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

Abstract

The infectious processes of the Frankia-Alnus and Rhizobium-legume symbioses present strong similarities, suggesting the existence of analogies between Frankia root hair deforming factor and rhizobia Nod factors. Biochemical and functional analogies were tested using ACoN24d Frankia strain. The putative chitin-like nature of the Frankia deforming factor was explored by (i) gas chromatography coupled to mass spectrometry and thin layer chromatography, after radioactive labeling of the culture for detection of chitin oligomers, and (ii) following the root hair deforming activity of the supernatant after discriminating treatments (temperature, chitinase, butanol extraction). In parallel, the functional analogy was questioned by testing the mitotic activity of the Frankia supernatant onAlnus 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 approaches used suggest that rhizobia Nod factors and Frankia root hair deforming factor are two structurally divergent symbiotic factors. However, functionnal differences between Frankia root hair factor and the Nod factors have to be confirmed.Key words: Frankia, root hair deforming factor, Nod factor, actinorhizal plants.