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Laboratory tests and greenhouse experiments were carried out to investigate the abilities of Bacillus subtilis Y-IVI to promote plant growth and to colonize the rhizosphere and interior tissues of muskmelon. Laboratory tests showed that B. subtilis Y-IVI can produce indole acetic acid, siderophores, and ammonia. The inoculation of soil with green fluorescent protein-tagged Y-IVI (GY-IVI) significantly increased plant shoot and root dry weights as compared with the non-inoculated soils. The inoculation of soil with B. subtilis GY-IVI maintained approximately 10 colony-forming units (cfu) of GY-IVI per gram of dry rhizosphere soil for 1 month. The GY-IVI recovered from the interior of crowns and roots in the inoculated soil were 10 and 10 cfu g dry weight, respectively, suggesting that GY-IVI acted as an endophyte. In the present study, we combined the two important growth promotion ingredients, colonization ability and growth promotion metabolites produced by biological agents, to investigate B. subtilis Y-IVI's promotion effects on muskmelon growth. [ABSTRACT FROM AUTHOR]

The rhizosphere and phyllosphere of plants are home to a diverse range of microorganisms that play pivotal roles in ecosystem services. Consequently, plant growth‐promoting bacteria (PGPB) are extensively utilized as inoculants to enhance plant growth and boost productivity. Despite this, the interactions between the rhizosphere and phyllosphere, which are influenced by PGPB inoculation, have not been thoroughly studied to date. In this study, we inoculated Bacillus velezensis SQR9, a PGPB, into the bulk soil, rhizosphere or phyllosphere, and subsequently examined the bacterial communities in the rhizosphere and phyllosphere using amplicon sequencing. Our results revealed that PGPB inoculation increased its abundance in the corresponding compartment, and all treatments demonstrated plant growth promotion effects. Further analysis of the sequencing data indicated that the presence of PGPB exerted a more significant impact on bacterial communities in both the rhizosphere and phyllosphere than in the inoculation compartment. Notably, the PGPB stimulated similar rhizosphere‐beneficial microbes regardless of the inoculation site. We, therefore, conclude that PGPB can promote plant growth both directly and indirectly through the interaction between the rhizosphere and phyllosphere, leading to the enrichment of beneficial microorganisms. [ABSTRACT FROM AUTHOR]

Rhizosphere microbes play critical roles for plant's growth and health. Among them, the beneficial rhizobacteria have the potential to be developed as the biofertilizer or bioinoculants for sustaining the agricultural development. The efficient rhizosphere colonization of these rhizobacteria is a prerequisite for exerting their plant beneficial functions, but the colonizing process and underlying mechanisms have not been thoroughly reviewed, especially for the nonsymbiotic beneficial rhizobacteria. This review systematically analyzed the root colonizing process of the nonsymbiotic rhizobacteria and compared it with that of the symbiotic and pathogenic bacteria. This review also highlighted the approaches to improve the root colonization efficiency and proposed to study the rhizobacterial colonization from a holistic perspective of the rhizosphere microbiome under more natural conditions. [ABSTRACT FROM AUTHOR]

Summary: Rhizomicrobiome plays important roles in plant growth and health, contributing to the sustainable development of agriculture. Plants recruit and assemble the rhizomicrobiome to satisfy their functional requirements, which is widely recognized as the 'cry for help' theory, but the intrinsic mechanisms are still limited.In this study, we revealed a novel mechanism by which plants reprogram the functional expression of inhabited rhizobacteria, in addition to the de novo recruitment of soil microbes, to satisfy different functional requirements as plants grow. This might be an efficient and low‐cost strategy and a substantial extension to the rhizomicrobiome recruitment theory.We found that the plant regulated the sequential expression of genes related to biocontrol and plant growth promotion in two well‐studied rhizobacteria Bacillus velezensis SQR9 and Pseudomonas protegens CHA0 through root exudate succession across the plant developmental stages. Sixteen key chemicals in root exudates were identified to significantly regulate the rhizobacterial functional gene expression by high‐throughput qPCR.This study not only deepens our understanding of the interaction between the plant–rhizosphere microbiome, but also provides a novel strategy to regulate and balance the different functional expression of the rhizomicrobiome to improve plant health and growth. [ABSTRACT FROM AUTHOR]

The underground root–soil–microbe interactions are extremely complex, but vitally important for aboveground plant growth, health and fitness. The pressure to reduce our reliance on agrochemicals, and sustainable efforts to develop agriculture makes rhizosphere interactions’ research a hotspot. Recent advances provide new insights about the signals, pathways, functions and mechanisms of these interactions. In this review, we provide an overview about recent progress in rhizosphere interaction networks in crops. We also discuss a holistic view of the root–soil–rhizomicrobiome interactions achieved through the advances of omics and bioinformatics technologies, and the potential strategies to manage the complex rhizosphere interactions for enhancing crop production. [ABSTRACT FROM AUTHOR]

Hydrochar aging may mitigate the adverse effects of direct hydrochar application on plant growth. However, little is known about the strategies for accelerating aging process and the microbiological mechanisms involved. This study explored the effects of three aging strategies, including the addition of straw and efficient-degrading microorganisms, on the aging processes of food waste-derived hydrochar, and identified the key microbial drivers. The bacterial and fungal sequencing was performed to estimate the species composition in hydrochar at different aging periods (i.e., day 1, 7, 14 and 35). The results showed that the addition of straw and microbial inoculum improved the maximum reaction temperature by 13%, and shortened the aging time by ∼30%. Three bacterial guilds, mainly including Bacillus -like species, were identified that showed significant correlations with the nitrogen and phosphorus dynamics during aging. This study demonstrates the feasibility of manipulating key microbial guilds artificially to achieve efficient harmless-treatment of hydrochar. [Display omitted] • Straw and microbial inoculum addition reduced aging duration by 30%. • Microbial inoculum addition increases the aging reaction temperature by 13%. • Bacteria, rather than fungi, play the critical role in hydrochar aging. • Bacillus and related species drive nitrogen and phosphorus cycles of aging. [ABSTRACT FROM AUTHOR]

Plant growth depends on a range of functions provided by their associated rhizosphere microbiome, including nutrient mineralization, hormone co-regulation and pathogen suppression. Improving the ability of plant-associated microbiomes to deliver these functions is thus important for developing robust and sustainable crop production. However, it is yet unclear how beneficial effects of probiotic microbial inoculants can be optimized and how their effects are mediated. Here, we sought to enhance tomato plant growth by targeted introduction of probiotic bacterial consortia consisting of up to eight plant-associated Pseudomonas strains. We found that the effect of probiotic consortium inoculation was richness-dependent: consortia that contained more Pseudomonas strains reached higher densities in the tomato rhizosphere and had clearer beneficial effects on multiple plant growth characteristics. Crucially, these effects were best explained by changes in the resident community diversity, composition and increase in the relative abundance of initially rare taxa, instead of introduction of plant-beneficial traits into the existing community along with probiotic consortia. Together, our results suggest that beneficial effects of microbial introductions can be driven indirectly through effects on the diversity and composition of the resident plant rhizosphere microbiome. [ABSTRACT FROM AUTHOR]

Summary: The secretomes of filamentous fungi contain a diversity of small secreted cysteine‐rich proteins (SSCPs) that have a variety of properties ranging from toxicity to surface activity. Some SSCPs are recognized by other organisms as indicators of fungal presence, but their function in fungi is not fully understood. We detected a new family of fungal surface‐active SSCPs (saSSCPs), here named hyphosphere proteins (HFSs). An evolutionary analysis of the HFSs in Pezizomycotina revealed a unique pattern of eight single cysteine residues (C‐CXXXC‐C‐C‐C‐C‐C) and a long evolutionary history of multiple gene duplications and ancient interfungal lateral gene transfers, suggesting their functional significance for fungi with different lifestyles. Interestingly, recombinantly produced saSSCPs from three families (HFSs, hydrophobins and cerato‐platanins) showed convergent surface‐modulating activity on glass and on poly(ethylene‐terephthalate), transforming their surfaces to a moderately hydrophilic state, which significantly favoured subsequent hyphal attachment. The addition of purified saSSCPs to the tomato rhizosphere had mixed effects on hyphal attachment to roots, while all tested saSSCPs had an adverse effect on plant growth in vitro. We propose that the exceptionally high diversity of saSSCPs in Trichoderma and other fungi evolved to efficiently condition various surfaces in the hyphosphere to a fungal‐beneficial state. [ABSTRACT FROM AUTHOR]

Lateral root formation is coordinated by both endogenous and external factors. As biotic factors, plant growth‐promoting rhizobacteria can affect lateral root formation, while the regulation mechanism is unclear. In this study, by applying various marker lines, we found that volatile compounds (VCs) from Bacillus amyloliquefaciens SQR9 induced higher frequency of DR5 oscillation and prebranch site formation, accelerated the development and emergence of the lateral root primordia and thus promoted lateral root development in Arabidopsis. We demonstrated a critical role of auxin on B. amyloliquefaciens VCs‐induced lateral root formation via respective mutants and pharmacological experiments. Our results showed that auxin biosynthesis, polar transport and signalling pathway are involved in B. amyloliquefaciens VCs‐induced lateral roots formation. We further showed that acetoin, a major component of B. amyloliquefaciens VCs, is less active in promoting root development compared to VC blends from B. amyloliquefaciens, indicating the presence of yet uncharacterized/unknown VCs might contribute to B. amyloliquefaciens effect on lateral root formation. In summary, our study revealed an auxin‐dependent mechanism of B. amyloliquefaciens VCs in regulating lateral root branching in a non‐contact manner, and further efforts will explore useful VCs to promote plant root development. The volatile compounds from Bacillus spp. increase the frequency of prebranch site formation and further accelerated the emergence of lateral root primordia (LRP) from the primary root (PR) in Arabidopsis, resulting in a denser lateral root (LR) along the PR spatially. This process is dependent on auxin signaling pathway; fully functional machinery of YUCs‐mediated auxin biosynthesis and polar auxin transport are also required. [ABSTRACT FROM AUTHOR]

Although interactions between plants and microbes at the plant–soil interface are known to be important for plant nutrient acquisition, relatively little is known about how root exudates contribute to nutrient exchange over the course of plant development. In this study, root exudates from slow‐ and fast‐growing stages of Arabidopsis thaliana plants were collected, chemically analysed and then applied to a sandy nutrient‐depleted soil. We then tracked the impacts of these exudates on soil bacterial communities, soil nutrients (ammonium, nitrate, available phosphorus and potassium) and plant growth. Both pools of exudates shifted bacterial community structure. GeoChip analyses revealed increases in the functional gene potential of both exudate‐treated soils, with similar responses observed for slow‐growing and fast‐growing plant exudate treatments. The fast‐growing stage root exudates induced higher nutrient mineralization and enhanced plant growth as compared to treatments with slow‐growing stage exudates and the control. These results suggest that plants may adjust their exudation patterns over the course of their different growth phases to help tailor microbial recruitment to meet increased nutrient demands during periods demanding faster growth. Here, we found that the fast‐growing stage root exudates induced higher nutrients mineralization resulted in better plant growth as compared to treatments with slow‐growing stage exudates and the controls. Plants appear to recruit specific beneficial microbiomes throughout their different growth phases, thereby tailoring microbial activities to meet increased nutrient demands during fast‐growing stages. [ABSTRACT FROM AUTHOR]

Summary: The rhizosphere microbiome is essential for plant growth and health, and numerous studies have attempted to link microbiome functionality to species and trait composition. However, to date little is known about the actual ecological processes shaping community composition, complicating attempts to steer microbiome functionality. Here, we assess the development of microbial life history and community‐level species interaction patterns that emerge during plant development. We use microbial phenotyping to experimentally test the development of niche complementarity and life history traits linked to microbiome performance. We show that the rhizosphere microbiome assembles from pioneer assemblages of species with random resource overlap into high‐density, functionally complementary climax communities at later stages. During plant growth, fast‐growing species were further replaced by antagonistic and stress‐tolerant ones. Using synthetic consortia isolated from different plant growth stages, we demonstrate that the high functional diversity of 'climax' microbiomes leads to a better resistance to bacterial pathogen invasion. By demonstrating that different life‐history strategies prevail at different plant growth stages and that community‐level processes may supersede the importance of single species, we provide a new toolbox to understand microbiome assembly and steer its functionality at a community level. [ABSTRACT FROM AUTHOR]

Even though bacteria are important in determining plant growth and health via volatile organic compounds (VOCs), it is unclear how these beneficial effects emerge in multi-species microbiomes. Here we studied this using a model plant–bacteria system, where we manipulated bacterial community richness and composition and determined the subsequent effects on VOC production and VOC-mediated pathogen suppression and plant growth-promotion. We assembled VOC-producing bacterial communities in different richness levels ranging from one to 12 strains using three soil-dwelling bacterial genera (Bacillus, Paenibacillus and Pseudomonas) and investigated how the composition and richness of bacterial community affect the production and functioning of VOCs. We found that VOC production correlated positively with pathogen suppression and plant growth promotion and that all bacteria produced a diverse set of VOCs. However, while pathogen suppression was maximized at intermediate community richness levels when the relative amount and the number of VOCs were the highest, plant growth promotion was maximized at low richness levels and was only affected by the relative amount of plant growth-promoting VOCs. The contrasting effects of richness could be explained by differences in the amount and number of produced VOCs and by opposing effects of community productivity and evenness on pathogen suppression and plant-growth promotion along the richness gradient. Together, these results suggest that the number of interacting bacterial species and the structure of the rhizosphere microbiome drive the balance between VOC-mediated microbe–pathogen and microbe–plant interactions potentially affecting plant disease outcomes in natural and agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Plant growth-promoting rhizobacteria (PGPR) substantially improve plant growth and health, but their effects on the succession of rhizosphere microbiota throughout the growth period triggered by pre-inoculation have not yet been considered. Methods: Pepper seedlings cultured from a bio-nursery substrate containing Bacillus velezensis NJAU-Z9 and ordinary nursery substrate were used in this study to evaluate the effects of pre-colonization of a PGPR strain at the seedling stage on yield enhancement. To elucidate the underlying mechanisms involved in the rhizosphere microbiota succession during the whole growth period and their association with yield enhancement, high-throughput sequencing combined with qPCR was conducted. Results: The results showed that, compared to the control without inoculation, pre-inoculation led to a steady yield enhancement in two-season field trials, as well as higher rhizosphere bacterial richness (Chao1) and diversity (Shannon-Wiener). The plant growth stage as the first driving factor, followed by pre-colonization drove the variations of the rhizosphere microbial community composition according to multivariate regression tree analysis and principal coordinate analysis. Variance partitioning analysis (VPA) and Mantel test results showed that the previous plant growth period induced variations in the fungal and bacterial communities at the next stage. Compared to the seedling and flowering stages, the mature-stage microbial community showed a higher degree of explanation of yield enhancement. Additionally, pre-inoculation led to distinctive rhizosphere microbiota succession compared to the control, due to alteration of the initial community. The heat map analysis showed that the rhizosphere microbiota was related to crop yield. In addition to Bacillus velezensis NJAU-Z9, which showed stable abundance in the pepper rhizosphere, stable higher relative abundance of the bacterial genera Sphingomonas, Sphingopyxis, Bradyrhizobium, Chitinophaga, Dyadobacter, Streptomyces, Lysobacter, Pseudomonas and Rhizomicrobium, and the fungal genera Cladorrhinum, Cladosporium and Aspergillus throughout the growth period induced by pre-colonization was associated with yield enhancement. Conclusions: Overall, we conclude that pre-colonization with PGPR changed the initial rhizosphere microbiota and that the plant was triggered to further select distinctive microbes to form unique rhizosphere microbial consortia at the later growth stages, which resulted in plant growth promotion. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) have been reported to influence plant growth, yield, and nutrient uptake by an array of mechanisms. Uncovering the behavioral dynamics of PGPR is one of the most important issues necessary for understanding their functional performances. In this study, strain NJAU-Z9 which was found to possess complex functions and efficient rhizospheric colonization ability was selected from plenty of bacterial strains isolated randomly from the pepper rhizosphere soil and identified as Bacillus velezensis. Repeated seedling nursing tests performed absolute growth-promoting advantage for the novel isolated strain. After that, primers for the quantitative detection were designed based on its whole genome sequence (WGS), and a real-time PCR method was utilized to explore strategies for monitoring the strain in natural soil and in the pepper rhizosphere. Results showed based on the whole genome, two primers were identified as NJAU-Z9-specific quantitative PCR primers. Two seasonal pot experiments demonstrated that strain NJAU-Z9 effectively colonized the rhizosphere measured by the novel abundance detecting strategy, improved plant growth, and showed a positive correlation between bacterial number and biomass. This study offers a strategy based on a real-time PCR method for directly monitoring B. velezensis strain NJAU-Z9 in the soil and the rhizosphere and provides a reference for the quantitative study of other PGPR strains based on WGSs. [ABSTRACT FROM AUTHOR]

Fungal communities may have different response to fertilization under different conditions. Therefore, it is necessary to reveal the effects of fertilizations on fungal communities considering temporal heterogeneity at different crop stages. To address this, soil samples were collected across eight typical plant growth stages of a wheat-rice rotation system under four fertilization regimes: no nitrogen fertilizer (NNF), chemical fertilizer (CF), organic-inorganic mixed fertilizer (OIMF), and organic fertilizer (OF). Soil temperature and moisture that co-vary with plant growth stages were the strongest predictors of fungal community compositions; meanwhile, fertilization regimes also played important roles. Shannon index and the relative abundance of Ascomycota were consistently increased when compared OF treatment with CF and OIMF treatments, while CF treatment had a higher relative abundance of Zygomycota when compared with NNF and OF treatments. For the functional guilds, application of urea-nitrogen fertilizers (CF and OIMF treatments) significantly decreased the relative abundance of saprotrophs and symbiotrophs, while soil treated with OF had less relative abundance of pathotrophs when compared to inorganic fertilizers. Our study provided a detailed picture of how fungal community composition responded to fertilization regimes across different plant growth stages. [ABSTRACT FROM AUTHOR]

Bacillus velezensis strain SQR9 is a well-investigated rhizobacterium with an outstanding ability to colonize roots, enhance plant growth and suppress soil-borne diseases. The recognition that biofilm formation by plant-beneficial bacteria is crucial for their root colonization and function has resulted in increased interest in understanding molecular mechanisms related to biofilm formation. Here, we report that the gene ftsE , encoding the ATP-binding protein of an FtsEX ABC transporter, is required for efficient SQR9 biofilm formation. FtsEX has been reported to regulate the atolysin CwlO. We provided evidence that FtsEX-CwlO was involved in the regulation of SQR9 biofilm formation; however, this effect has little to do with CwlO autolysin activity. We propose that regulation of biofilm formation by CwlO was exerted through the spo0A pathway, since transcription of spo0A cascade genes was altered and their downstream extracellular matrix genes were downregulated in SQR9 ftsE/cwlO deletion mutants. CwlO was also shown to interact physically with KinB/KinD. CwlO may therefore interact with KinB/KinD to interfere with the spo0A pathway. This study revealed that FtsEX-CwlO plays a previously undiscovered regulatory role in biofilm formation by SQR9 that may enhance root colonization and plant-beneficial functions of SQR9 and other beneficial rhizobacteria as well. [ABSTRACT FROM AUTHOR]

Nitrogen is a macronutrient which plays an important role in the net primary productivity of terrestrial ecosystems, and is critical to understand how nitrogen addition affects above- and below-ground organisms. However, direct and indirect interactions between microbial species response to nitrogen addition for wheat growth are still unclear. In this study, arbuscular mycorrhizal fungi (AMF) and diazotrophs ( nifH gene) were selected as two groups of key functional microbes in wheat soil to investigate the comprehensive impact of diversity and community structures between them on wheat yield under a nitrogen gradient. Nitrogen addition resulted in a significant shift in AMF and nifH phylogenetic diversity and community structure. The interactions among AMF and nifH species were diminished in high N-treated soils compared to those in low N-treated soils. Structural equation model analysis showed that AMF community structure affected wheat yield directly, however, which was influenced by AMF diversity, diazotrophic diversity and community structure indirectly. The comprehensive effects of AMF and diazotrophs on wheat productivity indicated the importance of soil functional microbes as drivers for farmland ecosystem and plant growth. These results could be useful in understanding soil nutrient cycling and may help improve the mechanistic understanding of the tripartite interaction among nitrogen addition, microbes and wheat productivity. [ABSTRACT FROM AUTHOR]

Rhizome rot of ginger caused by Fusarium oxysporum f. sp. zingiberi ( Foz ) is a soil-borne disease that adversely affects the seed rhizomes and crop production. Bacillus amyloliquefaciens NJPRHSDAQ-1 (NP-1), which has a substantial inhibitory effect on Foz in vitro , was isolated from the ginger rhizosphere. A pot experiment indicated that a bio-organic fertilizer made from NP-1 (BIO2) or other universal biocontrol agents (BIO1), the suspension of NP-1 (NP-1), and its cell-free fermentation broth (NP-1fb), all effectively reduced the disease incidence of rhizome rot, stimulated plant growth, and improved the microbial community compared to the control. The best control effect (78.3%) and the most significant suppression of Foz abundance (75.8% compared to control) were all observed in the BIO2 treatment. Two field experiments further indicated that BIO2 amendment can significantly increase ginger yield by 8.0–11.5% and can decrease the Foz population by 30.8–51.0% compared to control plants receiving only chemical fertilizer. Application of BIO2 also increased the growth and nutrient quality of ginger and soil enzyme activity. Pearson correlation analysis indicated a significant negative relationship between the abundance of culturable bacteria and Foz , while a negative correlation between culturable actinomycetes/fungi population and invertase/urease activity was observed. This study highlights the application prospect of a novel bio-organic fertilizer in ginger production for both disease suppression and growth promotion. [ABSTRACT FROM AUTHOR]

Aims: Investigating shifts in soil microbiomes driven by different fertilization regimes would be helpful for lessening the negative effect of monoculture in agricultural systems. Methods: In the present work, we employed MiSeq sequencing to evaluate the response of local microbial communities to three different fertilization regimes, i.e., heavy chemical fertilizer application (CF) and reduced chemical fertilizer applications supplemented with organic (OF) or Trichoderma-enriched organic fertilizer (BF), in a continuous five-season pot experiment on tomato. Results: The CF-treated soil resulted in a bacterial community with the lowest diversity, while the BF-treated soil had the highest diversity level. The OF-treated soil had the lowest diversity in the fungal community, while the CF- and BF-treated soils had higher diversity. Moreover, better plant growth and soil fertility status were obtained in the BF treatment followed by the OF and CF treatments. Conclusions: Compared to the CF and OF regimes, reduced chemical fertilizer plus Trichoderma-enriched organic fertilizer (BF) is the most suitable regime to control microbiome degeneration of monocropped soil and to thus maintain tomato plant growth and health. [ABSTRACT FROM AUTHOR]

Paenibacillus polymyxa (SQR-21) is not only a plant growth-promoting rhizobacteria, but also an effective biocontrol agent against Fusarium wilt disease of watermelon. For the better understanding and clarifying the potential mechanisms of SQR-21 to improve watermelon growth and disease resistance, a split-root methodology in hydroponic and LC-MS technology with the label free method was used to analyze the key root proteins involved in watermelon metabolism and disease resistance after the inoculation of SQR-21. Out of 623 identified proteins, 119 proteins were differentially expressed when treatment (SQR-21 inoculation) and control (no bacterial inoculation) were compared. Among those, 57 and 62 proteins were up-regulated and down-regulated, respectively. These differentially expressed proteins were identified to be involved in signal transduction (ADP-ribosylation factor, phospholipase D), transport (aspartate amino-transferase), carbohydratemetabolic (glucose-6-phosphate dehydrogenase, UDP-glucose pyrophosphorylase), defense and response to stress (glutathione S-transferase, Ubiquitin-activating enzyme E1), and oxidation-reduction process (thioredoxin peroxidase, ascorbate peroxidase). The results of this study indicated that SQR-21 inoculation on the watermelon roots benefits plant by inducing the expression of several proteins involved in growth, photosynthesis, and other metabolic and physiological activities. [ABSTRACT FROM AUTHOR]

The volatile organic compounds (VOCs) produced by soil microbes have a significant role in the control of plant diseases and plant growth promotion. In this study, we examined the effect of VOCs produced by Pseudomonas fluorescens strain WR-1 on the growth and virulence traits of tomato wilt pathogen Ralstonia solanacearum . The VOCs produced by P. fluorescens WR-1 exhibited concentration dependent bacteriostatic effect on the growth of R. solanacearum on agar medium and in infested soil. The VOCs of P. fluorescens WR-1 also significantly inhibited the virulence traits of R. solanacearum . The proteomics analysis showed that the VOCs of P. fluorescens WR-1 downregulated cellular proteins of R. solanacearum related to the antioxidant activity, virulence, inclusion body proteins, carbohydrate and amino acid synthesis and metabolism, protein folding and translation, methylation and energy transfer, while the proteins involved in the ABC transporter system, detoxification of aldehydes and ketones, protein folding and translation were upregulated. This study revealed the significance of VOCs of P. fluorescens WR-1 to control the tomato wilt pathogen R. solanacearum . Investigation of the modes of action of biocontrol agents is important to better comprehend the interactions mediated by VOCs in nature to design better control strategies for plant pathogens. [ABSTRACT FROM AUTHOR]

Background and aims: Plant growth and photosynthetic ability have been frequently demonstrated to increase with nitrogen (N) supply. N can also promote changes in root water absorption and shoot water status via mechanisms that remain poorly understood. This study aims at investigating the effects of N supply on water absorption. Methods: A hydroponic experiment with two independent rice varieties (cv. 'Shangyou63' hybrid indica and cv. 'Yangdao6' conventional indica, China) supplied by three distinct N levels was performed in a greenhouse. Physiological characteristics were analyzed after a few weeks. Results: Compared to low N supply (20 mg·L), exposure to high N supply (100 mg·L) increased the light-saturated photosynthetic rate ( A) and water use efficiency (WUE) by 17 % and 22 %, respectively, in Shanyou63 and by 43 % and 26 %, respectively, in Yangdao6. The leaf water potential was significantly decreased in Shanyou63 but not in Yangdao6. There were increases in the rate of water uptake and the root hydraulic conductance ( L) under high N supply in both rice cultivars; these changes were accompanied by increased transcription levels of aquaporins (AQPs), decreased aerenchyma formation and root porosity, and decreased root lignin content. Under high N supply, Yangdao6 also exhibited much higher AQP activity, lower aerenchyma and root porosity compared with those of Shanyou63, indicating that Yangdao6 had an increased ability to absorb water compared with that of Shanyou63. Conclusions: The enhanced expression of AQPs and decreased root aerenchyma and lignin contributed to increased water absorption ability under high N supply. In addition, the responses of each of the two rice cultivars (hybrid and conventional) to N supply is related to their water uptake ability, resulting from root porosity and an increase in AQP activity. [ABSTRACT FROM AUTHOR]

Phosphate ( Pi) transporters mediate acquisition and transportation of Pi within plants. Here, we investigated the functions of Os Pht1;4 ( Os PT4), one of the 13 members of the Pht1 family in rice. Quantitative real-time RT- PCR analysis revealed strong expression of Os PT4 in roots and embryos, and Os PT4 promoter analysis using reporter genes confirmed these findings. Analysis using rice protoplasts showed that Os PT4 localized to the plasma membrane. Os PT4 complemented a yeast mutant defective in Pi uptake, and also facilitated increased accumulation of Pi in Xenopus oocytes. Further, Os PT4 genetically modified ( GM) rice lines were generated by knockout/knockdown or over-expression of Os PT4. Pi concentrations in roots and shoots were significantly lower and higher in knockout/knockdown and over-expressing plants, respectively, compared to wild-type under various Pi regimes. 33 Pi uptake translocation assays corroborated the altered acquisition and mobilization of Pi in Os PT4 GM plants. We also observed effects of altered expression levels of Os PT4 in GM plants on the concentration of Pi, the size of the embryo, and several attributes related to seed development. Overall, our results suggest that Os PT4 encodes a plasma membrane-localized Pi transporter that facilitates acquisition and mobilization of Pi, and also plays an important role in development of the embryo in rice. [ABSTRACT FROM AUTHOR]

Bacillus amyloliquefaciens SQR9, isolated from the rhizosphere of cucumber, can control Fusarium wilt of cucumber and directly stimulate plant growth. To evaluate its potential agricultural use, the plant growth promotion of B. amyloliquefaciens SQR9 was evaluated, and the relative mechanisms, especially the production of the phytohormone indole-3-acetic acid (IAA), were investigated. The related plant-growth-promoting factors were genetically and chemically analyzed, and a mutant library was constructed for selecting strains with different IAA production. B. amyloliquefaciens SQR9 showed a growth-promoting activity in greenhouse experiments. Plant-growth-promoting factors like extracellular phytase, volatile components including acetoin, 2,3-butanediol, and phytohormone IAA were detected in B. amyloliquefaciens SQR9 cultures grown under laboratory conditions. Three IAA production mutant strains showed variation in plant-growth-promoting effect. IAA production in B. amyloliquefaciens SQR9 was related to its plant-growth-promoting effect, but IAA alone could not account for the overall observed plant-growth-promoting effect. The promoted plant growth by the rhizospheric strain B. amyloliquefaciens SQR9 can be attributed to multiple factors, including production of phytohormones, volatile compounds, and extracellular enzymes. Therefore, the strain B. amyloliquefaciens SQR9 may be used as a plant-growth-promoting agent to increase crop yield. [ABSTRACT FROM AUTHOR]

Aims: This research was to study the capacity of Trichoderma harzianum strain SQR-T037 to colonize tomato roots and how this strain and its bio-organic fertilizer stimulate plant growth and increase yields under field conditions. Methods: Field trials were conducted with a reduced application of chemical fertilizer (75 % of the recommended application) plus Trichoderma-enriched bio-organic fertilizer (BF) or organic fertilizer (OF) or Trichoderma spore suspension (SS), while 100 % of the recommended chemical fertilizer (CF) was used as control. Results: Trichoderma SQR-T037 could efficiently colonize tomato roots and soils based on the reverse transcription-quantitative PCR analysis, and significantly stimulate biomass accumulation at an early stage. The 75 % rates of chemical fertilizer coupled with bio-organic fertilizer (BF) produced tomato yields equivalent to those obtained using the 100 % rates of chemical fertilizer (CF), while inoculation with the Trichoderma alone (SS) or supplement with organic fertilizer alone (OF) would cause 11 and 13 % decreases in yield over the control (CF). The efficacy of BF for maintaining a stable tomato yield may be due to the enhanced soil nutrients availability and the increased abundance of soil microflora, including bacteria, fungi, actinomycetes and Trichoderma communities, which had a positive linear correlation in most of the cases revealed by the Pearson correlation analysis. Conclusions: The results of this study imply that the reason by which the bio-organic fertilizer promotes plant growth and increases the tomato yields can be attributed to the enhancement of the rhizospheric microflora, which promotes nutrient activation. Therefore, T. harzianum could be employed in a combination with composts. In this way, the application rate of chemical fertilizers can be practically decreased by 25 % to obtain maximum benefits. [ABSTRACT FROM AUTHOR]

Plant-related microbial communities are essential to plant growth and development, and empirical evidence suggests that inoculation with a synthetic microbial consortium can enhance plant performance; however, to manipulate the functions of these communities, we require a better understanding of the influencing factors. Here, we used the biodiversity ecosystem function (BEF) framework to specifically test the impact of community richness (1, 2, 4, or 8 strains per community) and antagonistic intensity on plant growth promotion in two kinds of nutritional environments. We found that increasing the richness of microbes can improve the accumulation of plant biomass, revealing that diversity effects were stronger than single-strain effects. The intensity of antagonism between highly diverse microbes may have a consistent negative effect on plant growth in comparison with the effects of communities with the same richness; intriguingly, this negative effect did not change positive BEF relationships. These results suggested that high diversity in the synthetic microbial consortia harboured stable and effective plant growth promotion capability and, in turn, also increased susceptibility to the negative effects of antagonism among microbial strains. • Increasing microbial community richness had a positive effect on plant growth. • Increasing antagonism intensity had a clear passive effect on plant growth. • Synthetic community with lower diversity showed inconsistent performance in different resource conditions. • Antagonistic intensity among strains does not change the positive BEF relationship. [ABSTRACT FROM AUTHOR]

Root exudates play important roles in root-soil microorganism interactions and can mediate tripartite interactions of beneficial microorganisms-plant-pathogen in the rhizosphere. However, the roles of organic acid components in this process have not been well studied. In this study the colonization of a plant growth-promoting rhizobacterium, Bacillus amyloliquefaciens SQR9, on cucumber root infected by Fusarium oxysporum f. sp. cucumerinum J. H. Owen ( FOC) was investigated. Chemotaxis and biofilm formation response of SQR9 to root exudates and their organic acid components were analysed. Infection of FOC on cucumber had a positive effect (3.30-fold increase) on the root colonization of SQR9 compared with controls. Root secretion of citric acid (2.3 ± 0.2 μM) and fumaric acid (5.7 ± 0.5 μM) was enhanced in FOC-infected cucumber plants. Bacillus amyloliquefaciens SQR9 exhibited enhanced chemotaxis to root exudates of FOC-infected cucumber seedlings. Further experiments demonstrated that citric acid acts as a chemoattractant and fumaric acid as a stimulator of biofilm formation in this process. These results suggest that root exudates mediate the interaction of cucumber root and rhizosphere strain B. amyloliquefaciens SQR9 and enhance its root colonization. [ABSTRACT FROM AUTHOR]

Large amounts of refloated algal sludge from Taihu Lake result in secondary environmental pollution due to annual refloatation. This study investigated the possibility to produce bio-organic fertilizer (BIO) using algal sludge as a solid-state fermentation (SSF) medium. Results showed that addition of algal sludge contributed to efficient SFF by a plant growth-promoting rhizobacteria (PGPR) strain SQR9 and improved the nutrient contents in the novel BIO. The optimum water content and initial inoculation size were 45% and 5%, respectively. After 6 days of SSF, the biomass of strain SQR9 was increased to a cell density of more than 5 × 107 CFU g−1. Microcystins were rapidly degraded, and a high germination index value was observed. Plant growth experiments showed that the produced BIO efficiently promoted plant growth. Additional testing showed that the novel SSF process was also suitable for other PGPR strains. This study provides a novel way of high-value utilization of algal sludge from Taihu Lake by producing low-cost but high-quality BIOs. [Copyright &y& Elsevier]

Highlights: [•] Liquid residue (LR) from SSF was analyzed for its biochemical properties. [•] Under greenhouse condition, it significantly increased the growth of tomato plants. [•] It had positive effects on microbial community of rhizosphere soil. [•] The enzyme activity and quality of soil were improved by LR. [•] This study showed an example for waste utilization in SSF industry. [ABSTRACT FROM AUTHOR]

Abstract: We previously developed a method for the application of bioorganic fertilizer to improve the biocontrol efficacy of Fusarium wilt (). However, the detailed behavior of Fusarium oxysporum f. sp. niveum (FON) and its antagonistic bacterium, Paenibacillus polymyxa SQR-21 (SQR-21), in the rhizosphere of watermelon after application of the bioorganic fertilizer had not been elucidated. A rhizobox experiment was carried out to investigate the distribution of FON and its antagonistic bacterium, SQR-21, in the soil at different distances from the watermelon rhizoplane by real-time PCR. The results confirmed that the bioorganic fertilizer (BIO) significantly suppressed Fusarium wilt and promoted the growth of the watermelon plants. Furthermore, we found that the application of BIO significantly enhanced the abundance of SQR-21 and reduced the population of FON in the soil near the rhizoplane as compared to the control. A maximal quantity (7.14log10copies/g soil) of P. polymyxa SQR-21 was obtained in the rhizosphere under the BIO treatment, and this number was decreased with increasing distance from the rhizoplane. The population of FON in the rhizosphere of the control was 2 orders of magnitude higher than under the BIO treatment, and with increasing distance from the rhizoplane, the FON abundance increased in the SQR-21 inoculated treatments and decreased in the treatments without SQR-21. In the soil far from the rhizoplane (bulk soil), both FON and SQR-21 reached a level that was not statistically different between the treatments, which might be attributed to the background level of the infested soil. The localization and pattern of colonization of SQR-21 on the root surface was examined in an in vitro experiment by following green fluorescent protein (gfp)-labeled SQR-21. The colonization of P. polymyxa SQR-21 was found to occur at any site on the roots, yet it was preferentially found in defined regions of the root tip and root bend. These results revealed that the BIO applied with the developed method suppressed Fusarium wilt by the promotion of SQR-21 colonization in the rhizosphere, which largely reduced the population of the pathogen. The findings also indicated that the method of nursery application of BIO satisfies the ecological requirements of the biocontrol products. [Copyright &y& Elsevier]

Greenhouse experiments were conducted to evaluate the effect of Glomus mosseae on maize growth at different organic fertilizer rates (0.0, 0.5, 1.0, 2.0 and 4.0 g kg−1 soil). There were two AM fungi treatments (inoculation with G. mosseae, +AM and uninoculated control, −AM) at every organic fertilizer rate. Generally, both inoculated G. mosseae and organic fertilizer significantly improved plant growth. In the inoculated pots, the growth of plant and AM colonization varied with the rates of organic fertilization. The plant height, chlorophyll content, biomass, phosphorus (P) uptake, and AM colonization increased by the increasing of organic fertilizer rate up to 2.0 g kg−1, but decreased or had no significant difference compared to the uninoculated plants at the highest fertilizer rate (4.0 g kg−1). The results suggested that optimal organic fertilizer rate is needed to stimulate AM fungi and improve the maximal growth of plant in agricultural systems. [ABSTRACT FROM AUTHOR]

Abstract: In order to study the effects of different nitrogen (N) forms on drought tolerance of rice seedlings, both hydroponic and pot experiments were conducted in green house. In hydroponic experiments, water stress was simulated by treatment with polyethylene glycol (PEG, 10% in w/v, MW6000); in pot experiments, rice seedlings were cultivated under non-flooded conditions. The results showed that: (1) under water stress conditions, the decrease in plant growth and photosynthesis under ammonium supply was less than under nitrate supply; (2) under non-flooded cultivation, the biomass and photosynthesis in rice plants supplied with ammonium and ammonium+dicyandiamide (DCD, a nitrification inhibitor) were higher than those in nitrate fertilization; (3) in hydroponic experiments, water uptake of rice seedlings under ammonium nutrition was higher than under nitrate nutrition. It is concluded that, ammonium nutrition can enhance the tolerance of rice plants to water stress. [Copyright &y& Elsevier]

Rice grown under anaerobic waterlogged soil condition takes up ammonium as a major source of nitrogen (N). A substantial quantity of nitrate is taken up by rice when aeration conditions prevail. This work compared the physiological and molecular responses of N-depleted rice ( Oryza sativa L. japonica ssp. cv. Wuyunjing) to re-supply of different N sources in a hydroponic system. Expression of six genes known to be related to N uptake and assimilation in roots was analyzed by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). N starvation increased root growth but decreased shoot biomass and nitrate reductase (NR) activity. In comparison to nitrate as N source, ammonium tended to inhibit root growth but significantly improved shoot growth, total N uptake, and, particularly, the translocation of N to the above ground parts. Replacing half of the ammonium by nitrate in the single ammonium solution increased glutamine synthetase (GS) activity and total N uptake. This replacement enhanced expression of OsAMT1;3 but decreased the expression of OsAMT1;2 in the roots. Likewise, replacing half of the nitrate by ammonium in the single nitrate solution, increased NR activity and expression of an NR gene ( OsNR1) but suppressed expression of OsNRT2 in the roots. Expression of both OsAMT1;1 and a GS gene ( OsGS1;1) was relatively constant and not affected by the N form or starvation in the rice roots. Predominant beneficial effects of dual supply of the two forms of N in comparison with a single form of N either as ammonium or as nitrate might be due to improvement of ammonium uptake due to nitrate presence near the roots and enhanced reduction of nitrate in leaves by ammonium. [ABSTRACT FROM AUTHOR]

Chemotaxis, the ability of motile bacteria to direct their movement in gradients of attractants and repellents, plays an important role during the rhizosphere colonization by rhizobacteria. The rhizosphere is a unique niche for plant–microbe interactions. Root exudates are highly complex mixtures of chemoeffectors composed of hundreds of different compounds. Chemotaxis towards root exudates initiates rhizobacteria recruitment and the establishment of bacteria–root interactions. Over the last years, important progress has been made in the identification of root exudate components that play key roles in the colonization process, as well as in the identification of the cognate chemoreceptors. In the first part of this review, we summarized the roles of representative chemoeffectors that induce chemotaxis in typical rhizobacteria and discussed the structure and function of rhizobacterial chemoreceptors. In the second part we reviewed findings on how rhizobacterial chemotaxis and other root–microbe interactions promote the establishment of beneficial rhizobacteria-plant interactions leading to plant growth promotion and protection of plant health. In the last part we identified the existing gaps in the knowledge and discussed future research efforts that are necessary to close them. [ABSTRACT FROM AUTHOR]

Background: Colonization of Trichoderma spp. is essential for exerting their beneficial functions on the plant. However, the interactions between Trichoderma spp. and plant roots are still not completely understood. The aim of this study was to investigate how TgSWO affect Trichoderma guizhouense to establish themselves in the plant rhizosphere and promote plant growth. In this study, we deeply analyzed the molecular mechanism by which the functional characterization of the TgSWO by expressing different functional region deletion proteins (FRDP) of TgSWO. Results: Root scanning analysis results showed that TgSWO could dramatically increase root density and promote growth. In addition, we also found that TgSWO could expand root cell walls, subsequently increase root colonization. Moreover, knockout of TgSWO mutants (KO) or overexpression of TgSWO mutants (OE) produced greatly reduced or increased the number of cucumber root, respectively. To clarify the molecular mechanism of TgSWO in plant-growth-promotion, we analyzed the ability of different FRDP to expand the root cell wall. The root cell wall architecture were considerably altered when treated by ΔCBD protein (the TgSWO gene of lacking in the CBD domain was cloned and heterologously expressed), in correlation with the present YoaJ domain of TgSWO. In contrast, neither the expansion of cell walls nor the increase of roots was detectable in ΔYoaJ protein. Conclusions: Our results emphasize the YoaJ domain is the most critical functional area of TgSWO during the alteration of cell wall architecture. Simultaneously, the results obtained in this study also indicate that TgSWO might play a plant-growth-promotion role in the Trichoderma-plant interactions by targeting the root cell wall. [ABSTRACT FROM AUTHOR]

A correction to the article "Contribution of indole-3-acetic acid in the plant growth promotion by the rhizospheric strain Bacillus amyloliquefaciens SQR9," by Jiahui Shao and colleagues that was published in the 2015 issue is presented.