Natures wonders: plant munchers defend themselves (Introduction)

by David Turell @, Sunday, February 19, 2017, 23:57 (1234 days ago) @ David Turell

A strange symbiotic relationship in which worms and beetles and caterpillars have a symbiotic relationship with bacteria who help turn off the plants own defenses:

"'Plants are subject to attack by an onslaught of microbes and herbivores, yet are able to specifically perceive the threat and mount appropriate defenses," said Gary W. Felton, professor and head of entomology. "But, herbivores can evade plant defenses by using symbiotic bacteria that deceive the plant into perceiving an herbivore threat as microbial, suppressing the plant's defenses against herbivores."

"Felton's research looked at two crop pests—tomato fruit worms and the Colorado potato beetle—plant reactions to the pests, and the microbes that they carry.


"Plants have two lines of defense against these predators. One reaction, regulated by jasmonic acid, comes into play when insects chew on the plant's leaves, stems or fruit, damaging the plant and leaving insect saliva. The other is turned on when an insect regurgitates stomach contents containing microbes onto the plant triggering a response by the plant to microbial pathogens that uses salicylic acid.

"When microbes—viruses and bacteria—are symbiotic companion of the insects, these pathways can be interrupted.

"'Parasitoids (predatory insects) inject eggs into the caterpillar and the developing parasitoid eventually kills the caterpillar," said Felton. "Along with the eggs, the parasitoid injects a symbiotic virus that knocks out the immune system of the caterpillar and kill the component in the caterpillar saliva that signals the plant that it is being attacked."

"When a parasitoid-infected tomato fruit worm attacks a plant, the plant does not realize the caterpillar is chewing on it, none of the chemical defense systems in the plant activate. This benefits the caterpillar and the symbiotic microbe, but does not do much for the plant.

"When the Colorado potato beetle—which likes potato plants, but will eat all the plants in the nightshade family—regurgitates its stomach contents onto a leaf, the bacteria from the beetle's gut triggers the plant's microbial response, but turns off the plant's response to chewing. The bacteria are able to spread and the herbivore, the beetle, gets to strip the leaves without encountering the plant's chemical response


"The Colorado potato beetle suppresses the plants chewing response only when the beetles feed on tomatoes or potatoes, not when they feed on other members of the nightshade family like eggplants or peppers. The symbiotic bacteria only develop in the beetle gut when feeding on tomatoes and potatoes."

Comment: How this complex action of organisms developed is difficult to understand, especially when considering a stepwise process. Could it have developed all at once fully intact? Note the last paragraph above, in which symbiotic bacteria are allowed to develop selectively based on the type of plant preyed upon.

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