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Plant iron acquisition strategy exploited by an insect herbivore

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Science  17 Aug 2018:
Vol. 361, Issue 6403, pp. 694-697
DOI: 10.1126/science.aat4082

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Pest subverts host plant's foraging

Plants need iron as a micronutrient, and they extract it from the rhizosphere by secreting chelating agents. Insect pests, such as the western corn rootworm, which annually cause millions of dollars' worth of lost yield, need iron, too. Hu et al. show that the rootworm exploits the plant's own iron-foraging system to detect its host and to seize iron for itself (see the Perspective by Kliebenstein). Plants produce benzoxazinoid compounds not only as a defense against many insects but also as iron chelators. Rootworm larvae are not harmed by benzoxazinoids; instead, they take advantage of their presence as a signal that food is near and of their properties as an iron chelator.

Science, this issue p. 694; see also p. 642

Abstract

Insect herbivores depend on their host plants to acquire macro- and micronutrients. Here we asked how a specialist herbivore and damaging maize pest, the western corn rootworm, finds and accesses plant-derived micronutrients. We show that the root-feeding larvae use complexes between iron and benzoxazinoid secondary metabolites to identify maize as a host, to forage within the maize root system, and to increase their growth. Maize plants use these same benzoxazinoids for protection against generalist herbivores and, as shown here, for iron uptake. We identify an iron transporter that allows the corn rootworm to benefit from complexes between iron and benzoxazinoids. Thus, foraging for an essential plant-derived complex between a micronutrient and a secondary metabolite shapes the interaction between maize and a specialist herbivore.

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