REGULATION OF PROVITAMIN A CAROTENOID BIOSYNTHESIS IN MAIZE

描述(申请人提供)：维生素A缺乏症是一个影响近2亿儿童的全球健康问题。维生素A不能从头合成，对生长和发育是必不可少的；缺乏表现为干眼症、失明和死亡率增加。植物来源的类胡萝卜素在人类体内被转化为维生素A。缓解世界范围内维生素A缺乏的一种方法是通过代谢工程和/或结合标记辅助选择来提高玉米、小麦和大米等主食中的维生素A原胡萝卜素水平。该途径在植物中代谢工程的初步成功表明了这种方法的潜力。然而，在这种转基因植物中产生意想不到的产品表明，这项技术受到目前对内源基因表达理解的缺陷的限制。合理的代谢工程策略必须考虑尚未完全了解的内源性途径的调节。 我们认为，维生素A原类胡萝卜素的相对积累是通过控制生物合成和降解酶的转录水平来调节的；玉米胚乳中转录水平的修饰(增强或抑制)可以导致相对于其他非维生素A原类胡萝卜素的维生素A原胡萝卜素水平的增加。NIH SCORE基金使我们能够开始开发工具和研究，这些工具和研究最直接适用于世界上最重要的两种粮食作物--玉米和水稻。我们发现，一些途径酶是由小基因家族编码的，这就提出了一个问题：基因家族成员对不同组织、不同发育阶段和质膜定位的类胡萝卜素生物合成和积累有什么贡献？我们将继续我们的NIH-SCORE支持的工作，对编码类胡萝卜素途径的酶的内源基因的表达以及为类胡萝卜素生物合成提供底物的相关类异戊二烯生物合成途径进行全面的研究。我们还将研究编码酶的基因，这些酶可以降解或修饰类胡萝卜素，从而减少维生素A原的含量。拟议的研究将分为两个领域：(1)与类胡萝卜素合成/降解相关的转录谱及其与类胡萝卜素含量/组成的相关性；(2)影响维生素A原胡萝卜素转化为非维生素A黄叶的胡萝卜素环羟基酶的特征。 相关性：维生素A缺乏症是一个影响近2亿儿童的全球健康问题。为了缓解世界范围内的短缺，可以改善农作物中维生素A类胡萝卜素原的含量，这一目标需要育种工具和基础研究，从玉米(玉米)和水稻开始，研究如何调节粮食作物中的类胡萝卜素组成。

DESCRIPTION (provided by applicant): Vitamin A deficiency is a global health problem affecting close to 200 million children. Vitamin A can not be synthesized de novo and it is essential for growth and development; deficiencies manifest as xerophthalmia, blindness, and increased mortality. Plant-derived carotenoids are converted in humans to vitamin A. An approach to alleviating worldwide deficiency is to improve provitamin A carotenoid levels in food staples such as corn, wheat, and rice by metabolic engineering and/or in combination with marker-assisted selection. Preliminary success with metabolic engineering of the pathway in plants points to the potential of this approach. Unexpected products in such transgenic plants, however, suggest that the technology is limited by current deficiencies in understanding of endogenous gene expression. Rational metabolic engineering strategies must take into account the regulation of the endogenous pathway which is not yet completely understood. We propose that the relative accumulation of provitamin A carotenoids is mediated by control of transcript levels for the biosynthetic and degradative enzymes; and that modification (enhancement or repression) of transcript levels in corn endosperm can lead to increased levels of provitamin A carotenoids relative to other non-provitamin A carotenoids. NIH SCORE funding has allowed us to begin to develop tools and research which are most immediately applicable to two of the most important food crops worldwide--corn and rice. We discovered that several pathway enzymes are encoded by small gene families, which raises the question: what is the contribution of gene family members to carotenoid biosynthesis and accumulation in different tissues, developmental stages, and plastid membrane localization? We will continue our NIH-SCORE supported work to conduct a comprehensive investigation of expression of endogenous genes which encode enzymes of the carotenoid pathway and the related isoprenoid biosynthetic pathway which provides substrates for carotenoid biosynthesis. We will also investigate genes encoding enzymes that degrade or modify carotenoids and thus diminish provitamin A content. The proposed research will be divided into two areas: (1) transcript profiling related to carotenoid synthesis/ degradation and correlation with carotenoid content/ composition and (2) characterization of the carotene ring hydroxylases as they impact conversion of provitamin A carotenes to non-provitamin A xanthophylls. Relevance: Vitamin A deficiency is a global health problem affecting close to 200 million children. To alleviate deficiency worldwide, crop plants can be improved for provitamin A carotenoid content, the goal of which requires breeding tools and basic research on how carotenoid composition is regulated in food crops, beginning with corn (maize) and rice as models.