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Hope for Aphid Infested Plants

Betrayal of the Aphids: Internal Bacteria can Turn on its Host

University of California - Riverside

June 2, 2014 —

Aphids are devastating insect pests and cause great losses toagriculture worldwide. These sap-feeding plant pests harbor in their body cavity bacteria, which are essential for the aphids' fecundity and survival. Buchnera, the bacterium, benefits also because it cannot grow outside the aphid. This mutually beneficial relationship is sabotaged, however, by the bacterium which proceeds to betray the aphid, a research team led by scientists at the University of California, Riverside has found.

student demonstrating how to build trap
Aphids feeding on a stem.
Credit: Scott Edwards, UC Riverside

"Although this betrayal is unintentional, it nevertheless alerts the plant about the aphid's presence and the aphids are unable to reproduce in large numbers," said Isgouhi Kaloshian, a professor of nematology, who led the research project. "A protein from the bacterium, found in the aphid saliva and likely delivered inside the plant host by the aphid, triggers plant immune responses against the aphid. It seems that the plant immune system targets the bacterium and exploits the strict mutual dependency between the plant and aphid to recognize the aphid as the intruder."

Study results appear online in the Proceedings of the National Academy of Sciences.

While feeding, aphids secrete saliva in the plant. To identify the protein composition of the aphid saliva, the researchers collected saliva from more than 100,000 aphids. Using mass spectrometry, they detected 105 proteins. They discovered these proteins were of both aphid and Buchnera origins. One of these Buchnera proteins, GroEL, was found to induce immune responses in plants.

"GroEL was known previously to trigger immunity in animals," said Kaloshian, a member of UC Riverside's Institute for Integrative Genome Biology. "However, our finding that it induces immunity in plants is new. Since most aphids harbor Buchnera, and likely have GroEL in their saliva, this bacterial protein may generally alert plants of the presence of aphids. How it is recognized by plants is still unknown. GroEL can now be exploited to engineer durable resistance of crops against aphids."

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