A root-knot nematode effector targets the spliceosomal plant machinery facilitating the giant cells formation

Abstract

Root-knot nematodes are phytoparasites that trigger a long-lasting and intimate relationship within their host plant. To complete their life cycle, nematodes first invade the root system and secondly induce the reprogramming of 5 to 7 vascular root cells into a feeding site built-up of giant cells. Via their stylet, Meloidogyne species secrete in the host cells effectors protein synthesized in esophageal glands. In planta, these effectors manipulate some important processes such as cell cycle, cytoskeleton remodeling, plant defenses, transcriptional regulations or phytohormones signaling, leading to the formation of the giant cells. MiEFF18 was identified as such a putative effector secreted to favor parasitism (Rutter et al, 2014; Nguyen et al, 2017).

The MiEFF18 effector carries a signal peptide for secretion and nuclear and nucleolar localisation signals. MiEFF18 localised into the nucleus, and particularly within the nucleolus, when transiently expressed in planta. Because MiEFF18 does not have any known function, a yeast two hybrid approach was used to search for plant partners of this effector using a tomato root cDNA library. We found the spliceosomal protein Sm as a high scored target of MiEFF18. We validated this interaction in planta using Bimolecular Fluorescent Complementation (BiFC). Pathogenicity tests using VIGS-silenced N. benthamiana plants and  A. thaliana KO mutant lines showed that Sm protein is an essential protein in the nematode parasitic success. Staining of galls showed that M. incognita is not able to develop correctly in plants missing Sm. We are investigating the outcomes of MiEFF18 interaction with its target, and the cellular functions, including alternative splicing, RNA quality control or PTGS modulation that may be hijacked by this effector.

• Rutter et al, 2014. Mol Plant Microbe Interact. Sep;27(9):965-74.
• Nguyen et al, 2017. New Phytol. Jan;217(2):687-699.