Interspecific proteomic comparisons reveal ash phloem genes potentially involved in constitutive resistance to the emerald ash borer.

Justin G A Whitehill,Daniel A Herms,Pierluigi Bonello,Jennifer L Koch,Kari B Green-Church,Alexandra Popova-Butler,Haibing Yang

doi:10.1371/journal.pone.0024863

Justin G A Whitehill, Daniel A Herms + Show 5 more

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https://doi.org/10.1371/journal.pone.0024863

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Abstract

The emerald ash borer (Agrilus planipennis) is an invasive wood-boring beetle that has killed millions of ash trees since its accidental introduction to North America. All North American ash species (Fraxinus spp.) that emerald ash borer has encountered so far are susceptible, while an Asian species, Manchurian ash (F. mandshurica), which shares an evolutionary history with emerald ash borer, is resistant. Phylogenetic evidence places North American black ash (F. nigra) and Manchurian ash in the same clade and section, yet black ash is highly susceptible to the emerald ash borer. This contrast provides an opportunity to compare the genetic traits of the two species and identify those with a potential role in defense/resistance. We used Difference Gel Electrophoresis (DIGE) to compare the phloem proteomes of resistant Manchurian to susceptible black, green, and white ash. Differentially expressed proteins associated with the resistant Manchurian ash when compared to the susceptible ash species were identified using nano-LC-MS/MS and putative identities assigned. Proteomic differences were strongly associated with the phylogenetic relationships among the four species. Proteins identified in Manchurian ash potentially associated with its resistance to emerald ash borer include a PR-10 protein, an aspartic protease, a phenylcoumaran benzylic ether reductase (PCBER), and a thylakoid-bound ascorbate peroxidase. Discovery of resistance-related proteins in Asian species will inform approaches in which resistance genes can be introgressed into North American ash species. The generation of resistant North American ash genotypes can be used in forest ecosystem restoration and urban plantings following the wake of the emerald ash borer invasion.

Highlights

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive insect that has killed tens of millions of ash (Fraxinus spp.) trees in the U.S and Canada [1,2]
We identified four proteins that may play a role in the resistance of Manchurian ash to emerald ash borer: a major allergen (PR-10), a putative aspartic protease, a phenylcoumaran benzylic ether reductase, and a thylakoid-bound ascorbate peroxidase
This is the first study to identify constitutive proteins that are strongly associated with the resistant Manchurian ash

Summary

Introduction

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive insect that has killed tens of millions of ash (Fraxinus spp.) trees in the U.S and Canada [1,2]. All North American species of ash that emerald ash borer has encountered far are susceptible to colonization, even when growing on high quality sites and in the absence of obvious environmental stress [3,6,7]. Asian species of ash, which share a coevolutionary history with emerald ash borer, appear to be colonized only when weakened by abiotic or biotic stress [8,9]. In a common garden experiment, Rebek et al [6] found Manchurian ash (F. mandshurica Ruprecht), which is a primary host in its endemic range, to be much more resistant to emerald ash borer than North American green (F. pennsylvanica Marsh) and white ash (F. americana L.).

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