title: Downregulation of the lycopene ε-cyclase gene increases carotenoid synthesis via the β-branch-specific pathway and enhances salt-stress tolerance in sweetpotato transgenic calli.
abstract: Lycopene ε-cyclase (LCY-ε) is involved in the first step of the α-branch synthesis pathway of carotenoids from lycopene in plants. In this study, to enhance carotenoid synthesis via the β-branch-specific pathway [which yields β-carotene and abscisic acid (ABA)] in sweet potato, the expression of IbLCY-ε was downregulated by RNAi (RNA interference) technology. The RNAi-IbLCY-ε vector was constructed using a partial cDNA of sweet potato LCY-ε isolated from the storage root and introduced into cultured sweet potato cells by Agrobacterium-mediated transformation. Both semi-quantitative Reverse transcription polymerase chain reaction (RT-PCR) of carotenoid biosynthesis genes and high-performance liquid chromatography (HPLC) analysis of the metabolites in transgenic calli, in which the LCY- εgene was silenced, showed the activation of β-branch carotenoids and its related genes. In the transgenic calli, the β-carotene content was approximately 21-fold higher than in control calli, whereas the lutein content of the transgenic calli was reduced to levels undetectable by HPLC. Similarly, expression of the RNAi-IbLCY-ε transgene resulted in a twofold increase in ABA content compared to control calli. The transgenic calli showed significant tolerance of 200 mM NaCl. Furthermore, both the β-branch carotenoids content and the expression levels of various branch-specific genes were higher under salt stress than in control calli. These results suggest that, in sweet potato, downregulation of the ε-cyclization of lycopene increases carotenoid synthesis via the β-branch-specific pathway and may positively regulate cellular defenses against salt-mediated oxidative stress.
authors.affiliation: Environmental Biotechnology Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 125 Gwahak-ro, Yuseong-gu, Daejeon, South Korea.
authors.forename: Sun Ha
authors.initials: SH
authors.lastname: Kim
authors.forename: Yun-Hee
authors.initials: YH
authors.lastname: Kim
authors.forename: Young Ock
authors.initials: YO
authors.lastname: Ahn
authors.forename: Mi-Jeong
authors.initials: MJ
authors.lastname: Ahn
authors.forename: Jae Cheol
authors.initials: JC
authors.lastname: Jeong
authors.forename: Haeng-Soon
authors.initials: HS
authors.lastname: Lee
authors.forename: Sang-Soo
authors.initials: SS
authors.lastname: Kwak
mesh_terms: D000040:Abscisic Acid / Q000235:genetics / Q000378:metabolism; D000975:Antioxidants / Q000378:metabolism; D002338:Carotenoids / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D019753:Intramolecular Lyases / Q000235:genetics* / Q000378:metabolism; D027723:Ipomoea batatas / Q000235:genetics* / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D055049:Salt Tolerance / Q000235:genetics
chemical_list: D000975:Antioxidants; D010940:Plant Proteins; D002338:Carotenoids; D000040:Abscisic Acid; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase