Abstract
The phylogeny of symbiotic genes of Astragalus glycyphyllos L. (liquorice milkvetch) nodule isolates was studied by comparative sequence analysis of nodA, nodC, nodH and nifH loci. In all these genes phylograms, liquorice milkvetch rhizobia (closely related to bacteria of three species, i.e. Mesorhizobium amorphae, Mesorhizobium septentrionale and Mesorhizobium ciceri) formed one clearly separate cluster suggesting the horizontal transfer of symbiotic genes from a single ancestor to the bacteria being studied. The high sequence similarity of the symbiotic genes of A. glycyphyllos rhizobia (99–100% in the case of nodAC and nifH genes, and 98–99% in the case of nodH one) points to the relatively recent (in evolutionary scale) lateral transfer of these genes. In the nodACH and nifH phylograms, A. glycyphyllos nodule isolates were grouped together with the genus Mesorhizobium species in one monophyletic clade, close to M. ciceri, Mesorhizobium opportunistum and Mesorhizobium australicum symbiovar biserrulae bacteria, which correlates with the close relationship of these rhizobia host plants. Plant tests revealed the narrow host range of A. glycyphyllos rhizobia. They formed effective symbiotic interactions with their native host (A. glycyphyllos) and Amorpha fruticosa but not with 11 other fabacean species. The nodules induced on A. glycyphyllos roots were indeterminate with apical, persistent meristem, an age gradient of nodule tissues and cortical vascular bundles. To reflect the symbiosis-adaptive phenotype of rhizobia, specific for A. glycyphyllos, we propose for these bacteria the new symbiovar “glycyphyllae”, based on nodA and nodC genes sequences.
Highlights
Rhizobia are soil bacteria, capable of forming nitrogen-fixing symbiosis with fabacean plants, which is beneficial for agriculture and other environmental systems [1, 2]
Symbiotic Genes Phylogeny of Astragalus glycyphyllos Nodulators taxonomy splits rhizobia into two groups, i.e.; “classical rhizobia”, affiliated to the genera; Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Ensifer (Sinorhizobium) as well as “new rhizobia”, comprising of bacterial species belonging to the genera; Aminobacter, Devosia, Methylobacterium, Microvirga, Ochrobactrum, Phylobacterium, Shinella (Alpha-Proteobacteria), Burkholderia and Cupriavidus (Beta-Proteobacteria) which for many years were not treated as fabacean symbionts [3]
In plant test Mesorhizobium albiziae CCBAU61158, Mesorhizobium caraganae CCBAU11299, M. amorphae ICMP15022, Mesorhizobium chacoense USDA4963, M. ciceri USDA3383, Mesorhizobium gobiense CCBAU83330, Mesorhizobium huakuii USDA4779, Mesorhizobium loti USDA3471, Mesorhizobium plurifarium USDA3707, M. septentrionale SDW018, Mesorhizobium temperatum LMG23931 and Mesorhizobium tianshanense USDA3592 were used in order to determine their ability to form symbiosis with A. glycyphyllos
Summary
Capable of forming nitrogen-fixing symbiosis with fabacean plants, which is beneficial for agriculture and other environmental systems [1, 2]. Symbiotic Genes Phylogeny of Astragalus glycyphyllos Nodulators taxonomy splits rhizobia into two groups, i.e.; “classical rhizobia”, affiliated to the genera; Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Ensifer (Sinorhizobium) as well as “new rhizobia”, comprising of bacterial species belonging to the genera; Aminobacter, Devosia, Methylobacterium, Microvirga, Ochrobactrum, Phylobacterium, Shinella (Alpha-Proteobacteria), Burkholderia and Cupriavidus (Beta-Proteobacteria) which for many years were not treated as fabacean symbionts [3]. It is well established that rhizobia with a broad host range are able to nodulate a high number of fabacean genera, as for example Ensifer fredii NGR234, which forms symbiotic interactions with 232 fabacean species, belonging to 112 genera and with nonfabacean plants of the genus Parasponia (the Cannabaceae family) whereas, rhizobia exhibiting a narrow host range can nodulate only a few hosts, e.g. Rhizoium leguminosarum bv. It is well established that rhizobia with a broad host range are able to nodulate a high number of fabacean genera, as for example Ensifer fredii NGR234, which forms symbiotic interactions with 232 fabacean species, belonging to 112 genera and with nonfabacean plants of the genus Parasponia (the Cannabaceae family) whereas, rhizobia exhibiting a narrow host range can nodulate only a few hosts, e.g. Rhizoium leguminosarum bv. trifolii form nodules only on plants of the genus Trifolium [4, 5]
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