Analysis of phloem function as a signaling center

植物体计划是由紧密的细胞-细胞通讯网络调控的。维管植物具有独特的营养物质和信号长距离运输系统，称为维管系统。维管系统由木质部、韧皮部和原形成层组成，原形成层产生木质部和韧皮部细胞。我们已经确定了TDIF，一种从韧皮部分泌的调节血管发育的细胞间信号的十二肽。因此，在本研究中，我们分析了韧皮部相关信号在血管发育中的作用。为此，我们着重于以下三个主题。1)阐明TDIF作为韧皮部信号的作用，从而了解韧皮部的状态。2)分析COE1受体激酶的功能，该基因可能在水稻韧皮部细胞中表达，并在维管模式形成中起作用。3)寻找新的调控韧皮部TDIF表达的转录因子。因此，我们成功地证明了韧皮部细胞在维持血管干细胞（如原形成层细胞和形成层细胞）中作为生态位细胞的功能，通过提供TDIF作为促进干细胞自我更新和抑制木质部细胞分化的细胞间因子。我们还发现COE1与生长素和油菜素内酯信号一起在维管组织分化的空间调节中起作用。最后，采用一种新的综合转录因子筛选方法，分离出调节编码TDIF的CLE41基因的转录因子。这些发现对韧皮部细胞作为信号中心的功能有了新的认识。

Plant body plan is regulated by the tight network of cell-cell communication. Vascular plants possess a unique long-distance transport system of nutrients and signals, named the vascular system. The vascular system consists of xylem, phloem and procambium/cambium, which gives rise to xylem and phloem cells. We have identified TDIF, a dodeca-peptide that regulates vascular development as an intercellular signal secreted from phloem. In this study, therefore, we analyzed the function of phloem-related signals involved in vascular development. For this purpose we focused on the following three themes. 1) To elucidate the function of TDIF as a phloem signal and consequently to understand of the status of phloem. 2) To analyze the function of COE1 receptor kinase, whose gene may be expressed in phloem cells and function in vascular pattern formation of rice. 3) To identify new transcription factors that regulate TDIF expression in phloem. As a result, we succeeded in demonstrating that phloem cells functions as niche cells in the maintenance of vascular stem cells such as procambial and cambial cells by providing TDIF as a intercellular factor promoting self-renewal of stem cells and inhibiting xylem cell differentiation. We also indicated that COE1 functions in spatial regulation of vascular tissue differentiation in concert with auxin and brassinosteroid signals. Finally we isolated transcription factors regulating the CLE41 gene encoding TDIF, using a new comprehensive transcription factor screening method. These findings casted a new light on function of the phloem cells as a signal center.