ALTERATION OF PLANT-GROWTH AND DEVELOPMENT BY RHIZOBIUM NODA AND NODBGENES 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 elic it nodule organogenesis in roots of leguminous plants. Recently, it ha s been shown that NodB deacetylates chitooligosaccharides at the non-r educing terminus, so that the free amino group of the chitooligosaccha ride backbone can then be acylated by a specific fatty acid. The Rhizo bium NodA protein together with the nodB encoded chitooligosaccharide deacetylase are involved in generating small, heat-stable compounds th at stimulate mitosis in protoplasts derived from either legumes or oth er plant species. To test whether these gene products could play a rol e 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 correl ating 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.