When was the last time you did some digging in the dirt? You probably came across a friendly earthworm, but did you know that lurking in a handful of soil could be microscopic roundworms “a.k.a. nematodes” and some of these make plants sick. In fact, plant-parasitic nematodes cause billions of dollars in crop losses worldwide every year. They are a farmers’ hidden enemy.
There are many types of plant-parasitic nematodes and they can infect most cultivated plants. One group of plant-parasitic nematodes, the cyst nematodes, are specialist feeders that have adapted to parasitize certain plant species and not others. There are corn cyst nematodes, soybean cyst nematodes, sugar beet cyst nematodes, potato cyst nematodes, to name a few. They use a hollow mouth spear to release secretions (a.k.a. SPIT) containing effector proteins into the roots of plants to establish a parasitic association. These effector proteins are used by the nematode to modify root cells into a specialized feeding site that then diverts and disrupts water and nutrient flow to the nematode at the detriment of its host. Belowground root feeding by nematodes typically results in visible aboveground symptoms such as stunting, wilting, and chlorosis, ultimately leading to lost yield.
Without these secreted effector proteins, the nematode would be ineffective as a parasite. This is why researchers have focused their efforts on identifying the effector proteins in nematode SPIT and determining how they are used by the nematode to alter host cellular functions for their advantage.
In a recent article, researchers identified an effector protein produced in the secretory dorsal gland cell of cyst nematodes called 2D01. 2D01 was found to interact with the plant protein HAESA, known as a key regulator of a cellular signalling pathway; activating cell wall remodelling enzymes important for cell separation during lateral root emergence and leaf abscission. Cell wall remodelling is one of the hallmarks of the feeding site formed by cyst nematodes within roots, called the syncytium. HAESA was found to be expressed at these nematode feeding sites. When this protein was knocked out in the plant, the plants became less susceptible to cyst nematode infection, further validating the importance of this host protein in nematode parasitism.
Future work directed at how this effector protein impacts the function of HAESA will provide a clearer understanding of how the nematode is exploiting this plant signalling pathway and may even open the door to identifying counter strategies to control these devastating soilborne pathogens to improve crop yields.
Anju Verma, Marriam Lin, Dante Smith, John C. Walker, Tarek Hewezi, Eric L. Davis, Richard. S. Hussey, Thomas J. Baum, and Melissa G. Mitchum published this study in Molecular Plant Pathology:
TITLE IMAGE: Nematode worm – root infection. A cross-section of an infected plant root shows blue (GUS) staining next to nematode feeding sites. The diagram indicates how the nematode effector protein, 2D01, enters the plant through the worm’s mouth. The plant HAESA protein (indicated as a blue cell wall structure on the diagram and with blue GUS staining on the micrograph) is the predicted target protein. The nematode 2D01 effector may bind the plant HAESA protein to suppress plant defence and mould plant cell walls to form a syncytium, the feeding site of the nematode. All images used with permission of the author.