期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：38
页码：13918-13923
DOI：10.1073/pnas.1415482111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMeiotic recombination between homologous paternal and maternal chromosomes allows the shuffling of genes that otherwise would be coinherited and originates at nonrandom sites termed hotspots. In maize, an organism with >90% repetitive DNA, recombination hotspots correspond to genes. Gene conversion is a nonreciprocal form of recombination that leads to an aberrant allelic segregation ratio. In most higher organisms, gene conversions can be identified as intragenic recombinants having a parental arrangement of flanking markers. Here, we show that in maize heterozygotes where most recombinants can be attributed to gene conversion, mutant sites at either end of the gene convert to WT more frequently than those in the middle, arguing for a polarized distribution of recombination initiation sites within the gene. Nucleotide diversity is greater in maize than in most organisms studied to date, so allelic pairs in a hybrid tend to be highly polymorphic. Most recombination events between such pairs of maize polymorphic alleles are crossovers. However, intragenic recombination events not associated with flanking marker exchange, corresponding to noncrossover gene conversions, predominate between alleles derived from the same progenitor. In these dimorphic heterozygotes, the two alleles differ only at the two mutant sites between which recombination is being measured. To investigate whether gene conversion at the bz locus is polarized, two large diallel crossing matrices involving mutant sites spread across the bz gene were performed and more than 2,500 intragenic recombinants were scored. In both diallels, around 90% of recombinants could be accounted for by gene conversion. Furthermore, conversion exhibited a striking polarity, with sites located within 150 bp of the start and stop codons converting more frequently than sites located in the middle of the gene. The implications of these findings are discussed with reference to recent data from genome-wide studies in other plants.
