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An engineered extraplastidial pathway for carotenoid biofortification of leaves
Plant Biotechnology Journal ( IF 13.8 ) Pub Date : 2020-12-12 , DOI: 10.1111/pbi.13526
Trine B Andersen 1 , Briardo Llorente 1, 2, 3 , Luca Morelli 1 , Salvador Torres-Montilla 1 , Guillermo Bordanaba-Florit 1 , Fausto A Espinosa 1 , Maria Rosa Rodriguez-Goberna 1 , Narciso Campos 1, 4 , Begoña Olmedilla-Alonso 5 , Manuel J Llansola-Portoles 6 , Andrew A Pascal 6 , Manuel Rodriguez-Concepcion 1, 7
Affiliation  

Carotenoids are lipophilic plastidial isoprenoids highly valued as nutrients and natural pigments. A correct balance of chlorophylls and carotenoids is required for photosynthesis and therefore highly regulated, making carotenoid enrichment of green tissues challenging. Here we show that leaf carotenoid levels can be boosted through engineering their biosynthesis outside the chloroplast. Transient expression experiments in Nicotiana benthamiana leaves indicated that high extraplastidial production of carotenoids requires an enhanced supply of their isoprenoid precursors in the cytosol, which was achieved using a deregulated form of the main rate-determining enzyme of the mevalonic acid (MVA) pathway. Constructs encoding bacterial enzymes were used to convert these MVA-derived precursors into carotenoid biosynthetic intermediates that do not normally accumulate in leaves, such as phytoene and lycopene. Cytosolic versions of these enzymes produced extraplastidial carotenoids at levels similar to those of total endogenous (i.e. chloroplast) carotenoids. Strategies to enhance the development of endomembrane structures and lipid bodies as potential extraplastidial carotenoid storage systems were not successful to further increase carotenoid contents. Phytoene was found to be more bioaccessible when accumulated outside plastids, whereas lycopene formed cytosolic crystalloids very similar to those found in the chromoplasts of ripe tomatoes. This extraplastidial production of phytoene and lycopene led to an increased antioxidant capacity of leaves. Finally, we demonstrate that our system can be adapted for the biofortification of leafy vegetables such as lettuce.

中文翻译:

工程改造的叶外类固醇强化途径

类胡萝卜素是亲脂性质体类异戊二烯,被高度评价为营养素和天然色素。叶绿素和类胡萝卜素的正确平衡是光合作用所必需的,因此受到高度调节,这使得绿色组织中类胡萝卜素的富集具有挑战性。在这里,我们表明,通过设计叶绿体外部的生物合成可以提高叶片类胡萝卜素的水平。本氏烟草的瞬时表达实验叶表明,类胡萝卜素的高质外生成需要在胞质溶胶中增加其类异戊二烯前体的供应,这是通过使用甲羟戊酸(MVA)途径的主要速率决定酶的失调形式实现的。编码细菌酶的构建体用于将这些MVA衍生的前体转化为类胡萝卜素生物合成中间体,而这些通常不会积聚在叶片中,例如八氢番茄红素和番茄红素。这些酶的胞质形式产生的膜外类胡萝卜素水平与全部内源性(即叶绿体)类胡萝卜素水平相似。由于潜在的质膜外类胡萝卜素存储系统,无法增强内膜结构和脂质体发育的策略并未成功地进一步增加类胡萝卜素的含量。发现番茄红素在质体外部积累时更易于生物利用,而番茄红素形成的胞质晶体与成熟番茄的染色体中非常相似。番茄红素和番茄红素的这种质外生成导致叶片抗氧化能力增强。最后,我们证明了我们的系统可以适用于生菜等叶菜的生物强化。
更新日期:2020-12-12
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