Prevalence of interspecific hybrids amongst asexual fungal endophytes of grasses
Prevalence of interspecific hybrids amongst asexual fungal endophytes of grasses
复制标题
DOI：
10.1111/j.1365-294x.2004.02138.x
复制
发表时间：
2004-06-01
影响因子：
4.9
通讯作者：
Schardl, CL
中科院分区：
文献类型：
--
作者：
Moon, CD;Craven, KD;Schardl, CL
附生植物内生菌是跨越连续体的禾本科真菌共生体，包括垂直传播的无性共生体、水平传播的专性有性病原体以及具有共生和致病能力的混合策略共生体。在这里，我们表明，不同共生体类型的基因组进化过程存在显着差异。对有性和无性分离株的广泛分类学、生态和地理样本进行了遗传和系统发育分析，其中对 β-微管蛋白 (tub2) 和翻译延伸因子 1-α (tef1) 基因的等位基因进行了鉴定和测序，并通过长度多态性鉴定了微卫星等位基因。大多数无性分离株的大多数基因座具有两个或三个等位基因，但每个有性分离株的每个基因座仅具有单个等位基因。 tube2 和 tef1 的系统发育分析表明，在分离株中多个等位基因的所有实例中，等位基因都源自不同的性物种。结论是，虽然水平传播的物种具有单倍体基因组并且物种形成是按分支发生的，但大多数严格种子传播的互利共生体是具有异倍体（非整倍体或多倍体）基因组的种间杂种。此外，系统发育证据表明，至少在某些情况下，杂交是跟随而不是导致严格种子传播习性的进化。因此，禾本科内生菌中杂种的丰富性及其在许多寄主群体中的流行表明，杂交对共生内生菌具有选择性优势。
Epichloe endophytes are fungal symbionts of grasses that span a continuum including asexual mutualists that are vertically transmitted, obligately sexual pathogens that are horizontally transmitted, and mixed-strategy symbionts with both mutualistic and pathogenic capabilities. Here we show that processes of genome evolution differ markedly for the different symbiont types. Genetic and phylogenetic analysis was conducted of a broad taxonomic, ecological and geographical sample of sexual and asexual isolates, in which were identified and sequenced alleles of genes for beta-tubulin (tub2) and translation elongation factor 1-alpha (tef1), and microsatellite alleles were identified by length polymorphisms. The majority of asexual isolates had two or three alleles of most loci, but every sexual isolate had only single alleles for each locus. Phylogenetic analysis of tub2 and tef1 indicated that in all instances of multiple alleles in an isolate, the alleles were derived from different sexual species. It is concluded that, whereas horizontally transmissible species had haploid genomes and speciation occurred cladistically, most of the strictly seedborne mutualists were interspecific hybrids with heteroploid (aneuploid or polyploid) genomes. Furthermore, the phylogenetic evidence indicated that, in at least some instances, hybridization followed rather than caused evolution of the strictly seedborne habit. Therefore, the abundance of hybrid species among grass endophytes, and their prevalence in many host populations suggests a selective advantage of hybridization for the mutualistic endophytes.