Mandyam Keerthi G, Jumpponen Ari
Department of Agriculture, Alcorn State University Lorman, MS, USA.
Division of Biology, Ecological Genomics Institute, Kansas State University Manhattan, KS, USA.
Front Microbiol. 2015 Jan 12;5:776. doi: 10.3389/fmicb.2014.00776. eCollection 2014.
Plant tissues host a variety of fungi. One important group is the dark septate endophytes (DSEs) that colonize plant roots and form characteristic intracellular structures - melanized hyphae and microsclerotia. The DSE associations are common and frequently observed in various biomes and plant taxa. Reviews suggest that the proportion of plant species colonized by DSE equal that colonized by AM and microscopic studies show that the proportion of the root system colonized by fungi DSE can equal, or even exceed, the colonization by AM fungi. Despite the high frequency and suspected ecological importance, the effects of DSE colonization on plant growth and performance have remained unclear. Here, we draw from over a decade of experimentation with the obscure DSE symbiosis and synthesize across large bodies of published and unpublished data from Arabidopsis thaliana and Allium porrum model systems as well as from experiments that use native plants to better resolve the host responses to DSE colonization. The data indicate similar distribution of host responses in model and native plant studies, validating the use of model plants for tractable dissection of DSE symbioses. The available data also permit empirical testing of the environmental modulation of host responses to DSE colonization and refining the "mutualism-parasitism-continuum" paradigm for DSE symbioses. These data highlight the context dependency of the DSE symbioses: not only plant species but also ecotypes vary in their responses to populations of conspecific DSE fungi - environmental conditions further shift the host responses similar to those predicted based on the mutualism-parasitism-continuum paradigm. The model systems provide several established avenues of inquiry that permit more detailed molecular and functional dissection of fungal endophyte symbioses, identifying thus likely mechanisms that may underlie the observed host responses to endophyte colonization.
植物组织中存在多种真菌。其中一个重要的类群是深色有隔内生菌（DSEs），它们定殖于植物根部并形成特征性的细胞内结构——黑化菌丝和微菌核。DSE共生关系很常见，在各种生物群落和植物类群中经常能观察到。综述表明，被DSE定殖的植物物种比例与被丛枝菌根（AM）定殖的植物物种比例相当，显微镜研究表明，真菌DSE定殖的根系比例可以与AM真菌的定殖比例相当，甚至超过后者。尽管DSE定殖的频率很高且具有潜在的生态重要性，但其对植物生长和表现的影响仍不清楚。在这里，我们借鉴了十多年来对这种鲜为人知的DSE共生关系的实验，并综合了来自拟南芥和韭葱模型系统以及使用本地植物的实验中大量已发表和未发表的数据，以便更好地解析宿主对DSE定殖的反应。数据表明，在模型植物和本地植物研究中宿主反应的分布相似，这验证了使用模型植物对DSE共生关系进行易于处理的剖析的可行性。现有数据还允许对宿主对DSE定殖反应的环境调节进行实证检验，并完善DSE共生关系的“共生-寄生连续体”范式。这些数据突出了DSE共生关系对环境的依赖性：不仅不同植物物种，而且不同生态型对同种DSE真菌种群的反应也不同——环境条件进一步改变宿主反应，类似于基于共生-寄生连续体范式所预测的反应。模型系统提供了几个既定的研究途径，允许对真菌内生菌共生关系进行更详细的分子和功能剖析，从而确定可能是观察到的宿主对内生菌定殖反应基础的潜在机制。
