Recognition of S-RNases by an S locus F-box like protein and an S haplotype-specific F-box like protein in the Prunus-specific self-incompatibility system
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S-RNase was demonstrated to be predominantly recognized by an S locus F-box-like protein and an S haplotype-specific F-box-like protein in compatible pollen tubes of sweet cherry.
Self-incompatibility (SI) is a reproductive barrier that rejects self-pollen and inhibits self-fertilization to promote outcrossing. In Solanaceae and Rosaceae, S-RNase-based gametophytic SI (GSI) comprises S-RNase and F-box protein(s) as the pistil and pollen S determinants, respectively. Compatible pollen tubes are assumed to detoxify the internalized cytotoxic S-RNases to maintain growth. S-RNase detoxification is conducted by the Skp1-cullin1-F-box protein complex (SCF) formed by pollen S determinants, S locus F-box proteins (SLFs), in Solanaceae. In Prunus, the general inhibitor (GI), but not pollen S determinant S haplotype-specific F-box protein (SFB), is hypothesized to detoxify S-RNases. Recently, SLF-like proteins 1–3 (SLFL1–3) were suggested as GI candidates, although it is still possible that other proteins function predominantly in GI. To identify the other GI candidates, we isolated four other pollen-expressed SLFL and SFB-like (SFBL) proteins PavSLFL6, PavSLFL7A, PavSFBL1, and PavSFBL2 in sweet cherry. Binding assays with four PavS-RNases indicated that PavSFBL2 bound to PavS1, 6-RNase while the others bound to nothing. PavSFBL2 was confirmed to form an SCF complex in vitro. A co-immunoprecipitation assay using the recombinant PavS6-RNase as bait against pollen extracts and a mass spectrometry analysis identified the SCF complex components of PavSLFLs and PavSFBL2, M-locus-encoded glutathione S-transferase (MGST), DnaJ-like protein, and other minor proteins. These results suggest that SLFLs and SFBLs could act as predominant GIs in Prunus-specific S-RNase-based GSI.
KeywordsGeneral inhibitor Prunus Self-incompatibility SFBL SLFL S-RNase
This work was supported by a Grant-in-Aid (No. 16H06184) for Young Scientists (A) from the Japan Society for the Promotion of Science to D. M.
D. M. designed and conducted the experiments and drafted the manuscript. Both authors edited the manuscript and approved the final manuscript.
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Conflict of interest
The authors declare that they have no conflict of interest.
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