A lycopene β-cyclase gene, IbLCYB2, enhances carotenoid contents and abiotic stress tolerance in transgenic sweetpotato

Lycopene beta-cyclase (LCYB) is an essential enzyme that catalyzes the conversion of lycopene into alpha-carotene and beta-carotene in carotenoid biosynthesis pathway. However, the roles and underlying mechanisms of the LCYB gene in plant responses to abiotic stresses are rarely known. This gene has not been used to improve carotenoid contents of sweetpotato, Ipomoea batatas (L.) Lam.. In the present study, a new allele of the LCYB gene, named IbLCYB2, was isolated from the storage roots of sweetpotato line HVB 3. Its overexpression significantly increased the contents of alpha-carotene, beta-carotene, lutein, beta-cryptoxanthin and zeaxanthin and enhanced the tolerance to salt, drought and oxidative stresses in the transgenic sweetpotato (cv. Shangshu 19) plants. The genes involved in carotenoid and abscisic acid (ABA) biosynthesis pathways and abiotic stress responses were upregulated in the transgenic plants. The ABA and proline contents and superoxide dismutase (SOD) activity were significantly increased, whereas malonaldehyde (MDA) and H2O, contents were significantly decreased in the transgenic plants under abiotic stresses. The overall results indicate that the IbLCYB2 gene enhances carotenoid contents and abiotic stress tolerance through positive regulation of carotenoid and ABA biosynthesis pathways in sweetpotato. This gene has the potential to improve carotenoid contents and abiotic stress tolerance in sweetpotato and other plants.