Sassa H, Nishio T, Kowyama Y, Hirano H, Koba T, Ikehashi H
Faculty of Horticulture, Chiba University, Matsudo, Chiba, Japan.
Mol Gen Genet. 1996 Mar 20;250(5):547-57. doi: 10.1007/BF02174443.
Stylar ribonucleases (RNases) are associated with gametophytic self-incompatibility in two plant families, the Solanaceae and the Rosaceae. The self-incompatibility-associated RNases (S-RNases) of both the Solanaceae and the Rosaceae were recently reported to belong to the T2 RNase gene family, based on the presence of two well-conserved sequence motifs. Here, the cloning and characterization of S-RNase genes from two species of Rosaceae, apple (Malus x domestica) and Japanese pear (Pyrus serotina) is described and these sequences are compared with those of other T2-type RNases. The S-RNases of apple specifically accumulated in styles following maturation of the flower bud. Two cDNA clones for S-RNases from apple, and PCR clones encoding a further two apple S-RNases as well as two Japanese pear S-RNases were isolated and sequenced. The deduced amino acid sequences of the rosaceous S-RNases contained two conserved regions characteristic of the T2/S-type RNases. The sequences showed a high degree of diversity, with similarities ranging from 60.4% to 69.2%. Interestingly, some interspecific sequence similarities were higher than those within a species, possibly indicating that diversification of S-RNase alleles predated speciation in the Rosaceae. A phylogenetic tree of members of the T2/S-RNase superfamily in plants was obtained. The rosaceous S-RNases formed a new lineage in the tree that was distinct from those of the solanaceous S-RNases and the S-like RNases. The findings suggested that self-incompatibility mechanisms in Rosaceae and Solanaceae are similar but arose independently in the course of evolution.
花柱核糖核酸酶（RNases）与茄科和蔷薇科这两个植物科的配子体自交不亲和性相关。最近有报道称，基于两个高度保守的序列基序的存在，茄科和蔷薇科的自交不亲和相关核糖核酸酶（S-RNases）都属于T2核糖核酸酶基因家族。本文描述了蔷薇科两种植物苹果（Malus x domestica）和日本梨（Pyrus serotina）中S-RNase基因的克隆和特性分析，并将这些序列与其他T2型核糖核酸酶的序列进行了比较。苹果的S-RNases在花芽成熟后特异性地在花柱中积累。分离并测序了两个苹果S-RNases的cDNA克隆，以及另外两个编码苹果S-RNases和两个日本梨S-RNases的PCR克隆。蔷薇科S-RNases推导的氨基酸序列包含T2/S型核糖核酸酶的两个保守区域。这些序列显示出高度的多样性，相似度在60.4%至69.2%之间。有趣的是，一些种间序列相似度高于种内相似度，这可能表明S-RNase等位基因的多样化在蔷薇科物种形成之前就已经发生。获得了植物T2/S-RNase超家族成员的系统发育树。蔷薇科的S-RNases在树中形成了一个新的谱系，与茄科的S-RNases和S类核糖核酸酶的谱系不同。这些发现表明，蔷薇科和茄科的自交不亲和机制相似，但在进化过程中是独立出现的。
