The evolutionary origins of Epichloe endophytes from annual ryegrasses
The evolutionary origins of Epichloe endophytes from annual ryegrasses
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DOI：
10.2307/3761478
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发表时间：
2000-11-01
期刊：
影响因子：
2.8
通讯作者：
Christensen, MJ
中科院分区：
文献类型：
--
作者：
Moon, CD;Scott, B;Christensen, MJ
对一年生黑麦草（黑麦草）物种进行了调查，了解种子传播的无性附生菌：内生菌（即 Neotyphodium spp.）。从所有七种一年生黑麦草属植物中均鉴定出了在培养物中生长极其缓慢的内生菌。确定了 β-微管蛋白基因 (tu62) 内含子和核糖体 RNA (rDNA-ITS) 的内部转录间隔区的序列，以及基于五个微卫星位点的概况。一年生黑麦草内生菌的两个分类群通过形态、可培养性和基因型进行区分。其中一组被命名为 Neotyphodium ocultans，仅包含无法在马铃薯葡萄糖琼脂培养基上传代培养的分离株。这些分离株在微卫星位点包含多个 tube2 基因和多个等位基因，表明存在种间杂交起源。系统发育分析结果表明，N, ocultans的祖先包括Epichloe； baconii 和 E. bromicola 或近亲。一年生黑麦草内生菌的第二个分类群，以分离株 Lc4 为例，仅在 L. canariense 中发现。该分类单元具有单一的 tube2 序列和微卫星基因型，与感染早熟禾的现存火蜥蜴分离株几乎相同。因此，有人提出，Lc4 是与 P. nemoralis 现有菌株密切相关的火炬杆菌基因型的无性衍生物。我们建议将其命名为 Neotyphodiumtyphinum var。加那利岛这个分类单元。这两个来自一年生黑麦草的新内生菌类群是由有性附生菌产生的无性新菌属物种的进一步例子。种。要么直接通过有性状态的丧失，要么通过种间杂交事件。
The annual Lolium (ryegrass) species were surveyed for seedborne, asexual Epichloe: endophytes (i.e., Neotyphodium spp.). Endophytes that were extremely slow growing in culture were identified from all seven annual ryegrass spp. Sequences of beta -tubulin gene (tu62) introns and the internal transcribed spacers of the nuclear ribosomal RNA (rDNA-ITS) were determined, as were profiles based on five microsatellite loci. Two taxonomic groups of annual ryegrass endophytes were distinguishable by morphology, culturability and genotypes. One group, for which the name Neotyphodium occultans is proposed, comprised only isolates that could not be subcultured on potato dextrose agar medium. These isolates contained multiple tub2 genes and multiple alleles at microsatellite loci, suggestive of an interspecific hybrid origin. The results of phylogenetic analysis implied that the ancestors of N, occultans included Epichloe; baconii and E. bromicola, or close relatives. The second taxonomic group of annual ryegrass endophytes, exemplified by isolate Lc4, was found only in L. canariense. This taxon had a single tub2 sequence and microsatellite genotype that was nearly identical to those of extant Epichloe typhina isolates that infect Poa nemoralis. Therefore, it is proposed that Lc4 is an asexual derivative of an E. typhina genotype closely related to extant strains from P. nemoralis. We propose the name Neotyphodium typhinum var. canariense for this taxon. These two new endophyte taxa from the annual ryegrasses are further examples of asexual Neotyphodium species that have arisen from sexual Epichloe; spp. either directly by loss of the sexual state, or by interspecific hybridization events.