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Front. Microbiol. | doi: 10.3389/fmicb.2018.02852

Conserved Composition of Nod Factors and Exopolysaccharides Produced by Different Phylogenetic Lineage Sinorhizobium Strains Nodulating Soybean

 Dan Wang1, Francois Couderc2,  Chang-Fu Tian3,  Wen-Jie Gu1,  Li-Xue Liu3 and Verena Poinsot2*
  • 1Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, China
  • 2UMR5623 Laboratoire Interactions Moleculaires et Reactivite Chimique et Photochimique (IMRCP), France
  • 3State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, China

The structural variation of symbiotic signals released by rhizobia determines the specificity of their interaction with legume plants. Previous studies showed that Sinorhizobium strains from different phylogenetic lineage had different symbiotic phenotype on certain cultivated soybeans. Whether they released similar or different symbiotic signals remained unclear. In this study, we compared their nod and exo gene clusters and made a detailed structural analysis of Nod factors and EPS by ESI-MS/MS and two dimensions NMR. Even if there are some differences among nod or exo gene clusters; they produced much conserved Nod factor and EPS compositions. The Nod factors consist of a cocktail of β-(1, 4)-linked tri-, tetra-, and pentamers of N-acetyl-D-glucosamine (GlcNAc). The C2 position on the non-reducing terminal end is modified by a lipid chain that contains 16 or 18 of carbon - with or without unsaturations- , and the C6 position on the reducing residue is decorated by a fucose or a 2-O-methylfucose. Their EPS are composed of glucose, galactose, glucuronic acid, pyruvic acid in the ratios 5:1:2:1 or 6:1:2:1. These findings indicate that soybean cultivar compatibility of Sinorhizobium strains does not result from Nod factor or EPS structure variations. The structure comparison of the soybean microbionts with other Sinorhizobium strains showed that Nod factor structures of soybean microbionts are much conserved, although there are no specific genes shared by the soybean microsymbionts. EPS produced by Sinorhizobium strains are much different from those of Bradyrhizobium. All above is consistent with the previous deduction that Nod factor structures are related to host range, when those of EPS are connected with phylogenetic.

Keywords: Exopolysaccharide, Mass Spectrometry, Nod factors (lipochitooligosaccharides), Sinorhizobium, soybean.

Received: 23 Aug 2018; Accepted: 06 Nov 2018.

Edited by:

Christian Sohlenkamp, National Autonomous University of Mexico, Mexico

Reviewed by:

Daniela Medeot, National University of Río Cuarto, Argentina
Jose M. Vinardell, Universidad de Sevilla, Spain  

Copyright: © 2018 Wang, Couderc, Tian, Gu, Liu and Poinsot. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Verena Poinsot, UMR5623 Laboratoire Interactions Moleculaires et Reactivite Chimique et Photochimique (IMRCP), Toulouse, 31062, Midi-Pyrénées, France, poinsot@chimie.ups-tlse.fr