Identification, Evolutionary Patterns and Intragenic Recombination of the Gametophytic Self Incompatibility Pollen Gene (SFB) in Tunisian Prunus Species (Rosaceae)

Abstract

Plum (Prunus L.) is a species which exhibits a gametophytic self-incompatibility system BGSI^as the majority of species belonging to the Rosaceae family. The selfincompatibility system is genetically controlled by a single and multiallelic locus named the S locus which contains at least two linked genes, one is expressed in pistil named SRNase gene, the second is expressed in pollen called SFB gene (S-haplotype-specific F-box). In this work, 16 Tunisian plums cultivars were considered. The PCR amplification of the SFB gene and the automatic sequencing of amplicons have identified the SFB alleles of each variety. The analysis of both nucleotide and peptide sequences shows the high degree of polymorphism in SFB alleles. Moreover, the mutational events show a high proportion of transversions and nonsynonymous mutations. Furthermore, sequence analysis has proved that the intragenic recombination can occur within the SFB gene. Regions characterizing the SFB gene: the F-Box conserved domain, and three variable and two hypervariable regions were detected. These (hyper) variable regions seem to be hydrophilic or at least not strongly hydrophobic. Dendrograms were basically constructed on nucleotide, and peptide sequences provide relationships and similarity of cultivars representing the same allele independently from geographic origin and provide a valuable scenario on the evolutionary history of the SFB gene. Moreover, the neutrality tests show that the SFB gene is the seat of positive selection that plays in favor of the rare alleles. Finally, the study of the relationship between the SFB gene and the S-RNase gene shows that both genes are contiguous and have an opposite transcription direction. To conclude, the study of self-incompatibility genes, as ideal markers of the self-incompatibility system, forms an essential node for understanding the origin and evolution of this system.

Analysis of Self-Incompatibility and Genetic Diversity in Diploid and Hexaploid Plum Genotypes

“…These results highlight the allelic singularity and the rich variability characterizing the Tunisian plum germplasm as an unexplored source of genetic variation. In fact, several Tunisian Prunus varieties have disappeared during the last years due to the lack of programs addressed to preserve these local germplasm (Nabli, 2011; Abdallah et al, 2016; Baraket et al, 2019), which require the establishment of appropriate germplasm collections. The results obtained in this study could complement previous work of Baraket et al (2019) in which 23 Tunisian plums accessions were phenotypically and genetically characterized.…”

Research advances in and prospects of ornamental plant genomics

“…According to different hereditary patterns of pollen incompatibility phenotypes, the regeneration disorder whereby plants reject self-pollen can be divided into sporophytic self-incompatibility and gametophytic self-incompatibility 95 . Various flowers of the Rosaceae family, including P. mume , P. yedoensis and P. persica , all exhibit gametophytic self-incompatibility, which is controlled by an S-locus with multiple alleles, including two linked genes: one is the S-RNase gene specifically expressed in pistil tissue, and the other is the S-haplotype-specific F-box gene specifically expressed in pollen 96 . In Tarenaya hassleriana , three syntenic regions containing most of the genes of the S-locus were found, and it was assumed that the single-copy ancestral region contained homologs of Pub8 , ARK3 , and B120 23 .…”

Overcoming self-incompatibility in grasses: a pathway to hybrid breeding

“…Similarly to the Z locus in grasses, the S locus in the Rosaceae family is located in a region were recombination is not suppressed though the male and female determinants are tightly linked, being less than 550 bp apart (Sapir et al, 2007). Nevertheless, evidence for recombination within the S locus was also found in Rosaceae (Vieira et al, 2003;Ortega et al, 2006;Donia et al, 2015). Very low recombination rates were suggested in the S locus region of the Brassicaceae (Charlesworth et al, 2006) though recombination was detected within the S locus complex of genes but not between the male and female determinants (SP11 and SRK, respectively) (Takuno et al, 2007).…”

“…In Solanum chacoense (Solanaceae), new specificities can arise from few or even single base-pair substitutions at the hypervariable regions of the S-RNase gene (Saba-El-Leil et al, 1994;Matton et al, 1997;Matton et al, 1999) and thus, mutations may result in new functional alleles. Likewise, point mutations at the hypervariable regions of the F-box gene in Prunus species, contribute to allele diversity (Donia et al, 2015). Such a new specificity in the S-RNase gene would lead to non-recognition by the stigma of any self-pollen.…”