Shimizu Kentaro K, Shimizu-Inatsugi Rie, Tsuchimatsu Takashi, Purugganan Michael D
Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, CH-8008, Zurich, Switzerland.
Mol Ecol. 2008 Jan;17(2):704-14. doi: 10.1111/j.1365-294X.2007.03605.x. Epub 2007 Dec 20.
The evolution from outcrossing based on self-incompatibility (SI) to a selfing system is one of the most prevalent transitions in flowering plants. It has been suggested that the loss of SI in Arabidopsis thaliana is associated with pseudogene formation at the SCR male component of the S locus. Recent work, however, suggests that alternative alleles with large deletions at the S locus are also present and may be responsible for the evolution of self-compatibility in this species. We demonstrate that most of these deletion alleles are evolutionarily derived from an S haplotype (haplogroups A) that already possessed the SCR pseudogene. This haplotype and its deletion variants are nearly fixed in Europe. Together with previous transgenic data, these results suggest that the pseudogenization of PsiSCR1 gene changed the SI phenotype in the majority of A. thaliana accessions, and was a critical step in the evolution of selfing in this species. Two other haplogroups (B and C) were also identified, the former of which contains a novel and possibly functional SCR allele. In contrast to haplogroups A, these two haplogroups are found primarily in Africa and Asia. These results suggest that self-compatibility, which appears to be fixed in this species, arose multiple times with different genetic bases, and indicates that a species-specific trait is associated with parallel evolution at the molecular level.
从基于自交不亲和性（SI）的异交到自交系统的演化是开花植物中最普遍的转变之一。有人提出，拟南芥中SI的丧失与S位点的SCR雄性成分处假基因的形成有关。然而，最近的研究表明，S位点存在大量缺失的替代等位基因也可能存在，并且可能是该物种自交亲和性进化的原因。我们证明，这些缺失等位基因中的大多数在进化上源自已经拥有SCR假基因的S单倍型（单倍群A）。这种单倍型及其缺失变体在欧洲几乎是固定的。结合先前的转基因数据，这些结果表明PsiSCR1基因的假基因化改变了大多数拟南芥种质的SI表型，并且是该物种自交进化中的关键步骤。还鉴定出另外两个单倍群（B和C），前者包含一个新的且可能具有功能的SCR等位基因。与单倍群A不同，这两个单倍群主要分布在非洲和亚洲。这些结果表明，该物种中似乎固定的自交亲和性以不同的遗传基础多次出现，这表明物种特异性性状与分子水平上的平行进化有关。
