Title: Over-expression and analysis of two Vitis vinifera carotenoid biosynthetic genes in transgenic Arabidopsis
Abstract: Plants have evolved mechanisms to efficiently protect the photosynthetic apparatus against the damaging effects of excess light. Carotenoids, especially the xanthophyll cycle pigments, play important roles in the dissipation of excess light energy as heat. The β-carotene hydroxylase (VvBCH) and zeaxanthin epoxidase (VvZEP) genes were isolated from Vitis vinifera L. cv Pinotage. Respectively, they encode proteins that convert β-carotene to zeaxanthin and zeaxanthin to violaxanthin. To determine the effect of these genes on the carotenoid concentrations and their roles in photoprotection, they were transformed into the model plant Arabidopsis thaliana. Several independent transgenic lines stably over-expressing the VvBCH and VvZEP genes were generated, harbouring one to multiple copies of the transgene. Homozygous populations of the transgenic lines, the untransformed control as well as two well characterised Arabidopsis mutants affected in the xanthophyll cycle, npq1 and npq2 were used to evaluate the effect of the over-expressed genes on pigment levels and photosynthetic parameters under normal and excessive light conditions. The transgenic lines over-expressing the VvBCH gene had elevated xanthophyll cycle pigments, specifically violaxanthin, which was available for de-epoxidation under a high light stress treatment, resulting in a two-fold increase in zeaxanthin compared to the wild type. The additional zeaxanthin under high light conditions however, did not affect the magnitude of non-photochemical quenching (NPQ) of chlorophyll fluorescence. In contrast, the VvZEP over-expressing lines had reduced zeaxanthin levels possibly due to faster epoxidation of zeaxanthin to violaxanthin than the de-epoxidation of violaxanthin to zeaxanthin. This resulted in decreased induction and final extent of NPQ, and significantly increased photoinhibition compared to the wild type under high light conditions. These lines demonstrated that accumulation of zeaxanthin does not necessarily lead to increased photoprotection and that even small decreases in zeaxanthin can result in significantly increased photoinhibition.
Publication Year: 2006
Publication Date: 2006-03-01
Language: en
Type: dissertation
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Cited By Count: 2
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