The Skp1-like protein SSK1 is required for cross-pollen compatibility in S-RNase-based self-incompatibility.
The self-incompatibility (SI) response occurs widely in flowering plants as a means of preventing self-fertilization. In these self/non-self discrimination systems, plant pistils reject self or genetically related pollen. In the Solanaceae, Plantaginaceae and Rosaceae, pistil-secreted S-RNases enter the pollen tube and function as cytotoxins to specifically arrest self-pollen tube growth. Recent studies have revealed that the S-locus F-box (SLF) protein controls the pollen expression of SI in these families. However, the precise role of SLF remains largely unknown. Here we report that PhSSK1 (Petunia hybrida SLF-interacting Skp1-like1), an equivalent of AhSSK1 of Antirrhinum hispanicum, is expressed specifically in pollen and acts as an adaptor in an SCF(Skp1-Cullin1-F-box)(SLF) complex, indicating that this pollen-specific SSK1-SLF interaction occurs in both Petunia and Antirrhinum, two species from the Solanaceae and Plantaginaceae, respectively. Substantial reduction of PhSSK1 in pollen reduced cross-pollen compatibility (CPC) in the S-RNase-based SI response, suggesting that the pollen S determinant contributes to inhibiting rather than protecting the S-RNase activity, at least in solanaceous plants. Furthermore, our results provide an example that a specific Skp1-like protein other than the known conserved ones can be recruited into a canonical SCF complex as an adaptor.
Zhao
Lan
L
Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences and National Center for Plant Gene Research, Beijing 100190, China.
Huang
Jian
J
Zhao
Zhonghua
Z
Li
Qun
Q
Sims
Thomas L
TL
Xue
Yongbiao
Y
D000595:Amino Acid Sequence; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D007178:Inbreeding; D008969:Molecular Sequence Data; D032306:Petunia / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011058:Pollen / Q000235:genetics*; D012260:Ribonucleases / Q000235:genetics / Q000378:metabolism*; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
D010940:Plant Proteins; D044843:SKP Cullin F-Box Protein Ligases; D012260:Ribonucleases; C022542:ribonuclease S