Vertical evolution and intragenic spread of lichen-fungal group I introns
Vertical evolution and intragenic spread of lichen-fungal group I introns
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DOI：
10.1007/s00239-001-2305-x
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发表时间：
2002-07-01
影响因子：
3.9
通讯作者：
Helms, G
中科院分区：
文献类型：
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作者：
Bhattacharya, D;Friedl, T;Helms, G
真囊菌科（子囊菌科）中的一个科，即形成地衣的Physciaceae，特别富含核糖体DNA I族内含子。我们使用I族内含子和地衣-真菌宿主细胞的系统发育分析来解决关于地衣和所有真核生物中I族内含子进化的四个问题：1)内含子在地衣中的传播是否与真菌和光合细胞的密切联系有关？2)地衣真菌中的多I族内含子是独立起源的，还是已经存在的内含子扩散到rDNA的新位点？3)如果内含子已经移动到新的位点，那么这些位点的外显子上下文是否提供了内含子传播机制的见解？4)地衣真菌小亚基rDNA基因内含子丢失的模式是什么？我们的分析表明，地衣真菌和地衣藻类（以及地衣化蓝藻）中的I族内含子并没有密切的进化关系，这表明这些内含子不会在共生体之间移动。许多I类内含子似乎起源于Lecanorales的共同祖先，而另一些则通过反向剪接到新的rRNA位点而在这个谱系中传播（特别是在Physciaceae中）。我们认为，大多数地衣真菌I群内含子的进化史特征是罕见的获得，随后在后代中大量丢失，导致内含子分布零星。因此，需要对内含子和宿主细胞进行详细的系统发育分析，以区分这种情况与在不同地衣-真菌谱系中广泛而独立的内含子获得的另一种假设。
One family within the Euascomycetes (Ascomycota), the lichen-forming Physciaceae, is particularly rich in nuclear ribosomal [r]DNA group I introns. We used phylogenetic analyses of group I introns and lichen-fungal host cells to address four questions about group I intron evolution in lichens, and generally in all eukaryotes: 1) Is intron spread in the lichens associated with the intimate association of the fungal and photosynthetic cells that make Lip the lichen thallus? 2) Are the Multiple group I introns in the lichen-fungi of independent origins, or have existing introns spread into novel sites in the rDNA? 3) If introns have moved to novel sites, then does the exon context of these sites provide insights into the mechanism of intron spread? and 4) What is the pattern of intron loss in the small subunit rDNA gene of lichen-fungi? Our analyses show that group I introns in the lichen-fungi and in the lichen-algae (and lichenized cyanobacteria) do not share a close evolutionary relationship, suggesting that these introns do not move between the symbionts. Many group I introns appear to have originated in the common ancestor of the Lecanorales, whereas others have spread within this lineage (particularly in the Physciaceae) putatively through reverse-splicing into novel rRNA sites. We suggest that the evolutionary history of most lichen-fungal group I introns is characterized by rare gains followed by extensive losses in descendants, resulting in a sporadic intron distribution. Detailed phylogenetic analyses of the introns and host cells are required, therefore, to distinguish this scenario from the alternative hypothesis of widespread and independent intron gains in the different lichen-fungal lineages.