Identification and partial amino acid sequences of seven S-RNases associated with self-incompatibility of Japanese pear, Pyrus pyrifolia Nakai

• Published in: Journal of biochemistry (Tokyo) 1996-08, Vol.120 (2), p.326-334
• Main Authors: Ishimizu, T, Sato, Y, Saito, T, Yoshimura, Y, Norioka, S, Nakanishi, T, Sakiyama, F
• Format: Article
• Language: English
• Subjects: Alleles; Amino Acid Sequence; amino acid sequences; Binding Sites - genetics; comparisons; Crosses, Genetic; cultivars; Electrophoresis, Gel, Two-Dimensional; flowers; Fruit - enzymology; Fruit - genetics; Genotype; Japanese pear; Molecular Sequence Data; Plant Proteins - genetics; Plant Proteins - isolation & purification; Pyrus pyrifolia; ribonucleases; Ribonucleases - genetics; Ribonucleases - isolation & purification; S-allele; S-RNase; self incompatibility; sequence alignment; Sequence Homology, Amino Acid; two-dimensional gel electrophoresis
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/oxfordjournals.jbchem.a021417

S-allele-specific proteins (S-proteins) were separated and identified by two-dimensional (2D) gel electrophoresis from the style extract of 14 cultivars of Japanese pear, Pyrus pyrifolia Nakai, which exhibits gametophytic self-incompatibility. These S-proteins were 30-32 kDa basic proteins with putative pIs of 9.6-10.1 and were distinct from the other proteins, which were common for all cultivars examined. Each S-protein was assigned to a given S-genotype based on electrophoretic mobility and the partial amino acid sequence. For S1 - to S7-proteins, five different N-terminal amino acid sequences sharing the YFQFTQ-QY sequence were determined. Since the same N-terminal amino acid sequences were found for both S1- and S7-proteins, and for S3- and S5-proteins, the two S-proteins of each pair were distinguished based on their electrophoretic behavior. The internal amino acid sequences of S2- and S4-proteins, determined for Achromobacter protease I (API) digests, revealed that these proteins are S2- and S4-RNases, respectively. In the cultivar Nijisseiki, these two RNases were expressed from the white bud to mature flower stages when the cultivar acquires and enforces self-incompatibility. Osa-Nijisseiki, a self-compatible mutant of Nijisseiki, produced S2-RNase, but did not produce S2-RNase. The absence of S4-RNase was also observed in self-compatible offsprings derived from Osa-Nijisseiki. These results suggest that Japanese pear in the family Rosaceae possesses a gametophytic self-incompatibility system involving an S-RNase, and that a reduction or lack of expression of S4-RNase in the style is responsible for the self-compatibility of Osa-Nijisseiki.