Hessian fly larval attack triggers elevated expression of disease resistance dirigent-like protein-encoding gene, HfrDrd, in resistant wheat

Dirigent proteins regulate coupling of monolignol plant phenols to generate the cell wall polymers lignins and lignans that are involved in structural fortification and defense against pathogens and pests. In this study, we report the temporal expression of a putative Hessian fly-responsive disease resistance dirigent-like protein-encoding gene, HfrDrd, in wheat. HfrDrd transcript abundance was quantified under biotic stresses imposed by Hessian fly, bird cherry-oat aphid, barley and cereal yellow dwarf virus, fall army worm and silverleaf white fly, after mechanical wounding, as well as during treatment with signaling elicitors. Quantitative transcriptional analysis indicated increased abundance of HfrDrd mRNA in both susceptible and resistant wheat after Hessian fly attack. However, within 24 h, resistant wheat accumulated 2.5- to >20-fold higher HfrDrd mRNA levels than the susceptible wheat. The increase in transcripts as early as 2 h after egg hatch suggested a role for HfrDrd in early defense against Hessian fly larvae. HfrDrd transcript abundance was not responsive to exogenous application of plant defense-signaling pathway molecules, salicylic acid, methyl jasmonate or abscisic acid. Lack of HfrDrd response during other wheat–insect interactions or mechanical wounding indicated that HfrDrd is not a general stress-responsive gene, but is specific to the defense mechanisms responding to probing by Hessian fly larvae.