Department of Biology, University of Scranton, Scranton, PA 18508, USA.
Genetics. 2013 Mar;193(3):985-94. doi: 10.1534/genetics.112.146787. Epub 2013 Jan 10.
The switch from an outcrossing mode of mating enforced by self-incompatibility to self-fertility in the Arabidopsis thaliana lineage was associated with mutations that inactivated one or both of the two genes that comprise the self-incompatibility (SI) specificity-determining S-locus haplotype, the S-locus receptor kinase (SRK) and the S-locus cysteine-rich (SCR) genes, as well as unlinked modifier loci required for SI. All analyzed A. thaliana S-locus haplotypes belong to the SA, SB, or SC haplotypic groups. Of these three, the SC haplotype is the least well characterized. Its SRKC gene can encode a complete open-reading frame, although no functional data are available, while its SCRC sequences have not been isolated. As a result, it is not known what mutations were associated with inactivation of this haplotype. Here, we report on our analysis of the Lz-0 accession and the characterization of its highly rearranged SC haplotype. We describe the isolation of its SCRC gene as well as the subsequent isolation of SCRC sequences from other SC-containing accessions and from the A. lyrata S36 haplotype, which is the functional equivalent of the A. thaliana SC haplotype. By performing transformation experiments using chimeric SRK and SCR genes constructed with SC- and S36-derived sequences, we show that the SRKC and SCRC genes of Lz-0 and at least a few other SC-containing accessions are nonfunctional, despite SCRC encoding a functional full-length protein. We identify the probable mutations that caused the inactivation of these genes and discuss our results in the context of mechanisms of S-locus inactivation in A. thaliana.
拟南芥谱系中由自交不亲和性强制的异交交配模式向自交可育的转变与突变有关，这些突变使构成自交不亲和性（SI）特异性决定 S 座单倍型的两个基因之一或两个基因失活，即 S 座受体激酶（SRK）和 S 座富含半胱氨酸（SCR）基因，以及 SI 所需的不连锁修饰基因座。所有分析的拟南芥 S 座单倍型都属于 SA、SB 或 SC 单倍型组。在这三个中，SC 单倍型的特征最少。其 SRKC 基因可以编码完整的开放阅读框，尽管没有功能数据，但其 SCRC 序列尚未分离。因此，尚不清楚与该单倍型失活相关的突变是什么。在这里，我们报告了对 Lz-0 品系的分析及其高度重排的 SC 单倍型的特征。我们描述了其 SCRC 基因的分离以及随后从其他含有 SC 的品系和 A. lyrata S36 单倍型中分离 SCRC 序列，S36 单倍型是拟南芥 SC 单倍型的功能等效物。通过使用带有 SC 和 S36 衍生序列构建的嵌合 SRK 和 SCR 基因进行转化实验，我们表明 Lz-0 和至少其他几个含有 SC 的品系的 SRKC 和 SCRC 基因失活，尽管 SCRC 编码功能完整的全长蛋白。我们确定了导致这些基因失活的可能突变，并在拟南芥 S 座失活机制的背景下讨论了我们的结果。
