Laboratory of Genetics, Wageningen University & Research, Wageningen, the Netherlands.
Biometris, Wageningen University & Research, Wageningen, the Netherlands.
BMC Genomics. 2023 Mar 16;24(1):123. doi: 10.1186/s12864-023-09210-x.
The termite-fungus symbiosis is an ancient stable mutualism of two partners that reproduce and disperse independently. With the founding of each termite colony the symbiotic association must be re-established with a new fungus partner. Complementarity in the ability to break down plant substrate may help to stabilize this symbiosis despite horizontal symbiont transmission. An alternative, non-exclusive, hypothesis is that a reduced rate of evolution may contribute to stabilize the symbiosis, the so-called Red King Effect.
To explore this concept, we produced the first linkage map of a species of Termitomyces, using genotyping by sequencing (GBS) of 88 homokaryotic offspring. We constructed a highly contiguous genome assembly using PacBio data and a de-novo evidence-based annotation. This improved genome assembly and linkage map allowed for examination of the recombination landscape and its potential effect on the mutualistic lifestyle.
Our linkage map resulted in a genome-wide recombination rate of 22 cM/Mb, lower than that of other related fungi. However, the total map length of 1370 cM was similar to that of other related fungi.
The apparently decreased rate of recombination is primarily due to genome expansion of islands of gene-poor repetitive sequences. This study highlights the importance of inclusion of genomic context in cross-species comparisons of recombination rate.
白蚁-真菌共生关系是两种合作伙伴独立繁殖和传播的古老稳定的互利共生关系。随着每个白蚁群体的建立，共生协会必须与新的真菌伙伴重新建立。尽管存在水平共生体传播，但分解植物基质的能力互补有助于稳定这种共生关系。另一种非排他性的假设是，进化速度的降低可能有助于稳定共生关系，这就是所谓的“红王效应”。
为了探索这个概念，我们使用 88 个同质后代的测序（GBS）生成了第一个 Termitomyces 物种的连锁图谱。我们使用 PacBio 数据和基于证据的从头注释构建了一个高度连续的基因组组装。这个改进的基因组组装和连锁图谱允许检查重组景观及其对互惠生活方式的潜在影响。
我们的连锁图谱导致全基因组重组率为 22 cM/Mb，低于其他相关真菌的重组率。然而，全长 1370 cM 的图谱与其他相关真菌相似。
明显降低的重组率主要是由于基因贫乏重复序列岛的基因组扩张。本研究强调了在重组率的跨物种比较中包括基因组上下文的重要性。
