Genetic diversity and symbiotic efficiency difference of endophytic rhizobia of Medicago sativa

Abstract

Research on rhizobium diversity has paved the way for diversification of rhizobial germplasm resources. Seventy-three endophytic bacterial isolates were collected from seven tissues of five alfalfa cultivars in three geographic locations in Gansu, China. Restriction fragment length polymorphism (RFLP) fingerprinting of 16S rRNA and analysis of concatenated sequence of three housekeeping genes (atpD, glnII, and recA) and two symbiotic genes (nodC and nifH) were used for strain identification. Results showed that the endophytic strains were genetically diverse at different taxonomic levels, and Ensifer meliloti (31) and Agrobacterium radiobacter (12) are common Medicago sativa endophytic bacteria in Gansu, China. The nifH genes (97%–98% sequence identity) of E. meliloti strains were more diverse than the nodC genes (99%–100% sequence identity), even though the strains evolved from a common ancestor. The degree of dispersion of symbiotic phenotypes of E. meliloti strains on M. sativa ‘Gannong No. 3’, ‘Gannong No. 9’, and ‘Qingshui’ was much less than that on M. sativa ‘Longzhong’ and ‘WL168HQ’. This suggested that the symbiotic efficiency of E. meliloti strains on the former three alfalfa cultivars was similar but on the latter two was discrepant. Their symbiotic efficiency differed primarily according to alfalfa cultivars and, to a lesser extent, to the tested strains, indicating the difference in the sensitivity of different alfalfa cultivars to rhizobial strains.

Plant transcriptome analysis reveals specific molecular interactions between alfalfa and its rhizobial symbionts below the species level

“…In accordance with our previous conclusion, alfalfa cultivars differ in their sensitivity to infections by different rhizobial strains [45,46]. However, it remains unclear if the extent of the transcriptomic variation is correlated with the phylogenetic distance among the rhizobial symbionts.…”

“…Alfalfa seeds and plants with rhizosphere soil were collected in May and August 2014 from three pasture experimental stations administrated by Gansu Agricultural University, Gansu, China (Additional file 1) using standard methods as previously described [45,46]. For phylogenetic analysis, genomic DNAs were extracted from leaf samples and subsequently used for PCR amplification of four housekeeping genes matK1, matK2, matK3, and rbcL as previously described [54].…”

“…DNA sequencing was performed using the services of TSINGKE Biological Technology Company (Xian, Shan'xi, China). Neighbor-Joining trees were constructed using the MEGA 6.0 software [46,55]. Voucher specimens for the five alfalfa cultivars are deposited in the cognitive pavilion herbarium of Gansu Agricultural University with accession numbers from ms-20140421-01 to ms-20140421-05 for plants, and ms-20140813-04 to ms-20140813-08 for seeds.…”

“…Rhizobia were isolated from various types of samples such as nodule, leaf, stem, flower, root epidermis, root stele, rhizosphere soil, field soil and seed [45]. All the 32 isolates were subjected to identification by 16S rRNA gene sequencing and subsequent phylogenetic analysis using the standard methods [46].…”

Sustainable Management of Medicago sativa for Future Climates: Insect Pests, Endophytes and Multitrophic Interactions in a Complex Environment

“…Genome sequencing and subsequent comparative genome analyses will provide the necessary foundation to develop novel hypotheses to be validated by a wide spectrum of -omics technologies. While research on the genetic blueprint is slowly emerging, it often is limited to the investigation of microbiome phylogeny via 16S rRNA and housekeeping gene sequencing (Kumar et al, 2018;Liotti et al, 2018;Kang et al, 2019) or high-level biochemical characterization via proteome and metabolome studies (López et al, 2018). Genomic analysis of Bacillus spp.…”