Ishimizu T, Shinkawa T, Sakiyama F, Norioka S
Division of Protein Chemistry, Institute for Protein Research, Osaka University, Suita, Japan.
Plant Mol Biol. 1998 Aug;37(6):931-41. doi: 10.1023/a:1006078500664.
We isolated cDNA clones encoding five S-RNases (S1-, S3-, S5-, S6-, S7-RNases) from pistils of Pyrus pyrifolia (Japanese pear), a member of the Rosaceae. Their amino acid sequences were aligned with those of other rosaceous S-RNases sequenced so far. A total of 76 conserved amino acid residues were stretched throughout the sequence, but were absent from the 51-66 region which was designated the hypervariable (HV) region. The phylogenetic tree of rosaceous S-RNases showed that S-RNase polymorphism predated the divergence of Pyrus and Malus. Pairwise comparison of these S-RNases detected two highly homologous pairs, P. pyrifolia S1- and S4-RNases (90.0%) and P. pyrifolia S3- and S5-RNases (95.5%). The positions of amino acid substitutions between S1- and S4-RNases were spread over the entire region, but in the pair of S3- and S5-RNases, amino acid substitutions were found in the 21-90 region including the HV region. The substitutions in this restricted region appear to be sufficient to discriminate between S3 and S5 pollen and to trigger the self-incompatible reaction.
我们从蔷薇科植物梨（Pyrus pyrifolia，日本梨）的雌蕊中分离出编码5种S-核酸酶（S1-、S3-、S5-、S6-、S7-核酸酶）的cDNA克隆。将它们的氨基酸序列与迄今已测序的其他蔷薇科S-核酸酶的序列进行比对。整个序列共有76个保守氨基酸残基，但在51-66区域没有，该区域被指定为高变（HV）区。蔷薇科S-核酸酶的系统发育树表明，S-核酸酶多态性早于梨属和苹果属的分化。对这些S-核酸酶进行成对比较，发现了两对高度同源的序列，即梨S1-核酸酶和S4-核酸酶（同源性90.0%）以及梨S3-核酸酶和S5-核酸酶（同源性95.5%）。S1-核酸酶和S4-核酸酶之间氨基酸替换的位置分布在整个区域，但在S3-核酸酶和S5-核酸酶这一对中，在包括HV区在内的21-90区域发现了氨基酸替换。在这个受限区域的替换似乎足以区分S3和S5花粉，并引发自交不亲和反应。
