Molecular Genetic Analysis of Shoot Apical Meristem Development in Arabidopsis Thaliana

干细胞在许多生物体中都存在。 它们最重要的属性是它们自我补充并产生许多终末分化的细胞类型。 在植物中，根或芽的分生组织或生长尖是干细胞群。 被子植物茎尖分生组织是在胚胎发生过程中形成的，由少量未分化的分裂细胞组成。 这些细胞将产生植物的所有地上部分。 因此，了解茎尖分生组织的发育生物学是了解植物生长和发育的绝对基础。 茎尖分生组织在胚胎发生过程中是如何发生的？ 叶腋的额外分生组织是如何胚后发生的？ 一群未分化的分裂细胞是如何维持在分生组织中的？ 由分生组织产生的器官的位置是如何确定的？ 这项研究的长期目标是在分子细节上回答这些问题。 小型十字花科植物拟南芥已被选为实验生物-其短世代时间和小基因组大小使其特别适合分子遗传分析。 本项目的重点是茎无分生组织（STM）位点。 在该基因中缺失功能突变的纯合幼苗缺乏茎顶端分生组织，但其他方面正常。 对纯合stm-1突变体的仔细形态学检查表明，缺陷在于它们在胚胎发生过程中不能启动茎顶端分生组织。 STM基因对应于玉米结基因的拟南芥同源物的证据。 该基因编码含有同源结构域的蛋白质，因此可能充当转录调节因子。 虽然同源异型结构域蛋白已被确定在植物中以前，这是第一次的情况下，在这种基因中的功能丧失突变已被确定，因此其野生型功能推断。 为了了解STM如何促进茎尖分生组织的形成，提出了旨在阐明STM基因是如何调控的实验，并从长远来看，以确定STM反过来调控的基因。

Populations of stem cells exist in many organisms. Their most significant attribute is that they replenish themselves as well as give rise to many terminally differentiated cell types. In plants, the meristems or growing tips of roots or shoots are groups of stem cells. Shoot apical meristems in angiosperm plants are formed during embryogenesis and are comprised of a small number of undifferentiated, dividing cells. These cells will give rise to all of the above- ground portions of the plant. Thus, understanding the developmental biology of shoot apical meristems is absolutely fundamental to understanding plant growth and development. How is the shoot apical meristem initiated during embryogenesis? How are additional meristems initiated postembryonically in the axils of leaves? How is a group of undifferentiated, dividing cells maintained in the meristem? How are the positions of organs generated by the meristem determined? The long term goal of this study is to answer these questions in molecular detail. The small cruciferous plant Arabidopsis thaliana has been chosen as an experimental organism -- its short generation time and small genome size make it especially well suited for molecular genetic analysis. The focus of this project is the shoot meristemless (STM) locus. Seedlings homozygous for a loss- of-function mutation in this gene lack a shoot apical meristem but are otherwise normal. Careful morphological examination of homozygous stm-1 mutants has shown that the defect lies in their inability to initiate a shoot apical meristem during embryogenesis. Evidence that the STM gene corresponds to an Arabidopsis homolog of the maize Knotted gene is presented. This gene encodes a homeodomain containing protein and therefore probably acts as a transcriptional regulator. Although homeodomain proteins have been identified in plants previously, this is the first case in which a loss-of-function mutation has been identified in such a gene and hence its wild-type function deduced. To understand how STM promotes shoot apical meristem formation, experiments are proposed that are designed to shed light on how the STM gene is regulated and, in the long term, to identify genes that STM in turn regulates.