Triticeae Research Institute, Sichuan Agricultural University, Chengdu, Sichuan, China.
Department of Botany and Plant Sciences, University of California, Riverside, CA, USA.
Plant J. 2021 Mar;105(6):1665-1676. doi: 10.1111/tpj.15140. Epub 2021 Jan 19.
Allopolyploid wheat (Triticum aestivum L.) carries three pairs of homoeologous genomes but its meiotic pairing is diploid-like. This is the effect of the Ph (pairing homoeologous) system which restricts chromosome pairing to strictly homologous. Ph1 is the locus with the strongest effect. Disabling Ph1 permits pairing between homoeologues and is routinely used in chromosome engineering to introgress alien variation into breeding stocks. Whereas the efficiency of Ph1 and the general pattern of homoeologous crossovers in its absence are quite well known from numerous studies, other characteristics of such crossovers remain unknown. This study analyzed the crossover points in four sets of the ph1b-induced recombinants between wheat homologues as well as between three wheat and rye (Secale cereale) homoeologous chromosome arms, and compared them to crossovers between homologues in a reference wheat population. The results show the Ph1 locus also controls crossing over of homologues, and the general patterns of homologous (with Ph1) and homoeologous (with ph1b) crossing over are the same. In all intervals analyzed, homoeologous crossovers fell within the range of frequency distribution of homologous crossovers among individual families of the reference population. No specific DNA sequence characteristics were identified that could be recognized by the Ph1 locus; the only difference between homologous and homoeologous crossing over appears to be in frequency. It is concluded that the Ph1 locus likely recognizes DNA sequence similarity; crossing over is permitted between very similar sequences. In the absence of Ph1 dissimilarities are ignored, in proportion to the level of the sequence divergence.
异源多倍体小麦（Triticum aestivum L.）携带三对同源基因组，但它的减数分裂配对类似于二倍体。这是 Ph（配对同源）系统的作用，该系统限制染色体配对为严格的同源。Ph1 是具有最强效应的基因座。失活 Ph1 允许同源基因之间配对，并且通常用于染色体工程将外源变异引入育种品系中。尽管来自众多研究已经相当了解 Ph1 的效率及其在缺乏 Ph1 时同源重组的一般模式，但此类重组的其他特征仍未知。本研究分析了四组 Ph1b 诱导的小麦同源重组体以及三组小麦和黑麦（Secale cereale）同源染色体臂之间的重组点，并将其与参考小麦群体中同源重组体进行了比较。结果表明，Ph1 基因座还控制同源重组的交换，并且具有 Ph1 的同源（with Ph1）和具有 ph1b 的同源（with homoeologous）交换的一般模式是相同的。在所分析的所有间隔中，同源重组体落在参考群体中各个家系同源重组体频率分布的范围内。未识别出 Ph1 基因座可以识别的特定 DNA 序列特征；同源重组和异源重组之间的唯一区别似乎在于频率。因此，Ph1 基因座可能识别 DNA 序列相似性；在非常相似的序列之间允许发生重组。在没有 Ph1 的情况下，差异被忽略，与序列差异的程度成比例。
