Project description:The bird cherry-oat aphid (Rhopalosiphum padi L.) (Homoptera: Aphididae) is an important pest on cereals causing plant growth reduction but no specific leaf symptoms. Breeding of barley (Hordeum vulgare L.) for R. padi resistance shows that there are several resistance genes involved, reducing aphid growth. In an attempt to identify candidate sequences for resistance-related genes, we performed a microarray analysis of gene expression after two days of aphid infestation in two susceptible barley lines and two genotypes with partial resistance. One of the four lines is a descendant of two of the other genotypes. The analysis revealed large differences in gene induction between the four lines, indicating substantial variation in response even between closely related genotypes. Genes induced in the aphid-infested tissue were mainly related to defence, primary metabolism and signalling. Only twenty-four genes were induced in all lines, none of them related to oxidative stress or secondary metabolism. Few genes were down-regulated and none of those was common to all four lines. There were differences in aphid-induced gene regulation between resistant and susceptible lines, and results from control plants without aphids also revealed differences in constitutive gene expression between the two types of lines. Candidate sequences for both induced and constitutive resistance factors have been identified, among them a proteinase inhibitor, a Ser/Thr kinase and several thionins. Experiment Overall Design: Four barley genotypes, two (Lina, Kara) with susceptibility to the bird cherry-oat aphid (Rhopalosiphum padi) and two (Hsp5, 28:4) with partial resistance, were infested with R. padi. After 48 h of aphid feeding, changes in transcript accumulation were analysed by comparing aphid-infested plants with control (uninfested) plants for each genotype. For each treatment, 3 biological replicates were analysed. Overlaps and differences in regulation of RNA abundance were identified between the four genotypes. 28:4 is a descendant of Hsp5 and Lina.