Evolution: corn plant pest adaptation (Evolution)

by David Turell , Thursday, August 16, 2018, 19:46 (2071 days ago) @ David Turell

It uses the same iron protein complex as the plant:

https://phys.org/news/2018-08-herbivore-hijacks-nutrient-uptake-strategy.html

"Christelle Robert and Matthias Erb from the University of Bern had shown in the past that the corn rootworm is resistant to the most important class of maize defense metabolites, the benzoxazinoids. Robert demonstrated that rootworm larvae are even attracted by benzoxazinoids and can use these substances for their own defense against beneficial nematodes. However, until now, it was unclear which benzoxazinoids attract the rootworm. A combination of genetics, chemistry and behavioral ecology has now enabled the scientists to solve this puzzle: Rootworm larvae recognize specific iron complexes that are formed at the root surface when benzoxazinoids bind to iron.

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"The roots of young maize plants release benzoxazinoids, which bind to iron and form complexes in the soil. The researchers found that these complexes increase iron availability for maize plants and thus improve plant growth. But the rootworm uses these exact same iron complexes too—rootworm larvae use the benzoxazinoid-iron complexes to guide them to the nutrient-rich crown roots of maize plants. At the same time, they ingest these complexes for their own needs.

"'The corn rootworm has evolved a clever strategy to exploit its host plant's ability to make iron biologically available. Tragically, this strategy enables the insect to severely damage maize plants and thereby cause massive crop failure," says Christelle Robert. "This behavior also poses a dilemma for plant breeders. In order to get rid of rootworms, they would have to reduce the release of benzoxazinoids in the roots. However, this would also undermine the plants' ability to absorb iron.

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"The results of the study highlight the dilemma faced by plants when an herbivore breaks through and evolves tolerance to a defense. "Since benzoxazinoids function both in herbivore defense and nutrient uptake, it is difficult for the plant to immediately stop producing a defense compound that has so many other important functions.

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" The fact that the Western corn rootworm is able to perceive iron complexes and to adjust its dietary behavior accordingly is also relevant for the understanding of food chains. "Many important trace elements are bound to organic molecules in nature. We therefore expect that other higher organisms also have the ability to perceive biologically available forms of trace elements and to ingest them to improve their nutrient balance," says Matthias Erb. "The Western corn rootworm is a frustrating, yet highly fascinating pest that has just taught us a new trick of nature.'"

Comment: This is an amazing adaptation the larvae worked out.