The Roles of Auxins and Cytokinins in Mycorrhizal Symbioses |
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Authors: | Susan Jane Barker Denis Tagu |
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Institution: | (1) Plant Sciences, Faculty of Agriculture, University of Western Australia, Nedlands, WA 6907, Australia, AU;(2) Institut National de la Recherche Agronomique, Centre de Nancy, Microbiologie Forestière, 54280 Champenoux, France, FR |
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Abstract: | Abstract
Most land plant species that have been examined exist naturally with a higher fungus living in and around their roots in a
symbiotic partnership called a mycorrhiza. Several types of mycorrhizal symbiosis exist, defined by the host/partner combination
and the morphology of the symbiotic structures. The arbuscular mycorrhiza (AM) is ancient and may have co-evolved with land
plants. Emerging results from gene expression studies have suggested that subsets of AM genes were co-opted during the evolution
of other biotrophic symbioses. Here we compare the roles of phytohormones in AM symbiosis and ectomycorrhizas (EC), a more
recent symbiosis. To date, there is little evidence of physiologic overlap between the two symbioses with respect to phytohormone
involvement. Research on AM has shown that cytokinin (CK) accumulation is specifically enhanced by symbiosis throughout the
plant. We propose a pathway of events linking enhanced CK to development of the AM. Additional and proposed involvement of
other phytohormones are also described. The role of auxin in EC symbiosis and recent research advances on the topic are reviewed.
We have reflected the literature bias in reporting individual growth regulator effects. However, we consider that gradients
and ratios of these molecules are more likely to be the causal agents of morphologic changes resulting from fungal associations.
We expect that once the individual roles of these compounds are explained, the subtleties of their function will be more clearly
addressed. |
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Keywords: | : Phytohormones Arbuscular mycorrhiza Ectomycorrhiza Cytokinin ENOD40 Auxin Root morphology |
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