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Uncovering the mechanisms involved in regulating cuticular wax biosynthesis in Arabidopsis thaliana Lam, Patricia


The cuticle is a protective layer that coats the primary aerial surfaces of land plants, and mediates plant interactions with the environment. It is synthesized by epidermal cells and is composed of a cutin polyester matrix that is embedded and covered with cuticular waxes. My overall interest in this thesis is to uncover the mechanisms in how cuticular wax biosynthesis is regulated in developing stems of Arabidopsis thaliana. Previous work proposed that the CER7 exoribonuclease degrades an mRNA specifying a repressor of CER3 transcription thereby activating cuticular wax biosynthesis via the alkane pathway. In this thesis, I investigated the mechanisms of CER7-mediated silencing of CER3, and how this contributes to regulating cuticular wax biosynthesis. Specifically, I wanted to uncover the putative repressor of CER3 and to unravel the mechanism of CER7 mediated regulation of wax production. To do this, I performed a genetic screen to isolate suppressors of cer7-1 which restore cer7-related stem wax deficiency to wild-type wax levels. The screen resulted in the isolation of components of the RNA silencing machinery, implicating RNA silencing in the control of cuticular wax deposition during inflorescence stem development in Arabidopsis. Using a reverse genetics approach, I have also identified AGO1 in this pathway. Over all, I demonstrate that in the wild type, the CER7 exoribonuclease degrades a precursor of a small RNA that acts as a repressor of CER3, allowing for expression of CER3, and thus production of alkanes. However, in the cer7 mutant, this small RNA is not degraded and is used for the production of a small RNA silencing via a pathway. The generated small RNA silences CER3, leading to the wax deficient phenotype.

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