Local and systemic responses to Myzus persicae in Arabidopsis. A role for redox components

The mechanisms that enable plants to perceive and respond to aphids remain poorly characterised, particularly with respect to systemic signalling pathways. The aim of the studies reported in this thesis was to characterise the local and systemic signalling pathways induced by Myzus persicae infestation of Arabidopsis thaliana with translational aspects to potato (Solanum tuberosum). Particular emphasis was placed on the role of redox signalling pathways, which were studied in wild type A. thaliana (Col0) and in mutants that were deficient either in the major low molecular weight antioxidant ascorbic acid vitamin C defective 2 (vtc2) or in the abscisic acid (ABA) Insensitive-4 (ABI4) transcription factor or both components. Transcriptome analysis and metabolite profiling of leaves infested by M. persicae and on leaves from the same rosettes that were remote from the site of aphid attack revealed that the plant responses to aphids involved rapid local and systemic transcriptome re-programming in the absence of marked changes in the metabolite profiles. Moreover, the transcriptome reprogramming observed in infested leaves was different from the systemic response. The aphid-induced transcriptome signature of the infested leaves bore strong hallmarks of redox-signalling, salicylic acid (SA) signalling and ABA signalling, while that of the systemic leaves revealed a transcript profile where redox signalling was present but SA signalling was decreased. The vtc2 mutant showed decreased aphid fecundity, while aphid numbers were increased on the abi4 mutants. The differences in resistance to aphids between these genotypes are linked to alterations in ABA-dependent jasmonate-signalling pathways. When potato leaves were enriched in asorbate aphid fecundity was increased. These findings demonstrate the central role of redox signalling pathways in plant responses to aphids. Further characterisation of genes crucial for maintenance of redox homeostasis following aphid attack will inevitably facilitate development of aphid-resistant crops through GM technologies and marker-assisted selection.