基因编辑技术创制黄色牵牛花

       牵牛花最初只开蓝色花，经过多年的改良和培育，现已有红色、桃色、紫色、茶色和白色等多种颜色，而唯独没有黄色。开黄花需要植物体内有类胡萝卜素、橙酮等黄色色素，而牵牛花恰恰缺乏这种色素。在日本，牵牛花又被称为朝颜花，具有丰富的文化内涵。之前的研究表明花瓣中类胡萝卜素相关基因的低表达是类胡萝卜素微量存在的主要原因，但可能也受到其它因素的影响。近日，日本筑波大学的科研人员发现类胡萝卜素裂解双加氧酶（CCD）能够调控牵牛花花瓣中类胡萝卜的含量。该酶特异地裂解类胡萝卜素多烯链的双键。通过生物信息学分析发现，牵牛花的基因组中有7个CCD基因。测序和表达分析的结果显示InCCD4与类胡萝卜素的降解有关。进一步，研究人员利用CRISPR/Cas9系统在白色牵牛花AK77品种中敲除了InCCD4基因，使其白色花瓣变成了黄色。与非转基因植株相比，ccd4突变植株中类胡萝卜素的含量增加了20倍。该研究不仅进一步解释了牵牛花缺乏黄色的原因，而且证实了通过生物技术手段培育黄色牵牛花的可行性。
Transgenic Research, 15 December 2017
Alteration  of  flower  colour  in Ipomoea  nil through CRISPR/Cas9-mediated mutagenesis of carotenoid cleavage dioxygenase 4
Authors
Kenta Watanabe, Chihiro Oda-Yamamizo, Kimiyo Sage-Ono, Akemi Ohmiya, Michiyuki Ono
Abstract
Japanese morning glory, Ipomoea nil, exhibits a variety of flower colours, except yellow, reflecting the accumulation of only trace amounts of carotenoids in the petals. In a previous study, we attributed this effect to the low expression levels of carotenogenic genes in the petals, but there may be other contributing factors. In the present study, we investigated the possible involvement of carotenoid cleavage dioxygenase (CCD), which cleaves specific double bonds of the polyene chains of carotenoids, in the regulation of carotenoid accumulation in the petals of I. nil. Using bioinformatics analysis, seven InCCD genes were identified in the I. nil genome. Sequencing and expression analyses indicated potential involvement of InCCD4 in carotenoid degradation in the petals. Successful knockout of InCCD4 using the CRISPR/Cas9 system in the white-flowered cultivar I. nil cv. AK77 caused the white petals to turn pale yellow. The total amount of carotenoids in the petals of ccd4 plants was increased 20-fold relative to non-transgenic plants. This result indicates that in the petals of I. nil, not only low carotenogenic gene expression but also carotenoid degradation leads to extremely low levels of carotenoids.