RPG: Molecular Tools for Studying Cotton Fiber Elongation

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This is a research planning grant for women. Cell elongation depends on the irreversible extension of the cell wall and on hydraulic conductivity and turgor of the cell. The uptake and production of osmotically active solutes for maintenance of turgor is essential to maintain cell elongation for extended time periods. The cellular mechanisms that coordinate the osmoregulation of the cell and extension of the cell wall during cell elongation are poorly understood. Cotton fibers provide an excellent experimental system for studying molecular mechanisms regulating cellelongation. The fibers on the cotton ovule grow synchronously allowing fiber elongation to be followed developmentally. Each fiber is a single cell which eliminates the complications of cell division. In cotton fibers, malate is one of the osmotically active solutes responsible for the maintenance of turgor. As an initial step in ultimately identifying the signal transduction mechanism(s) responsible for coordinating osmoregulation and cell wall loosening, the regulation of PEP carboxylase, the enzyme involved in malate synthesis during fiber elongation, is being studied. Five isoforms of the fiber PEP carboxylase have been identified and are distinguishable by their electrophoretic mobility on SDS polyacrylamide gels. Two of these isoforms are preferentially expressed during maturation of fiber elongation. The immediate aim of this project is to determine how these different PEP carboxylase isoforms are produced. Two complimentary approaches will be taken: (1) isolation and characterization of the PEP carboxylase gene(s) and (2) purification and characterization of the different forms of the PEP carboxylase protein. These studies provide the necessary background to define thephysiological function of these different isoforms during fiber elongation and more specifically, the role of these isoforms in the osmoregulation of the fiber cell. The cotton fiber is commercially valuable in the manufacture of a large percentage of the world's textiles. Improved spinning systems and increased production speeds place increasing demands on the cotton fiber by the textile industry. Efforts to improve the fiber quality of existing cotton germplasm in terms of uniformity, strength and extensibility of the fiber are essential for the US to remain competitive in world markets. Defining the underlying regulatory mechanism(s) controlling fiber elongation utilizing modern molecular tools will be of immense importance in future development of breeding and genetic engineering strategies for improving the fiber's spin value.