Recent evolution of the human pathogen Cryptococcus neoformans by intervarietal transfer of a 14-gene fragment
Recent evolution of the human pathogen Cryptococcus neoformans by intervarietal transfer of a 14-gene fragment
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DOI：
10.1093/molbev/msl070
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发表时间：
2006-10-01
影响因子：
10.7
通讯作者：
Dietrich, Fred S.
中科院分区：
文献类型：
--
作者：
Kavanaugh, Laura A.;Fraser, James A.;Dietrich, Fred S.
人类病原真菌新隐球菌的2个已知变种的全基因组序列的可用性为研究遗传易感生物物种形成过程中分化和渐渗的相对贡献提供了机会。在基因组水平上，这些品种几乎是完全同源的，具有相似的85-90%的核苷酸同源性，并且被认为是类似于18 MYA的分化。通过比较基因组学方法，我们确定了一个14个基因区域（约40 kb），在两个品种之间几乎相同，这是由类似于2 MYA的从格鲁比变种到新形态变种的非互惠转移事件造成的。来自世界各地的大多数临床和环境新生变体菌株都含有从格鲁比变种获得的这一序列。这种渗入事件可能是通过一个不完整的品种间性循环发生的，创造了一个杂交中间体，在这个中间体中，两个谱系共有的可移动元素介导了交换。随后在实验室菌株中同一基因组区域片段的重复支持了进化理论，即亚端粒区域的不稳定性通过基因扩增和随后的适应促进了适应性进化。这些数据表明，在密切相关的同域品种或物种之间的DNA交换可能是真菌物种进化过程中一个反复出现的主题，此外，还有一个更古老的预测转移事件发生在C. neoformans和最近报道的一个来自酿酒酵母的例子。这进一步表明，虽然进化分化是驱动物种形成的主要力量，但罕见的基因渗入事件也起着潜在的重要作用。
The availability of the whole-genome sequence from the 2 known varieties of the human pathogenic fungus Cryptococcus neoformans provides an opportunity to study the relative contribution of divergence and introgression during the process of speciation in a genetically tractable organism. At the genomic level, these varieties are nearly completely syntenic, share similar to 85-90% nucleotide identity, and are believed to have diverged similar to 18 MYA. Via a comparative genomic approach, we identified a 14-gene region (similar to 40 kb) that is nearly identical between the 2 varieties that resulted from a nonreciprocal transfer event from var. grubii to var. neoformans similar to 2 MYA. The majority of clinical and environmental var. neoformans strains from around the world contain this sequence obtained from var. grubii. This introgression event likely occurred via an incomplete intervarietal sexual cycle, creating a hybrid intermediate where mobile elements common to both lineages mediated the exchange. The subsequent duplication in laboratory strains of a fragment of this same genomic region supports evolutionary theories that instabilities in subtelomeric regions promote adaptive evolution through gene amplification and subsequent adaptation. Along with a more ancient predicted transfer event in C. neoformans and a recently reported example from Saccharomyces cerevisiae, these data indicate that DNA exchange between closely related sympatric varieties or species may be a recurrent theme in the evolution of fungal species. It further suggests that although evolutionary divergence is the primary force driving speciation, rare introgression events also play a potentially important role.