Root-knot nematodes (RKN) of the genus Meloidogyne are microscopic worms responsible for significant damage to thousands of plant species by causing root deformations known as galls. These parasites interact with their host in a fascinating way. Juveniles invade the roots and migrate into the vascular tissue, where they induce the formation of hypertrophied and multinucleate ‘giant’ feeding cells. These specialised cells provide the nematodes with the nutrients they need to grow and reproduce. RKNs evade the plant’s immune system and manipulate plant cell physiology by secreting a cocktail of proteins, called effectors, into the host plant.
To understand how these parasites are able to hijack plant functions, Dr Michaël Quentin and his colleagues from France’s National Research Institute for Agriculture, Food and Environment (INRAE) and Chinese Academy of Agricultural Sciences (CAAS) are investigating the function of these effectors in the plant. During her PhD, Dr Salomé Soulé identified a new RKN effector family, called EFFECTOR12 (EFF12), which is critical for RKN parasitism. EFF12 proteins are conserved in RKN species and are specific to these RKN, i.e. other animal species do not appear to possess similar proteins. During infection, Meloidogyne incognita (Mi) EFF12 proteins, produced in the salivary glands of the nematode, are injected into the plant cell and target the endoplasmic reticulum (ER), a critical cellular organelle involved in protein synthesis and stress responses.
To study the function of EFF12, the researchers looked for plant proteins that would interact with this nematode protein. Research shows that MiEFF12 interacts with two ER-associated proteins in the host plant called PLANT BAP-LIKE (PBL) proteins. The two proteins are orthologous to, meaning the parallel of, the human B-CELL RECEPTOR-ASSOCIATED PROTEIN 31 (BAP31 or BCAP31) and a stress responsive transcription factor BASIC LEUCINE ZIPPER 60 (BZIP60). Both proteins are involved in the plant’s ER quality control system, which ensures proper protein folding and responds to ER stress.
By studying gene expression changes in the presence of MiEFF12 (RNA-sequencing analysis) and the impact on the plant immune response (immunity-suppression bioassays), the researchers were able to reveal the contribution of MiEFF12 to the modulation of host immunity. The interaction between MiEFF12 and the ER-associated proteins helps the nematodes suppress plant immune responses, such as the production of reactive oxygen species (ROS), making the plant more susceptible to infection. Silencing the PBL genes in plants reduces their susceptibility to RKN, highlighting the importance of these proteins in nematode parasitism.
Overall, the study provides new insights into how RKN effectors manipulate plant processes to promote infection. Understanding these interactions may help to develop new strategies to improve plant resistance to these harmful parasites. By targeting host proteins manipulated by the pathogens, scientists may be able to create plants that are more resistant to RKN attack, thus limiting the use of pesticides and reducing agricultural losses.
Salomé Soulé, Kaiwei Huang, Karine Mulet, Joffrey Mejias, Jérémie Bazin, Nhat My Truong, Junior Lusu Kika, Stéphanie Jaubert, Pierre Abad, Jianlong Zhao, Bruno Favery, and Michaël Quentin published this work in Molecular Plant Pathology Journal:
The Meloidogyne incognita effector MiEFF12 targets endoplasmic reticulum-resident proteins and corrupts their function in the host immune response to promote parasitism.
