Legume plants and nodule bacteria form a root symbiosis that is important as an ecologically acceptable source of nitrogen for agricultural systems due to the nodule bacteria ability to fix atmospheric nitrogen, where the plant ability to form symbiosis is determined by symbiotic genes whose changes (mutations) lead to the loss of the symbiotic competence. Since the function of many symbiotic genes is not known to date, a set of pea symbiotic mutants was screened for the production of flavonoid activators of nodule bacteria as a potential function of the mutated gene, as well as for the ability to respond with increased production of flavonoid activators upon contact with bacteria. The presence or loss of the flavonoid response in individual pea lines allowed to determine the functional order of chosen symbiotic genes in the signal transduction pathway from the bacterium to the plant and showed the possibility to dissociate the processes of flavonoid induction and the induction of new symbiotic nodules.