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 chi tin oligomer backbone linked with a fatty acid at the nonreducing end, Modi fications of the Nod factor structures influence their stability in the rhi zosphere and their biological activity, To test the function of N-acetyl gr oups in Nod factors, NodSm-IV(C-16:2,S) from Sinorhizobium meliloti was enz ymatically N-deacetylated in vitro with purified chitin deacetylase from Co lletotrichum lindemuthianum. A family of partially and completely deacetyla ted derivatives was produced and purified. The most abundant chemical struc tures identified by mass spectrometry were GlcN(C-16:2)-GlcNAc-GlcNH(2)-Glc NAc(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 p urified N-deacetylated derivatives were stable in the rhizosphere of Medica go 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 inducin g root hair deformation. Furthermore, the N-deacetylated molecules were not able to stimulate Nod factor degradation by M. sativa roots, a response el icited by active Nod factors, These data show that N-acetyl groups of Nod f actors are required for biological activity.