SKP1-like protein, CrSKP1-e, interacts with pollen-specific F-box proteins and assembles into SCF-type E3 complex in ‘Wuzishatangju’ (Citrus reticulata Blanco) pollen

Abstract

S-ribonuclease (S-RNase)-based self-incompatibility (SI) mechanisms have been extensively studied in Solanaceae, Rosaceae and Plantaginaceae. S-RNase-based SI is controlled by two closely related genes, S-RNase and S-locus F-box (SLF), located at a polymorphic S-locus. In the SI system, the SCF-type (SKP1-CUL1-F-box-RBX1) complex functions as an E3 ubiquitin ligase complex for ubiquitination of non-self S-RNase. Pummelo (Citrus grandis) and several mandarin cultivars are suggested to utilize an S-RNase-based SI system. However, the molecular mechanism of the non-S-factors involved in the SI reaction is not straightforward in Citrus. To investigate the SCF-type E3 complex responsible for the SI reaction in mandarin, SLF, SKP1-like and CUL1 candidates potentially involved in the SI reaction of ‘Wuzishatangju’ (Citrus reticulata Blanco) were identified based on the genome-wide identification and expression analyses. Sixteen pollen-specific F-box genes (CrFBX1-CrFBX16), one pollen-specific SKP1-like gene (CrSKP1-e) and two CUL1 genes (CrCUL1A and CrCUL1B) were identified and cloned from ‘Wuzishatangju’. Yeast two-hybrid (Y2H) and in vitro binding assays showed that five CrFBX proteins could bind to CrSKP1-e, which is an ortholog of SSK1 (SLF-interacting-SKP1-like), a non-S-factor responsible for the SI reaction. Luciferase complementation imaging (LCI) and in vitro binding assays also showed that CrSKP1-e interacts with the N-terminal region of both CrCUL1A and CrCUL1B. These results indicate that CrSKP1-e may serve as a functional member of the SCF-type E3 ubiquitin ligase complex in ‘Wuzishatangju’.

Gene coexpression analysis reveals key pathways and hub genes related to late-acting self-incompatibility in Camellia oleifera

“…Protein hydrolysis mediated by ubiquitination plays an important role in the GSI reaction, and this mechanism was first proposed in the study of SI in petunia ( Zhang et al., 2016 ; Chen et al., 2018 ; Ren et al., 2020 ; Zhao et al., 2021 ). In self-incompatible Petunia and Antirrhinum species, S-RNase , which is the S-determinant of pistils, could be recognized by pollen S-determinant SLFs and ubiquitinated by forming functional SCF complexes in a nonself-recognition manner and then degraded by the 26S proteasome pathway, restricting the cytotoxicity of S-RNase and allowing pollen tubes to grow normally ( Qiao et al., 2004 ; Hua and Kao, 2006 ; Hua et al., 2008 ; Kubo et al., 2010 ; Liu et al., 2014 ).…”

Comparative transcriptome profiling and weighted gene co-expression network analysis to identify core genes in maize (Zea mays L.) silks infected by multiple fungi

“…The results also suggest that it could change the metabolic activity during fungal invasion in maize silks ( Vina-Vilaseca et al., 2011 ; Yang et al., 2014 ). It is reported that SKIP19 protein genes influence and respond to biotic and abiotic stress and play a key role in soybean pollen tube germination and salt and drought tolerance ( Chen et al., 2008 ; Yang et al., 2008 ; Chang et al., 2009 ; Ren et al., 2020 ). There is variable expression in Fg and Um infections, but the strong expression in Fv and Ta infections confirms the SKIP19 gene’s role in Z. mays Fv and Ta defense.…”

The Identification and Analysis of the Self-Incompatibility Pollen Determinant Factor SLF in Lycium barbarum

“…This mechanism is usually governed by a single S locus, which comprises at least two genes that are closely associated and exhibit tissue specificity, encoding the male (pollen) and female (stigma) S-determinants [7,8]. Although research has shown that plant self-incompatibility is regulated by the S-RNase gene (responsible for stigma determinants) and the SLF (S-locus F-box) gene, which encodes F-box proteins, in families such as Solanaceae, Plantaginaceae, and Rosaceae [9][10][11], studies have revealed that the functions of SLF/SFB genes vary among these families. In Rosaceae, SLF gene mutations or losses in the Prunus genus can lead to the self-S-RNase accepting pollen, whereas in Solanaceae and Plantaginaceae, SLF genes act as degradative factors to break down non-self S-RNase [5,12].…”