UBC Theses and Dissertations
A molecular approach to study the monoterpene-induced response in Arabidopsis thaliana Godard, Kimberley-Ann
A wound- and insect-inducible expression system for transgenic plants was developed. Specifically, I demonstrate wound- and insect-inducible, localized gene expression driven by the potato proteinase inhibitor II (pinII)-promoter in transformed Arabidopsis, tobacco and white spruce. As reporter and target genes driven by the pinII-promoter, I used the GUS gene and a terpenoid synthase gene, respectively. In addition, I found that the pinII-promoter drives trichome-specific, systemically-induced gene expression in tobacco and Arabidopsis. Finally, I demonstrate that the pinII–promoter, when transformed into Arabidopsis, is extremely sensitive to subtle, low-impact stress treatment. This latter finding prompted me to use, in the second part of my thesis, the pinII-promoter in conjunction with GUS reporter gene expression to test if intact Arabidopsis plants can respond to exposure to monoterpene volatiles. My experiments using the pinII–promoter GUS reporter system clearly established that Arabidopsis plants respond to the exposure of the monoterpene volatiles tested. It is thought that monoterpenes and other volatiles can act as airborne signals between plants under stress or between distant parts of the same plant. At the outset of my thesis research, and to some extent still today, the concept of plant-plant signalling with volatiles has been met with scepticism. After establishing that Arabidopsis plants do respond in a laboratory setting to certain monoterpene volatiles, I further tested the extent of the response at the transcriptome level using a 30 K microarray platform. The gene expression analysis revealed several hundred transcripts that respond with a change of abundance in response to treatment of intact Arabidopsis plants with the monoterpenes ocimene or myrcene. Many of these transcripts were annotated as stress and defense genes including genes involved in octadecanoid signaling. Real-time PCR analyses of octadecanoid mutants confirmed a role for octadecanoid signaling in the response to the monoterpene ocimene. In addition, treatment with ocimene or myrcene caused increased levels of methyl jasmonate (MeJA) in Arabidopsis rosette leaves. However, plants treated with monoterpene prior to wounding or feeding by cabbage looper did not reveal any significant priming effect for these pre-treatments.
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