Nodule-inducing activity of synthetic Sinorhizobium meliloti nodulation factors and related lipo-chitooligosaccharides on alfalfa. Importance of the acyl chain structure. |
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| Authors: | N Demont-Caulet F Maillet D Tailler J C Jacquinet J C Promé K C Nicolaou G Truchet J M Beau J Dénarié |
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| Affiliation: | Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique (CNRS), 205 Route de Narbonne, 31077 Toulouse cedex, France. |
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| Abstract: | Sinorhizobium meliloti nodulation factors (NFs) elicit a number of symbiotic responses in alfalfa (Medicago sativa) roots. Using a semiquantitative nodulation assay, we have shown that chemically synthesized NFs trigger nodule formation in the same range of concentrations (down to 10(-10) M) as natural NFs. The absence of O-sulfate or O-acetate substitutions resulted in a decrease in morphogenic activity of more than 100-fold and approximately 10-fold, respectively. To address the question of the influence of the structure of the N-acyl chain, we synthesized a series of sulfated tetrameric lipo-chitooligosaccharides (LCOs) having fatty acids of different lengths and with unsaturations either conjugated to the carbonyl group (2E) or located in the middle of the chain (9Z). A nonacylated, sulfated chitin tetramer was unable to elicit nodule formation. Acylation with short (C8) chains rendered the LCO active at 10(-7) M. The optimal chain length was C16, with the C16-LCO being more than 10-fold more active than the C12- and C18-LCOs. Unsaturations were important, and the diunsaturated 2E,9Z LCO was more active than the monounsaturated LCOs. We discuss different hypotheses for the role of the acyl chain in NF perception. |
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