Sym Plasmid and Chromosomal Gene Products of Rhizobium trifolii Elicit Developmental Responses on Various Legume Roots

Rhizobium trifolii strains capable of inducing nodulation on clovers can produce heat-stable, water-soluble substances, which can induce a variety of responses on the roots of both clovers and vetches. These responses are: a significant shortening of the root; an increase in the number of root hairs, and a distortion or curling of the root hairs formed. Our results indicate that the Rhizobium genes responsible for the production of these substances are located on the bacterial chromosome. However, substances in the rhizosphere of the roots of clovers and vetches can affect the expression of particular genes in the nodulation region of the Sym plasmid of R. trifolii to enhance the production of these bacterial compounds which inhibit root growth and development.