Haudry A, Cenci A, Guilhaumon C, Paux E, Poirier S, Santoni S, David J, Glémin S
UMR Diversité et Adaptation des Plantes Cultivées, Montpellier SupAgro, Institut National de la Recherche Agronomique-IRD-UMII, 2 Place Pierre Viala, Montpellier Cedex 1, France.
Genet Res (Camb). 2008 Feb;90(1):97-109. doi: 10.1017/S0016672307009032.
Mating systems and recombination are thought to have a deep impact on the organization and evolution of genomes. Because of the decline in effective population size and the interference between linked loci, the efficacy of selection is expected to be reduced in regions with low recombination rates and in the whole genome of self-fertilizing species. At the molecular level, relaxed selection is expected to result in changes in the rate of protein evolution and the pattern of codon bias. It is increasingly recognized that recombination also affects non-selective processes such as the biased gene conversion towards GC alleles (bGC). Like selection, this kind of meiotic drive in favour of GC over AT alleles is expected to be reduced in weakly recombining regions and genomes. Here, we investigated the effect of mating system and recombination on molecular evolution in four Triticeae species: two outcrossers (Secale cereale and Aegilops speltoides) and two selfers (Triticum urartu and Triticum monococcum). We found that GC content, possibly driven by bGC, is affected by mating system and recombination as theoretically predicted. Selection efficacy, however, is only weakly affected by mating system and recombination. We investigated the possible reasons for this discrepancy. A surprising one is that, in outcrossing lineages, selection efficacy could be reduced because of high substitution rates in favour of GC alleles. Outcrossers, but not selfers, would thus suffer from a 'GC-induced' genetic load. This result sheds new light on the evolution of mating systems.
交配系统和重组被认为对基因组的组织和进化有深远影响。由于有效种群大小的下降以及连锁位点之间的干扰，在重组率低的区域以及自花受精物种的整个基因组中，选择的效力预计会降低。在分子水平上，选择放松预计会导致蛋白质进化速率和密码子偏好模式的变化。人们越来越认识到，重组也会影响非选择性过程，比如向GC等位基因的偏向性基因转换（bGC）。与选择一样，这种有利于GC而非AT等位基因的减数分裂驱动在弱重组区域和基因组中预计会减弱。在这里，我们研究了交配系统和重组对四种小麦族物种分子进化的影响：两种异交物种（黑麦和节节麦）以及两种自交物种（乌拉尔图小麦和一粒小麦）。我们发现，如理论预测的那样，可能由bGC驱动的GC含量受交配系统和重组的影响。然而，选择效力仅受到交配系统和重组的微弱影响。我们探究了这种差异的可能原因。一个令人惊讶的原因是，在异交谱系中，由于有利于GC等位基因的高替换率，选择效力可能会降低。因此，异交物种而非自交物种会遭受“GC诱导”的遗传负荷。这一结果为交配系统的进化提供了新的见解。
