Barley tolerance of Russian wheat aphid (Hemiptera: Aphididae) biotype 2 herbivory involves expression of defense response and developmental genes

Abstract

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is an invasive insect pest that causes serious yield losses in bread wheat, Triticum aestivum L., durum wheat, T. turgidum L and barley, Hordeum vulgare L. Successful management of D. noxia has been achieved through resistant varieties via plant antixenosis (aphid non-preference), antibiosis (reduced aphid growth or fecundity), tolerance (plant compensatory growth after aphid feeding), or a combination of each. Previous phenotyping experiments revealed that plants of the variety Stoneham resist D. noxia damage via tolerance. In the present study, genes involved in upstream regulation of jasmonic acid (JA), salicylic acid (SA), ethylene (ET), auxin (AUX) and abscisic acid (ABA) biosynthetic pathways were monitored using qRT-PCR in Stoneham and susceptible Otis barley plants after D. noxia biotype 2 feeding. Results indicate that D. noxia tolerance in Stoneham plants is related to greater constitutive expression of JA-, ET- and AUX-biosynthetic pathway genes than in susceptible Otis plants, suggesting the possibility of immediate plant adjustments due to the stress of D. noxia feeding. There was limited induction of genes in the ET-(ACCS) and IAA (TDC) pathways in Stoneham tissues after D. noxia feeding. JA pathway genes upregulated in Otis tissues after D. noxia infestation failed to successfully defend Otis plants. AUX and ABA transcripts in Otis may be associated with developmental collapses resulting from source and sink adjustment failures.

Figure 1.

Constitutive transcript levels (mean ± SE log2 fold change) of the jasmonate pathway genes phospholipase Dα1 (PLD α1), Ω-3 fatty acid desaturase (FAD3, lipoxygenase 2 (LOX2), allene oxide synthase (AOS), allene oxide cyclase (AOC) and 12-oxophytodienoate reductase 3 (OPR3) in two-leaf stage Stoneham and Otis barley plant tissues un-infested by Diuraphis noxia biotype 2. Fold change calculated as ΔΔCt = [(Ct for sample cDNA – Ct for control cDNA)_GOI ] − [(Ct for sample cDNA – Ct for control cDNA)_HK]. (Schmittgen et al. 2008); GOI, gene of interest. HK, UCE internal control gene. For each gene, means below a different letter differ significantly at p < 0.05 (PROC TTEST).

Figure 2.

Constitutive transcript levels (mean ± SE log2 fold change) of ethylene [ACCO and ACCS] and auxin-indole acetic acid [TDC, T5M, amidase] pathway genes in two-leaf stage Stoneham and Otis barley plant tissues un-infested by Diuraphis noxia biotype 2. Fold change calculated as ΔΔCt = [(Ct for sample cDNA – Ct for control cDNA)_GOI] − [(Ct for sample cDNA – Ct for control cDNA)_HK]. (Schmittgen and Livak 2008); GOI = gene of interest. HK = UCE internal control gene. For each gene, means below a different letter differ significantly at p < 0.05 (PROC TTEST).