REGULATION OF PROVITAMIN A CAROTENOID BIOSYNTHESIS IN MAIZE

维生素A缺乏症是一个全球性的健康问题，影响着近2亿儿童。维生素A不能从头合成，它对生长和发育至关重要;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体内转化为维生素A。缓解世界范围内缺乏的一种方法是通过代谢工程和/或与标记辅助选择相结合来提高斯台普斯如玉米、小麦和大米中的维生素A原类胡萝卜素水平。在植物中对该途径进行代谢工程的初步成功表明了这种方法的潜力。然而，这种转基因植物中的意外产物表明，该技术受到目前对内源基因表达理解不足的限制。合理的代谢工程策略必须考虑到尚未完全理解的内源性途径的调节。 我们建议，维生素原A类胡萝卜素的相对积累介导的生物合成和降解酶的转录水平的控制，并修改（增强或抑制）在玉米胚乳中的转录水平可以导致维生素原A类胡萝卜素相对于其他非维生素原A类胡萝卜素的水平增加。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两种最重要的粮食作物--玉米和水稻。我们发现，几个途径酶编码的小基因家族，这提出了一个问题：什么是基因家族成员的类胡萝卜素的生物合成和积累在不同的组织，发育阶段，质体膜定位的贡献？我们将继续我们的NIH-SCORE支持的工作，进行一个全面的研究内源基因的表达，这些基因编码类胡萝卜素途径的酶和相关的类异戊二烯生物合成途径，为类胡萝卜素生物合成提供底物。我们也将研究基因编码的酶降解或修改类胡萝卜素，从而减少维生素原A的含量。拟议的研究将分为两个领域：（1）与类胡萝卜素合成/降解相关的转录谱分析以及与类胡萝卜素含量/组成的相关性，以及（2）胡萝卜素环羟化酶的表征，因为它们影响维生素A原胡萝卜素向非维生素A原叶黄素的转化。 相关性：维生素A缺乏症是一个全球性的健康问题，影响到近2亿儿童。为了减轻世界范围内的缺乏，可以改善作物的维生素A原类胡萝卜素含量，其目标需要育种工具和关于如何在粮食作物中调节类胡萝卜素组成的基础研究，从玉米和水稻开始作为模型。

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.