Molecular mechanisms of regulation of cell division by Myb transcription factors in plants.

Myb转录因子在Myb结构域有3个重复序列（3R-Myb），是由植物Myb基因大家族中一个相对较小的亚家族编码的。我们之前已经证明这种类型的Myb蛋白在烟草G2/ m期基因调控中具有重要作用。植物3R-Myb蛋白根据其一级序列可分为a型、b型和c型3R-Myb 3类。本研究的目的是阐明3R-Myb转录调控的分子机制，并发现调节3R-Myb蛋白活性的新因子。我们发现c型3R-Myb蛋白在烟草细胞中作为CYCB1启动子的转录抑制因子。烟草a型3R-Myb蛋白NtmybA2的转激活电位受到位于其C端的调控结构域的抑制。该结构域的删除显著增强了其交互激活活性。我们的微阵列实验显示，c端缺失版本NtmybA2的过表达导致许多含有MSA元件的G2/M基因的选择性上调。这些结果使得在烟草细胞中鉴定NtmybA2转录调控的潜在靶基因成为可能。在另一种方法中，我们旨在鉴定由拟南芥中a型3R-Myb基因myb3r4的T-DNA插入突变引起的细胞分裂缺陷的突变。我们发现一个这样的突变存在于野生型兰斯伯格的基因组中。我们可以将其定位在3号染色体上臂400 kb的区域内。对该位点的进一步定位和互补实验将使我们能够确定在myb3r4背景下负责增强细胞分裂缺陷的基因。

Myb transcription factors with three repeats in the Myb domain (3R-Myb) are encoded by a relatively small subfamily in the large Myb gene family in plants. We have previously shown that this type of Myb proteins have important roles in regulation of G2/M-phase genes in tobacco. The 3R-Myb proteins in plants can be divided into 3 classes (A-type, B-type and C-type 3R-Myb) based on their primary sequences. The aim of this research was to elucidate the molecular mechanisms of transcriptional regulation by 3R-Myb and to identify novel factors that regulate activities of 3R-Myb proteins.1. We showed that C-type 3R-Myb proteins act as transcriptional repressors on CYCB1 promoter in tobacco cells.2. The transactivation potential of NtmybA2, a tobacco A-type 3R-Myb protein, is repressed by a regulatory domain located at its C terminus. Deletion of this domain dramatically enhanced its transactivation activity. Our microarray expriments revealed that overexpression of C-terminally deleted version of NtmybA2 resulted in selective upregulation of many G2/M genes that contain MSA elements. The results allowed a genome-wide identification of potential target genes of transcriptianl regulation by NtmybA2 in tobacco cells.3. In another approach, we aimed to identify the mutation that enhances the cytokinesis defect caused by T-DNA insertion mutation of myb3r4, an A-type 3R-Myb gene in Arabidopsis thaliana. We found that one such mutation is present in genome of the wild-type Lansberg. We could map its locus within a 400-kb region located in upper arm of chromosome 3. Further mapping of this locus and complementation experiments would allow us to identify the gene that are responsible for enhancing the cytokinesis defect in myb3r4 background.