Microevolution of Cryptococcus neoformans Driven by Massive Tandem Gene Amplification
Microevolution of Cryptococcus neoformans Driven by Massive Tandem Gene Amplification
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DOI：
10.1093/molbev/mss066
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发表时间：
2012-08-01
影响因子：
10.7
通讯作者：
Fraser, James A.
中科院分区：
文献类型：
--
作者：
Chow, Eve W. L.;Morrow, Carl A.;Fraser, James A.
从原生生物到真菌，生物体的亚端粒区域经历了比在基因组其他部分观察到的更高的重排速度。在对这些类似于人类真菌病原体新生隐球菌40kb区域的特征进行分析的同时，我们发现了最近在3号染色体右侧端粒附近发生的一个基因扩增事件，该事件涉及一个编码亚砷外排转运蛋白(ARR3)的基因。3,177个碱基对的扩增子存在于2-15个拷贝的串联阵列中，并且仅存在于具有新生链球菌变种的菌株中。Grubii亚枝VNI A5 MLST剖面。携带扩增片段的菌株对亚砷酸盐的抗性显著增强，这与重复序列的拷贝数有关；通过对酿酒酵母亚砷酸盐转运体突变体的功能互补，证实了耐药性增加的来源与运输有关。随后在亚砷酸盐浓度增加的情况下进行的实验进化产生了高度耐药的菌株，ARR3扩增子进一步扩增到50多个拷贝，占整个基因组的近1%，使该重复序列的拷贝数与核糖体DNA的拷贝数一样高。因此，这里描述的例子代表了一种罕见的进化中间产物--当前处于动态变化状态的阵列，这与过去由于核苷酸分歧而无法进一步扩增的相对常见的静态串联复制遗迹形成了鲜明对比。除了鉴定和改造对亚砷酸盐具有高度抗性的真菌分离株，并描述了首次报道的新生葡萄球菌通过大规模基因扩增进行微进化的实例外，这些结果表明，通过基因扩增进行适应可能是新生葡萄球菌应对环境压力的重要机制，可能包括感染期间遇到的压力。更重要的是，ARR3阵列将成为进一步分析串联基因复制如何产生和扩展的分子遗传学分析的理想模型。
The subtelomeric regions of organisms ranging from protists to fungi undergo a much higher rate of rearrangement than is observed in the rest of the genome. While characterizing these similar to 40-kb regions of the human fungal pathogen Cryptococcus neoformans, we have identified a recent gene amplification event near the right telomere of chromosome 3 that involves a gene encoding an arsenite efflux transporter (ARR3). The 3,177-bp amplicon exists in a tandem array of 2-15 copies and is present exclusively in strains with the C. neoformans var. grubii subclade VNI A5 MLST profile. Strains bearing the amplification display dramatically enhanced resistance to arsenite that correlates with the copy number of the repeat; the origin of increased resistance was verified as transport-related by functional complementation of an arsenite transporter mutant of Saccharomyces cerevisiae. Subsequent experimental evolution in the presence of increasing concentrations of arsenite yielded highly resistant strains with the ARR3 amplicon further amplified to over 50 copies, accounting for up to similar to 1% of the whole genome and making the copy number of this repeat as high as that seen for the ribosomal DNA. The example described here therefore represents a rare evolutionary intermediate-an array that is currently in a state of dynamic flux, in dramatic contrast to relatively common, static relics of past tandem duplications that are unable to further amplify due to nucleotide divergence. Beyond identifying and engineering fungal isolates that are highly resistant to arsenite and describing the first reported instance of microevolution via massive gene amplification in C. neoformans, these results suggest that adaptation through gene amplification may be an important mechanism that C. neoformans employs in response to environmental stresses, perhaps including those encountered during infection. More importantly, the ARR3 array will serve as an ideal model for further molecular genetic analyses of how tandem gene duplications arise and expand.