ABSTRACT
This chapter examines some of the recent findings on the isolation of microbial and plant genes involved in the Frankia-actinorhizal symbiosis and the state of research concerning genetic transformation systems. It then discusses recent developments that may be helpful for an understanding of the taxonomic classification of Frankia. Early studies on the molecular biology of Frankia were hampered by difficulties with. growing enough cellular material for DNA extraction and also by the low efficiency of classical lysis techniques of Frankia cells. The nif structural genes encode the nitrogenase enzyme: nifH codes for the polypeptides of the Fe protein and nifDK codes for the alpha and beta subunits of the MoFe protein. Several genetic and physical studies have now clearly established that in fast-growing Rhizobium species the genes involved in symbiosis, particularly the nif genes, are located on large plasmids. Theoretically DNA can be introduced in recipient cells by four strategies: Transduction, Conjugation, Transformation, Protoplast fusion.
