Development of the Populus-Laccaria bicolor ectomycorrhiza modifies root auxin metabolism, signalling and response
Plant Physiol. 2015, 169(1):890-902

Vayssières A, Pěnčík A, Felten J, Kohler A, Ljung K, Martin FM, Legue V

Abstract
Root systems of host trees are known to establish ectomycorrhizal (ECM) interactions with rhizospheric fungi. This mutualistic association leads to dramatic developmental modifications in root architecture with the formation of numerous short and swollen lateral roots ensheathed by a fungal mantle. Knowing that auxin plays a crucial role in root development, we investigated how auxin metabolism, signalling and response are affected in Populus-Laccaria bicolor ECM roots. The plant-fungus interaction leads to the arrest of lateral root growth with simultaneous attenuation of the DR5 auxin response. Measurement of auxin-related metabolites in the free-living partners revealed that the mycelium of L. bicolor produces high concentrations of the auxin indole-3-acetic acid (IAA). Metabolic profiling showed an accumulation of IAA and changes in the indol-3-pyruvic acid dependent IAA biosynthesis, and IAA conjugation and degradation pathways during ECM formation. The global analysis of auxin response gene expression and the regulation of PtaAFB5s, PtaAux/IAAs and PtaARFs expression in ECM roots suggested that a symbiosis-dependent auxin signalling is activated during the colonization by L. bicolor. Taking all this evidence into account, we propose a model in which auxin signalling plays a crucial role in the modification of root growth during ECM formation.

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