Dimerization of Floral Organ Identity Proteins in Arabidopsis

大量证据支持这样的假设，即不同开花植物中控制花发育的基因产物和机制在很大程度上是保守的。许多植物发育控制蛋白含有一个保守的DNA结合域，称为MADS结构域。拟南芥MADS家族由30多个基因组成。MADS蛋白参与植物发育的各个方面，包括开花时间控制、分生组织规范、花器官识别和果实发育。尽管这些MADS蛋白在植物发育中很重要，但人们对它们的功能和相互作用知之甚少。本文主要研究拟南芥（Arabidopsis thaliana） MADS蛋白APETALA3 （AP3）和pisttillata （PI）的花器官特性。AP3和PI在拟南芥花中起指导花瓣和雄蕊发育的作用。所有MADS蛋白都以异二聚体或同二聚体的形式与DNA结合。拟南芥中的大多数MADS蛋白能够与多种伴侣蛋白形成同型二聚体和异源二聚体。相比之下，AP3和PI不能同二聚体形成专性异二聚体。AP3/PI异源二聚体具有高度特异性和进化保守性，在远亲植物Antirrhinum majus中AP3和PI同源物之间存在类似的相互作用。本项目的重点是鉴定AP3和PI蛋白中介导AP3和PI之间高度特异性异源二聚体相互作用的氨基酸和亚结构域；这将通过位点特异性诱变和利用“反向”酵母双杂交方法来实现。通过这项研究，我们希望能够确定这类重要植物发育调节剂二聚化的规则。这项研究的第二个重点是PI的一个不寻常的等位基因PI -5。与所有其他ap3和pi突变体不同，pi-5-仅在花的单个轮上表现出表型缺陷。PI-5蛋白与野生型AP3伴侣蛋白的相互作用存在缺陷。pi-5的遗传实验表明，螺旋特异性因子可调节pi-5的活性。利用遗传和分子方法，将分离和表征影响花器官特性的轮特异性因子。

Considerable evidence supports the hypothesis that the gene products and mechanisms that control flower development in different flowering plant species are largely conserved. Many plant developmental control proteins contain a conserved DNA binding domain called the MADS domain. The MADS family in Arabidopsis consists of more than 30 genes. MADS proteins are involved in diverse aspects of plant development including flowering time control, meristem specification, floral organ identity, and fruit development. Despite the importance of these MADS proteins in plant development, little is known about how these proteins function and interact. This proposal focuses on the floral organ identity MADS proteins APETALA3 (AP3) and PISTILLATA (PI) in Arabidopsis thaliana. AP3 and PI function to direct the development of petal and stamens in the Arabidopsis flower. All MADS proteins bind to DNA either as heterodimers or homodimers. Most MADS proteins in Arabidopsis are capable of forming both homodimers and heterodimers with a variety of partner proteins. AP3 and PI, by contrast, are unable to homodimerize and form an obligate heterodimer. The AP3/PI heterodimer is highly specific and is evolutionarily conserved as evidenced by a similar interaction between the AP3 and PI homologs in the distantly related plant species Antirrhinum majus. This project is focused on identifying the amino acids and subdomains in the AP3 and PI proteins that mediate the highly specific heterodimer interaction between AP3 and PI; this will be done both by site-specific mutagenesis and by utilizing "reverse" yeast two-hybrid approaches. Through this research, we hope to be able to define the rules for dimerization of this importance class of plant developmental regulators. A second focus of this research centers on an unusual allele of PI called pi-5. Unlike all other ap3 and pi mutants, pi-5- exhibits phenotypic defects only in a single whorl of the flower. The PI-5 protein exhibits defects in protein-protein interaction with a wild-type AP3 partner protein. Genetic experiments with pi-5 suggest that whorl-specific factors modulate the activity of PI-5. Using both genetic and molecular approaches, whorl-specific factors that affect floral organ identity will be isolated and characterized.