类胡萝卜素生物合成途径及其控制与遗传操作

Carotenoid biosynthetic pathway and its control, and genetic manipulation

类胡萝卜素在真菌和植物细胞胞液/内质网上是由乙酰CoA经甲羟戊酸途径合成的,在细菌与植物质体中由磷酸甘油醛与丙酮酸经1-脱氧木酮糖-5-磷酸途径合成.形成的异戊烯基焦磷酸经多次缩合生成第一个类胡萝卜素八氢番茄红素,再经脱氢、环化、羟基化、环氧化等转变为其它类胡萝卜素.类胡萝卜素生物合成中涉及的酶都是膜结合的或整合入膜中的.类胡萝卜素合成是通过底物可利用性与环化分支方式进行控制的.白色体到叶绿体的转变以及花与果实成熟时类胡萝卜素合成增加是在基因转录水平调节的.进行类胡萝卜素合成酶基因的转化,可增加转化体类胡萝卜素的积累.

Carotenoids are synthesized from acetyl-CoA via the mevalonate pathway in fungi and plant cytosol/endoplasmic reticulum or from glyceraldehyde-3-phosphate and pyruvate via methylerythritol pathway in bacteria and plastids of plants. The first carotenoid phytoene is formed by successive condensations of isopentenyl pyrophosphate. Subsequently phytoene is conversed to various other carotenoids by dehydrogenation, cyclization, hydroxylation, epoxidation/de-epoxidation reactions. Enzymes involved in carotenoid biosynthesis are all membrane-associated or integrated into membranes. Two likely control points of the carotenoid pathway in plants are the availability of substrate and branching of the pathway. Transcriptional regulation of carotenoid biosynthetic genes is the major regulatory mechanism in the process of carotenogenesis during light-dependent transformation from etioplasts to chloroplasts and flowers and fruit ripening. Genetic manipulation of carotenoid pathway has achieved the production of carotenoids and higher carotenoid content in the cooresponding transformants through gene transfer techniques.