Characterization of lycopene β-cyclase gene from Lycium chinense conferring salt tolerance by increasing carotenoids synthesis and oxidative stress resistance in tobacco

Salt stress is a principal cause for yield reduction in crops. In plants, carotenoids are involved in abiotic stress resistance, while the underlying mechanisms for that have not been identified. In this study, the lycopene beta-cyclase (LclycB) gene of Lycium chinense was identified to be related to salt stress and was found to have the highest expression level in leaves through quantitative RT-PCR. The coding region of this gene was obtained through reverse transcription-PCR. The function of LclycB was confirmed in vitro with an Escherichia coli expression system. To study the function of LclycB, it was transformed into tobacco and maintained till T2 generation. Four-week old transgenic plants treated with 150 mM NaCl showed enhanced tolerance to oxidation and less reactive oxygen species (ROS) accumulation. Eight-week old transgenic plants treated with NaCl showed better growth than the control with higher photosystem activity and total antioxidants activity. The detection of photosynthetic pigments demonstrated that the transgenic plants retained higher contents of chlorophyll and carotenoids than the control under normal and salt-treated conditions. Furthermore, the thylakoid structure of chloroplast was notably disorganized in WT leaves compare to that of transformants by electron microscopy. Although carotenoid is the precursor of abscisic acid (ABA), the ABA content and stomatal conductance reflect nearly no differences between transgenic and control plants. These results demonstrated that the salt tolerance of LclycB might be ascribed to the enhanced carotenoid content for its ROS scavenging ability, photoprotection and membrane stabilization.