Induction of defense responses against Magnaporthe oryzae in rice seedling by a new potential biocontrol agent Streptomyces JD211

Effect of Streptomyces JD211 application on soil physicochemical properties and N2O emission characteristics of rice rhizosphere

Biocontrol agent, as a pollution-free and sustainable plant disease control method, can inhibit the spread of soil-borne diseases and promote the growth of crops. However, there are few studies on the effect of biocontrol agent on N2O emission in rice soil. In this study, after the application of the biocontrol agent Streptomyces JD211, N2O emission from rice soil were measured, and the relationship between the agent and soil N2O emissions were studied in soil chemistry and molecular biology. The results showed that the application of Streptomyces JD211 can significantly reduce the rate of N2O emission from rice soil. The NH4+-N and NO3--N contents in rice soil decreased in a short period of time after the application of Streptomyces JD211, while the mineral N content in the soil remained stable with rice growth. 16S rRNA gene sequencing and metagenomic sequencing revealed Streptomyces JD211 application mainly increased the relative abundance of Burkholderia and Streptomyces in the soil microbial community, reduced the relative abundance of hao, norB, norC genes, and increased the relative abundance of nosZ and hcp genes. Streptomyces JD211 application promoted N2O transformation and weakened N2O production pathways, which ultimately reduced N2O emissions from rice soils. This study provided new insight of biocontrol agents to regulate soil N2O emissions, which is of great significance for the development and application of biocontrol bacteria and farmland environmental protection.

Microbial Lipopeptides: Properties, Mechanics and Engineering for Novel Lipopeptides

Microorganisms produce active surface agents called lipopeptides (LPs) which are amphiphilic in nature. They are cyclic or linear compounds and are predominantly isolated from Bacillus and Pseudomonas species. LPs show antimicrobial activity towards various plant pathogens and act by inhibiting the growth of these organisms. Several mechanisms are exhibited by LPs, such as cell membrane disruption, biofilm production, induced systematic resistance, improving plant growth, inhibition of spores, etc., making them suitable as biocontrol agents and highly advantageous for industrial utilization. The biosynthesis of lipopeptides involves large multimodular enzymes referred to as non-ribosomal peptide synthases. These enzymes unveil a broad range of engineering approaches through which lipopeptides can be overproduced and new LPs can be generated asserting high efficacy. Such approaches involve several synthetic biology systems and metabolic engineering techniques such as promotor engineering, enhanced precursor availability, condensation domain engineering, and adenylation domain engineering. Finally, this review provides an update of the applications of lipopeptides in various fields.

Anti-Biofilm Activity and Biocontrol Potential of Streptomyces Cultures Against Ralstonia solanacearum on Tomato Plants

Biological control of phytopathogen is a promising approach when compared to the use of chemical agents. In the present study, seven Streptomyces cultures showing promising anti biofilm activity against Ralstonia solanacearum was mixed individually with farmyard manure. All the Streptomyces fortified farmyard manure (SFYM) were screened for plant growth promotion and control of bacterial wilt caused by R. solanacearum on tomato. Further, the ability of SFYM on stimulating the production of defense-related enzymes in R. solanacearum-inoculated tomato plants was investigated. When compared to the control tomato plants, the SFYM-treated plants had longer shoot and root length along with higher fresh and dry weight. The maximum level of chlorophyll was observed in the plants treated with strain UP1A-1 (2.21 ± 0.18 mg g^-1). Strain UP1A-1 also showed maximum of 96.8 ± 1.4% biocontrol efficacy in tomato plants challenged with R. solanacearum. In addition, the UP1A-1 treated tomato plants showed maximum accumulation of total phenolics (3.02 ± 0.09 mg g^-1) after 6 days of pathogen inoculation (DPI). Similarly, tomato plants treated with UP1A-1 showed highest level of peroxides, polyphenol oxidase and phenylalanine ammonia lyase during 1-9 DPI. Findings of present study revealed that the Streptomyces culture UP1A-1 fortified farm yard manure could be applied as an eco-friendly alternative to synthetic agents for controlling bacterial wilt in tomato plants.

Microbial Contributions for Rice Production: From Conventional Crop Management to the Use of 'Omics' Technologies

Rice, the main staple food for about half of the world's population, has had the growth of its production stagnate in the last two decades. One of the ways to further improve rice production is to enhance the associations between rice plants and the microbiome that exists around, on, and inside the plant. This article reviews recent developments in understanding how microorganisms exert positive influences on plant growth, production, and health, focusing particularly on rice. A variety of microbial species and taxa reside in the rhizosphere and the phyllosphere of plants and also have multiple roles as symbiotic endophytes while living within plant tissues and even cells. They alter the morphology of host plants, enhance their growth, health, and yield, and reduce their vulnerability to biotic and abiotic stresses. The findings of both agronomic and molecular analysis show ways in which microorganisms regulate the growth, physiological traits, and molecular signaling within rice plants. However, many significant scientific questions remain to be resolved. Advancements in high-throughput multi-omics technologies can be used to elucidate mechanisms involved in microbial-rice plant associations. Prospectively, the use of microbial inoculants and associated approaches offers some new, cost-effective, and more eco-friendly practices for increasing rice production.

Identification of Salicylic Acid Mechanism against Leaf Blight Disease in Oryza sativa by SR-FTIR Microspectroscopic and Docking Studies

The present study was to investigate the application and mechanism of salicylic acid (SA) as SA-Ricemate for the control of leaf blight disease using a Synchrotron Radiation-based Fourier-Transform Infra-Red (SR-FTIR) microspectroscopy and docking studies. After treating rice plants cv. KDML 105 with SA-Ricemate, the leaves were inoculated with Xanthomonas oryzae pv. oryzae, the causal agent of leaf blight, and disease severity were assessed. The leaves were also used to detect changes in endogenous SA content. The results indicated that SA-Ricemate, as an activated compound, reduced disease severity by 60% at three weeks post-inoculation and increased endogenous content by 50%. The SR-FTIR analysis of changes in the mesophyll of leaves (treated and untreated) showed that the groups of lipids, pectins, and proteins amide I and amide II occurred at higher values, and polysaccharides were shown at lower values in treated compared to untreated. Besides, docking studies were used to model a three-dimensional structure for Pathogenesis-related (PR1b) protein and further identify its interaction with SA. The results showed that ASP28, ARG31, LEU32, GLN97, and ALA93 are important residues that have strong hydrogen bonds with SA. The docking results showed that SA has a good interaction, confirming its role in expression.

Phyllosphere Colonization by a Soil Streptomyces sp. Promotes Plant Defense Responses Against Fungal Infection

Streptomycetes are soil-dwelling, filamentous actinobacteria and represent a prominent bacterial clade inside the plant root microbiota. The ability of streptomycetes to produce a broad spectrum of antifungal metabolites suggests that these bacteria could be used to manage plant diseases. Here, we describe the identification of a soil Streptomyces strain named AgN23 which strongly activates a large array of defense responses when applied on Arabidopsis thaliana leaves. AgN23 increased the biosynthesis of salicylic acid, leading to the development of salicylic acid induction deficient 2 (SID2)-dependent necrotic lesions. Size exclusion fractionation of plant elicitors secreted by AgN23 showed that these signals are tethered into high molecular weight complexes. AgN23 mycelium was able to colonize the leaf surface, leading to plant resistance against Alternaria brassicicola infection in wild-type Arabidopsis plants. AgN23-induced resistance was found partially compromised in salicylate, jasmonate, and ethylene mutants. Our data show that Streptomyces soil bacteria can develop at the surface of plant leaves to induce defense responses and protection against foliar fungal pathogens, extending their potential use to manage plant diseases.