Formin蛋白是一类肌动蛋白成核因子，在许多真核生物内包括真菌、动物和植物中已经被鉴定出来。它们主要通过促进单体肌动蛋白成核和微丝成束调节细胞内微丝动态变化进而参与极性生长、细胞分裂及膜泡运输等许多重要的生理活动。植物中的Formin基因已经越来越多的被鉴定出来，越来越多的研究集中在Formin蛋白在植物中所发挥的作用。在拟南芥中Formin家族有21个基因，AtFH8是其中的一个，体外生化实验表明AtFH8蛋白能够与微丝的正端和侧面结合发挥成核、封端和成束的作用。关于AtFH8在细胞内如何调节微丝结构的研究仍较为初步，在已有的生化性质的基础上，本文进一步深入研究AtFH8在植物体内是如何调节微丝结构动态变化。通过AtFH8内源启动子驱动GUS基因表达的实验发现，AtFH8在拟南芥根尖分生区和侧根发生部位有较多表达，这表明AtFH8可能在拟南芥根的分生组织区发挥作用。将GFP与带有不同结构域的AtFH8的融合基因转化拟南芥植株后发现，在根中，AtFH8的N端跨膜结构域能够指导AtFH8主要定位在细胞分裂间期细胞核膜上，而全长AtFH8蛋白除了在细胞核膜分布外还分布于细胞周质中。在根尖分生区处于胞质分裂的细胞中，AtFH8在其N端跨膜结构域的指导下定位在成膜体及正在生长的细胞板上。免疫荧光实验也证实AtFH8在间期细胞的细胞核膜及胞质分裂期的成膜体和细胞板上的定位。AtFH8和其N端跨膜结构域在拟南芥中过表达使种子萌发延迟，同时N端跨膜结构域截短蛋白的过表达使得主根分生区处于细胞分裂期的细胞数目减少而使主根长度变短，而全长AtFH8的过表达种子在延迟一天萌发的情况下通过增加主根分生区处于细胞分裂期的细胞数目使得其主根长度在生长到7 d时与野生型植株主根长度一致。AtFH8 T-DNA插入突变体atfh8在用微丝相关药物Latrunculin B（LatB）及Cytochalasin D (Cyt D)处理的条件下相比野生型植株表现出主根长度缩短和侧根数目减少的表型。统计分析发现atfh8突变体植株根尖分生区的处于细胞分裂期的细胞数目少于野生型植株。相比野生型植株，atfh8突变体植株对微丝相关药物更加敏感，主根分生区和侧根发生位置的微丝及微丝束在药物处理后发生解聚。此外，我们选用了适合观察细胞分裂过程的烟草BY-2悬浮细胞为材料，以期对AtFH8调节细胞微丝结构的机制进行研究。初步研究结果表明，AtFH8主要定位在间期细胞核膜及胞质分裂期的成膜体和细胞板上，AtFH8过表达可以增加间期细胞中微丝束的数目；N端跨膜结构域的过表达破坏和减少了间期细胞微丝束结构且使得细胞内的微丝结构对LatB更加敏感。关于过表达AtFH8在细胞分裂中对微丝结构的作用还在进一步的研究中。综上所述，本论文通过AtFH8的定位分析、过表达和T-DNA插入突变体的表型及其根器官细胞内微丝结构动态变化观察等方面的研究结果证明AtFH8在植物体内主要定位于间期细胞的细胞核膜和胞质分裂期的成膜体及细胞板上，在受到微丝解聚的胁迫下AtFH8通过促进微丝束的形成维持微丝束结构的完整性参与主根生长和侧根发生。

Formin proteins are actin nucleators and have been identified in various eukaryotic orgnisms, including fungi, animals, and plants. They are active in a variety of cell functions, including polarized growth, fusion, division and the regulation of organelle and cell motility through nucleating, capping and bundling activity. More and more plant formins have been identified and paid much attention for their potent nucleating activity. In Arabidopsis, there are 21 members in formin protein family and AtFH8 is one gene of the family. In our previous study, we had identified and characterized the bundling activity of AtFH8 in vitro. Biochemical analysis showed that AtFH8(FH1FH2) could nucleate actins, form dimers and bundle preformed actin filaments or induce stellar structures during actin polymerization. In this study, we found that AtFH8 was predominantly expressed in Arabidopsis root meristem, vasculature, and outgrowth points of lateral roots by expressing the GUS gene driven by the native promoter of AtFH8, indicating that AtFH8 might play roles in root meristem. We further studied the subcellular localization of AtFH8 in Arabidopsis root through expressing truncated forms of AtFH8 fusion with GFP proteins. AtFH8 localized primarily to nuclear envelope in interphase and to phragmoplast and cell plate after cytokinesis in root tips depending primarily on its N terminal transmembrane domain and immunolocalization analysis confirmed this localization. The germination of seeds was delayed after overexpressing of AtFH8 and its N terminal transmembrane. Overexpressing of the N terminal tranmembrane of AtFH8, the primary root length was shorter than that of wild type because of the little number of dividing cells in primary root tips and AtFH8 overexpression induced the primary root growth quickly due to the increased numbers of dividing cells in root tips than that of wild type in the few days after germinating. The primary root growth and lateral root initiation of atfh8 could be decreased by Latrunculin B (LatB) and Cytochalasin D (Cyt D). Analysis of the number of dividing cells in Arabidopsis root tips showed that much fewer dividing cells in LatB-treated atfh8 than wild-type plants, which indicated that AtFH8 was involved in cell division. Actin cytoskeleton in root meristem and lateral root initiation places of atfh8 was more sensitive to treatment of drugs related with actin filaments than that of wild type. Furthermore, we selected the tobacco BY-2 cells to analysis the machine-processed of how AtFH8 changes the actin structures dynamic in cell cycle. Overexpression of AtFH8 in tobacco BY-2 suspension cells induced the numbers of cytoplasmic transvacular strands; overexpression of N terminal tranmembrane of AtFH8 in tobacco BY-2 suspension cells decreased the numbers of cytoplasmic transvacular strands and induced the actin filaments sensitive to LatB treatment.Altogether, the study of the localization, overexpression and T-DNA insertion mutant of AtFH8 in vivo indicate that AtFH8 is primarily localized to nuclear envelope in interphase and to phragmoplast and cell plate after cytokinesis and participates in root development by regulating the actin filaments dynamic in cell division at the stress of depolymerizing the actin filaments. The work confirms and extends our understanding of the functions of plant formin proteins.