School of Health and Allied Sciences, Pokhara University, Pokhara 30, Dhungepatan, Pokhara, Gandaki, 33700, Nepal.
Plant Cell Rep. 2021 May;40(5):799-804. doi: 10.1007/s00299-021-02684-7. Epub 2021 Mar 23.
The carotenoids available in food are vital dietary micronutrients for human health. Plants synthesize and accumulate different carotenoids in plastids in a tissue-specific manner. The level of β-carotene (provitamin A) and other nutritionally important carotenoids is substantially low in the green tissues such as leaves compared to the fruits and roots. In photosynthetic tissues, chloroplasts can accumulate a moderate level of carotenoids, mainly to facilitate photosynthesis and environmental stress tolerance. However, chromoplasts from the storage tissues such as tomato fruit and carrot root can synthesize and accumulate carotenoids to a substantially higher level. A synthetic biology approach that utilizes a transient expression of bacterial phytoene synthase (crtB) gene in the photosynthetic leaves can induce the transition of chloroplasts into chromoplasts. The plastid-localized heterologous expression of crtB in leaves can induce the overaccumulation of phytoene, triggering the chloroplast-to-chromoplast transition; therefore, enhancing the biosynthesis and accumulation of carotenoids, including provitamin A. The transition of chloroplasts into chromoplasts, however, altered the photosynthetic thylakoids, consequently reducing the photosynthetic efficiency and plant growth. An efficient metabolic engineering strategy is desirable to enhance the production of targeted carotenoids in leaves without perturbing the photosynthetic efficiency and plant growth. Collectively, a synthetic biology strategy that triggers the transformation of chloroplasts into chromoplasts in photosynthetic tissues unfolds new avenues for carotenoid biofortification in the leafy food and vegetable crops, which can increase the dietary intake of carotenoids, therefore, combating the crisis of vitamin A deficiency.
食物中的类胡萝卜素是人类健康的重要膳食微量营养素。植物以组织特异性的方式在质体中合成和积累不同的类胡萝卜素。与果实和根相比，绿叶等绿色组织中的β-胡萝卜素（维生素 A 前体）和其他营养上重要的类胡萝卜素的水平要低得多。在光合组织中，叶绿体可以积累中等水平的类胡萝卜素，主要是为了促进光合作用和环境胁迫耐受性。然而，来自储存组织（如番茄果实和胡萝卜根）的有色体可以将类胡萝卜素合成和积累到更高的水平。利用细菌八氢番茄红素合酶（crtB）基因在光合叶片中的瞬时表达的合成生物学方法可以诱导叶绿体向有色体转化。crtB 在叶片中的质体定位异源表达可以诱导类胡萝卜素的过度积累，引发叶绿体向有色体的转化；因此，增强了类胡萝卜素，包括维生素 A 前体的生物合成和积累。然而，叶绿体向有色体的转化改变了光合类囊体，从而降低了光合作用效率和植物生长。需要有效的代谢工程策略来提高叶片中目标类胡萝卜素的产量，而不干扰光合作用效率和植物生长。总之，一种触发光合组织中叶绿体向有色体转化的合成生物学策略为叶类食物和蔬菜作物中的类胡萝卜素生物强化开辟了新途径，可以增加类胡萝卜素的膳食摄入量，从而应对维生素 A 缺乏症的危机。
