Laboratory of Social Evolution and Behavior, The Rockefeller University, New York, New York 10065, USA.
Genome Res. 2018 Nov;28(11):1757-1765. doi: 10.1101/gr.237123.118. Epub 2018 Sep 24.
The massive expansions of odorant receptor (OR) genes in ant genomes are notable examples of rapid genome evolution and adaptive gene duplication. However, the molecular mechanisms leading to gene family expansion remain poorly understood, partly because available ant genomes are fragmentary. Here, we present a highly contiguous, chromosome-level assembly of the clonal raider ant genome, revealing the largest known OR repertoire in an insect. While most ant ORs originate via local tandem duplication, we also observe several cases of dispersed duplication followed by tandem duplication in the most rapidly evolving OR clades. We found that areas of unusually high transposable element density (TE islands) were depauperate in ORs in the clonal raider ant, and found no evidence for retrotransposition of ORs. However, OR loci were enriched for transposons relative to the genome as a whole, potentially facilitating tandem duplication by unequal crossing over. We also found that ant OR genes are highly AT-rich compared to other genes. In contrast, in flies, OR genes are dispersed and largely isolated within the genome, and we find that fly ORs are not AT-rich. The genomic architecture and composition of ant ORs thus show convergence with the unrelated vertebrate ORs rather than the related fly ORs. This might be related to the greater gene numbers and/or potential similarities in gene regulation between ants and vertebrates as compared to flies.
在蚂蚁基因组中，气味受体 (OR) 基因的大规模扩张是快速基因组进化和适应性基因复制的显著例子。然而，导致基因家族扩张的分子机制仍知之甚少，部分原因是可用的蚂蚁基因组是不完整的。在这里，我们展示了一种高度连续的、基于染色体的克隆掠夺蚁基因组组装，揭示了昆虫中最大的已知 OR 基因库。虽然大多数蚂蚁 OR 是通过局部串联复制产生的，但我们也观察到在进化最快的 OR 进化枝中，存在分散复制后串联复制的几个例子。我们发现，在克隆掠夺蚁中，异常高的转座元件密度（TE 岛）区域的 OR 很少，并且没有发现 OR 反转录的证据。然而，相对于整个基因组，OR 基因座富含转座子，这可能通过不等交换促进了串联复制。我们还发现，与其他基因相比，蚂蚁 OR 基因富含 AT。相比之下，在果蝇中，OR 基因是分散的，并且在基因组中基本是孤立的，并且我们发现果蝇的 OR 基因不含 AT。因此，蚂蚁 OR 基因的基因组结构和组成与无亲缘关系的脊椎动物 OR 基因趋同，而不是与相关的果蝇 OR 基因趋同。这可能与与果蝇相比，蚂蚁和脊椎动物的基因数量更多和/或基因调控的潜在相似性有关。
