Spider mite spit breaches plant firewall

Spider mites can suppress the natural defense system of plants by manipulating plant genes with proteins in their saliva. This enables them to reproduce more quickly. During her PhD, researcher Joséphine Blaazer unraveled the underlying mechanism, which offers perspectives for a new form of pest control, according to the Institute for Agricultural, Fisheries, and Food Research (ILVO).

Through mutations, breeders could make the vulnerable plant genes inaccessible to the mites. This is good news for growers of tomatoes, cucumbers, and strawberries grown in greenhouses because spider mites can do great damage to them.

Spider mites on tomato plant. © Floriankittemann | Dreamstime.com

Spider mite spit breaches plant firewall
Plants have a natural defense system against pests, but through years of selection, this defense system has become less effective. One of the pests that occur both in the field and in greenhouses is the spider mite. Because spider mites are very small and reproduce at light speed, it is extremely difficult to notice them in time. Moreover, spider mites suppress the natural defense system of plants, making them even more susceptible. How exactly this works was investigated by Joséphine Blaazer during her doctoral study with Professor Merijn Kant of the University of Amsterdam and under the supervision of Wannes Dermauw of ILVO.

Specifically, she investigated the function of the saliva protein SHOT2b in spider mites. SHOT2b turned out to have a special interaction with an important plant protein, MLK4. This plant protein is important for plant growth and flowering, but also regulates the production of toxins against mites. SHOT2b in turn reduces the production of some of those toxins.

You would think that spider mites would seek out plants without MLK4, as they have no toxins to throw into the fray. Strangely enough, Joséphine Blaazer discovered that the mites actually lay fewer eggs on plants without MLK4. She investigated why this was the case and discovered that the mite's saliva protein can probably hijack the MLK4 protein and reprogram it so that the plant is weakened and the mite can reproduce better.

Security against hackers
So can't we just switch off MLK4 in plants? No, the plant needs the gene to grow and flower properly. But the results of the research do offer potential for making plants more resilient in a different way: through targeted mutations in the MLK4 plant gene, the interaction with the SHOT2b spider mite protein could be broken. The MLK4 gene would still be there, but the spider mite protein SHOT2b would no longer be able to recognize it and so would not be able to switch off the plant's defense in order to become stronger itself.

"This route is very interesting for strengthening the natural defense system of plants, but further research is certainly needed before this can be applied in practice. In wheat, there is already a success story where plants were made more resistant to mildew by adapting a susceptibility gene (also called S-gene)" says supervisor Wannes Dermauw (ILVO). "As far as spider mite infestations in Flanders are concerned, we should mainly focus on making tomatoes, cucumbers and strawberries more resistant. These are mainly grown in greenhouses, which provide an ideal microclimate for spider mites."

Source: ILVO

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