Draft Genome Sequence of the Nitrogen-Fixing Rhizobium sullae Type Strain IS123T Focusing on the Key Genes for Symbiosis with its Host Hedysarum coronarium L.

Abstract

The prominent feature of rhizobia is their molecular dialogue with plant hosts. Such interaction is enabled by the presence of a series of symbiotic genes encoding for the synthesis and export of signals triggering organogenetic and physiological responses in the plant. The genome of the Rhizobium sullae type strain IS123T nodulating the legume Hedysarum coronarium, was sequenced and resulted in 317 scaffolds for a total assembled size of 7,889,576 bp. Its features were compared with those of genomes from rhizobia representing an increasing gradient of taxonomical distance, from a conspecific isolate (Rhizobium sullae WSM1592), to two congeneric cases (Rhizobium leguminosarum bv. viciae and Rhizobium etli) and up to different genera within the legume-nodulating taxa. The host plant is of agricultural importance, but, unlike the majority of other domesticated plant species, it is able to survive quite well in the wild. Data showed that that the type strain of R. sullae, isolated from a wild host specimen, is endowed with a richer array of symbiotic genes in comparison to other strains, species or genera of rhizobia that were rescued from domesticated plant ecotypes. The analysis revealed that the bacterium by itself is incapable of surviving in the extreme conditions that its host plant can tolerate. When exposed to drought or alkaline condition, the bacterium depends on its host to survive. Data are consistent with the view of the plant phenotype as the primary factor enabling symbiotic nitrogen fixing bacteria to survive in otherwise limiting environments.

Effects of Hedysarum leguminous plants on soil bacterial communities in the Mu Us Desert, northwest China

“…This study demonstrated that nitrogen‐fixing bacteria occupied a dominant position in the roots of xeric leguminous plants, but also that many non‐nitrogen‐fixing microbes were present. These results confirmed that nitrogen‐fixing rhizobia co‐exist with other bacteria in the roots of desert xeric leguminous plants, which is consistent with previously reported results, where isolated cultures were used to assess the Rhizobium strains of leguminous plants (Sablok et al., 2017; Toniutti et al, 2017; Yates et al., 2015). This study showed that in addition to dominant nitrogen‐fixing rhizobia, there were also other, nonsymbiotic endophytes in the roots of Hedysarum plants.…”

“…They can infect and live on leguminous plants, form nodules in their roots, supply the nitrogen nutrients needed by leguminous plants during growth through nitrogen fixation from soil and air, and build a mutualistic symbiotic relationship with leguminous plants (Batut & Boistard, 1994; He & Zhu, 1998). This interaction is based on unique transcription and the signal transmission of symbiotic genes of the host plant and rhizobia, which in turn trigger the corresponding organogenesis and adaptive physiological response of the host plant (Sablok et al., 2017). Various studies have shown that R. sullae is an efficient nitrogen‐fixing rhizobium that can enter the root system of the genus Hedysarum and establish a mutually beneficial symbiotic relationship with the host (Yates et al., 2015).…”

“…Various studies have shown that R. sullae is an efficient nitrogen‐fixing rhizobium that can enter the root system of the genus Hedysarum and establish a mutually beneficial symbiotic relationship with the host (Yates et al., 2015). Although R. sullae cannot survive in the extreme environment that the genus Hedysarum can tolerate, the bacteria can rely on the host plant to survive in an arid or alkaline environment (Sablok et al., 2017). And the interaction between such a wide range of plants and microorganisms mostly occurs in the rhizosphere soil, where plant root systems are in close contact with the soil.…”

Genome Sequence of Rhizobium sullae HCNT1 Isolated from Hedysarum coronarium Nodules and Featuring Peculiar Denitrification Phenotypes

“…The plant is still occurring both as a cropped legume and as a spontaneous weed in Mediterranean habitats, and it is particularly tolerant to drought and alkalinity. The genome sequences of two other strains of the same bacterial species have been published, including that of the type strain IS123 (2) isolated in southern Spain from its host growing in the wild, and that of strain WSM1592 (3), isolated from cropped sulla on the island of Sardinia (Italy). The present isolate, HCNT1 (=IMAP 801, =ATCC 43676) (4), was isolated from root nodules of its host collected under spontaneous conditions in the highly calcareous pliocenic clays near Volterra (Tuscany, Italy).…”

Diversity and structural differences of bacterial microbial communities in rhizocompartments of desert leguminous plants

“…The role of rhizobia has always been the main research focus, and its most notable feature lies in its ability to establish a compatible interaction with molecules in the root of the host plant. This interaction depends on the expression of symbiosis-specific genes involving in gene compiling and signal output, and genes that can eventually trigger the unique organogenesis and other corresponding physiological responses of the host plants [ 35 ]. One study has shown that Rhizobium sullae is a highly efficient nitrogen-fixing rhizobium that can form symbiotic associations with Hedysarum plants [ 36 ].…”