title: Sterol side chain reductase 2 is a key enzyme in the biosynthesis of cholesterol, the common precursor of toxic steroidal glycoalkaloids in potato.
abstract: Potatoes (Solanum tuberosum) contain α-solanine and α-chaconine, two well-known toxic steroidal glycoalkaloids (SGAs). Sprouts and green tubers accumulate especially high levels of SGAs. Although SGAs were proposed to be biosynthesized from cholesterol, the biosynthetic pathway for plant cholesterol is poorly understood. Here, we identify sterol side chain reductase 2 (SSR2) from potato as a key enzyme in the biosynthesis of cholesterol and related SGAs. Using in vitro enzyme activity assays, we determined that potato SSR2 (St SSR2) reduces desmosterol and cycloartenol to cholesterol and cycloartanol, respectively. These reduction steps are branch points in the biosynthetic pathways between C-24 alkylsterols and cholesterol in potato. Similar enzymatic results were also obtained from tomato SSR2. St SSR2-silenced potatoes or St SSR2-disrupted potato generated by targeted genome editing had significantly lower levels of cholesterol and SGAs without affecting plant growth. Our results suggest that St SSR2 is a promising target gene for breeding potatoes with low SGA levels.
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Graduate School of Pharmaceutical Sciences, Chiba University, Chuo-ku, Chiba 260-8675, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Sawai
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Department of Chemistry and Materials Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Ohyama
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Yasumoto
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Hikaru
authors.initials: H
authors.lastname: Seki
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Tetsushi
authors.initials: T
authors.lastname: Sakuma
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Takebayashi
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Kojima
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.affiliation: Department of Applied Biological Sciences, Nihon University, Fujisawa, Kanagawa 252-0880, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Aoki
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Toshiya
authors.initials: T
authors.lastname: Muranaka
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Graduate School of Pharmaceutical Sciences, Chiba University, Chuo-ku, Chiba 260-8675, Japan kazuki.saito@riken.jp.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.affiliation: Central Laboratories for Key Technologies, Kirin Co., Kanazawa-ku, Yokohama, Kanagawa 236-0004, Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Umemoto
mesh_terms: D000470:Alkaloids / Q000737:chemistry / Q000378:metabolism*; D053898:Biosynthetic Pathways; D002784:Cholesterol / Q000031:analogs & derivatives / Q000096:biosynthesis* / Q000737:chemistry; D057075:Enzyme Assays; D020868:Gene Silencing; D017343:Genes, Plant; D018551:Solanum lycopersicum / Q000235:genetics; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000378:metabolism; D010802:Phylogeny; D010840:Phytosterols / Q000096:biosynthesis / Q000737:chemistry; D017393:RNA Editing; D011198:Solanum tuberosum / Q000201:enzymology* / Q000235:genetics; D057891:Tetraploidy
chemical_list: D000470:Alkaloids; D010840:Phytosterols; C021273:campesterol; D002784:Cholesterol; D010088:Oxidoreductases