RibBX of Bradyrhizobium ORS285 Plays an Important Role in Intracellular Persistence in Various Aeschynomene Host Plants

International audienceBradyrhizobium ORS285 forms a nitrogen-fixating symbiosis with both Nod factor (NF)-dependent and NF-independent Aeschynomene spp. The Bradyrhizobium ORS285 ribBA gene encodes for a putative bifunctional enzyme with 3,4-dihydroxybutanone phosphate (3,4-DHBP) synthase and guanosine triphosphate (GTP) cyclohydrolase II activities, catalyzing the initial steps in the riboflavin biosynthesis pathway. In this study, we show that inactivating the ribBA gene does not cause riboflavin auxotrophy under free-living conditions and that, as shown for RibBAs from other bacteria, the GTP cyclohydrolase II domain has no enzymatic activity. For this reason, we have renamed the annotated ribBA as ribBX. Because we were unable to identify other ribBA or ribA and ribB homologs in the genome of Bradyrhizobium ORS285, we hypothesize that the ORS285 strain can use unconventional enzymes or an alternative pathway for the initial steps of riboflavin biosynthesis. Inactivating ribBX has a drastic impact on the interaction of Bradyrhizobium ORS285 with many of the tested Aeschynomene spp. In these Aeschynomene spp., the ORS285 ribBX mutant is able to infect the plant host cells but the intracellular infection is not maintained and the nodules senesce early. This phenotype can be complemented by reintroduction of the 3,4-DHBP synthase domain alone. Our results indicate that, in Bradyrhizobium ORS285, the RibBX protein is not essential for riboflavin biosynthesis under free-living conditions and we hypothesize that its activity is needed to sustain riboflavin biosynthesis under certain symbiotic conditions. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license

Dendritic cells containing apoptotic melanoma cells prime human CD8 T cells for efficient tumor cell lysis

Dendritic cells (DCs) phagocytose apoptotic influenza-infected monocytes and cross-present influenza antigen to CD8 T cells, generating a specific CTL response. We investigated whether apoptotic melanoma cells, presented by this mechanism, can lead to CTL responses to tumor-associated antigens and melanom

A gene-based map of the Nod factor-independent Aeschynomene evenia sheds new light on the evolution of nodulation and legume genomes

International audienceAeschynomene evenia has emerged as a new model legume for the deciphering of the molecular mechanisms of an alternative symbiotic process that is independent of the Nod factors. Whereas most of the research on nitrogen-fixing symbiosis, legume genetics and genomics has so far fo-cused on Galegoid and Phaseolid legumes, A. evenia falls in the more basal and understudied Dalbergioid clade along with peanut (Arachis hypogaea). To provide insights into the symbiotic genes content and the structure of the A. evenia genome, we established a gene-based genetic map for this species. Firstly, an RNAseq analysis was performed on the two parental lines selected to generate a F 2 mapping population. The transcriptomic data were used to develop molecular markers and they allowed the identification of most symbiotic genes. The resulting map comprised 364 markers arranged in 10 linkage groups (2n ¼ 20). A comparative analysis with the sequenced genomes of Arachis duranensis and A. ipaensis, the diploid ancestors of peanut, indicated blocks of conserved macrosynteny. Altogether, these results provided important clues regarding the evolution of symbiotic genes in a Nod factor-independent context. They provide a Downloaded from https://academic.oup.com/dnaresearch/article-abstract/23/4/365/2469965 by BIU Montpellier user on 12 March 2020 basis for a genome sequencing project and pave the way for forward genetic analysis of symbio-sis in A. evenia