The collaborative non‐self‐recognition model for S‐
- Award ID(s):
- NSF-PAR ID:
- Publisher / Repository:
- Date Published:
- Journal Name:
- The Plant Journal
- Page Range / eLocation ID:
- p. 1348-1368
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The collaborative non‐self‐recognition model for S‐
RNase‐based self‐incompatibility predicts that multiple S‐locus F‐box proteins ( SLFs) produced by pollen of a given S‐haplotype collectively mediate ubiquitination and degradation of all non‐self S‐ RNases, but not self S‐ RNases, in the pollen tube, thereby resulting in cross‐compatible pollination but self‐incompatible pollination. We had previously used pollen extracts containing GFP‐fused S2‐ SLF1 ( SLF1 with an S2‐haplotype) of Petunia inflatafor co‐immunoprecipitation (Co‐ IP) and mass spectrometry ( MS), and identified Pi CUL1‐P (a pollen‐specific Cullin1), Pi SSK1 (a pollen‐specific Skp1‐like protein) and Pi RBX1 (a conventional Rbx1) as components of the SCFS2– SLF1complex. Using pollen extracts containing Pi SSK1: FLAG: GFPfor Co‐ IP/ MS, we identified two additional SLFs ( SLF4 and SLF13) that were assembled into SCFSLFcomplexes. As 17 genes ( SLF to SLF1 ) have been identified in SLF17 S2and S3pollen, here we examined whether all 17 SLFs are assembled into similar complexes and, if so, whether these complexes are unique to SLFs. We modified the previous Co‐ IP/ MSprocedure, including the addition of style extracts from four different S‐genotypes to pollen extracts containing Pi SSK1: FLAG: GFP, to perform four separate experiments. The results taken together show that all 17 SLFs and an SLF‐like protein, SLFLike1 (encoded by an S‐locus‐linked gene), co‐immunoprecipitated with Pi SSK1: FLAG: GFP. Moreover, of the 179 other F‐box proteins predicted by S2and S3pollen transcriptomes, only a pair with 94.9% identity and another pair with 99.7% identity co‐immunoprecipitated with Pi SSK1: FLAG: GFP. These results suggest that SCFSLFcomplexes have evolved specifically to function in self‐incompatibility.
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
Abstract In Petunia (Solanaceae family), self-incompatibility (SI) is regulated by the polymorphic S-locus, which contains the pistil-specific S-RNase and multiple pollen-specific S-Locus F-box (SLF) genes. SLFs assemble into E3 ubiquitin ligase complexes known as Skp1–Cullin1–F-box complexes (SCFSLF). In pollen tubes, these complexes collectively mediate ubiquitination and degradation of all nonself S-RNases, but not self S-RNase, resulting in cross-compatible, but self-incompatible, pollination. Using Petunia inflata, we show that two pollen-expressed Cullin1 (CUL1) proteins, PiCUL1-P and PiCUL1-B, function redundantly in SI. This redundancy is lost in Petunia hybrida, not because of the inability of PhCUL1-B to interact with SSK1, but due to a reduction in the PhCUL1-B transcript level. This is possibly caused by the presence of a DNA transposon in the PhCUL1-B promoter region, which was inherited from Petunia axillaris, one of the parental species of Pe. hybrida. Phylogenetic and syntenic analyses of Cullin genes in various eudicots show that three Solanaceae-specific CUL1 genes share a common origin, with CUL1-P dedicated to S-RNase-related reproductive processes. However, CUL1-B is a dispersed duplicate of CUL1-P present only in Petunia, and not in the other species of the Solanaceae family examined. We suggest that the CUL1s involved (or potentially involved) in the SI response in eudicots share a common origin.more » « less
Distyly is an intriguing floral adaptation that increases pollen transfer precision and restricts inbreeding. It has been a model system in evolutionary biology since Darwin. Although the
S‐locus determines the long‐ and short‐styled morphs, the genes were unknown in Turnera. We have now identified these genes.
We used deletion mapping to identify, and then sequence,
BACclones and genome scaffolds to construct S/shaplotypes. We investigated candidate gene expression, hemizygosity, and used mutants, to explore gene function.
s‐haplotype possessed 21 genes collinear with a region of chromosome 7 of grape. The S‐haplotype possessed three additional genes and two inversions. Tswas expressed in filaments and anthers, SPH1 Tsin anthers and YUC6 Tsin pistils. Long‐homostyle mutants did not possess BAHD Tsand a short‐homostyle mutant did not express BAHD Ts. SPH1
Three hemizygous genes appear to determine S‐morph characteristics in
T. subulata. Hemizygosity is common to all distylous species investigated, yet the genes differ. The pistil candidate gene, Ts, differs from that of BAHD Primula, but both may inactivate brassinosteroids causing short styles. Tsis involved in auxin synthesis and likely determines pollen characteristics. YUC6 Tsis likely involved in filament elongation. We propose an incompatibility mechanism involving SPH1 Tsand YUC6 Ts. BAHD
Soybean growers widely use the
Resistance to 1 ( Heterodera glycines Rhg1) locus to reduce yield losses caused by soybean cyst nematode (SCN). Rhg1is a tandemly repeated four gene block. Two classes of SCN resistance‐conferring Rhg1haplotypes are recognized: rhg1‐a(“Peking‐type,” low‐copy number, three or fewer Rhg1repeats) and rhg1‐b(“PI 88788‐type,” high‐copy number, four or more Rhg1repeats). The rhg1‐aand rhg1‐bhaplotypes encode α‐SNAP (alpha‐ Soluble NSF Attachment Protein) variants α‐SNAP Rhg1LC and α‐SNAP Rhg1HC, respectively, with differing atypical C‐terminal domains, that contribute to SCN resistance. Here we report that rhg1‐asoybean accessions harbor a copia retrotransposon within their Rhg1 Glyma.18G022500(α‐SNAP‐encoding) gene. We termed this retrotransposon “ RAC,” for Rhg1 alpha‐SNAP copia. Soybean carries multiple RAC‐like retrotransposon sequences. The Rhg1 RACinsertion is in the Glyma.18G022500genes of all true rhg1‐ahaplotypes we tested and was not detected in any examined rhg1‐bor Rhg1WT(single‐copy) soybeans. RACis an intact element residing within intron 1, anti‐sense to the rhg1‐a α‐SNAPopen reading frame. RAChas intrinsic promoter activities, but overt impacts of RACon transgenic α‐SNAP Rhg1LC mRNA and protein abundance were not detected. From the native rhg1‐a RAC+genomic context, elevated α‐SNAP Rhg1LC protein abundance was observed in syncytium cells, as was previously observed for α‐SNAP Rhg1HC (whose rhg1‐bdoes not carry RAC). Using a SoySNP50K SNP corresponding with RACpresence, just ~42% of USDA accessions bearing previously identified rhg1‐aSoySNP50K SNP signatures harbor the RACinsertion. Subsequent analysis of several of these putative rhg1‐aaccessions lacking RACrevealed that none encoded α‐SNAPRhg1LC, and thus, they are not rhg1‐a. rhg1‐ahaplotypes are of rising interest, with Rhg4, for combating SCN populations that exhibit increased virulence against the widely used rhg1‐bresistance. The present study reveals another unexpected structural feature of many Rhg1loci, and a selectable feature that is predictive of rhg1‐ahaplotypes.