ALTERATION OF PLANT-GROWTH AND DEVELOPMENT BY RHIZOBIUM NODA AND NODB GENES INVOLVED IN THE SYNTHESIS OF OLIGOSACCHARIDE SIGNAL MOLECULES

The highly conserved Rhizobium nodulation genes nodABC are required to produce lipid-tinked chitooligosaccharide signal molecules which elicit nodule organogenesis in roots of leguminous plants. Recently, it has been shown that NodB deacetylates chitooligosaccharides at the non-reducing terminus, so that the free amino group of the chitooligosaccharide backbone can then be acylated by a specific fatty acid. The Rhizobium NodA protein together with the nodB encoded chitooligosaccharide deacetylase are involved in generating small, heat-stable compounds that stimulate mitosis in protoplasts derived from either legumes or other plant species. To test whether these gene products could play a role in regulation of plant development, we introduced and expressed the Rhizobium meliloti nodA and nodB genes singly or in combination under the control of diverse promoters in tobacco. Altered phenotypes correlating with nodA and nodB gene expression in transgenic plants indicate that tobacco contains the necessary substrates for the NodA and NodB proteins to produce signal molecules modulating plant growth and organ development.