Department of Biology, McGill University, 1205 Avenue Docteur Penfield, Montreal, QC, Canada, H3A1B1.
Department of Plant Biology, University of Minnesota, St Paul, MN, 55108, USA.
New Phytol. 2017 Dec;216(4):1247-1255. doi: 10.1111/nph.14764. Epub 2017 Sep 14.
The Leavenworthia self-incompatibility locus (S locus) consists of paralogs (Lal2, SCRL) of the canonical Brassicaceae S locus genes (SRK, SCR), and is situated in a genomic position that differs from the ancestral one in the Brassicaceae. Unexpectedly, in a small number of Leavenworthia alabamica plants examined, sequences closely resembling exon 1 of SRK have been found, but the function of these has remained unclear. BAC cloning and expression analyses were employed to characterize these SRK-like sequences. An SRK-positive Bacterial Artificial Chromosome clone was found to contain complete SRK and SCR sequences located close by one another in the derived genomic position of the Leavenworthia S locus, and in place of the more typical Lal2 and SCRL sequences. These sequences are expressed in stigmas and anthers, respectively, and crossing data show that the SRK/SCR haplotype is functional in self-incompatibility. Population surveys indicate that < 5% of Leavenworthia S loci possess such alleles. An ancestral translocation or recombination event involving SRK/SCR and Lal2/SCRL likely occurred, together with neofunctionalization of Lal2/SCRL, and both haplotype groups now function as Leavenworthia S locus alleles. These findings suggest that S locus alleles can have distinctly different evolutionary origins.
石山蒜芥自交不亲和位点（S 位点）由经典芸薹科 S 位点基因（SRK、SCR）的同源基因（Lal2、SCRL）组成，位于与芸薹科祖先位置不同的基因组位置。出人意料的是，在少数石山蒜芥植物中发现了与 SRK 外显子 1 非常相似的序列，但这些序列的功能仍不清楚。采用 BAC 克隆和表达分析来表征这些 SRK 样序列。发现一个 SRK 阳性的细菌人工染色体克隆包含完整的 SRK 和 SCR 序列，彼此靠近，位于石山蒜芥 S 位点的衍生基因组位置，取代了更典型的 Lal2 和 SCRL 序列。这些序列分别在柱头和花药中表达，杂交数据表明，SRK/SCR 单倍型在自交不亲和中具有功能。种群调查表明，<5%的石山蒜芥 S 位点具有这样的等位基因。涉及 SRK/SCR 和 Lal2/SCRL 的祖先易位或重组事件，以及 Lal2/SCRL 的新功能化，可能同时发生，现在这两个单倍型群体都作为石山蒜芥 S 位点等位基因发挥作用。这些发现表明，S 位点等位基因可能具有明显不同的进化起源。
