Ectopic expression of a Citrus kinokuni β-carotene hydroxylase gene (chyb) promotes UV and oxidative stress resistance by metabolic engineering of zeaxanthin in tobacco.

To investigate the biological function of zeaxanthin under UV light and oxidative stress we have increased its biosynthesis capacity in tobacco plants (Nicotiana tabacum cv. SR-1) by transformation with Citrus kinokuni β-carotene hydroxylase gene (chyb) under constitutive promoter control. The chyb transformants synthesized zeaxanthin about 30% more than the controls under UV irradiation. For revelation of direct effects, pigment composition, chlorophyll fluorescence, and photosynthesis were detected immediately after UV treatment. Pre-illuminated chyb transgenics showed higher photosynthesis (NPQ capacity and F v / F m ratio of chyb transformants about 50% more than the controls). In addition, the transgenic plants showed less lipid peroxidation (MDA level was reduced about 40%) and the SOD activity was about 1.5 times of the control plants. Furthermore, the methylviologen treatment assay (more than 60% of chlorophyll in the chyb transformants) suggested that the transgenic plants suffered less oxidative damage than the controls. Our results indicate that enhancing zeaxanthin amount in plant cell contributes to UV and oxidative stress protection.