Pistil-function breakdown in a new S-allele of European pear, S21*, confers self-compatibility.
European pear exhibits RNase-based gametophytic self-incompatibility controlled by the polymorphic S-locus. S-allele diversity of cultivars has been extensively investigated; however, no mutant alleles conferring self-compatibility have been reported. In this study, two European pear cultivars, 'Abugo' and 'Ceremeño', were classified as self-compatible after fruit/seed setting and pollen tube growth examination. S-genotyping through S-PCR and sequencing identified a new S-RNase allele in the two cultivars, with identical deduced amino acid sequence as S(21), but differing at the nucleotide level. Test-pollinations and analysis of descendants suggested that the new allele is a self-compatible pistil-mutated variant of S(21), so it was named S(21)*. S-genotypes assigned to 'Abugo' and 'Ceremeño' were S(10)S(21)* and S(21)*S(25) respectively, of which S(25) is a new functional S-allele of European pear. Reciprocal crosses between cultivars bearing S(21) and S(21)* indicated that both alleles exhibit the same pollen function; however, cultivars bearing S(21)* had impaired pistil-S function as they failed to reject either S(21) or S (21)* pollen. RT-PCR analysis showed absence of S(21)* -RNase gene expression in styles of 'Abugo' and 'Ceremeño', suggesting a possible origin for S(21)* pistil dysfunction. Two polymorphisms found within the S-RNase genomic region (a retrotransposon insertion within the intron of S(21)* and indels at the 3'UTR) might explain the different pattern of expression between S(21) and S(21)*. Evaluation of cultivars with unknown S-genotype identified another cultivar 'Azucar Verde' bearing S(21)*, and pollen tube growth examination confirmed self-compatibility for this cultivar as well. This is the first report of a mutated S-allele conferring self-compatibility in European pear.
Sanzol
Javier
J
Unidad de Fruticultura, Centro de Investigación y Tecnología Agroalimentaria de Aragón (CITA), Zaragoza, Spain. jsanzol@aragon.es
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005838:Genotype; D008969:Molecular Sequence Data; D009154:Mutation; D011058:Pollen / Q000235:genetics / Q000502:physiology; D011110:Polymorphism, Genetic; D031989:Pyrus / Q000235:genetics* / Q000502:physiology; D012260:Ribonucleases / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D018744:DNA, Plant; D012260:Ribonucleases; C022542:ribonuclease S