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New Phytol. 2015 Oct;208(1):224-40. doi: 10.1111/nph.13427. Epub 2015 Apr 28.

Combined genetic and transcriptomic analysis reveals three major signalling pathways activated by Myc-LCOs in Medicago truncatula.

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INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, F-31326, Castanet-Tolosan, France.
CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, F-31326, Castanet-Tolosan, France.
INPT-Université de Toulouse, ENSAT, Avenue de l'Agrobiopole, Auzeville-Tolosane, F-31326, Castanet-Tolosan, France.


Myc-LCOs are newly identified symbiotic signals produced by arbuscular mycorrhizal (AM) fungi. Like rhizobial Nod factors, they are lipo-chitooligosaccharides that activate the common symbiotic signalling pathway (CSSP) in plants. To increase our limited understanding of the roles of Myc-LCOs we aimed to analyse Myc-LCO-induced transcriptional changes and their genetic control. Whole genome RNA sequencing (RNA-seq) was performed on roots of Medicago truncatula wild-type plants, and dmi3 and nsp1 symbiotic mutants affected in nodulation and mycorrhizal signalling. Plants were treated separately with the two major types of Myc-LCOs, sulphated and nonsulphated. Generalized linear model analysis identified 2201 differentially expressed genes and classified them according to genotype and/or treatment effects. Three genetic pathways for Myc-LCO-regulation of transcriptomic reprogramming were highlighted: DMI3- and NSP1-dependent; DMI3-dependent and NSP1-independent; and DMI3- and NSP1-independent. Comprehensive analysis revealed overlaps with previous AM studies, and highlighted certain functions, especially signalling components and transcription factors. These data provide new insights into mycorrhizal signalling mechanisms, supporting a role for NSP1, and specialisation for NSP1-dependent and -independent pathways downstream of DMI3. Our data also indicate significant Myc-LCO-activated signalling upstream of DMI3 and/or parallel to the CSSP and some constitutive activity of the CSSP.


Medicago truncatula; Symbiosis; Transcriptomics; arbuscular mycorrhizal (AM) fungi; common symbiotic signalling pathway (CSSP); lipo-chitooligosaccharides (LCOs)

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