背景回顾：Polyploidy is a major driver of evolutionary change. Autopolyploids, which arise by within-species whole-genome duplication, carry multiple nearly identical copies of each chromosome. This presents an existential challenge to sexual reproduction. Meiotic chromosome segregation requires formation of DNA crossovers (COs) between two homologous chromosomes. 

提出问题：How can this outcome be achieved when more than two essentially equivalent partners are available?

主要研究：We addressed this question by comparing diploid, neo-autotetraploid, and established autotetraploid Arabidopsis arenosa using new approaches for analysis of meiotic CO patterns in polyploids. 

结果1：We discover that crossover interference, the classical process responsible for patterning of COs in diploid meiosis, is defective in the neo-autotetraploid but robust in the established autotetraploid. The presented findings suggest that, initially, diploid-like interference fails to act effectively on multivalent pairing and accompanying pre-CO recombination interactions and that stable autopolyploid meiosis can emerge by evolution of a “supercharged” interference process, which can now act effectively on such configurations. 

结论：Thus, the basic interference mechanism responsible for simplifying CO patterns along chromosomes in diploid meiosis has evolved the capability to also simplify CO patterns among chromosomes in autopolyploids, thereby promoting bivalent formation. We further show that evolution of stable autotetraploidy preadapts meiosis to higher ploidy, which in turn has interesting mechanistic and evolutionary implications.

 摘 要 

多倍化是演化改变的主要驱动因子。种内通过全基因组复制事件形成的同源多倍体，每条染色体都会有一个近乎一致的拷贝。而这对于有性生殖是一个挑战。减数分裂染色体分离需要在两条同源染色体之间形成DNA交换（crossovers，COs）。但是，在同源多倍体中，存在多条同源染色体，减数分裂染色体分离又要如何进行呢？本文中，作者通过比较拟南芥属物种Arabidopsis arenosa的二倍体、新形成的同源四倍体、以及已建立稳定的同源四倍体，分析了多倍体中减数分裂CO的模式。作者发现二倍体减数分裂过程中作用于COs模式的交换干扰（crossover interference）在新形成的同源四倍体中存在缺陷，但是在已建立稳定的同源四倍体中的功能十分稳健。该结果说明在同源四倍体形成之初，类似于二倍体中的交换干扰不能有效地作用于多价配对和伴随的交换前重组互作，而稳定的同源多倍体减数分裂可以通过演化出一个增强型干扰过程，有效作用于此类染色体构型。因此，作用于二倍体有丝分裂过程中简化染色体上CO模式的基础干扰机制已经演化出能够简化同源多倍体中染色体上的CO模式的功能，从而促进二价染色体的形成。作者进一步表明稳定同源四倍体的演化为更高倍性的减数分裂提供了可能，从而具有了更加有趣的机制和演化上的意义。

doi: https://doi.org/10.1016/j.cub.2021.08.028