Seeking the elusive function of the root-colonising dark septate endophytic fungi
Seeking the elusive function of the root-colonising dark septate endophytic fungi
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DOI：
10.3114/sim.53.1.173
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发表时间：
2005
影响因子：
16.5
通讯作者：
K. Mandyam;A. Jumpponen
中科院分区：
文献类型：
--
作者：
K. Mandyam;A. Jumpponen
对来自不同生态系统的菌根和深色有隔内生真菌（DSE）定殖的已发表估计值进行比较表明，从混合植物群落中宿主植物的定殖比例，或者从采样根系的定殖程度来判断，DSE可能与菌根真菌一样丰富。虽然在理解菌根真菌的生态意义方面已经取得了许多进展，但我们对DSE真菌作用的了解还处于起步阶段。为了提供一个可检验假设的框架，我们回顾并讨论了这一知之甚少的根际相关真菌类群最有可能的功能。我们提出，与菌根共生关系一样，DSE - 植物共生关系应被视为具有多种功能，而不限于养分获取以及由此产生的对宿主生长的积极影响。诚然，许多菌根和内生真菌的功能（例如抗逆性、对病原体或食草动物的威慑）可能是通过改善宿主的营养状况和提高其适应性来实现的。因此，确定DSE真菌是否参与宿主的养分获取至关重要，无论是从无机的易溶源，还是从有机的难溶源获取养分。DSE对植物利用有机氮、磷和硫源的促进作用是一个值得进一步关注和研究的课题。即使在没有明确的养分吸收功能的情况下，广泛发生的DSE定殖也可能通过减少宿主根际环境中可用的碳来预先或竞争性地阻止病原体。DSE的高黑色素含量以及它们可能产生的对食草动物有毒或有抑制作用的次生代谢产物，也可能是影响宿主表现的因素。最后，到目前为止，对大多数DSE真菌推测的广泛宿主范围表明，它们是通过宿主对定殖的不同反应来控制植物群落动态的候选者。我们强调需要进行简单的实验，以便在DSE真菌定殖宿主时揭示其基本生物学功能。
A comparison of published estimates of mycorrhizal and dark septate endophyte (DSE) colonisation from various ecosystems suggests that DSE may be as abundant as mycorrhizal fungi as judged by the proportion of host plants colonised in mixed plant communities, or by the extent of colonisation in sampled root systems. While many strides have been made in understanding the ecological significance of the mycorrhizal fungi, our knowledge about the role of DSE fungi is in its infancy. In order to provide a framework of testable hypotheses, we review and discuss the most likely functions of this poorly understood group of root-associated fungi. We propose that, like mycorrhizal symbioses, DSE-plant symbioses should be considered multifunctional and not limited to nutrient acquisition and resultant positive host growth responses. Admittedly, many mycorrhizal and endophyte functions, (e.g. stress tolerance, pathogen or herbivore deterrence) are likely to be mediated by improved nutritional status and increased fitness of the host. Accordingly, it is pivotal to establish whether or not the DSE fungi are involved in host nutrient acquisition, either from inorganic and readily soluble sources, or from organic and recalcitrant sources. Facilitation by DSE of the use of organic nitrogen, phosphorus and sulphur sources by plants is a topic that warrants further attention and research. Even in the absence of a clear nutrient uptake function, the extensive DSE colonisation that occurs is likely to pre-emptively or competitively deter pathogens by minimising the carbon available in host rhizosphere environment. The DSEs' high melanin levels and their potential production of secondary metabolites toxic or inhibitory to herbivores are also likely to be factors influencing host performance. Finally, the broad host ranges speculated for most DSE fungi thus far suggest that they are candidates for controlling plant community dynamics via differential host responses to colonisation. We emphasise the need for simple experiments that allow unravelling of the basic biological functions of DSE fungi when they colonise their hosts.