Integrated roles of BclA and DD-carboxypeptidase 1 in Bradyrhizobium differentiation within NCR-producing and NCR-lacking root nodules

Quentin Barrière (1, 2, 3) , Ibtissem Guefrachi (1, 2, 3, 4) , Djamel Gully (5) , Florian Lamouche (1, 2, 3, 4) , Olivier Pierre , Joël Fardoux (5) , Clémence Chaintreuil (5) , Benoît Alunni (1, 2, 3) , Tatiana Timchenko (6, 7, 1) , Eric Giraud (5) , Peter Mergaert (1, 2, 3)

1 I2BC - Institut de Biologie Intégrative de la Cellule
2 CNRS - Centre National de la Recherche Scientifique
3 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
4 INRA - Institut National de la Recherche Agronomique
5 UMR LSTM - Laboratoire des symbioses tropicales et méditerranéennes
6 Dpt Microbio - Département Microbiologie
7 PBI - Intéractions Plantes-Bactéries

Legumes harbor in their symbiotic nodule organs nitrogen fixing rhizobium bacteria called bacteroids. Some legumes produce Nodule-specific Cysteine-Rich (NCR) peptides in the nodule cells to control the intracellular bacterial population. NCR peptides have antimicrobial activity and drive bacteroids toward terminal differentiation. Other legumes do not produce NCR peptides and their bacteroids are not differentiated. Bradyrhizobia, infecting NCR-producing Aeschynomene plants, require the peptide uptake transporter BclA to cope with the NCR peptides as well as a specific peptidoglycan-modifying DD-carboxypeptidase, DD-CPase1. We show that Bradyrhizobium diazoefficiens strain USDA110 forms undifferentiated bacteroids in NCR-lacking soybean nodules. Unexpectedly, in Aeschynomene afraspera nodules the nitrogen fixing USDA110 bacteroids are hardly differentiated despite the fact that this host produces NCR peptides, suggesting that USDA110 is insensitive to the host peptide effectors and that nitrogen fixation can be uncoupled from differentiation. In agreement with the absence of bacteroid differentiation, USDA110 does not require its bclA gene for nitrogen fixing symbiosis with these two host plants. Furthermore, we show that the BclA and DD-CPase1 act independently in the NCR-induced morphological differentiation of bacteroids. Our results suggest that BclA is required to protect the rhizobia against the NCR stress but not to induce the terminal differentiation pathway.

Mots clés: PBI; MICROBIO

Domaines: Sciences du Vivant [q-bio]

Quentin Barrière, Ibtissem Guefrachi, Djamel Gully, Florian Lamouche, Olivier Pierre, et al.. Integrated roles of BclA and DD-carboxypeptidase 1 in Bradyrhizobium differentiation within NCR-producing and NCR-lacking root nodules. Scientific Reports, 2017, 7 (1), pp.9063. ⟨10.1038/s41598-017-08830-0⟩. ⟨hal-02187766⟩