Analysis of Meristem Function and Floral Patterning in the Arabidopsis ULTRAPETALA Mutant

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0110667FletcherThe control of stem cell activity is critical for the proper development of all higher organisms, as stem cells are the precursors of the organs and tissues that comprise the body. Plants make excellent model systems in which to study and manipulate stem cells, because they maintain pools of such cells throughout their life cycle at growing tips called apical meristems. The shoot apical meristem continuously maintains a stem cell reservoir while simultaneously generating organs such as leaves, stems and flowers. How the meristem keeps a constant balance between stem cell production and organogenesis is poorly understood, but studies by Dr. Fletcher and others using the model plant Arabidopsis thaliana are uncovering genes that regulate this balance and thereby affect shoot apical meristem activity. The goal of this project is to understand how the Arabidopsis ULTRAPETALA (ULT) locus controls the activity of shoot and floral meristems. We have isolated ult mutant plants that generate extra flowers and floral organs from enlarged meristems, and also have altered organ identity in the center of the flower. ULT is therefore a candidate regulator of both shoot apical meristem function and floral patterning. Our first objective is to identify the defect(s) underlying the ult shoot and floral meristem phenotypes by analyzing the distribution of region-specific molecular markers. We will also decipher the genetic relationship between ULT and other known regulators of shoot and flower development, which act in a number of different pathways. Our third goal is to map and clone the ULT gene, and determine its mRNA expression pattern during development as a prelude to functional analysis of the gene product. These experiments will identify specific mechanisms through which ULT regulates meristem size and floral patterning, and place ULT in context with other Arabidopsis genes known to affect these processes. Analysis of ULT provides a unique opportunity to investigate the mechanisms that balance life-long stem cell production and organogenesis, and also to determine how a single molecule functions both in growth control and pattern formation to coordinate these two crucial processes during development.