Molecular variation at the self-incompatibility locus in natural populations of the genera Antirrhinum and Misopates

Abstract

The self-incompatibility system of flowering plants is a classic example of extreme allelic polymorphism maintained by frequency-dependent selection. We used primers designed from three published Antirrhinum hispanicum Sallele sequences in PCR reactions with genomic DNA of plants sampled from natural populations of Antirrhinum and Misopates species. Not surprisingly, given the polymorphism of S-alleles, only a minority of individuals yielded PCR products of the expected size. These yielded 35 genomic sequences, of nine different sequence types of which eight are highly similar to the A. hispanicum S-allele sequences, and one to a very similar unpublished Antirrhinum S-like

Allelic diversity of S-RNase at the self-incompatibility locus in natural flowering cherry populations (Prunus lannesiana var. speciosa)

“…Richman et al (1995Richman et al ( , 1996a and Richman (2000) directly determined the putative S-genotypes of plants sampled from Solanaceae by sequence polymorphism at the S-RNase locus. Vieira and Charlesworth (2002) revealed sequence variation at the S-locus in Scrophulariaceae. In the Rosaceae, molecular techniques for identifying S-alleles by allele-specific PCR are now being developed for crossing and breeding of fruit cultivars (Sonneveld et al, 2001;Wiersma et al, 2001).…”

Evidence for rare recombination at the gametophytic self-incompatibility locus

“…Introns are known in gametophytic S-allele sequences of several species (reviewed in Vieira and Charlesworth, 2002). All S-allele genomic sequences so far obtained from species of Solanaceae (N ¼ 14), Rosaceae (N ¼ 18) and Scrophulariaceae (N ¼ 36) have one intron in the HVa region, and in the genomic sequences from Scrophulariaceae the intron lengths vary (Vieira and Charlesworth, 2002).…”

“…Most are partial sequences between conserved regions C2 and C5 (see Richman et al, 1996;Richman and Kohn, 2000;Vieira and Charlesworth, 2002). For each species, we combined the cDNA sequences with aminoacid sequences from exons deduced from genomic SRNase gene sequences, where available (see Table 2).…”

“…As alleles may persist for long periods of time, large sequence differences can develop if recombination between the S-alleles does not occur, or is very rare, consistent with the extreme differences found between allele sequences at incompatibility loci (eg Richman et al, 1996;Awadalla and Charlesworth, 1999;Richman and Kohn 2000;Vieira and Charlesworth, 2002). Hypervariability in certain regions of the S-locus has been taken as indicating parts of the gene that encode the regions of the stigmatic S protein involved in specificity differences (reviewed in Awadalla and Charlesworth, 1999).…”

“…Without such exchange, higher and lower variabilities can arise, due to differences in selective constraints, but the balanced polymorphism at the S-locus will increase variability throughout the gene, as is indeed observed for silent and intron sites as well as for nonsynonymous sites (Awadalla and Charlesworth, 1999;Schierup et al, 2001;Vieira and Charlesworth, 2002). It is therefore important to determine whether S-loci show recombination or not.…”