The Early Nodulin Gene Enod2: Symbiotic Control and Cytokinin Induction

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Nodulin genes are plant genes which are specifically induced during the formation of nitrogen-fixing root- stem nodules on leguminous plants. Early nodulin (Enod) genes are expressed within 10 days after inoculation and play a role in the rhizobial infection process and nodule ontogeny. Enod genes are not only symbiotically induced and developmentally controlled, but are also expressed in a tissue specific manner. The Enod2 gene is symbiotically activated in the nodule parenchyma cells and encodes a hydroxyproline rich protein, which probably is targeted to the plant cell wall, where it may be involved in creating an oxygen diffusion barrier. The focus of this proposal is to elucidate the signal transduction pathway involved in the expression of the Enod2 gene from the tropical stem-nodulated legume, Sesbania rostrata (SrEnod2). The SrEnod2 gene can be induced rapidly and specifically by physiologically significant concentrations of cytokinins. This gene is therefore not only an ideal candidate to study nodule-specific plant gene expression, but also serves as a unique model to study plant gene induction be cytokinin. The ability to manipulate the bacterial "inducer" offers a powerful experimental approach to study the process of plant cell division and differentiation.