Development of new resistance to root-knot nematodes: characterization of effector targets of parasitism in tomato

President of the jury :                       

Rapporteurs :                     

• Dr Élodie GAULIN, Maîtresse de conférences, LRSV
• Dr Isabelle FUDAL, Directrice de recherche, INRAE-Bioger        

Examiners

• Dr Harald KELLER, Directeur de recherche, Institut Sophia Agrobiotech
• Dr Fabienne VAILLEAU, Directrice de recherche, LIPME

Thesis Director :

• Dr Bruno FAVERY, Directeur de recherche, Institut Sophia Agrobiotech
• Dr Michaël QUENTIN, Maître de Conférence, Université Côte d’Azur     

Abstract :

Plant-parasitic nematodes of the Meloidogyne genus, commonly known as root-knot nematodes, represent a significant global threat to agriculture. These obligatory plant parasites have evolved intricate and unique parasitic mechanisms. By injecting proteins known as "effectors" into the host plant, they trigger cellular reprogramming, resulting in the transformation of root cells into hypertrophied, multinucleate feeding cells termed "giant cells." However, the mechanisms underlying the formation of these newly developed structures remain largely elusive. This work delves into the investigation of two secreted proteins from the root-knot nematode M. incognita, namely MiEFF12 and MiEFF17. Using a yeast two-hybrid strategy, their respective plant protein targets were identified, and their roles in the interaction and formation of giant cells were investigated. In situ hybridization experiments showed that MiEFF12 is expressed in the salivary glands of the RKN juveniles, suggesting that it is secreted in planta. Fusion of MiEFF12 with GFP revealed its localization to the endoplasmic reticulum (ER) of plant cells. Among its plant targets, the PLANT BAP-LIKE PROTEINs (PBLs) proteins were identified in tomato. These PBLs are crucial in regulating ER homeostasis. Transcriptome analysis (RNA-seq) of roots of Arabidopsis plants overexpressing MiEFF12, compared to wild-type plants, showed that this effector can modulate defense and ER stress functions. In N. benthamiana, plants affected in PBLs expression showed increased resistance to root-knot nematodes. These results confirm that the EFF12 effectors manipulate PBL functions to enable nematode parasitism in N. benthamiana. In addition, the expression of the MiEFF17 effector in salivary glands was demonstrated. Yeast two-hybrid assays were used to identify its host targets, the Kinesin Light Chain Related proteins (KLCRs) in tomato and Arabidopsis. Functional analysis showed that manipulation of KLCR by MiEFF17 is pivotal for the parasitic success of M. incognita. This research highlights the importance of studying the molecular dialogue between parasites and plants, in particular characterizing the proteins targeted by these pests. Such knowledge will contribute to the development of novel resistance strategies against these crop-damaging nematodes.

Keywords :

Meloidogyne incognita, effector, endoplasmic reticulum (ER), ER quality control, plants

The thesis can also be followed remotely via Zoom:

https://inrae-fr.zoom.us/j/4878440533?pwd=aFJaMnF4Nmg5Q1NvVHdJenkxUVplUT09