Surplus sugar helps whiteflies protect the plant

Surplus sugar helps whiteflies protect the plant

In Malawi, South East Africa, the pest threatens the food supply of thousands of people. The insect is not to be confused with the greenhouse whitefly Trilarodes vaperiorum, which is more frequently found in Europe. Credit: Daniel G. Vasso

While attacking the cross, the sap-sucking whitefit Bemisia can activate the chemical defenses of these plants. In a new study, an international team of researchers demonstrated that the insect is able to harm a large portion of plant toxins by binding surplus sugar to them. Thus the whitefly is completely new and so far implements detoxification mechanisms to reduce plant protection, which may explain the success of this major agricultural pest. The study is published in Nature Chemical Biology.

Crop pests of hundreds of plant species worldwide

Whiteflies are a family of sucker worms that feed on phloem containing plant sugar. The silver-white Bemisia class is particularly widespread worldwide and is highly feared as an agricultural pest. Strictly speaking, it is not a single species, but there are about two dozen barely distinguishable species.

Real damage to plants occurs when pests emit sweet honeydew, which causes fungi to colonize plants, and are transmitted from plant viruses by a variety of insects. For researchers studying the detoxification mechanism of plant pests, Bemisia tabis is a particularly interesting study system.

“This insect is probably one of the most successful, phloem pests found in hundreds of different species of insects in the world, which faces a diverse landscape of chemical defense compounds in their diet,” says Michael Easson. One of the two first authors of the study, who is a doctoral researcher at the Max Planck Institute for Chemical Ecology. For this reason, he worked closely with an international research team, in which the Hebrew University of Jerusalem played an important role, to find out how to make Bemisia tabaci such a successful insect pest and how it would feed its edible plants. How to deal with chemical defense of

The team around Daniel Vaso, project group leader in the Department of Biochemistry at the Max Planck Institute, has been studying detoxification mechanisms in various herbs for many years. Of particular interest is how pests are defined to crucify the so-called mustard oil bomb: the defense mechanism of this plant has two components, glucosinolates and the enzyme myosinase, which are stored in various plant cells.

If plant tissues are damaged by herbivores, glucose sugars from glucosinolates form enzyme cleavage and produce toxic mustard oil. Since sap-sucking insects do not chew leaf tissue and only cause minor tissue damage with their style, the narrow vocal they use to drink phloem, it was previously believed that this defense mechanism of plants. Aphids play only a small role in the protection of whitelists. However, recent research has shown that not only chewing, but also sucking insects can activate the mustard oil bomb.

Surplus sugar helps whiteflies protect the plant

When an additional glucose group is bound to it, protoxin (glucosinolate) is inactivated. In comparison, protoxin is converted into an active toxin (mustard oil) in non-adapted herbs. Credit: Kimberly Falk

A novel detoxification path

Scientists used the model plant Arabidopsis thaliana, a cruciferous plant whose defense is also based on glucosinolates to study the metabolism of whiteflys in more detail. They specifically analyzed honeydew, the sugar-containing secretion of many sap-sucking insects, through chemical analysis and isotope labeling of individual chemical compounds. The researchers were surprised that the defense mechanism of Arabidopsis thaliana was actually activated by whitefill as they found toxic mustard oil. However, they also discovered that the biochemical pathways known for detoxification are entirely a novel type of reaction in which sugar from phloem is used to extract plant toxins. “This reaction basically costs these pests, because this sugar is in such a surplus and is secreted as honey anyway,” says study leader Daniel Vasso.

The detoxification process is based on a simple reaction in which the sugars in the form of a glucose group are bound to another sugar that is already part of the glucosinolate. Researchers showed that the resulting new chemical product could not be activated by the plant’s enzyme, perhaps because it is too heavy.

For this novel glucosylation pathway, researchers were able to identify enzymes in Bemisia genus that catalyze the chemical reaction. They were surprised at the variety of detoxification toolboxes of this insect. Although they focused on only one category of plant protection, glucosinolates, they have already found at least three independent pathways for detoxification. Vaso states, “It will be interesting to see how common these detoxification pathways are and whether whitefires also have specific detoxification pathways for other plant defensive compounds on their repertoire, and which enzymes regulate these processes. ”

Fungal pathogen neutralizes plant defense mechanism

more information:
Easson et al., Glucosylation inhibits plant defense activation in phloem-feeding insects, Nature Chemical Biology (2020). DOI: 10.1038 / s41589-020-00658-6,

Provided by the Max Planck Society

Quotes: Help to reclaim surplus Chinese whiteflies from plant rescue (2020, 28 September) to 30 September 2020 from Does.

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