N-deacetylation of Sinorhizobium meliloti Nod factors increases their stability in the Medicago sativa rhizosphere and decreases their biological activity

Nod factors excreted by rhizobia are signal molecules that consist of a chitin oligomer backbone linked with a fatty acid at the nonreducing end, Modifications of the Nod factor structures influence their stability in the rhizosphere and their biological activity, To test the function of N-acetyl groups in Nod factors, NodSm-IV(C-16:2,S) from Sinorhizobium meliloti was enzymatically N-deacetylated in vitro with purified chitin deacetylase from Colletotrichum lindemuthianum. A family of partially and completely deacetylated derivatives was produced and purified. The most abundant chemical structures identified by mass spectrometry were GlcN(C-16:2)-GlcNAc-GlcNH(2)-GlcNAc(OH)(S) GlcN(C-16:2)-GlcNAc-GlcNH(2)-GlcNHz(2)(OH)(S), and GlcN(C-16:2)-GlcNH(2)-GlcNH(2)-GlcNH(2)(OH)(S). In contrast to NodSm-IV(C-16:2,S), the purified N-deacetylated derivatives were stable in the rhizosphere of Medicago sativa, indicating that the N-acetyl groups make the carbohydrate moiety of Nod factors accessible for glycosyl hydrolases of the host plant. The N-deacetylated derivatives displayed only a low level of activity in inducing root hair deformation. Furthermore, the N-deacetylated molecules were not able to stimulate Nod factor degradation by M. sativa roots, a response elicited by active Nod factors, These data show that N-acetyl groups of Nod factors are required for biological activity.