Seeking the elusive function of the root-colonising dark septate endophytic fungi

By K. Mandyam, A. Jumpponen. 2005

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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.

Subfields: Cell Biology, Pharmacology, Plant Science

View Paper: https://www.semanticscholar.org/paper/4df68102c0ff0c847d4795b805b622d7cc049c3c

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Citations in the corpus

Dark septate root endophytic fungi increase growth of Scots pine seedlings under elevated CO2 through enhanced nitrogen use efficiency (2010, background): “Addy et al. (2005) and Mandyam and Jumpponen (2005) suggested alternative explanations for enhanced plant growth without a nutritional interface over which C and nutrients are exchanged.”
Fungal endophytes: diversity and functional roles. (2009, background): “Mandyam & Jumpponen (2005) emphasize the need for simple experiments to determine the basis of biological functions of DSE and urge the scientific community to do so, with which we agree whole-heartedly.”
Effect of Dark Septate Endophytic Fungus Gaeumannomyces cylindrosporus on Plant Growth, Photosynthesis and Pb Tolerance of Maize (Zea mays L.) (2017, background): “degradation of main organic nutrients (Mandyam and Jumpponen, 2005; Newsham, 2011) may contribute to the increase of root biomass.”
Mycorrhizas and dark septate root endophytes in polar regions (2009, background): “Although there are many different questions about the interactions between DSE and plants that are yet to be answered (Mandyam & Jumpponen 2005), we suggest that Koch’s Postulate experiments under realistic conditions, coupled with a thorough understanding of the mechanisms responsible for any…”
Role of Diverse Non-Systemic Fungal Endophytes in Plant Performance and Response to Stress: Progress and Approaches (2010, background): “In some ecosystems, DSEs live more frequently as dominant root mycobiota than do mycorrhizal fungi (Wilberforce and others 2002a, b), which is indicative of equally important functions of root endophytic fungi.”
Regulation and accumulation of secondary metabolites in plant-fungus symbiotic system (2007, background): “Endophytes usually occur in above-ground plant tissues, but also occasionally in roots (for example, dark septate endophytic fungi have been isolated from various plants), and are different from mycorrhizae by lacking external hyphae (Mandyam and Jumpponen, 2005; Faeth and Fagan, 2002).”
Characterization of melanin isolated from a dark septate endophyte (DSE), Exophiala pisciphila (2011, background): “DSE might function as mutualistic fungi taking part in nutrient and altering the environmental tolerance of host plants, especially in stressed environments (Jumpponen and Trappe 1998; Mandyam and Jumpponen 2005 ).”
A general suite of fungal endophytes dominate the roots of two dominant grasses in a semiarid grassland (2010, background): “(2002) and others (Bell and Wheeler, 1986; Mandyam and Jumpponen, 2005) suggest that fungal melanins provide protection to the plant against extreme temperatures.”