Soutenance de thèse - Yara NOUREDDINE

En présentiel (limité) ou via Zoom https://univ-cotedazur.zoom.us/j/81322205634?pwd=SFpQQWxFMVB1TldzMXRrSDJtV25pUT09
ID de réunion : 813 2220 5634
Code secret : 742595

devant le jury composé de :

Président/te du jury :

• Dr. Paula FURLA, Professeure, UCA, Nice

Rapporteurs/trices :

• Dr. Nicolas BOUCHE, DR, INRAE, Versailles
• Dr. Maria MANZANARES-DAULEUX, Professeure, ENSAR

Examinateurs/trices :

• Dr. Sébastien THOMINE, DR, I2BC, Gif-sur-Yvette
• Dr. Christine LELANDAIS, MCU, IPS2, Gif-sur-Yvette

Directeur/trice de Thèse :

• Dr. Bruno FAVERY, DR, ISA, Sophia Antipolis
• Dr. Stéphanie JAUBERT-POSSAMAI, CR, ISA, Sophia Antipolis

Abstract :

Root-knot nematodes (RKN), genus Meloidogyne, are microscopic plant parasitic worms which infect roots of more than 5 000 cultivated plant species and cause massive crop yield losses worldwide. Within host root, RKN induce the formation of root galls by inducing the dedifferentiation of root vascular cells into giant and multinucleated feeding cells. The formation of feeding cells can be split into two phases: successive nuclear divisions during the first ten days post infection (dpi), then from 10 to 21 dpi feeding cells nuclei undergo extensive endoreduplication and plant growth. These feeding cells supply water and nutrients essential for nematode development. The formation of these feeding cells is the result of an extensive reprogramming of gene expression in targeted root cells as shown by transcriptome analyses. However, few data are available on the regulation of gene expression in these
structures. The objective of my PhD thesis was to study small non-coding RNAs, microRNAs, that are key regulators of gene expression. microRNAs act at the post-transcriptional level by inducing the degradation or inhibition of the translation of targeted messenger RNAs (mRNAs). During my PhD thesis, sequencing of small RNAs from tomato (Solanum lycopersicum) galls induced by Meloidogyne incognita RKN and uninfected roots identified 174 microRNAs that are differentially expressed in galls at 7 and/or 14 dpi. mRNAs targeted by microRNAs in tomato galls were then identified by integrating microRNA sequencing data with data from transcriptome analysis and from a specific sequencing of cleaved mRNAs named degradome approach. This integrative analysis built a microRNA-gene regulatory network acting during the formation of galls and feeding cells in tomato roots. Three microRNAs families, miR167, miR398 and miR408, were selected for functional analyses.
MiR167 family targets the auxin-response factors ARF8A and ARF8B. These ARFs belong to auxin signaling pathway, a key hormone in plant-RKN interaction. Using tomato lines expressing the two ARF8 promoters fused to GUS reporter gene, I showed a strong activity of both ARF8 promoters in galls at 7 and 14 dpi, confirming the transcriptomic analyzes. Moreover, we analyzed the effect of a CRISPR deletion within ARF8A and ARF8B coding sequences on the infection by M. incognita. Both CRISPR lines showed a significantly increased resistance to nematode infection correlated with defects in feeding cell formation. Altogether, these result showed that ARF8A and ARF8B expression is required for successful tomato-RKN interaction.
The two conserved microRNA families, miR398 and miR408, are upregulated in tomato and Arabidopsis thaliana galls. miR398 and miR408 and their targets have been previously described to be involved in the copper signaling pathway. MIR398 and MIR408 expression is activated in response to copper starvation by the SPL7 transcription factor and mature miR398 and miR408 repress expression of genes encoding copper binding proteins non-essential for plant development. By using Arabidopsis lines expressing transcriptional fusion with GUS reporter gene, I showed that both MIR408 and SPL7 were expressed within nematode induced feeding cells. Moreover, infection assays with mir408 and spl7 mutants or lines expressing mutated targets resistant for miR398 cleavage showed an increased resistance of these lines to nematode infection. Finally, watering plants with copper sulfate, at concentration below toxic concentrations for the plants or for the nematodes, induced a strong resistance to nematode infection. Altogether, these results demonstrate the role of the copper signaling through activation of miR398 and miR408 by SPL7 in the formation of giant feeding cells.
To conclude, the work presented in this thesis demonstrates the important role of three microRNAs families and their targets in the formation of nematode-induced feeding cells.

Keywords:

microRNAs, Root-knot nematodes, Tomato, Arabidopsis thaliana, Galls