Abstract
Sedentary endoparasitic nematodes, such as root-knot nematodes (RKN; Meloidogyne spp.) and cyst nematodes (CN; Heterodera spp. and Globodera spp.) cause considerable damage to agricultural crops. RKN and CN spend most of their life cycle in plant roots, in which they induce the formation of multinucleate hypertrophied feeding cells, called “giant cells” and “syncytia,” respectively. The giant cells result from nuclear divisions of vascular cells without cytokinesis. They are surrounded by small dividing cells and they form a new organ within the root known as a root knot or gall. CN infection leads to the fusion of several root cells into a unique syncytium. These dramatically modified host cells act as metabolic sinks from which the nematode withdraws nutrients throughout its life, and they are thus essential for nematode development. Both RKN and CN secrete effector proteins that are synthesized in the oesophageal glands and delivered to the appropriate cell in the host plant via a syringe-like stylet, triggering the ontogenesis of the feeding structures. Within the plant cell or in the apoplast, effectors associate with specific host proteins, enabling them to hijack important processes for cell morphogenesis and physiology or immunity. Here, we review recent findings on the identification and functional characterization of plant targets of RKN and CN effectors. A better understanding of the molecular determinants of these biotrophic relationships would enable us to improve the yields of crops infected with parasitic nematodes and to expand our comprehension of root development.
Highlights
Plant-parasitic nematodes (PPN) are microscopic worms that withdraw nutrients from the cytoplasm of cells in the aerial or below-ground parts of plants
We review here the most recent advances in our understanding of Root-knot nematodes (RKN) and cyst nematodes (CN) effector functions, focusing on those for which the plant processes targeted have been identified
Nuclear translocation in host cells has been demonstrated by immunolocalisation for only three RKN effectors: the M. incognita MiEFF1 (Jaouannet et al, 2012) and the M. javanica MjNULG1a (Lin et al, 2012) of unknown functions, and the M. graminicola MgGPP involved in plant defense suppression (Chen et al, 2017)
Summary
Plant-parasitic nematodes (PPN) are microscopic worms that withdraw nutrients from the cytoplasm of cells in the aerial or below-ground parts of plants. Plant Targets of Nematode Effectors sedentary, triggering the formation of an unusual feeding site. Nematode effectors target the apoplast and different subcellular compartments, including the nuclei, reflecting the diversity of host cell processes manipulated to promote infection and feeding site formation (Table 1).
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