Genomes of three facultatively symbiotic Frankia sp. strains reflect host plant biogeography (original) (raw)
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Symbiosis, 2016
The actinorhizal symbiosis is a mutualistic relationship between an actinobacterium from the genus Frankia and a wide variety of dicotyledonous plants representing 8 different families of angiosperms. Molecular phylogenetic approaches have identified four major Frankia lineages that have distinctive plant host ranges. Since the first published three Frankia genomes, an effort was undertaken to provide full genomic databases covering all four well established Frankia lineages and to provide depth of the number of strains covered. Here, we report on the updated status of these sequencing efforts. At present, there are 25 complete or draft Frankia genomes that have been sequenced and annotated, and several others are now in the pipeline being sequenced. An overview of the Frankia genomes will be presented focusing on their general genomic properties including size of the pan-and core-gene pool, size relationship and genome plasticity. Furthermore, a description of biosynthetic potential and a discussion about genes (nitrogenase, hopanoid biosynthesis, truncated hemoglobin, hydrogenase uptake gene clusters) involved in the symbiosis will be discussed. The absence of common nod genes within these Frankia genomes provides clues about the host-microbe recognition process for the actinorhizal symbiosis
Alone Yet Not Alone: Frankia Lives Under the Same Roof With Other Bacteria in Actinorhizal Nodules
Frontiers in Microbiology, 2021
Actinorhizal plants host mutualistic symbionts of the nitrogen-fixing actinobacterial genus Frankia within nodule structures formed on their roots. Several plant-growth-promoting bacteria have also been isolated from actinorhizal root nodules, but little is known about them. We were interested investigating the in planta microbial community composition of actinorhizal root nodules using culture-independent techniques. To address this knowledge gap, 16S rRNA gene amplicon and shotgun metagenomic sequencing was performed on DNA from the nodules of Casuarina glauca. DNA was extracted from C. glauca nodules collected in three different sampling sites in Tunisia, along a gradient of aridity ranging from humid to arid. Sequencing libraries were prepared using Illumina NextEra technology and the Illumina HiSeq 2500 platform. Genome bins extracted from the metagenome were taxonomically and functionally profiled. Community structure based off preliminary 16S rRNA gene amplicon data was analy...
BMC genomics, 2014
Frankia is a genus of soil actinobacteria forming nitrogen-fixing root-nodule symbiotic relationships with non-leguminous woody plant species, collectively called actinorhizals, from eight dicotyledonous families. Frankia strains are classified into four host-specificity groups (HSGs), each of which exhibits a distinct host range. Genome sizes of representative strains of Alnus, Casuarina, and Elaeagnus HSGs are highly diverged and are positively correlated with the size of their host ranges. The content and size of 12 Frankia genomes were investigated by in silico comparative genome hybridization and pulsed-field gel electrophoresis, respectively. Data were collected from four query strains of each HSG and compared with those of reference strains possessing completely sequenced genomes. The degree of difference in genome content between query and reference strains varied depending on HSG. Elaeagnus query strains were missing the greatest number (22-32%) of genes compared with the c...
BMC genomics, 2016
The ability to establish root nodule symbioses is restricted to four different plant orders. Soil actinobacteria of the genus Frankia can establish a symbiotic relationship with a diverse group of plants within eight different families from three different orders, the Cucurbitales, Fagales and Rosales. Phylogenetically, Frankia strains can be divided into four clusters, three of which (I, II, III) contain symbiotic strains. Members of Cluster II nodulate the broadest range of host plants with species from four families from two different orders, growing on six continents. Two Cluster II genomes were sequenced thus far, both from Asia. In this paper we present the first Frankia cluster II genome from North America (California), Dg2, which represents a metagenome of two major and one minor strains. A phylogenetic analysis of the core genomes of 16 Frankia strains shows that Cluster II the ancestral group in the genus, also ancestral to the non-symbiotic Cluster IV. Dg2 contains the ca...
Applied and environmental microbiology, 2017
Actinorhizal plants form nitrogen-fixing root nodules in symbiosis with soil-dwelling actinobacteria within the genus Frankia, and specific Frankia taxonomic clusters nodulate plants in corresponding host infection groups. In same-soil microcosms, we observed some host species were nodulated (Alnus glutinosa, Alnus cordata, Shepherdia argentea, Casuarina equisetifolia) while others were not (Alnus viridis, Hippophaë rhamnoides). Nodule populations were represented by eight different sequences of nifH gene fragments. Two of these sequences characterized frankiae in S. argentea nodules, and three others frankiae in A. glutinosa nodules. Frankiae in A. cordata nodules were represented by five sequences, one of which was also found in nodules from A. glutinosa and C. equisetifolia, while another one was detected in nodules from A. glutinosa Quantitative PCR assays showed vegetation generally increased the abundance of frankiae in soil, independent of the target gene (i.e. nifH or 23S rR...
Molecular analysis of actinorhizal symbiotic systems: Progress to date
Plant and Soil, 1996
The application of molecular tools to questions related to the genetics, ecology and evolution of actinorhizal symbiotic systems has been especially fruitful during the past two years. Host plant phylogenies based on molecular data have revealed markedly different relationships among host plants than have previously been suspected and have contributed to the development of new hypotheses on the origin and evolution of actinorhizal symbiotic systems. Molecular analyses of host plant gene expression in developing nodules have confirmed the occurrence of nodulin proteins and in situ hybridization techniques have been successfully adapted to permit the study of the spatial and temporal patterns of gene expression within actinorhizal nodules. The use of heterologous probes in combination with nucleotide sequence analysis have allowed a number of n/f genes to be mapped on the Frankia chromosome which will ultimately contribute to the development of hypotheses related to nifgene regulation in Frankia. The use of both 16S and 23S rDNA nucleotide sequences has allowed the construction of phylogenetic trees that can be tested for congruence with symbiotic characters. In addition the development of Frankia-specific gene probes and amplification primers have contributed to studies on the genetic diversity and distribution of Frankia in the soil.