Characterization of the post-transcriptional regulations involved in the formation of giant cells induced by root-knot nematodes

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​Résumé :

Root-knot nematodes (RKN), genus Meloidogyne, are microscopic plant parasitic worms which infect roots of more than 4000 cultivated plant species and cause massive crop yield losses worldwide. RKN induce the formation of root galls by inducing the dedifferentiation of root vascular cells into giant and multinucleated feeding cells. 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 analyses of transcriptomes from galls or giant cells from various plant species. MicroRNAs are small non-coding RNAs of 20-22-nucleotides (nt), that are key regulators of gene expression in eukaryotes at the post-transcriptional level. During my PhD thesis, small RNAs (<35nt) and messenger RNAs from tomato (Solanum lycopersicum) galls induced by the nematode Meloidogyne incognita and from uninfected roots were sequenced using the Illumina technology. We identified 174 miRNAs genes that are differentially expressed in galls at 7 and/or 14 dai. mRNA targeted by microRNAs in tomato galls at 7 and 14 dai were then identified by a specific sequencing of mRNA cleaved degradation products by using the degradome approach. Integrative analyses combining small RNAs, degradome and transcriptome built a global vision of regulatory networks acting during the formation of galls and giant cells. These analyses allowed us to select three families of microRNAs for the functional analyses, whose expression is modified during infection and whose bibliographic data suggested a role in the plant response to nematodes: miR167 which is associated with auxin signaling as well as miR408 and miR398 which are linked to copper signaling. Our results highlight an important role of these miRNAs and their targets in nematode-induced giant cell formation.