title: Identification of a canonical SCF(SLF) complex involved in S-RNase-based self-incompatibility of Pyrus (Rosaceae).
abstract: S-RNase-based self-incompatibility (SI) is an intraspecific reproductive barrier to prevent self-fertilization found in many species of the Solanaceae, Plantaginaceae and Rosaceae. In this system, S-RNase and SLF/SFB (S-locus F-box) genes have been shown to control the pistil and pollen SI specificity, respectively. Recent studies have shown that the SLF functions as a substrate receptor of a SCF (Skp1/Cullin1/F-box)-type E3 ubiquitin ligase complex to target S-RNases in Solanaceae and Plantaginaceae, but its role in Rosaceae remains largely undefined. Here we report the identification of two pollen-specific SLF-interacting Skp1-like (SSK) proteins, PbSSK1 and PbSSK2, in Pyrus                 bretschneideri from the tribe Pyreae of Rosaceae. Both yeast two-hybrid and pull-down assays demonstrated that they could connect PbSLFs to PbCUL1 to form a putative canonical SCF(SLF) (SSK/CUL1/SLF) complex in Pyrus. Furthermore, pull-down assays showed that the SSK proteins could bind SLF and CUL1 in a cross-species manner between Pyrus and Petunia. Additionally, phylogenetic analysis revealed that the SSK-like proteins from Solanaceae, Plantaginaceae and Rosaceae form a monoclade group, hinting their shared evolutionary origin. Taken together, with the recent identification of a canonical SCF(SFB) complex in Prunus of the tribe Amygdaleae of Rosaceae, our results show that a conserved canonical SCF(SLF/SFB) complex is present in Solanaceae, Plantaginaceae and Rosaceae, implying that S-RNase-based self-incompatibility shares a similar molecular and biochemical mechanism.
authors.affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences and National Center for Plant Gene Research, Beijing 100101, China.
authors.forename: Chi
authors.initials: C
authors.lastname: Xu
authors.forename: Maofu
authors.initials: M
authors.lastname: Li
authors.forename: Junkai
authors.initials: J
authors.lastname: Wu
authors.forename: Han
authors.initials: H
authors.lastname: Guo
authors.forename: Qun
authors.initials: Q
authors.lastname: Li
authors.forename: Yu'e
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jijie
authors.initials: J
authors.lastname: Chai
authors.forename: Tianzhong
authors.initials: T
authors.lastname: Li
authors.forename: Yongbiao
authors.initials: Y
authors.lastname: Xue
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D018744:DNA, Plant / Q000235:genetics; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism; D035264:Flowers / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009928:Organ Specificity; D032306:Petunia / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011058:Pollen / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D011485:Protein Binding; D031989:Pyrus / Q000201:enzymology / Q000235:genetics* / Q000502:physiology; D018749:RNA, Plant / Q000235:genetics; D011993:Recombinant Fusion Proteins; D012260:Ribonucleases / Q000235:genetics / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D060436:Self-Incompatibility in Flowering Plants / Q000502:physiology*; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
chemical_list: D018744:DNA, Plant; D044783:F-Box Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D044786:S-Phase Kinase-Associated Proteins; D044843:SKP Cullin F-Box Protein Ligases; D012260:Ribonucleases; C022542:ribonuclease S