Nodulation of Discaria trinervis by Frankia

WALL, LG

Beijin, China

Conferencia; 14th International Congress on Nitrogen Fixation; 2004

Discaria trinervis-Frankia symbiosis is an example of an intercellular infected actinorhizal one. Nodulation is under autoregulatory control of the plant. Recognition between partners is expressed before infection since non infective Frankia dose not induce nodule primordia or regulatory inhibition. Very little is known about signaling between symbionts, and most studies have been done in root hair infected plants. A major interest is to discover  signal molecules involved in the early interactions between Frankia and actinorhizal plants. We analyzed the influence of different sources of diffusible signal factors on the nodulation rate and nodulation profile of Discaria trinervis taproots inoculated with Frankia isolate BCU110501. Nodulation rate was modified by co-inoculation  with non infective Frankia or Streptomyces coelicolor, but was not affected by co-inoculation with other rhizospheric bacteria. This enhancement of nodulation rate could be obtained by pre-treating a diluted BCU110501 inoculum with high concentrations of Frankia or Streptomyces within dialysis bags. The nodulation profile on the taproot was shifted basipetaly correlating with the concentrations of washed Frankia BCU110501 dialyzates, or culture supernatants. These results suggest that Frankia diffusible signal(s) can modify its own infectivity and the transient susceptibility for nodulation of the root.