**7.1. SSK1**

F-box proteins often serve as adaptors that bind specific substrate proteins to the SCF (Skp1- Cullin-F-box) E3 ubiquitin ligase complex [99]. This raised the possibility of whether the SLF involved in the SI also participates in an SCF complex, mediating S-RNase ubiquitination. Identification of other components in such a putative complex is obviously necessary to address this question. SSK1 (SLF-interacting SKP1-like1), a homolog of SKP1, was originally isolated in *A. hispanicum* through a yeast two-hybrid screening against a pollen cDNA library using AhSLF-S2 as bait [42] (Fig. 4.).

Pull-down assays encouraged that AhSSK1 could be an adaptor that connects SLF to CUL1 protein. Therefore, it can be thought that SLF and SSK1 will tend to be recruited to some anonical complicated SCF, which could be responsible for S-RNase ubiquitination.

**Figure 4.** Protein interactions in gametophytic self-incompatibility [110]

#### **7.2. SBP1**

In trying to isolate the real pollen S, Sims and Ordanic (2001) screened a yeast twohybrid library from mature pollen of *P. hybrida* making use of *P. hybrida* S1-RNase because bait, and identified any gene known as PhSBP1 (S-RNase Presenting Protein1). Its homolog in *S. chacoense* was obtained depending on a comparable approach [95]. Nonetheless, the SBP1 gene displayed no haplotype polymorphismand was found to be expressed in almost all tissues. Additionally, it has been unlinked for the S-locus and so is unlikely to encode the real pollen S-determinant. Nonetheless, sequence research revealed that SBP1 has a RING-finger website, which can be characteristic of E3 ubiquitin ligases [60], indicating a possible role of SBP1 in S-RNase ubiquitination and degradation [95, 110-113]. Oddly enough, *P. inflata* SBP1 (PiSBP1) has recently been shown to interact together with PiSLFs, Pi CUL1 and an ubiquitin-conjugating enzyme, along with a novel E3 ligase complex continues to be suggested, with the possibility that PiSBP1 has a mixed role in SKP1 and RBX1 [111, 40].
