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Understanding the basis of host and non-host defences during barley-aphid interactions

Carmen Escudero-Martinez: The James Hutton Institute

<div>Aphids are phloem-feeding insects that cause important yield losses on crops, including cereals such as barley. Most aphid species are limited to one or few host species, but some are able to reproduce on many plants belonging to different families. Interestingly, aphid probing-behaviour can be observed on both host and non-host plants indicating a requirement for molecular events to take place which may dictate the aphid host range. We found that the barley specialist <em>Rhopalosiphum padi</em> and the broad host range <em>Myzus persicae</em> showed strong differences in colonization, phenotype and probing-behaviour on barley. Preliminarily, the Electrical Penetration Graph (EPG) technique has shown that both aphids successfully penetrate the barley leaf surface; but differ in their ability to reach the phloem. EPG feeding patterns are being investigated to unravel the resistance source against <em>M. persicae</em>. Analyses of barley transcriptional responses revealed gene sets differentially regulated upon the different barley-aphid interactions, where <em>M. persicae</em> induced the strongest response. Interestingly, we identified several genes highly up-regulated upon <em>M. persicae</em> interaction, and to a lesser extent upon <em>R. padi</em>, including thionins and a late embryogenesis abundant gene. Ectopic expression of two barley thionins in <em>Nicotiana benthamiana</em> reduced host susceptibility to <em>M. persicae</em>, potentially reflecting a role in defence against aphids. We have generated barley knock-out lines, using CRISPR-Cas9 technology, for these genes to investigate their role in plant-aphid interactions. Our work thereby provides novel insights into host and non-host defences in a monocot crop against aphids and implicates thionins in the resistance to the global pest <em>M. persicae</em>.</div>