Schneider Kevin L, Xie Zidian, Wolfgruber Thomas K, Presting Gernot G
Department of Molecular Biosciences and Bioengineering, University of Hawaii, Honolulu, HI 96822.
Department of Molecular Biosciences and Bioengineering, University of Hawaii, Honolulu, HI 96822
Proc Natl Acad Sci U S A. 2016 Feb 23;113(8):E987-96. doi: 10.1073/pnas.1522008113. Epub 2016 Feb 8.
Functional centromeres, the chromosomal sites of spindle attachment during cell division, are marked epigenetically by the centromere-specific histone H3 variant cenH3 and typically contain long stretches of centromere-specific tandem DNA repeats (∼1.8 Mb in maize). In 23 inbreds of domesticated maize chosen to represent the genetic diversity of maize germplasm, partial or nearly complete loss of the tandem DNA repeat CentC precedes 57 independent cenH3 relocation events that result in neocentromere formation. Chromosomal regions with newly acquired cenH3 are colonized by the centromere-specific retrotransposon CR2 at a rate that would result in centromere-sized CR2 clusters in 20,000-95,000 y. Three lines of evidence indicate that CentC loss is linked to inbreeding, including (i) CEN10 of temperate lineages, presumed to have experienced a genetic bottleneck, contain less CentC than their tropical relatives; (ii) strong selection for centromere-linked genes in domesticated maize reduced diversity at seven of the ten maize centromeres to only one or two postdomestication haplotypes; and (iii) the centromere with the largest number of haplotypes in domesticated maize (CEN7) has the highest CentC levels in nearly all domesticated lines. Rare recombinations introduced one (CEN2) or more (CEN5) alternate CEN haplotypes while retaining a single haplotype at domestication loci linked to these centromeres. Taken together, this evidence strongly suggests that inbreeding, favored by postdomestication selection for centromere-linked genes affecting key domestication or agricultural traits, drives replacement of the tandem centromere repeats in maize and other crop plants. Similar forces may act during speciation in natural systems.
功能着丝粒是细胞分裂过程中纺锤体附着的染色体位点，在表观遗传上由着丝粒特异性组蛋白H3变体cenH3标记，通常包含长段的着丝粒特异性串联DNA重复序列（玉米中约1.8 Mb）。在选取的代表玉米种质遗传多样性的23个自交系中，串联DNA重复序列CentC的部分或几乎完全缺失先于57个独立的cenH3重新定位事件，这些事件导致了新着丝粒的形成。新获得cenH3的染色体区域被着丝粒特异性逆转座子CR2定殖，其定殖速率在20000 - 95000年后会形成着丝粒大小的CR2簇。三条证据表明CentC的缺失与近亲繁殖有关，包括：（i）温带谱系的CEN10被认为经历了遗传瓶颈，其CentC含量比热带亲缘种少；（ii）对驯化玉米中与着丝粒连锁基因的强烈选择使十个玉米着丝粒中的七个多样性降低到仅一两个驯化后单倍型；（iii）驯化玉米中具有最多单倍型的着丝粒（CEN7）在几乎所有驯化系中具有最高的CentC水平。罕见的重组引入了一个（CEN2）或更多（CEN5）替代的CEN单倍型，同时在与这些着丝粒连锁的驯化位点保留了单个单倍型。综合来看，这些证据有力地表明，近亲繁殖受驯化后对影响关键驯化或农业性状的着丝粒连锁基因的选择所青睐，驱动了玉米和其他作物中串联着丝粒重复序列的替换。类似的力量可能在自然系统的物种形成过程中起作用。
