Cytokinin Metabolic Genes and Enzymes

细胞分裂素是一种调节细胞分裂和分化的植物激素。最重要的天然存在的细胞分裂素是玉米素，一种具有高生物活性的化合物。在植物组织中发现了多种玉米素代谢物，其中一些是活性的，而另一些则不是，因此，了解玉米素代谢是如何调节的至关重要。该项目的长期目标是查明和描述实施这种控制的要素。先前的研究已经导致玉米素特异性酶的分离，包括O-糖基转移酶，其将糖基转移到玉米素，以及从豆类、拟南芥和玉米中克隆对应于这些酶的基因家族。O-葡糖基化玉米素广泛存在于植物组织中，其作为细胞分裂素的非活性、可逆（通过水解）储存形式发挥作用。与玉米素相反，O-葡糖基化玉米素对酶促分解具有抗性。因此，葡糖基转移酶基因的活性可能对活性细胞分裂素的水平具有显著影响，并且因此也对植物发育具有显著影响。另一种重要的酶是玉米素还原酶，它将玉米素转化为二氢玉米素，二氢玉米素是一种活性细胞分裂素，比玉米素稳定得多。虽然二氢玉米素存在于所有植物中，并且还原酶已从植物组织中分离出来，但与这种类型的酶相对应的基因尚未被鉴定。拟议的研究集中在玉米素O-葡萄糖基转移酶和还原酶，包括一系列的分子，酶，生理和发育研究。具体目标是：（1）检查玉米素O-葡萄糖基化在种子萌发，运输和衰老中的作用; 2）确定拟南芥中玉米素O-葡萄糖基转移酶的表达和细胞定位; 3）鉴定底物特异性关键酶的氨基酸序列; 4）分离玉米素还原酶编码基因。至于更广泛的影响，该项目涉及国际合作，R.捷克科学院的Vankova。该项目将研究与教育相结合，重点是本科生培训，包括为R实验室的学生提供国际经验。布拉格的万科娃。拟议的研究还包括与私营企业的合作，这进一步扩大了研究的影响，并加强了新发现的流动。

Cytokinins are plant hormones mediating cell division and differentiation. The most important naturally-occurring cytokinin is zeatin, a compound with high biological activity. Various zeatin metabolites are found in plant tissues, some of which are active while others are not, and therefore, it is crucial to understand how zeatin metabolism is regulated. The long-term goal of this project is to identify and characterize elements exerting such controls. Previous research has led to isolation of zeatin-specific enzymes, including O-glycosyltransferases, which transfer a sugar group to zeatin, and cloning of a family of genes corresponding to these enzymes from beans, Arabidopsis, and maize. O-glucosylated zeatin occurs widely in plant tissues where it functions as an inactive, reversible (via hydrolysis) storage form of cytokinin. In contrast to zeatin, O-glucosylated zeatin is resistant to enzymatic breakdown. Consequently, the activities of the glucosyltransferase genes are likely to have significant impact on the level of active cytokinins and, as a consequence, also on plant development. Another important enzyme is zeatin reductase, which converts zeatin to dihydrozeatin, an active cytokinin that is much more stable than zeatin. Although dihydrozeatin occurs in all plants and the reductase has been isolated from plant tissue, genes corresponding to this type of enzyme have not yet been identified. The proposed research focuses on zeatin O-glucosyltransferases and reductases and includes a range of molecular, enzymatic, physiological, and developmental investigations. The specific objectives are to: (1) examine the role of zeatin O-glucosylation in seed germination, transport, and senescence; 2) determine the expression and cytolocalization of zeatin O-glucosyltransferases in Arabidopsis; 3) identify amino acid sequences on the enzymes critical to substrate specificity; and 4) isolate genes encoding zeatin reductases. As to broader impacts, the project involves international collaboration, with Dr. R. Vankova of the Czech Academy of Sciences. The project integrates research with education, with an emphasis on undergraduate training that includes an international experience for students in the laboratory of R. Vankova in Prague. The proposed research also includes collaboration with private industry, which further broadens the impact of the research and enhances the flow of new findings.