Rhizobial Diversity and Nodulation Characteristics of the Extremely Promiscuous Legume Sophora flavescens

Abstract

In present study, we report our extensive survey on the diversity and biogeography of rhizobia associated with Sophora flavescens, a sophocarpidine (matrine)-containing medicinal legume. We additionally investigated the cross nodulation, infection pattern, light and electron microscopies of root nodule sections of S. flavescens infected by various rhizobia. Seventeen genospecies of rhizobia belonging to five genera with seven types of symbiotic nodC genes were found to nodulate S. flavescens in natural soils. In the cross-nodulation tests, most representative rhizobia in class α-Proteobacteria, whose host plants belong to different cross-nodulation groups, form effective indeterminate nodules, while representative rhizobia in class β-Proteobacteria form ineffective nodules on S. flavescens. Highly host-specific biovars of Rhizobium leguminosarum (bv. trifolii and bv. viciae) and Rhizobium etli bv. phaseoli could establish symbioses with S. flavescens, providing further evidence that S. flavescens is an extremely promiscuous legume and it does not have strict selectivity on either the symbiotic genes or the species-determining housekeeping genes of rhizobia. Root-hair infection is found as the pattern that rhizobia have gained entry into the curled root hairs. Electron microscopies of ultra-thin sections of S. flavescens root nodules formed by different rhizobia show that the bacteroids are regular or irregular rod shape and nonswollen types. Some bacteroids contain poly-β-hydroxybutyrate (PHB), while others do not, indicating the synthesis of PHB in bacteroids is rhizobia-dependent. The extremely promiscuous symbiosis between S. flavescens and different rhizobia provide us a basis for future studies aimed at understanding the molecular interactions of rhizobia and legumes.

Deciphering the Factors for Nodulation and Symbiosis of Mesorhizobium Associated with Cicer arietinum in Northwest India

“…The results revealed that the studied strains nodulated only C. arietinum and no cross-nodulation compatibility was observed between chickpea nodule rhizobia and other mesorhizobia leguminous plants. Thiswas in congruence with previous reports of cross nodulation tests [31,64]. Biofilm formation ability of all 54 tested strains can be considered as the key factor for symbiotic efficiency and it supports the possibility for their commercial use in stress condition [65].…”

Rhizobium anhuiense as the predominant microsymbionts of Lathyrus maritimus along the Shandong Peninsula seashore line

“…These results enlarged the host spectrum of R. anhuiense, originally reported for rhizobia isolated from effective nodules of Vicia faba and Pisum sativum [31], and revealed relatively low species richness in beach pea rhizobia compared with those detected in soybean, common bean and Sophora flavescens, etc. [3,5,11,32].…”

Specificity in Legume-Rhizobia Symbioses

“…However, the reports that Sophora alopecuroides and Sophora flavescens sampled in China are nodulated by Ensifer , Mesorhizobium , Phyllobacterium and Rhizobium with a wide range of symbiosis gene sequences [207,208] contrasts with the finding that New Zealand (NZ) native Sophora spp. were exclusively nodulated by Mesorhizobium spp.…”