Gerjets Tanja, Sandmann Manuela, Zhu Changfu, Sandmann Gerhard
Molecular Biosciences, J.W. Goethe Universität, Frankfurt/M., Germany.
Biotechnol J. 2007 Oct;2(10):1263-9. doi: 10.1002/biot.200700040.
Ketocarotenoids and especially astaxanthin are high-valued pigments used as feed additives. Conventionally, they are provided by chemical synthesis. Their biological production is a promising alternative. For the development of a plant production system, Nicotiana glauca, a species with carotenoid-containing yellow pigmented flower petals, was transformed with a cyanobacterial ketolase gene. The resulting plants accumulated 4-ketozeaxantin (adinoxanthin), which is the first ketocarotenoid synthesized in flower petals by genetic modification. Due to the very late flowering in this tobacco species, N. tabacum was used to optimize the yield and ketocarotenoid product pattern by metabolic engineering of the ketolation steps of carotenogenesis. The highly carotenogenic nectary tissue in the flowers represents a model of a flower chromoplast system. By expression of a ketolase gene, it was possible to engineer the biosynthetic pathway towards the formation of 3'-hydroxyechinenone, 3-hydroxyechinenone, 4-ketozeaxanthin, 4-ketozeaxanthin esters, 4-ketolutein and 4-ketolutein esters. Some of these ketocarotenoids were also formed in the leaves of the trangenic plants. In particular, by co-expression of the ketolase gene in combination with a hydroxylase gene under an ubiquitous promoter, the formation of total carotenoids in nectaries increased by more than 2.5-fold. In the nectaries of this type of transformants, more than 50% of the accumulating carotenoids were keto derivatives. In addition, the levels of ketocarotenoid esters were much lower and a higher percentage of the free ketocarotenoids accumulated. These results open new promising perspectives for a successful metabolic engineering of keto-hydroxy carotenoid production in carotenogenic flowers.
酮类胡萝卜素尤其是虾青素是用作饲料添加剂的高价值色素。传统上，它们是通过化学合成提供的。其生物生产是一种有前景的替代方法。为了开发植物生产系统，用蓝藻酮醇酶基因转化了含有类胡萝卜素的黄色花瓣的烟草物种——黄花烟草。所得植物积累了4-酮玉米黄质（阿地诺黄素），这是通过基因改造在花瓣中合成的第一种酮类胡萝卜素。由于这种烟草物种开花很晚，因此利用烟草通过类胡萝卜素生成酮化步骤的代谢工程来优化产量和酮类胡萝卜素产物模式。花中高度产类胡萝卜素的蜜腺组织代表了花色素体系统的一个模型。通过表达酮醇酶基因，可以改造生物合成途径以形成3'-羟基海胆酮、3-羟基海胆酮、4-酮玉米黄质、4-酮玉米黄质酯、4-酮黄体素和4-酮黄体素酯。其中一些酮类胡萝卜素也在转基因植物的叶片中形成。特别是，通过在遍在启动子下共表达酮醇酶基因和羟化酶基因，蜜腺中总类胡萝卜素的形成增加了2.5倍以上。在这种类型的转化体的蜜腺中，积累的类胡萝卜素中超过50%是酮衍生物。此外，酮类胡萝卜素酯的水平要低得多，并且积累的游离酮类胡萝卜素的比例更高。这些结果为在产类胡萝卜素的花中成功进行酮羟基类胡萝卜素生产的代谢工程开辟了新的有前景的前景。
