Sawai Satoru, Ohyama Kiyoshi, Yasumoto Shuhei, Seki Hikaru, Sakuma Tetsushi, Yamamoto Takashi, Takebayashi Yumiko, Kojima Mikiko, Sakakibara Hitoshi, Aoki Toshio, Muranaka Toshiya, Saito Kazuki, Umemoto Naoyuki
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.
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.
Plant Cell. 2014 Sep;26(9):3763-74. doi: 10.1105/tpc.114.130096. Epub 2014 Sep 12.
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.
马铃薯（Solanum tuberosum）含有α-茄碱和α-查茄碱，这两种是著名的有毒甾体糖苷生物碱（SGA）。芽和绿色块茎中SGA的积累水平尤其高。尽管有人提出SGA是由胆固醇生物合成的，但植物胆固醇的生物合成途径却知之甚少。在这里，我们鉴定出马铃薯中的甾醇侧链还原酶2（SSR2）是胆固醇和相关SGA生物合成中的关键酶。通过体外酶活性测定，我们确定马铃薯SSR2（St SSR2）分别将去氢胆固醇和环阿屯醇还原为胆固醇和环阿糖醇。这些还原步骤是马铃薯中C-24烷基甾醇和胆固醇生物合成途径中的分支点。从番茄SSR2也获得了类似的酶促结果。通过靶向基因组编辑产生的St SSR2沉默马铃薯或St SSR2破坏马铃薯的胆固醇和SGA水平显著降低，而不影响植物生长。我们的结果表明，St SSR2是培育低SGA水平马铃薯的一个有前景的靶基因。
