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Involvement of auxin in the arbuscular mycorrhizal symbiosis

Etemadi-Shalamzari, Mohammad. Involvement of auxin in the arbuscular mycorrhizal symbiosis. PhD, Institut National Polytechnique de Toulouse, 2014

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Official URL: http://ethesis.inp-toulouse.fr/archive/00002861/

Abstract

Most land plant species live in symbiosis with arbuscular mycorrhizal (AM) fungi. This is a very ancient symbiosis dating back to 450 million years. AM fungi are soil fungi that belong to the Glomeromycota. They are present in most terrestrial ecosystems. Thus they can be considered as an integral root component of plants. They form essential functional structures called arbuscules in root cortical cells at which mineral nutrients are released to the plant in exchange of sugars. The phytohormone auxin is involved in many developmental processes in plants, including apical dominance, tropisms, vascular patterning and lateral root formation. The main objective of our work was to investigate further the role of auxin in the mycorrhizal developmental process. We already know that AM symbiosis stimulates the lateral root formation in host plants, which could be due to modification of auxin metabolism, transport or perception. The microRNAs (miRNAs) are ~21-nucleotides noncoding RNAs that target corresponding mRNA transcripts for cleavage and transcriptional repression. Several miRNAs interact with auxin signaling and among them miR393 that targets auxin receptors. We investigated the role of miR393 in AM root colonization. In Solanum lycopersicum (Solanaceae), Medicago truncatula (Fabaceae) and Oryza sativa (Poaceae), expression of the precursors of the miR393 was down-regulated during mycorrhization. In addition DR5-GUS, a reporter for auxin response, was found to be preferentially expressed in root cells containing arbuscules. By over-expressing miR393 in roots and therefore down-regulating auxin receptor genes, arbuscules could not develop normally. As components of auxin receptor complexes, Aux/IAA proteins play a major role in auxin signaling pathway by repressing the activity of ARF type transcription factors. We checked the expression of 25 AUX/IAA genes in AM roots. Among them, we focused on IAA27 that was significantly up-regulated during the early stages of AM symbiosis. IAA27 down-regulation in plants led to a strong decrease of AM colonization and arbuscule abundance. We showed by different approaches that the positive regulation of mycorrhization by IAA27 was linked to strigolactone biosynthesis. Overall these results strongly support the hypothesis that auxin signaling plays an important role both in the early stage of mycorrhization and in the arbuscule formation.

Item Type:PhD Thesis
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
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Research Director:
Zouine, Mohamed and Combier, Jean-philippe
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Deposited On:11 Feb 2015 22:58

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