TPC1 forms a non specific, slowly activating, Ca2 regulated cation channel in vacuolar membranes. In fou2 the TPC1 channel has different electrophysiological properties, lower voltage is required for its activation and its time depen dent conductivity is higher compound library than in wt. Probably due to the increased sensitivity of voltage sensors in the mutated TPC1, the activation of the JA biosynthetic path way upon wounding is stronger in fou2 plants and the levels of free JA and OPDA are higher in the mutant rela tive to wt. Transcriptional analyses of aphid infested Arabidopsis plants have revealed substantial changes in the expres sion profiles of many defence related genes. Several genes whose products are involved in JA synth esis or JA dependent signalling have been reported to be up regulated, indicating that JA derived compounds play a role in the regulation of expressional changes.
As a result of transcriptional reprogramming, the production of proteins involved in defence is promoted and the metabolite profiles of plants are changed. Despite significant progress in our understanding of plant responses triggered by phloem feeders attack, it is largely unknown how much the induction of these defences relies on JA signalling. In this study, we provide new insights into the role of jasmonates in the regulation of defence responses upon aphid attack. A specialized phloem feeder is represented by the cabbage aphid, Brevicoryne brassicae, for which a model of Arabidopsis aphid interactions has been well established. Our aim is to identify the genes whose expressional changes are controlled by JA signalling.
The subsequent parts of this work concentrate on the follow ing problems, Which genes are primarily dependent on jasmonates for their expression How is the aphid induced plant defence affected by the absence of JA or the constitutive up regulation of the JA pathway How does the impact of the aos and fou2 mutations affect aphid performance To address these problems we have performed transcriptional profiling of both aphid chal lenged and non challenged wild type plants as well as aos and fou2 mutants using full genome oligonucleotide microarrays. Further, insect fitness experiments and Elec trical Penetration Graph analysis have been undertaken to determine how the JA status of the host plants influ ences the survival and behaviour of insects.
Results To investigate the importance of JA signalling in tran scriptional reprogramming of A. thaliana triggered by aphid attack, we designed an experiment Cilengitide that included comparisons of genome wide transcription profiles at three levels. Each level was comprised of a series of microarray hybridizations exploring transcrip tional changes in at least three biological replicates per comparison. At the first level, which we regard as the basic comparison, we aimed to identify and classify genes that are dependent on jasmonates for their basic expression.
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