Hessian flyAvirulencegene loss-of-function defeats plant resistance without compromising the larva's ability to induce a gall tissue

Abstract

Plant pathogen effectors encoded by Avirulence (Avr) genes benefit the pathogen by promoting colonization and benefit plants that have a matching resistance (R) gene by constituting a signal that triggers resistance. The Hessian fly,Mayetiola destructor (Say) (Diptera: Cecidomyiidae), resembles a plant pathogen in showing R/Avr interactions. Because of these interactions, a wheat plant with the H13 resistance gene can be resistant or susceptible depending on the genotype of the larva that attacks the plant, being resistant if attack comes from a larva with a functional vH13 gene, but susceptible if attack comes froma larva with a non-functional vH13 gene. In this study we asked: does this susceptible interaction involving plants with H13 look like susceptible interactions with plants lacking H13? Possibly, the H13 plant attacked by a larva with a non-functional vH13 is induced to partial rather than complete resistance. Or the larva, lacking its vH13-encoded effector, is compromised in its ability to induce susceptibility, which includes forcing the plant to create a gall nutritive tissue. Responses of epidermal cells to larval attack were explored using imaging techniques (light microscopy, scanning and transmission electron microscopy). Whole-organism responses were investigated by measuring the growth of plants and larvae.No evidence was found for partial resistance responses by H13 plants or for a compromise in the ability of vH13 loss-of-function larvae to induce susceptibility. It appears that disrupting vH13 function is sufficient for overcoming the induced resistance mediated by the H13 gene.