Structural and functional comparison of Frankia root hair deforming factorand rhizobia Nod factor

The infectious processes of the Frankia-Alnus and Rhizobium-legume symbiose s present strong similarities, suggesting the existence of analogies betwee n Frankia root hair deforming factor and rhizobia Nod factors. Biochemical and functional analogies were tested using ACoN24d Frankia strain. The puta tive chitin-like nature of the Frankia deforming factor was explored by (i) gas chromatography coupled to mass spectrometry and thin layer chromatogra phy, after radioactive labeling of the culture for detection of chitin olig omers, and (ii) following the root hair deforming activity of the supernata nt after discriminating treatments (temperature, chitinase, butanol extract ion). In parallel, the functional analogy was questioned by testing the mit otic activity of the Frankia supernatant on Alnus glutinosa (L.) roots. The implication in the symbiotic process of the Frankia factor was indirectly explored by testing the effect of a nodulation inhibitor (combined nitrogen ) on root hair deformation. The studies of the combined nitrogen effect on root hair deformation indicate that the deformation induced in vitro by the Frankia factor is linked to the symbiotic process. Moreover, the various a pproaches used suggest that rhizobia Nod factors and Frankia root hair defo rming factor are two structurally divergent symbiotic factors. However, fun ctionnal differences between Frankia root hair factor and the Nod factors h ave to be confirmed.