Revealing the underlying mechanisms mediated by endophytic actinobacteria to enhance the rhizobia - chickpea (Cicer arietinum L.) symbiosis

Abstract

Purpose The effects of endophytic actinobacterial strains, Microbispora sp. CP56, Actinomadura sp. CP84B, Streptomyces spp. CP200B and CP21A, on the chickpea-Mesorhizobium symbiosis, were investigated in planta, with the aim of revealing the underlying mechanisms of action. Methods The actinobacterial endophytes were co-inoculated with Mesorhizobium ciceri onto chickpea seedlings to study the effect on plant growth parameters, nodulation development and grain yield. The role of actinobacterial exudates on rhizobial growth was investigated, as was the role of root exudates of actinobacteria-colonized plants on the expression of rhizobial nod factors and biofilm formation. Changes in expression of plant flavonoids and bacterial N-fixation genes resulting from actinobacterial co-inoculation were assessed using qPCR. Results Application of actinobacterial endophytes, together with M. ciceri, showed growth promotion of chickpea with an increase in root nodule number and weight. Enhanced nodulation was accompanied by increases in total plant nitrogen, larger total plant weight and a 2–3-fold increase in grain yield. Factors associated with this tripartite symbiosis are promotion of rhizobial growth, earlier nodule formation, increased secondary root formation, up-regulated expression of genes related to flavonoid synthesis and nif genes. In addition, exudates of chickpea roots colonised with actinobacteria increased nodulation-related biological processes - rhizobial chemotaxis, biofilm formation and nod gene expression. Conclusion These endophytic actinobacteria positively affect many aspects of the chickpea-Mesorhizobium symbiosis resulting in increases in grain yield. Similar improvements recorded in chickpea growing in potted field soils, shows the potential to enhance chickpea production in the field.

Endophytic Streptomyces rochei BpR-2 GER (ON142045) from Bryophyllum pinnatum (Lam.) Oken with Antimicrobial and Antibiofilm Potential

“…differs in its morphological traits on various medium (Figure 1 A-B), which is consistent with past observations (8). Changes in the isolate's phenotype show that variation in the composition of media influence the primary and secondary metabolism (14) . Light microscopic observation revealed that the strain is polysporous with branched mycelium.…”

“…Presence of Streptomyces sp. as an endophyte could be a symbiotic association, since they produce bioactive compounds which exert beneficial functions for plant growth and protection in return the host plant allows the survival of these microorganisms (14) .…”

Contribution of Biofertilizers to Pulse Crops: From Single-Strain Inoculants to New Technologies Based on Microbiomes Strategies

“…The authors consider the consortium to be a potential biofertilizer for promoting sustainable agriculture. Co-inoculation of actinobacterial endophytes isolated from chickpea roots with M. ciceri increased total plant N and approximately 30% of shoot biomass [ 155 , 156 ]. Exudates from chickpea roots colonized by actinobacteria stimulate nodulation-related biological processes and may help improve chickpea production under field conditions.…”

Actinobacteria–Plant Interactions in Alleviating Abiotic Stress

“…CP84B, Streptomyces spp. CP200B, and CP21A with Mesorhizobium cicero in chickpea seedlings showed growth promotion and enhancement of the rhizobia–chickpea symbiosis by increasing nodulation-related biological processes such as rhizobial chemotaxis, biofilm formation, and nod gene expression [ 74 ]. When PGP endophytic strains Microbispora sp.…”