Parasitic worms aren’t only a threat to animal or insects, plants have to deal with them as well.
The Worms Attack
While these sorts of worms may not outright kill their target plants, they can significantly damage them by causing root and nutrient pathways, like the xylem and phloem, to become deformed from the worms invading them. Once inside of a plant, the parasites begin to drain nutrients and water from their host, weakening them, and leaving them open to attack from other parasites or pathogens.
Nematodes are especially aggressive toward plants and are responsible for major crop losses worldwide with losses including, for example, 30% of banana harvests from an infestation. Combating them is also difficult, as the method of parasitic worms of invading the body of a plant means that similarly invasive chemical responses must be used to kill them. These few available options are expensive and not always effective.
Plants are not without their own abilities to fight back, however. Normally, a nematode will attack a plant from the roots, burrowing up through these structures into the main body of the plant and the cylindrical pathways for nutrients to pass through. To stop the plant from responding to this, they release a number of molecules that down-regulate or just stop the function of immune response genes.
PTI For PAMP Defense
The best bet for a plant is to sense the threat from a nematode early through special mechanisms called pathogen-associated molecular patterns (or PAMPs). These are a list of recognized molecules that a plant’s pattern recognition receptors can notice and then activate the immune response in earnest.
This PAMP-triggered immunity, also known as PTI, starts by causing the release of a number of chemicals into the plant’s cells, along with a reinforcement of root cells to prevent invasion. Enzymes known as kinases begin activating and shuttling around energy-related molecules to keep the cells going, moving signals, and triggering cellular systems. Lastly, the plant alters its own transcriptome, that is the total set of messenger RNA being used to create proteins, in order to prevent the nematode molecules from affecting the plant’s gene expression.
Due to how important this system is, genes involved in recognizing PAMPs are highly conserved by plants from generation to generation and they are a great way of telling what specific pathogens attack plants in a certain region.
Kinases and Immunity
It is the kinases though that are of the most importance during an attack. They are the ones that help regulate and drive forward all the different cellular systems. Without them, signal transferring and many chemical reactions would not be able to take place.
One well known kinase is called BAK1 and a version exists in both mammals and plants, though they act fairly differently. In plants, it is a primary signaling kinase for the immunity response of PTI. When tests have been conducted that interfere with the gene that codes for BAK1, the altered plants have been shown to be even more susceptible to pathogen attack.
But that kinase protein is a more general one. Until now, no one has been able to identify specific nematode-associated molecular patterns. Recent studies suggested a place to look though, as it appears PTI responses to nematodes occurs on the surface of exterior cells. This is even though a fair number of nematode resistance genes have been identified in the genome of plants.
A Target Against Nematodes
Researchers at the University of Bonn in Germany focused on identifying kinases similar to BAK1 and that might be connected to those genes. What they found is that another kinase named NILR1 becomes specially up-regulated during nematode attacks. Through various tests, they were able to showcase how NILR1 is directly responsible for pathogen immune response to nematodes in particular. Similarly, in mutant Arabidopsis models that had the gene for the kinase turned off, they found that the plants became hypersusceptible to nematodes with barely any defenses at all.
This being the first discovery of a kinase receptor that responds to nematode parasites specifically gives multiple options in the future to protect plants and agricultural crops from infection. Up-regulation and other methods of increasing the responsiveness and ubiquity of the kinase should be helpful in producing plants that are vigilant against attack and able to defend themselves against nematodes without any other outside help.
Simple gene manipulation such as this to bolster the immune system of plants may be the key to future protective measures in both plants and animals. Perhaps even in humans as well.
Photo CCs: A juvenile root-knot nematode (Meloidogyne incognita) penetrates a tomato root – USDA-ARS from Wikimedia Commons