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Published: 2021-06-18

Aphids don’t spit in the glass, but preferably in plant sap

NEWS The gene SLI1 in Arabidopsis protects against infestation and causes aphids to spit 20 times before they start to absorb sugary juice from the plant. Researchers believe the spit helps lice break down the plant's defenses. The new study is published in the scientific journal Plant, Cell & Environment.

Text: Ingrid Söderbergh

Researchers at Umeå University, Wageningen University & Research and the company Keygene have discovered a resistance gene in arabidopsis plants that protects against infestation by peach aphids and two other types of aphids. But tobacco flour aphids and cabbage aphids are first unaffected by the SLI1 gene, but then, for the cabbage aphids, the partying quickly turns into an unusual spot ritual.

Identifying the genetic code for plant disease resistance is tricky. A single gene can usually only offer protection against a specific disease or parasite. But this time it's different. The SLI1 gene protects against several unrelated pests. Research done in part at Umeå Plant Science Centre at Umeå University, Sweden, sheds light on how plants protect themselves from insect pests - and vice versa.

Aphids and mealybugs are widespread on plants and crops. They feed on plant sap, but also spread viruses. Demands to reduce the use of insecticides in agriculture therefore include research on natural defense mechanisms in plants.

Karen Kloth, who is currently a researcher at Wageningen University & Research in the Netherlands and a former postdoctoral fellow in Benedicte Albrectsen's research group at Umeå University, specializes in this area. In 2017, she discovered a gene, SLI1, which makes the model plant arabidopsis (Arabidopsis thaliana) resistant to peach aphids.

In a new study published in Plant, Cell & Environment, the research team shows that this gene is only active in the so-called phloem - the cells that transport the sugar-rich juice through the plant. They also discovered that the gene works against several species of aphids and aphids which, like the peach aphids, feed on phloem juice.

The SLI1 gene reduces appetite and reproduction in lice

“Cabbage whitefly and two different kinds of aphids, tobacco aphids and cabbage aphids, do not thrive on plants with this gene. They get fewer offspring and eggs. With detailed behavioral tests, we have revealed that aphids produce more saliva and it takes longer before they start eating from plants with the gene, which seems to give them a poorer ability to absorb the phloem juice” says Karen Kloth.

However, the gene does not work against all sucking aphids. Mustard aphids showed an unusual behavior that the research team believes is a way to break the resistance. Karen Kloth explains:

“They repeatedly injected their needle-like mouthparts into the phloem and spat up to 20 times before actually starting to eat the SLI1 plants. This may indicate that repeated injections of saliva, which we know contain special proteins, can help lice overcome the plant's defenses.”

Against increased resistance in agricultural crops

That a simple gene can provide protection against several species of sucking insects at the same time is new knowledge that questions evolutionary theories. Aphids are a colossal problem in European plant cultivation and they are difficult to deal with. In addition to the damage they themselves cause to the plant, they spread plant viruses which are a major problem for agriculture. It is therefore quite remarkable to discover that a single gene in arabidopsis can provide protection against different species of aphids at the same time.

 “We hope that further research can reveal the underlying mechanism so that we, through plant breeding with this gene, can increase resilience in future crops” says Karen Kloth.

The new findings, developed in collaboration with Umeå University and the company KeyGene, are partly funded by a Veni grant awarded to Karen Kloth 2018 by the Dutch Research Council (NWO). The project is about research into natural defense mechanisms in plants against insect and virus damage that can reduce the use of insecticides.

About the scientific article:

Kloth, KJ, Shah, P, Broekgaarden, C, Ström, C, Albrectsen, BR, Dicke, M.: SLI1 confers broad-spectrum resistance to phloem-feeding insects. Plant Cell Environ. 2021; 1– 12. https://doi.org/10.1111/pce.14064

Press photo

ABOUT Aphids

All insects tested in the study can be called aphids.

These are plant lice:
Cabbage aphid (Brevicoryne brassicae
Mustard aphid (Lipaphis erysimi)
Peach aphid (Myzus persicae)

These are mealybugs:
Whitefly (Bemisia tabaci)
Cabbage whitefly (Aleyrodes proletella)
Tobacco aphid (Myzus persicae nicotianae)



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