- Award ID(s):
- 1645557
- NSF-PAR ID:
- 10399513
- Date Published:
- Journal Name:
- The Plant Cell
- Volume:
- 35
- Issue:
- 2
- ISSN:
- 1040-4651
- Page Range / eLocation ID:
- 673 to 699
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Self-incompatibility (SI), an inbreeding-preventing mechanism, is regulated in Petunia inflata by the polymorphic S-locus, which houses multiple pollen-specific S-locus F-box (SLF) genes and a single pistil-specific S-RNase gene. S2-haplotype and S3-haplotype possess the same 17 polymorphic SLF genes (named SLF1 to SLF17), and each SLF protein produced in pollen is assembled into an SCF (Skp1–Cullin1– F-box) E3 ubiquitin ligase complex. A complete suite of SLF proteins is thought to collectively interact with all non-self S-RNases to mediate their ubiquitination and degradation by the 26S proteasome, allowing cross-compatible pollination. For each SCFSLF complex, the Cullin1 subunit (named PiCUL1-P) and Skp1 subunit (named PiSSK1), like the F-box protein subunits (SLFs), are pollen-specific, raising the possibility that they also evolved specifically to function in SI. Here we used CRISPR/Cas9-meditated genome editing to generate frame-shift indel mutations in PiSSK1, and examined the SI behavior of a T0 plant (S2S3) with biallelic mutations in the pollen genome and two progeny plants (S2S2) each homozygous for one of the indel alleles and not carrying the Cas9-containing T-DNA. Their pollen was completely incompatible with pistils of seven otherwise compatible S-genotypes, but fully compatible with pistils of an S3S3 transgenic plant in which production of S3-RNase was completely suppressed by an antisense S3-RNase gene, and with pistils of immature flower buds, which produce little S-RNase. These results suggest that PiSSK1 specifically functions in SI, and support the hypothesis that SLF-containing SCF complexes are essential for compatible pollination.more » « less
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Summary The collaborative non‐self‐recognition model for S‐
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SUMMARY Self‐incompatibility in
Petunia is controlled by the polymorphicS ‐locus, which containsS‐RNase encoding the pistil determinant and 16–20S‐locus F‐box (SLF ) genes collectively encoding the pollen determinant. Here we sequenced and assembled approximately 3.1 Mb of theS2 ‐haplotype of theS ‐locus inPetunia inflata using bacterial artificial chromosome clones collectively containing all 17SLF genes,SLFLike1 , andS‐RNase . TwoSLF pseudogenes and 28 potential protein‐coding genes were identified, 20 of which were also found at theS ‐loci of both theS6a ‐haplotype ofP. inflata and theSN ‐haplotype of self‐compatiblePetunia axillaris , but not in theS ‐locus remnants of self‐compatible potato (Solanum tuberosum ) and tomato (Solanum lycopersicum ). Comparative analyses ofS ‐locus sequences of these threeS ‐haplotypes revealed potential genetic exchange in the flanking regions ofSLF genes, resulting in highly similar flanking regions between different types ofSLF and between alleles of the same type ofSLF of differentS ‐haplotypes. The high degree of sequence similarity in the flanking regions could often be explained by the presence of similar long terminal repeat retroelements, which were enriched at theS ‐loci of all threeS ‐haplotypes and in the flanking regions of allS ‐locus genes examined. We also found evidence of the association of transposable elements withSLF pseudogenes. Based on the hypothesis thatSLF genes were derived by retrotransposition, we identified 10F‐box genes as putativeSLF parent genes. Our results shed light on the importance of non‐coding sequences in the evolution of theS ‐locus, and on possible evolutionary mechanisms of generation, proliferation, and deletion ofSLF genes. -
Summary In self‐incompatible Solanaceae, the pistil protein S‐RNase contributes to
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Genome sequencing has uncovered tremendous sequence variation within and between species. In plants, in addition to large variations in genome size, a great deal of sequence polymorphism is also evident in several large multi-gene families, including those involved in the ubiquitin-26S proteasome protein degradation system. However, the biological function of this sequence variation is yet not clear. In this work, we explicitly demonstrated a single origin of retroposed Arabidopsis Skp1-Like ( ASK ) genes using an improved phylogenetic analysis. Taking advantage of the 1,001 genomes project, we here provide several lines of polymorphism evidence showing both adaptive and degenerative evolutionary processes in ASK genes. Yeast two-hybrid quantitative interaction assays further suggested that recent neutral changes in the ASK2 coding sequence weakened its interactions with some F-box proteins. The trend that highly polymorphic upstream regions of ASK1 yield high levels of expression implied negative expression regulation of ASK1 by an as-yet-unknown transcriptional suppression mechanism, which may contribute to the polymorphic roles of Skp1-CUL1-F-box complexes. Taken together, this study provides new evolutionary evidence to guide future functional genomic studies of SCF-mediated protein ubiquitylation.more » « less