Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA.
Genetics. 2010 Feb;184(2):455-65. doi: 10.1534/genetics.109.108175. Epub 2009 Nov 23.
Characterizing the genetic and molecular basis of hybrid incompatibilities is a first step toward understanding their evolutionary origins. We fine mapped the nuclear restorer (Rf) of cytoplasm-dependent anther sterility in Mimulus hybrids by identifying and targeting regions of the Mimulus guttatus genome containing large numbers of candidate pentatricopeptide repeat genes (PPRs). The single Mendelian locus Rf was first isolated to a 1.3-cM region on linkage group 7 that spans the genome's largest cluster of PPRs, then split into two tightly linked loci (Rf1 and Rf2) by <10 recombination events in a large (N = 6153) fine-mapping population. Progeny testing of fertile recombinants demonstrated that a dominant M. guttatus allele at each Rf locus was sufficient to restore fertility. Each Rf locus spans a physical region containing numerous PPRs with high homology to each other, suggesting recent tandem duplication or transposition. Furthermore, these PPRs have higher homology to restorers in distantly related taxa (petunia and rice) than to PPRs elsewhere in the Mimulus genome. These results suggest that the cytoplasmic male sterility (CMS)-PPR interaction is highly conserved across flowering plants. In addition, given our theoretical understanding of cytonuclear coevolution, the finding that hybrid CMS results from interactions between a chimeric mitochondrial transcript that is modified by Rf loci identified as PPRs is consistent with a history of selfish mitochondrial evolution and compensatory nuclear coevolution within M. guttatus.
描述杂种不亲和性的遗传和分子基础是理解其进化起源的第一步。我们通过鉴定和靶向包含大量候选五肽重复基因 (PPR) 的 Mimulus guttatus 基因组区域，精细定位了依赖细胞质的花药不育的核恢复基因 (Rf)。单个孟德尔基因 Rf 最初被分离到连锁群 7 上的 1.3-cM 区域，该区域跨越基因组中最大的 PPR 簇，然后通过在大型（N = 6153）精细映射群体中 10 次以内的重组事件分裂成两个紧密连锁的基因座 (Rf1 和 Rf2)。对可育重组体的后代进行测试表明，每个 Rf 基因座的显性 M. guttatus 等位基因足以恢复育性。每个 Rf 基因座跨越一个包含许多 PPR 的物理区域，这些 PPR 彼此之间具有高度同源性，表明最近发生了串联重复或转座。此外，这些 PPR 与远缘分类群（矮牵牛和水稻）中的恢复基因具有更高的同源性，而与 Mimulus 基因组其他区域的 PPR 相比则较低。这些结果表明，细胞质雄性不育 (CMS)-PPR 相互作用在开花植物中高度保守。此外，鉴于我们对核质协同进化的理论理解，杂种 CMS 是由 Rf 基因座识别的嵌合线粒体转录本与 PPR 之间的相互作用引起的这一发现与自私线粒体进化和 M. guttatus 内补偿性核协同进化的历史是一致的。
