Cabbage root fly resistant thanks to its gut bacteria

December 11, 2019 All

The cabbage root fly is an insect with a big impact. It is harmful to many cabbage plants due to the ability of its larvae to deal with the insecticidal toxins produced by cabbages. Tijs van den Bosch’s thesis demonstrates that the cabbage root fly harbours gut bacteria that break down toxins, contributing to its resistance. This is possible due to their saxA gene. It is also shown that this gene is important for plant pathogenic bacteria. Tijs van den Bosch will defend his thesis at Radboud University.
The cabbage root fly (Latin name: Delia radicum) is considered an unwanted guest by farmers and vegetable garden owners. The cabbage root fly larvae are harmful to cabbage plants, such as cauliflower, broccoli and Brussels sprout, because they infest their roots, causing the plants to shrivel and die. Their impact on rapeseed is even more considerable: up to 50% of yield loss has been reported. Many of the most effective cabbage root fly insecticides have been banned by the EU.
It is common knowledge that the cabbage root fly larvae are able to resist isothiocyanates, which are natural toxins released when cabbage plants are being infested. Isothiocyanates give a bitter flavour to broccoli and a pungent flavour to wasabi. However, Tijs van den Bosch, microbiologist, recently discovered that the cabbage root fly larvae partially owe their resistance to their gut bacteria.
Protein degrades toxin
Van den Bosch says: “We have dissected the larvae, removed their intestine and examined which gut bacteria were able to resist high levels of isothiocyanates. Upon discovering various bacterial strains, we wondered whether something in their DNA enables them to resist the toxin.” This turned out to be the saxA gene. By studying this gene, Van den Bosch and his colleagues found out that the protein encoded by the saxA gene degrades the isothiocyanate molecule in the presence of water.
Single gene produces pathogen
Van den Bosch and his fellow researchers also discovered that the SaxA protein plays an important role in other plant pathogens, such as Pectobacterium, which is known for its ability to cause bacterial soft rot in plants.
“We discovered that we could prevent two types of bacteria from harming cabbage plants by eliminating the saxA gene”, says Cornelia Welte, Assistant Professor of microbial interactions at Radboud University. “We also managed to convert a non-pathogenic bacterium to a plant pathogen, only by adding this gene to the bacterium. Therefore, this gene proves to play an important role in determining whether or not a bacterium is pathogenic to cabbage plants.“
Plant protection
Further research into plant protection focussing on the microbiome of insects is needed. “One option is to grow plants that ensure cessation of the SaxA protein production by bacteria. Another option is to develop and spread a bacterium with the ability to colonise the gut of cabbage root fly larvae and, as a result, outcompete harmful bacteria. However, this process requires setting up a close collaboration with the industry first,” Van den Bosch says.

Source : radboudrecharge

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