Regulation of Shoot Meristem Development

点击翻译按钮获取中文摘要

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.