title: Ubiquitin-proteasome-mediated degradation of S-RNase in a solanaceous cross-compatibility reaction.
abstract: Many plants have a self-incompatibility (SI) system in which the rejection of self-pollen is determined by multiple haplotypes at a single locus, termed S. In the Solanaceae, each haplotype encodes a single ribonuclease (S-RNase) and multiple S-locus F-box proteins (SLFs), which function as the pistil and pollen SI determinants, respectively. S-RNase is cytotoxic to self-pollen, whereas SLFs are thought to collaboratively recognize non-self S-RNases in cross-pollen and detoxify them via the ubiquitination pathway. However, the actual mechanism of detoxification remains unknown. Here we isolate the components of a SCF(SLF) (SCF = SKP1-CUL1-F-box-RBX1) from Petunia pollen. The SCF(SLF) polyubiquitinates a subset of non-self S-RNases in vitro. The polyubiquitinated S-RNases are degraded in the pollen extract, which is attenuated by a proteasome inhibitor. Our findings suggest that multiple SCF(SLF) complexes in cross-pollen polyubiquitinate non-self S-RNases, resulting in their degradation by the proteasome.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan.
authors.forename: Tetsuyuki
authors.initials: T
authors.lastname: Entani
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Kubo
authors.forename: Shin
authors.initials: S
authors.lastname: Isogai
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shirakawa
authors.forename: Akira
authors.initials: A
authors.lastname: Isogai
authors.forename: Seiji
authors.initials: S
authors.lastname: Takayama
mesh_terms: D008969:Molecular Sequence Data; D032306:Petunia / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism*; D054817:Pollination / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism / Q000502:physiology*; D012260:Ribonucleases / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism / Q000502:physiology*; D054875:Ubiquitination
chemical_list: D010940:Plant Proteins; D025801:Ubiquitin; D012260:Ribonucleases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
keywords: 26S proteasome; Petunia hybrida; SCF
  SLF; Solanaceae; self-/non-self discrimination; self-incompatibility; ubiquitination