Significance of the Expression of the CER6 Condensing Enzyme for Cuticular Wax Production in Arabidopsis

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Abstract
To learn more about the role of the CER6 condensing enzyme in Arabidopsis surface wax production, we determinedCER6 transcription domains and the timing ofCER6 transcription in vegetative and reproductive structures from juvenile, mature, and senescing tissues. We found thatCER6 is highly transcribed throughout development, exclusively in the epidermal cells in all tissues examined. The only exception to the epidermal expression was observed in anthers nearing maturity, in which CER6 mRNA was localized in the tapetum. To determine if environmental factors such as light and water deficit, which are known to stimulate wax accumulation, induceCER6 transcription, we examined the effects of these factors on CER6 transcript abundance. Our results demonstrate that light is essential for CER6transcription, and that osmotic stress and the presence of abscisic acid enhance CER6 transcript accumulation.CER6 promoter-directed expression of the β-glucuronidase reporter gene in transgenic plants demonstrated that the CER6 promoter was highly effective in directing epidermis-specific expression in Arabidopsis and tobacco (Nicotiana tabacum). Furthermore, CER6promoter-driven CER6 overexpression resulted in increased wax deposition in Arabidopsis stems. These experiments indicate that the expression level of CER6 in the epidermis is one of the factors controlling wax accumulation on Arabidopsis stems.