Regulation of Shoot Meristem Development

高等植物在其一生中启动新的器官(例如，叶子)。因此，他们面临两个问题。植物必须保持一个未分化的细胞池，以供器官起始使用，并且必须平衡这些未分化细胞的增殖和它们融入器官原基的过程。换句话说，在给定恒定数量的未分化细胞的情况下，未分化细胞的分裂速率必须等于这些细胞被导向器官形成的速率。这些过程发生在一种称为分生组织的结构中。在植物胚胎中，有两个分生组织：根分生组织和茎分生组织，根分生组织形成根系统，分生组织形成植株的地上部分。在茎分生组织的生长顶端，中心的细胞保持未分化状态，而中心区域周围的细胞指向器官形成。这项研究的目的是为了更好地了解指导茎分生组织器官形成的基因和过程。虽然拟议的项目是基础科学，但任何改变植物器官数量、空间格局或特性的应用项目都需要对新梢分生组织的理解。CLAVATA基因座(CLV1、CLV2、CLV3)根据功能丧失表型，在促进新梢和花分生组织器官形成的途径上具有相同的功能。CLV1和CLV2基因已经被克隆，似乎是参与信号转导的受体的编码。在之前的资助期间，分离了CLV1基因，并确定了其严格限制在新梢和花分生组织中的表达模式。CLV1在异位或扩大分生组织的突变体中异位表达。35S启动子不可能构成表达CLV1，这显然是由于CLV1在发育的早期阶段的毒性。然而，CLV1可以在花特异AP1启动子的控制下表达，这挽救了clv1突变的表型，但不影响野生型的发育。同时还确定了clv1和clv3突变体的主要缺陷是器官形成，而不是细胞分裂。对clv2突变体的分析表明，clv2同时调节分生组织和器官的发育。CLV2与CLV1/CLV3调节分生组织发育的途径相同，但调节器官发育的途径不同。对CLV2的需求对生理条件非常敏感。分离出了一些新的分生组织发育调控因子的突变。当前资助期的目标是产生可诱导的CLV1异位激活。这将使CLV1的功能问题得以解决，并将使CLV1信号转导的潜在靶点得以表征。我们将研究在短日照光周期条件下Clv2花表型被抑制的过程。调查将确定这是否是对日长生长速度的反应，以及哪些基因参与其中。CLV2将在各种组织特异性和诱导性启动子下表达，以解决CLV2功能的问题。最后，我们将研究一种新的分生组织发育调节因子--冠状细胞(COR)的突变。Cor突变体被鉴定为clv1器官形成缺陷的强增强子。Cor clv1-1双突变体在过渡到开花后完全失去了启动新器官的能力。初步的遗传学证据表明，COR促进器官形成的途径与CLV基因座不同。

Higher plants initiate new organs (e.g., leaves) throughout theirlife. Thus they face two problems. Plants must maintain a pool ofundifferentiated cells from which to draw upon for organ initiation, andmust balance the proliferation of these undifferentiated cells and theirincorporation into organ primordia. In other words, given a constantnumber of undifferentiated cells, the cell division rate of theundifferentiated cells must equal the rate at which these cells aredirected toward organ formation. These processes occur at a structuretermed a meristem. In the plant embryo, two meristems are established:the root meristem, which will give rise to the root system, and the shootmeristem, which will give rise to the above-ground portion of the plant.At the growing tip of the shoot meristem, cells in the very center aremaintained in an undifferentiated state, while cells surrounding thiscentral region are directed toward organ formation. The goal of theproposed research is to provide a better understanding of the genes andprocesses directing organ formation at the shoot meristem. While theproposed project is basic science, any applied projects to alter thenumber, spatial patterning or identity of plant organs will require anunderstanding of the shoot meristem. The CLAVATA loci (CLV1, CLV2, CLV3) function in the same pathwayto promote organ formation at the shoot and flower meristem based onloss-of-function phenotypes. The CLV1 and CLV2 genes have been cloned andappear to code for receptors involved in signal transduction. During theprevious funding period the CLV1 gene was isolated and its expressionpattern, which is tightly restricted to the shoot and flower meristem, wasdetermined. CLV1 becomes ectopically expressed in mutants that developectopic or enlarged meristems. Constitutive expression of CLV1 by the 35Spromoter was not possible, apparently due to the toxicity of CLV1 duringearly stages of development. CLV1 could be expressed, however, undercontrol of the flower-specific AP1 promoter, and this rescues the clv1mutant phenotype, but does not affect wild-type development. It was alsodetermined that the primary defect in clv1 and clv3 mutants is in organformation, not cell division. Analysis of clv2 mutants revealed that CLV2regulates both meristem and organ development. CLV2 functions in the samepathway as CLV1/CLV3 to regulate meristem development, but in a separatepathway to regulate organ development. The requirement for CLV2 is verysensitive to physiological conditions. Mutations in a number of novelregulators of meristem development were isolated. The goal in the current funding period is to generate inducibleectopic activation of CLV1. This will allow questions of CLV1 function tobe addressed, and will allow the characterization of potential targets ofCLV1 signal transduction. The process of suppression of clv2 flowerphenotypes under short day photoperiod conditions will be investigated.The investigations will determine whether this is a response to day lengthor growth rates, and what genes are involved. CLV2 will be expressedunder various tissue-specific and inducible promoters to address questionsof CLV2 function. Finally, a mutation in a novel regulator of meristemdevelopment, corona (cor), will be studied. The cor mutant was identifiedas a strong enhancer of the clv1 organ formation defect. cor clv1-1double mutants completely lose the ability to initiate new organ primordiashortly after the transition to flowering. Preliminary genetic evidencesuggest that COR promotes organ formation in a separate pathway from theCLV loci.