Wheat endogenous response to aphid infestation

• Main Author: Guan, Wenzhu
• Published: University of Newcastle Upon Tyne 2012
• Subjects: 633.119726
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582513

Plants use both constitutive and inducible defence system to protect themselves against attack from pests and pathogens. Aphids are major insect pests of cereal crops, acting as virus vectors as well as causing direct damage. The present study seeks to identify defence genes/gene products for a directed strategy in wheat breeding programmes to enhance wheat resistance to aphid pests. Early responses of wheat (Triticum aestivum) at the transcriptional level, to infestation by the grain aphid (Sitobion avenae) were investigated in 'Claire', a hexaploid winter wheat cultivar commercially grown in the UK, using subtractive hybridization. This technology allows us to identify genes unique to each treatment. Mechanically wounded wheat plants were used alongside aphid-infested wheat plants to distinguish between general wounding responses and insect specific responses of wheat. Following subtractive hybridization, 400 and 800 clones were obtained from the subtractive hybridization between aphid-infested and uninfested wheat cDNAs and between mechanically wounded and non-wounded wheat cDNAs, respectively. Over 70% oftotal clones were sequenced. The result reveals the responses of commercial wheat to aphid infestation and mechanical wounding and the similarity and differences between the two treatments. The majority of differentially expressed genes following aphid infestation or mechanical wounding were involved in metabolic processes and photosynthesis. Genes encoding glutathione transferase (GST), stress response, apoptosis and proteolysis were switched on after 24h aphid infestation, suggesting their importance towards plant defence/tolerance against aphid attack. These results suggest that commercial wheat lacks specific responses to aphids, but has low levels of defence/tolerance against aphids, as confirmed in bioassays. Furthermore, both early and long-term responses of wheat to aphid infestation were investigated in 'Claire' and the ancestral diploid wheat accessions (Triticum monococcum) ACC5PGR#1735 and ACC20PGR#1755, using a proteomics based approach. Both local and systemic responses of wheat to aphid infestation over time were investigated. Following 2D electrophoresis, approximately 200 protein spots were 'reproducibly detected in extracts from leaves of Claire, with 13 % and 16% of these proteins being expressed differently after 24h and 8 days aphid feeding, respectively. Approximately 70% of these were identified by peptide mass fingerprinting, revealing that the majority of proteins altered by aphid infestation were involved in metabolic processes and photosynthesis, thus confirming results obtained from the subtractive libraries. Responses to aphid attack in the commercial wheat at the proteome level were broadly similar to basal nonspecific defence and stress responses in wheat, with little evidence of insect specific defence mechanisms. However, screening of diploid wheat accessions identified one such accession (ACC20PGR#1755) as exhibiting significantly enhanced levels of resistance to s.' avenae. Proteomic analysis suggests that apoptosis, defence, oxidative response and stress response proteins play a role in the enhanced levels of resistance. Examples include: heat stress transcription factor A- 5 (Rice) and dehydrin (tobacco) up-regulated in ACC20PGR#1755 after 24h aphid feeding; and NBS-containing resistance-like protein (Hazel), putative stress-induced protein stil (Rice), non-symbiotic hemoglobin 1 (Alfalfa) and stress-induced protein sti-1 like protein (Arabidopsis) up-regulated in ACC20PGR#1755 after 8 days aphid feeding. These proteins were not detected in the susceptible accession following infestation. The results suggest that the resistant diploid line ACC20PGR#1755 may provide a valuable resource in breeding wheat for resistance to aphids.