Abstract
The Russian wheat aphid, Diuraphis noxia, an invasive phytotoxic pest of wheat, Triticum aestivum, and barley, Hordeum vulgare, causes huge economic losses in Africa, South America, and North America. Most acceptable and ecologically beneficial aphid management strategies include selection and breeding of D. noxia-resistant varieties, and numerous D. noxia resistance genes have been identified in T. aestivum and H. vulgare. North American D. noxia biotype 1 is avirulent to T. aestivum varieties possessing Dn4 or Dn7 genes, while biotype 2 is virulent to Dn4 and avirulent to Dn7. The current investigation utilized next-generation RNAseq technology to reveal that biotype 2 over expresses proteins involved in calcium signaling, which activates phosphoinositide (PI) metabolism. Calcium signaling proteins comprised 36% of all transcripts identified in the two D. noxia biotypes. Depending on plant resistance gene-aphid biotype interaction, additional transcript groups included those involved in tissue growth; defense and stress response; zinc ion and related cofactor binding; and apoptosis. Activation of enzymes involved in PI metabolism by D. noxia biotype 2 aphids allows depletion of plant calcium that normally blocks aphid feeding sites in phloem sieve elements and enables successful, continuous feeding on plants resistant to avirulent biotype 1. Inhibition of the key enzyme phospholipase C significantly reduced biotype 2 salivation into phloem and phloem sap ingestion.
Highlights
Arthropods exhibit remarkable genetic plasticity in adapting to stresses posed by both abiotic and biotic factors
The 18 D. noxia samples sequenced with the Hiseq 2500 sequencer generated 100 base pair single-end reads
In each of the 18 aphid samples, reads passing quality control (QC) were individually aligned to their respective assembly using pooled sequences. >91.5% of reads from each sample uniquely aligned to contigs generated using pooled sequences “S1 Table”
Summary
Arthropods exhibit remarkable genetic plasticity in adapting to stresses posed by both abiotic and biotic factors. Insect crop pests express virulence to virtually all insecticides and plant genes for insect resistance used for their control [1,2]. Most insect species virulent to plant resistance genes are aphids (Homoptera) [3]. Virulence is presently identified by exposing an aphid population of unknown virulence capability to plant genotypes with different aphid resistance genes [4].
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