Physiological Functions and Biochemical Properties of Plant Cytochromes b561

抗坏血酸（维生素C）具有保护植物免受干旱、伤害、暴露于污染物、高盐和病原体攻击等逆境影响的能力。此外，它是许多代谢酶的辅助因子，并参与植物激素的生物合成。因此，抗坏血酸在控制植物生长发育、防御病原体和氧化应激以及调节细胞氧化还原状态方面发挥着关键作用。虽然对抗坏血酸生物合成和分解代谢的了解正在迅速扩大，但对抗坏血酸发挥其作用的机制以及如何再生知之甚少。本研究的目的是利用拟南芥作为模型系统，确定一类新发现的膜蛋白细胞色素（Cyts） b561在抗坏血酸代谢和再生中的生理作用。基于先前的工作，中心假设是Cyts b561通过催化抗坏血酸作为电子供体的跨膜电子传递来促进抗坏血酸介导的细胞过程。部分氧化的抗坏血酸（单脱氢抗坏血酸）可以在该反应中重新还原为抗坏血酸，从而补充细胞的抗坏血酸库。本文的目的是：1)确定拟南芥Cyts b561的时空表达模式；2)通过改变Cyts b561的表达水平来确定其生理作用；3)确定拟南芥Cyts b561的生化特性。提出的研究是重要的，因为它是针对一类很少研究的膜蛋白参与抗坏血酸介导的反应。深入了解这些蛋白质的功能将有助于我们了解抗坏血酸在植物中的调节和代谢。更广泛的影响：PI实验室的多学科方法为学生和博士后研究人员提供了培训和专业发展的机会。PI将参与大学面向代表性不足群体的外展项目，这项工作的成果将得到广泛传播。

Proposal: 0416742ABSTRACTAscorbate (vitamin C) has the ability to protect plants against the damaging affects of stress situations, such as drought, wounding, exposure to pollutants, high salt and pathogen attack. In addition, it is a cofactor to numerous metabolic enzymes and is involved in the biosynthesis of plant hormones. Therefore, ascorbate plays a key role in the control of plant growth and development, defense against pathogens and oxidative stress and in the regulation of cellular redox status.While knowledge of ascorbate biosynthesis and catabolism is rapidly expanding, little is known about the mechanisms by which ascorbate exerts its effects, and how it is regenerated. The objective of the current proposal is to determine the physiological role of a newly-identified class of membrane proteins, cytochromes (Cyts) b561, in ascorbate metabolism and regeneration, using Arabidopsis thaliana as a model system. Based on previous work, the central hypothesis is that Cyts b561 contributes to ascorbate-mediated cellular processes by catalyzing trans-membrane electron transport with ascorbate as the electron donor. Partially-oxidized ascorbate (mono-dehydroascorbate) can be re-reduced to ascorbate in this reaction, thereby replenishing cellular ascorbate pools. The objective of this proposal will be attained by: 1) determining the spatial and temporal expression patterns of A. thaliana Cyts b561; 2) determining the physiological role of Cyts b561 by altering its expression levels, and 3) determining the biochemical properties of A. thaliana Cyts b561. The proposed research is significant in that it is aimed at a class of poorly-studied membrane proteins involved in ascorbate-mediated reactions. Insight into the function of these proteins should contribute to our understanding of ascorbate regulation and metabolism in plants. Broader Impacts: The multidisciplinary approaches in the laboratory of the PI provide an opportunity for training and professional development of students and postdoctoral researchers. The PI will take part in university outreach programs to underrepresented groups, and results from this work will be broadly disseminated.