Abstract
It has been proved that the gametophytic self-incompatibility (GSI), mainly exists in Rosaceae and Solanaceae, is controlled by S genes, which are two tightly linked genes located at highly polymorphic S-locus: the S-RNase for pistil specificity and the F-box gene (SFB/SLF) for pollen specificity, respectively. However, the roles of those genes in SI of peach are still a subject of extensive debate. In our study, we selected 37 representative varieties according to the evolution route of peach and identified their S genotypes. We cloned pollen determinant genes mutated PperSFB1m, PperSFB2m, PperSFB4m, and normal PperSFB2, and style determinant genes PperS1-RNase, PperS2-RNase, PperS2m-RNase, and PperS4-RNase. The mutated PperSFBs encode truncated SFB proteins due to a fragment insertion. The truncated PperSFBs and normal PperSFB2 interacted with PperS-RNases demonstrated by Y2H. Normal PperSFB2 was divided into four parts: box, box-V1, V1-V2, and HVa-HVb. The box domain of PperSFB2 did not interact with PperS-RNases, both of the box-V1 and V1-V2 had interactions with PperS-RNases, while the hypervariable region of PperSFB2 HVa-HVb only interacted with PperS2-RNase showed by Y2H and BiFC assay. Bioinformatics analysis of peach genome revealed that there were other F-box genes located at S-locus, and of which three F-box genes were specifically expressed in pollen, named as PperSLFL1, PperSLFL2, and PperSLFL3, respectively. In phylogenetic analysis PperSLFLs clustered with Maloideae SFBB genes, and PperSFB genes were clustered into the other group with other SFB genes of Prunus. Protein interaction analysis revealed that the three PperSLFLs interacted with PperSSK1 and PperS-RNases with no allelic specificity. In vitro ubiquitination assay showed that PperSLFLs could tag ubiquitin molecules onto PperS-RNases. The above results suggest that three PperSLFLs are the appropriate candidates for the “general inhibitor,” which would inactivate the S-RNases in pollen tubes, involved in the self-incompatibility of peach.
Highlights
Self-incompatibility (SI) allows the pistil to reject genetically related pollen and promotes out-crossing in flowering plants, which maintains plant genetic diversity (de Nettancourt, 2001)
S2-RNase and S2m-RNase were identified in the original species “Guang He Tao,” indicating that the mutation of S2-RNase had occurred before the formation of peach cultivars
The results showed that the mutated PperSFBs and normal PperSFB2 interacted with all the PperS-RNases cloned in the study, and these interactions displayed no S allelic specificity, while there was no interaction between PperPA1 and PperSFBs (Figure 2A)
Summary
Self-incompatibility (SI) allows the pistil to reject genetically related pollen and promotes out-crossing in flowering plants, which maintains plant genetic diversity (de Nettancourt, 2001). Many plants in Solanaceae, Rosaceae, and Plantaginaceae exhibit S-RNase-based gametophytic self-incompatibility (GSI). GSI is controlled by at least two genes in S-locus: one is pistil-part, a highly polymorphic S gene encoding extracellular ribonuclease called S-RNase (Huang et al, 1994), and the other is pollen-part specific S gene, which is tightly linked to the S-RNase (Entani et al, 2003). The pollen S genes of the S-RNase-based GSI are F-box genes called SLF (S-locus F-box) in Solanaceae and Plantaginaceae and SFB (S haplotype-specific F-box) in Prunus (Lai et al, 2002; Ushijima et al, 2003; Yamane et al, 2003; Sijacic et al, 2004; Sassa et al, 2010; Tao and Iezzoni, 2010; Meng et al, 2011). How F-box proteins discriminate between self and non-self S-RNases in pollen tubes of Rosaceae is still largely unknown
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