The rice foot rot pathogen Dickeya zeae alters the in-field plant microbiome

Variability of microbiomes in winter rye, wheat, and triticale affected by snow mold: predicting promising microorganisms for the disease control

BACKGROUND

Snow mold caused by different psychrophilic phytopathogenic fungi is a devastating disease of winter cereals. The variability of the snow mold pathocomplex (the quantitative composition of snow mold fungi) has not been evaluated across different crops or different agrocenoses, and no microbial taxa have been predicted at the whole-microbiome level as potential effective snow mold control agents. Our study aimed to assess the variability of the snow mold pathocomplex in different winter cereal crops (rye, wheat, and triticale) in different agrocenoses following the peak disease progression and to arrange a hierarchical list of microbial taxa predicted to be the main candidates to prevent or, conversely, stimulate the development of snow mold pathogens.

RESULTS

The variability of microbiomes between different crops within a particular agrocenosis was largely determined by fungal communities, whereas the variability of microbiomes of a particular crop in different agrocenoses was largely determined by bacterial communities. The snow mold pathocomplex was the most "constant" in rye, with the lowest level of between-replicate variability and between-agrocenoses variability and (similar to the triticale snow mold pathocomplex) strong dominance of Microdochium over other snow mold fungi. The wheat snow mold pathocomplex was represented by different snow mold fungi, including poorly investigated Phoma sclerotioides. To predict snow mold-control microorganisms, a conveyor of statistical methods was formed and applied; this conveyor enables considering not only the correlation between the abundance of target taxa and a phytopathogen but also the stability and fitness of taxa within plant-associated communities and the reproducibility of the predicted effect of taxa under different conditions. This conveyor can be widely used to search for biological agents against various plant infectious diseases.

CONCLUSIONS

The top indicator microbial taxa for winter wheat and rye following the winter period were Ph. sclerotioides and Microdochium, respectively, both of which are causal agents of snow mold disease. Bacteria from the Cellulomonas, Lechevalieria, and Pseudoxanthomonas genera and fungi from the Cladosporium, Entimomentora, Pseudogymnoascus, and Cistella genera are prime candidates for testing their plant-protective properties against Microdochium-induced snow mold disease and for further use in agricultural practice.

Host Metabolic Alterations Mediate Phyllosphere Microbes Defense upon Xanthomonas oryzae pv oryzae Infection

Rice bacterial leaf blight, caused by Xanthomonas oryzae pv oryzae (Xoo), is a significant threat to global food security. Although the microbiome plays an important role in protecting plant health, how the phyllosphere microbiome is recruited and the underlying disease resistance mechanism remain unclear. This study investigates how rice phyllosphere microbiomes respond to pathogen invasion through a comprehensive multiomics approach, exploring the mechanisms of microbial defense and host resistance. We discovered that Xoo infection significantly reshapes the physicosphere microbial community. The bacterial network became more complex, with increased connectivity and interactions following infection. Metabolite profiling revealed that l-ornithine was a key compound to recruiting three keystone microbes, Brevundimonas (YB12), Pantoea (YN26), and Stenotrophomonas (YN10). These microbes reduced the disease index by up to 67.6%, and these microbes demonstrated distinct defense mechanisms. Brevundimonas directly antagonized Xoo by disrupting cell membrane structures, while Pantoea and Stenotrophomonas enhanced plant immune responses by significantly increasing salicylic acid and jasmonic acid levels and activating defense-related enzymes. Our findings provide novel insights into plant-microbe interactions, demonstrating how host metabolic changes recruit and activate beneficial phyllosphere microbes to combat pathogenic invasion. This research offers promising strategies for sustainable agricultural practices and disease management.

Beyond correlation: Understanding the causal link between microbiome and plant health

Understanding the causal link between the microbiome and plant health is crucial for the future of crop production. Established studies have shown a symbiotic relationship between microbes and plants, reshaping our knowledge of plant microbiomes' role in health and disease. Addressing confounding factors in microbiome study is essential, as standardization enables precise identification of microbiome features that influence outcomes. The microbiome significantly impacts plant development, necessitating holistic investigation for maintaining plant health. Mechanistic studies have deepened our understanding of microbiome structure and function related to plant health, though much research still needs to be carried out. This review, therefore, discusses current challenges and proposes advancing studies from correlation to causation and translation. We explore current knowledge on the microbiome and plant health, emphasizing multi-omics approaches and hypothesis-driven research. Future studies should focus on developing translational research for producing probiotics and prebiotics from biomarkers that regulate the microbiome-plant health connection, promoting sustainable crop production through microbiome applications.

Molecular Insights into Plant-Microbe Interactions: A Comprehensive Review of Key Mechanisms

In most ecosystems, plants establish complex symbiotic relationships with organisms, such as bacteria and fungi, which significantly influence their health by promoting or inhibiting growth. These relationships involve biochemical exchanges at the cellular level that affect plant physiology and have evolutionary implications, such as species diversification, horizontal gene transfer, symbiosis and mutualism, environmental adaptation, and positive impacts on community structure and biodiversity. For these reasons, contemporary research, moving beyond observational studies, seeks to elucidate the molecular basis of these interactions; however, gaps in knowledge remain. This is particularly noticeable in understanding how plants distinguish between beneficial and antagonistic microorganisms. In light of the above, this literature review aims to address some of these gaps by exploring the key mechanisms in common interspecies relationships. Thus, our study presents novel insights into these evolutionary archetypes, focusing on the antibiosis process and microbial signaling, including chemotaxis and quorum sensing. Additionally, it examined the biochemical basis of endophytism, pre-mRNA splicing, and transcriptional plasticity, highlighting the roles of transcription factors and epigenetic regulation in the functions of the interacting organisms. These findings emphasize the importance of understanding these confluences in natural environments, which are crucial for future theoretical and practical applications, such as improving plant nutrition, protecting against pathogens, developing transgenic crops, sustainable agriculture, and researching disease mechanisms. It was concluded that because of the characteristics of the various biomolecules involved in these biological interactions, there are interconnected molecular networks in nature that give rise to different ecological scaffolds. These networks integrate a myriad of functionally organic units that belong to various kingdoms. This interweaving underscores the complexity and multidisciplinary integration required to understand plant-microbe interactions at the molecular level. Regarding the limitations inherent in this study, it is recognized that researchers face significant obstacles. These include technical difficulties in experimentation and fieldwork, as well as the arduous task of consolidating and summarizing findings for academic articles. Challenges range from understanding complex ecological and molecular dynamics to unbiased and objective interpretation of diverse and ever-changing literature.

Metagenomic insight to apprehend the fungal communities associated with leaf blight of Welsh onion in Taiwan

Plants are associated with a large diversity of microbes, and these complex plant-associated microbial communities are critical for plant health. Welsh onion (Allium fistulosum L.) is one of the key and oldest vegetable crops cultivated in Taiwan. The leaf of the Welsh onion is one of the famous spices in Taiwanese cuisine, thus, it is crucial to control foliar diseases. In recent years, Welsh onion cultivation in Taiwan has been severely threatened by the occurrence of leaf blight disease, greatly affecting their yield and quality. However, the overall picture of microbiota associated with the Welsh onion plant is still not clear as most of the recent etiological investigations were heavily based on the isolation of microorganisms from diseased plants. Therefore, studying the diversity of fungal communities associated with the leaf blight symptoms of Welsh onion may provide information regarding key taxa possibly involved in the disease. Therefore, this investigation was mainly designed to understand the major fungal communities associated with leaf blight to identify key taxa potentially involved in the disease and further evaluate any shifts in both phyllosphere and rhizosphere mycobiome assembly due to foliar pathogen infection by amplicon sequencing targeting the Internal Transcribed Spacer (ITS) 1 region of the rRNA. The alpha and beta-diversity analyses were used to compare the fungal communities and significant fungal groups were recognized based on linear discriminant analyses. Based on the results of relative abundance data and co-occurrence networks in symptomatic plants we revealed that the leaf blight of Welsh onion in Sanxing, is a disease complex mainly involving Stemphylium and Colletotrichum taxa. In addition, genera such as Aspergillus, Athelia and Colletotrichum were abundantly found associated with the symptomatic rhizosphere. Alpha-diversity in some fields indicated a significant increase in species richness in the symptomatic phyllosphere compared to the asymptomatic phyllosphere. These results will broaden our knowledge of pathogens of Welsh onion associated with leaf blight symptoms and will assist in developing effective disease management strategies to control the progress of the disease.

Time-Course Responses of Apple Leaf Endophytes to the Infection of Gymnosporangium yamadae

Apple rust, caused by Gymnosporangium yamadae, poses a significant challenge to apple production. Prior studies have underscored the pivotal role played by endophytic microbial communities, intimately linked with the host, in influencing plant diseases and their pathogenic outcomes. The objective of this study is to scrutinize alternations in endophytic microbial communities within apple leaves at different stages of apple rust using high-throughput sequencing technology. The findings revealed a discernible pattern characterized by an initial increase and subsequent decrease in the alpha diversity of microbial communities in diseased leaves. A microbial co-occurrence network analysis revealed that the complexity of the bacterial community in diseased leaves diminished initially and then rebounded during the progression of the disease. Additionally, employing the PICRUSt2 platform, this study provided preliminary insights into the functions of microbial communities at specific disease timepoints. During the spermogonial stage, endophytic bacteria particularly exhibited heightened activity in genetic information processing, metabolism, and environmental information processing pathways. Endophytic fungi also significantly enriched a large number of metabolic pathways during the spermogonial stage and aecial stage, exhibiting abnormally active life activities. These findings establish a foundation for comprehending the role of host endophytes in the interaction between pathogens and hosts. Furthermore, they offer valuable insights for the development and exploitation of plant endophytic resources, thereby contributing to enhanced strategies for managing apple rust.

A Synthetic Microbial Community of Plant Core Microbiome Can Be a Potential Biocontrol Tool

Microbes are accepted as the foremost drivers of the rhizosphere ecology that influences plant health in direct or indirect ways. In recent years, the rapid development of gene sequencing technology has greatly facilitated the study of plant microbiome structure and function, and various plant-associated microbiomes have been categorized. Additionally, there is growing research interest in plant-disease-related microbes, and some specific microflora beneficial to plant health have been identified. This Review discusses the plant-associated microbiome's biological control pathways and functions to modulate plant defense against pathogens. How do plant microbiomes enhance plant resistance? How does the plant core microbiome-associated synthetic microbial community (SynCom) improve plant health? This Review further points out the primary need to develop smart agriculture practices using SynComs against plant diseases. Finally, this Review provides ideas for future opportunities in plant disease control and mining new microbial resources.

Tool and techniques study to plant microbiome current understanding and future needs: an overview

Microorganisms are present in the universe and they play role in beneficial and harmful to human life, society, and environments. Plant microbiome is a broad term in which microbes are present in the rhizo, phyllo, or endophytic region and play several beneficial and harmful roles with the plant. To know of these microorganisms, it is essential to be able to isolate purification and identify them quickly under laboratory conditions. So, to improve the microbial study, several tools and techniques such as microscopy, rRNA, or rDNA sequencing, fingerprinting, probing, clone libraries, chips, and metagenomics have been developed. The major benefits of these techniques are the identification of microbial community through direct analysis as well as it can apply in situ. Without tools and techniques, we cannot understand the roles of microbiomes. This review explains the tools and their roles in the understanding of microbiomes and their ecological diversity in environments.

Genomic and phenotypic biology of a novel Dickeya zeae WH1 isolated from rice in China: Insights into pathogenicity and virulence factors

Soft rot caused by Dickeya zeae is an important bacterial disease affecting rice and other plants worldwide. In this study, Nanopore and Illumina sequencing platforms were used to sequence the high-quality complete genome of a novel D. zeae strain WH1 (size: 4.68 Mb; depth: 322.37x for Nanopore, 243.51x for Illumina; GC content: 53.59%), which was isolated from healthy rice root surface together with Paenibacillus polymyxa, a potential biocontrol bacterium against D. zeae strain WH1. However, the pure WH1 culture presented severe pathogenicity. Multilocus sequence analysis (MLSA) indicated that strains WH1, EC1, and EC2 isolated from rice were grouped into a clade differentiated from other D. zeae strains. The average nucleotide identity (ANI) and DNA-DNA hybridization (DDH) analyses demonstrated that WH1 was phylogenetically closest to EC2. Furthermore, the pathogenicity determinants and virulence factors of WH1 were mainly analyzed through genomic comparison with complete genomes of other D. zeae strains with high virulence (EC1, EC2, MS1, and MS2). The results revealed that plant cell wall-degrading extracellular enzymes (PCWDEs), flagellar and chemotaxis, and quorum sensing were highly conserved in all analyzed genomes, which were confirmed through phenotypic assays. Besides, WH1 harbored type I, II, III, and VI secretion systems (T1SS, T2SS, T3SS, and T6SS), but lost T4SS and T5SS. Like strains MS1 and MS2 isolated from bananas, WH1 harbored genes encoding both capsule polysaccharide (CPS) and exopolysaccharide (EPS) biosynthesis. The results of pathogenicity assays demonstrated that WH1 produced severe soft rot symptoms on potato tubers, carrots, radishes, and Chinese cabbage. Meanwhile, WH1 also produced phytotoxin(s) to inhibit rice seed germination with an 87% inhibitory rate in laboratory conditions. More importantly, we confirmed that phytotoxin(s) produced by WH1 are different from zeamines produced by EC1. Comparative genomics analyses and phenotypic and pathogenicity assays suggested that WH1 likely evolved through a pathway different from the other D. zeae strains from rice, producing a new type of rice foot rot pathogen. These findings highlight the emergence of a new type of D. zeae strain with high virulence, causing soft rot in rice and other plants.

Fungal endophytes in plants and their relationship to plant disease

The enigmatic endophytic fungi are beginning to reveal their secrets. Like pathogens, they can manipulate the host for their own benefit to create their own optimal habitat. Some endophytic manipulations induce resistance or otherwise outcompete pathogens and can thus be exploited for biological control. Like pathogens and other symbionts, endophytes produce effector proteins and other molecules, ranging from specialised metabolites, phytohormones and microRNAs, to manipulate their hosts and other microorganisms they meet. There is a continuum from endophyte to pathogen: some organisms can infest or cause disease in some hosts, but not in others. Molecular genetics approaches coupled with functional characterisation have demonstrated their worth for understanding the biological phenomena underlying endophytic fungal interactions.

Bacterial Endophytes Contribute to Rice Seedling Establishment Under Submergence

Flooding events caused by severe rains and poor soil drainage can interfere with plant germination and seedling establishment. Rice is one of the cereal crops that has unique germination strategies under flooding. One of these strategies is based on the fast coleoptile elongation in order to reach the water surface and re-establish the contact with the air. Microorganisms can contribute to plant health via plant growth promoters and provide protection from abiotic stresses. To characterise the community composition of the microbiome in rice germination under submergence, a 16S rRNA gene profiling metagenomic analysis was performed of temperate japonica rice varieties Arborio and Lamone seedlings, which showed contrasting responses in terms of coleoptile length when submerged. This analysis showed a distinct microbiota composition of Arborio seeds under submergence, which are characterised by the development of a long coleoptile. To examine the potential function of microbial communities under submergence, culturable bacteria were isolated, identified and tested for plant growth-promoting activities. A subgroup of isolated bacteria showed the capacity to hydrolyse starch and produce indole-related compounds under hypoxia. Selected bacteria were inoculated in seeds to evaluate their effect on rice under submergence, showing a response that is dependent on the rice genotype. Our findings suggest that endophytic bacteria possess plant growth-promoting activities that can substantially contribute to rice seedling establishment under submergence.

Plant Genotype Shapes the Bacterial Microbiome of Fruits, Leaves, and Soil in Olive Plants

The plant microbiome plays an important role in plant biology, ecology, and evolution. While recent technological developments enabled the characterization of plant-associated microbiota, we still know little about the impact of different biotic and abiotic factors on the diversity and structures of these microbial communities. Here, we characterized the structure of bacterial microbiomes of fruits, leaves, and soil collected from two olive genotypes (Sinopolese and Ottobratica), testing the hypothesis that plant genotype would impact each compartment with a different magnitude. Results show that plant genotype differently influenced the diversity, structure, composition, and co-occurence network at each compartment (fruits, leaves, soil), with a stronger effect on fruits compared to leaves and soil. Thus, plant genotype seems to be an important factor in shaping the structure of plant microbiomes in our system, and can be further explored to gain functional insights leading to improvements in plant productivity, nutrition, and defenses.

Improving Bambara Groundnut Production: Insight Into the Role of Omics and Beneficial Bacteria

With the rise in the world population, environmental hazards caused by chemical fertilizers, and a decrease in food supply due to global climate change, food security has become very pertinent. In addition, considerable parts of agriculture lands have been lost to urbanization. It has therefore been projected that at the present rate of population increase coupled with the other mentioned factors, available food will not be enough to feed the world. Hence, drastic approach is needed to improve agriculture output as well as human sustainability. Application of environmentally sustainable approach, such as the use of beneficial microbes, and improved breeding of underutilized legumes are one of the proposed sustainable ways of achieving food security. Microbiome-assisted breeding in underutilized legumes is an untapped area with great capabilities to improve food security. Furthermore, revolution in genomics adaptation to crop improvement has changed the approach from conventional breeding to more advanced genomic-assisted breeding on the host plant and its microbiome. The use of rhizobacteria is very important to improving crop yield, especially rhizobacteria from legumes like Bambara groundnut (BGN). BGN is an important legume in sub-Saharan Africa with high ability to tolerate drought and thrive well in marginalized soils. BGN and its interaction with various rhizobacteria in the soil could play a vital role in crop production and protection. This review focus on the importance of genomics application to BGN and its microbiome with the view of setting a potential blueprint for improved BGN breeding through integration of beneficial bacteria.

Pseudomonas spp. Mediate defense response in sugarcane through differential exudation of root phenolics

Pseudomonas spp., a ubiquitous biocontrol agent, protects the plants from phytopathogens by suppressing them directly by reinforcing the plant’s intrinsic defense mechanism. Root exudated phenolics play an important role in establishing the rhizobacteria population and cross the host boundaries in beneficial plant–microbe interaction. In this study, Pseudomonas spp. HU-8 & HU-9 antagonized the sugarcane red rot pathogen (C. falcatum) and showed a positive chemotactic response against different concentrations (10–30 µM) of synthetic phenolic acids like p-coumaric, vanillic, and 3,4 di-hydroxybenzoic acid. In a pot experiment, they effectively colonized the sugarcane rhizosphere and mediated defense response in sugarcane plants challenged with red rot pathogen C. falcatum by regulating the exudation of root phenolics under hydroponic conditions. They significantly induced the activity of the antioxidant enzymes CAT (1.24–1.64 fold), PO (0.78–1.61 fold), PAL (0.77–0.97 fold), and PPO (3.67–3.73 fold) over untreated plants in sugarcane. They also induced the total phenolic contents (TPC) in sugarcane in the presence (6.56–10.29 mg/g GAE) and absence (2.89–4.16 mg/g GAE) of the pathogen quantified through the Folin-Ciocalteu (FC) method. However, their effect was lower than that of the pathogen (4.34–8 mg/g GAE). The Pseudomonas spp. significantly colonized the sugarcane rhizosphere by maintaining a cell population of (1.0E + 07–1.3E + 08 CFU/mL). A significant positive Pearson’s correlation was observed between the root exudated total phenolic contents, antioxidant enzymatic activities, and rhizospheric population of inoculated bacteria. The 16S rRNA and rpoD gene analysis showed sequence conservation (C: 0.707), average number of nucleotide differences (k: 199.816), nucleotide diversity, (Pi): 0.09819), average number of informative nucleotide sites per site (Psi: 0.01275), GC content (0.57), and polymorphic sites (n = 656). These diverse Pseudomonas spp. could be an ideal bio-inoculants for a broad range of hosts especially graminaceous crops.