The genome-wide dynamics of purging during selfing in maize
First author: Kyria Roessler; Affiliations: University of California, Irvine (加州大学欧文分校): CA, USA
Corresponding author: Brandon S. Gaut
Self-fertilization (also known as selfing) is an important reproductive strategy in plants and a widely applied tool for plant genetics and plant breeding. Selfing can lead to inbreeding depression by uncovering recessive deleterious variants, unless these variants are purged by selection. Here we investigated the dynamics of purging in a set of eleven maize lines that were selfed for six generations. We show that heterozygous, putatively deleterious single nucleotide polymorphisms are preferentially lost from the genome during selfing. Deleterious single nucleotide polymorphisms were lost more rapidly in regions of high recombination, presumably because recombination increases the efficacy of selection by uncoupling linked variants. Overall, heterozygosity decreased more slowly than expected, by an estimated 35% to 40% per generation instead of the expected 50%, perhaps reflecting pervasive associative overdominance. Finally, three lines exhibited marked decreases in genome size due to the purging of transposable elements. Genome loss was more likely to occur for lineages that began with larger genomes with more transposable elements and chromosomal knobs. These three lines purged an average of 398 Mb from their genomes, an amount equivalent to three Arabidopsis thaliana genomes per lineage, in only a few generations.
自交是植物中比较重要的一个生殖策略，并且广泛应用于植物遗传育种进程中。自交会通过暴露隐性有害变异导致近交衰退，除非通过选择清除掉这些有害基因。本文中，作者研究了经过六个世代选择的十一个玉米株系中遗传清除的动态变化。作者的研究显示在自交过程中带有有害SNP的杂合子会首先从基因组中丢失。另外，基因组上高重组区域的有害SNP会丢失的更快，这有可能是由于重组通过解偶联连锁的变异增加了选择的效率。总体来说，基因组上的杂合性要比预期的降低的更慢，预期的每代降低50%左右，但预计降低35%到40%，这可能反映了基因组上广泛存在关联的过显性。最后，其中三个玉米株系由于转座元件的清除导致了基因组大小显著的减小。对于某些基因组更大，转座元件和染色体结更多的玉米谱系更加容易发生基因组丢失。这三个玉米株系平均清除了大约398Mb的基因组序列，相当于三个拟南芥基因组的大小，并且该事件仅仅发生在几个世代之内。
通讯：Brandon S. Gaut（https://gautlab.bio.uci.edu/people/)
个人简介：加州大学河滨分校，博士；北卡罗来纳州立大学，博士后。
研究方向：葡萄和北美砧木种群基因组学研究；植物基因组的表观与演化；大肠杆菌实验演化；驯化遗传学。
doi: https://doi.org/10.1038/s41477-019-0508-7
Journal: Nature Plants
Published online: September 02, 2019
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