Division of Ecology and Evolutionary Biology, University of Glasgow, Glasgow G12 8QQ, UK.
Ann Bot. 2011 Sep;108(4):699-713. doi: 10.1093/aob/mcr157. Epub 2011 Aug 5.
Sporophytic self-incompatibility (SI) prevents inbreeding in many members of the Brassicaceae, and has been well documented in a variety of high-profile species. Arabis alpina is currently being developed as a model system for studying the ecological genetics of arctic-alpine environments, and is the focus of numerous studies on population structure and alpine phylogeography. Although it is highly inbreeding throughout most of its range, populations in central Italy have been identified that show inbreeding coefficients (F(IS)) more typical of self-incompatible relatives. The purpose of this study was to establish whether this variation is due to a functioning SI system.
Outcrossing rate estimates were calculated based on 16 allozyme loci and self-compatibility assessed based on controlled pollinations for six Italian populations that have previously been shown to vary in F(IS) values. Putative SRK alleles (the gene controlling the female component of SI in other Brassicaceae) amplified from A. alpina were compared with those published for other species. Linkage of putative SRK alleles and SI phenotypes was assessed using a diallel cross.
Functional avoidance of inbreeding is demonstrated in three populations of A. alpina, corresponding with previous F(IS) values. The presence is described of 15 putative SRK-like alleles, which show high sequence identity to known alleles from Brassica and Arabidopsis and the high levels of synonymous and nonsynonymous variation typical of genes under balancing selection. Also, orthologues of two other members of the S-receptor kinase gene family, Aly8 (ARK3) and Aly9 (AtS1) are identified. Further to this, co-segregation between some of the putative S-alleles and compatibility phenotypes was demonstrated using a full-sibling cross design.
The results strongly suggest that, as with other species in the Brassicaceae, A. alpina has a sporophytic SI system but shows variation in the strength of SI within and between populations.
孢子体自交不亲和性（SI）阻止了十字花科的许多成员近亲繁殖，并且在各种备受瞩目的物种中都有很好的记录。Arabis alpina 目前正在被开发为研究北极高山环境生态遗传学的模式系统，并且是众多关于种群结构和高山系统地理学研究的重点。尽管在其大部分范围内高度自交，但在意大利中部发现了一些表现出更典型的自交不亲和相关近亲繁殖系数（F(IS)）的种群。本研究的目的是确定这种变异是否是由于一个功能 SI 系统。
基于 16 个同工酶基因座，计算了杂交率估计值，并根据先前显示 F(IS)值不同的六个意大利种群的控制授粉评估了自交亲和性。从 A. alpina 扩增的假定 SRK 等位基因（控制其他十字花科植物雌性 SI 的基因）与其他物种发表的等位基因进行了比较。通过双列杂交评估了假定的 SRK 等位基因和 SI 表型的连锁。
在三个与先前 F(IS)值相对应的 A. alpina 种群中，证明了功能性避免近亲繁殖的存在。描述了 15 个假定的 SRK 样等位基因，它们与 Brassica 和 Arabidopsis 中的已知等位基因具有高度的序列同一性，并且具有平衡选择下典型的高同义和非同义变异水平。此外，还鉴定了 S 受体激酶基因家族的另外两个成员 Aly8（ARK3）和 Aly9（AtS1）的同源物。此外，使用全同胞交叉设计证明了一些假定的 S 等位基因和相容性表型之间的共分离。
结果强烈表明，与十字花科的其他物种一样，A. alpina 具有孢子体 SI 系统，但在种群内和种群之间的 SI 强度存在差异。
