were treated with purified recombinant SCR6 and pollinated with S13 pollen treatment of stigma with “self” SP11/SCR protein induces signaling reactions in the pistil these signaling reactions lead to changes within the pistil that prevent growth of “cross” pollen Kachroo et al. 2001 Science 293:1824-1826

10. “solanaceae-TYPE” Rosaceae Scrophulariaceae solanaceae: GSI; ♀-determinant is a ribonuclease, ♂-determinant is an F-box protein the ribonuclease selectively degrades rRNA from pollen of the matching S-haplotype

11. a single origin of S-RNase mediated gametophytic self-incompatibility in eudicots? Steinbachs & Holsinger 2002 Mol. Biol. Evol 19: 825-829

12. Apocynaceae Rubiaceae Convolvulaceae Solanaceae ASTERIDS Scrophularaceae Bignoniaceae GAMETOPHYTIC Oleaceae SPOROPHYTIC Campanulaceae Asteraceae MIXED Ericaceae SI system S-RNase mediated Sasifragaceae Geraniaceae Malvaceae Brassicaceae ROSIDS Fabaceae RANUNCULIDAE Rosaceae Begoniaceae MAGNOLID DICOTS Betulaceae Fagaceae Papaveraceae

13. ♂-determinant: receptor or inhibitor? inhibitor model: all S-RNases are taken up by the pollen tube, but S-RNases of non-matching S-haplotypes are inhibited/degraded receptor model: whether or not a pollen tube is degraded depends on selective uptake of S-RNases by the pollen tube Golz et al .1999

15. additional factors: • HT-B (small, asparagine-rich protein expressed late in stylar development) • 4936-factor (not yet cloned, mutations result in self-compatibility) • 120kDa glycoprotein (abundant in style, taken up by growing pollen tubes, interacts with S-RNase in vitro) in the absence of HT-B or 4936-factor, S-RNase remains compartmentalized in pollen tubes and does not cause pollen rejection

16. Goldraij et al. 2006 Nature 439: 805-810

17. papaveraceae: GSI; ♀-determinant induces a calcium-dependent signaling network; ♂-determinant is not yet identified • stigmatic S-proteins isolated through in vitro assays of pollen tube inhibition • the male determinant is believed to be a receptor located at the pollen plasma membrane • SBP (S protein binding protein) specifically binds S-proteins, but without haplotype specificity • interaction of self-pollen with the stigma induces a calcium-dependent signaling cascade leading to programmed cell death in the pollen (Thomas & Franklin-Tong 2004)

19. Summary • SI is an important mechanism for preventing inbreeding in plants • 3 different mechanisms of SI have been described at the molecular level • Sporophytic SI dependent on a kinase-mediated signaling cascade • Gametophytic SI based on selective degradation of pollen rRNA by S-RNases • Gametophytic SI based on a calcium-dependent (MAPK) signaling cascade leading to cell death in pollen

20. Summary location of action G or S? signaling? direction ♀ ♂ to ♀ kinase-mediated S brassicaceae solanaceae papaveraceae G NO ♂ ♀to ♂ ♂ calcium-dependent G