Harvard University, FAS Center for Systems Biology, Cambridge, MA 02138, USA.
Mycologia. 2012 Jan-Feb;104(1):22-33. doi: 10.3852/11-056. Epub 2011 Sep 13.
Although most species in the genus Amanita form ectomycorrhizal associations, a few are reported to be saprotrophs living in grassland habitats. Little is known about the ecology and distribution of these free-living Amanita species. We describe the ecology of Amanita thiersii, a species commonly collected in lawns throughout the Mississippi River Basin. Stable isotopes of carbon, transcriptomic sequences and patterns of growth on complex carbon sources provide evidence for A. thiersii as a saprotrophic species. Sporocarps of A. thiersii are less depleted in (13)C compared to published data for ectomycorrhizal fungi, supporting a saprotrophic mode of carbon acquisition in the field. Orthologs of cellulase genes known to play key roles in the decomposition of cellulose in other basidiomycetes were identified in a transcriptome of A. thiersii, establishing that this species has the genetic potential to degrade cellulose. Amanita thiersii also can use artificial cellulose or sterile grass litter as a sole carbon source. DNA sequences of three nuclear gene regions and banding patterns from four inter-simple sequence repeat markers were identical across 31 populations from throughout the known range of the species, which suggests the genetic diversity of A. thiersii populations is low. Maps of A. thiersii collections made from the 1950s until present suggest this species is experiencing a range expansion. It was reported first in 1952 in Texas and now occurs in nine states north to Illinois. These data provide an ecological context for interpreting the genome of A. thiersii, currently being sequenced at the United States Department of Energy's Joint Genome Institute.
虽然鹅膏菌属的大多数物种形成外生菌根共生关系，但也有少数被报道为生活在草原生境中的腐生生物。关于这些自由生活的鹅膏菌物种的生态学和分布知之甚少。我们描述了在密西西比河流域各地草坪中常见采集的鹅膏菌 thiersii 的生态学。碳的稳定同位素、转录组序列和在复杂碳源上的生长模式为 A. thiersii 作为腐生物种提供了证据。与已发表的外生菌根真菌数据相比，A. thiersii 的子实体中（13）C 的丰度较低，这支持了该物种在野外通过腐生方式获取碳的模式。在 A. thiersii 的转录组中鉴定出了纤维素酶基因的同源物，这些基因在其他担子菌中对纤维素的分解起着关键作用，这表明该物种具有降解纤维素的遗传潜力。鹅膏菌 thiersii 也可以利用人工纤维素或无菌草屑作为唯一的碳源。从三个核基因区域的 DNA 序列和四个简单序列重复标记的带型来看，该物种 31 个种群的分布范围遍及整个已知范围，这表明 A. thiersii 种群的遗传多样性较低。从 20 世纪 50 年代至今采集的 A. thiersii 标本地图表明，该物种正在经历分布范围的扩大。它于 1952 年在德克萨斯州首次报道，现在分布在从伊利诺伊州北部的九个州。这些数据为解释 A. thiersii 的基因组提供了生态背景，目前美国能源部联合基因组研究所正在对其进行测序。
