Modulate Plant Growth Research Articles

Evidence for the role of sound on the growth and signal response in duckweed

ABSTRACT Sound vibration, an external mechanical force, has been proven to modulate plant growth and development like rain, wind, and vibration. However, the role of sound on plants, especially on signal response, has been usually neglected in research. Herein, we investigated the growth state, gene expression, and signal response in duckweed treated with soft music. The protein content in duckweed after music treatment for 7 days was about 1.6 times that in duckweed without music treatment. Additionally, the potential maximum photochemical efficiency of photosystem II (Fv/Fm) ratio in duckweed treated with music was 0.78, which was significantly higher in comparison with the control group (P < .01). Interestingly, music promoted the Glu and Ca signaling response. To further explore the global molecular mechanism, we performed transcriptome analysis and the library preparations were sequenced on an Illumina Hiseq platform. A total of 1296 differentially expressed genes (DEGs) were found for all these investigated genes in duckweed treated with music compared to the control group. Among these, up-regulation of the expression of metabolism-related genes related to glycolysis, cell wall biosynthesis, oxidative phosphorylation, and pentose phosphate pathways were found. Overall, these results provided a molecular basis to music-triggered signal response, transcriptomic, and growth changes in duckweed, which also highlighted the potential of music as an environmentally friendly stimulus to promote improved protein production in duckweed.

CAR modulates plasma membrane nano-organization and immune signaling downstream of RALF1-FERONIA signaling pathway.

In Arabidopsis, the receptor-like kinase (RLK) FERONIA (FER) senses peptide ligands in the plasma membrane (PM), modulates plant growth and development, and integrates biotic and abiotic stress signaling for downstream adaptive responses. However, the molecular interplay of these diverse processes is largely unknown. Here, we show that FER, the receptor of Rapid Alkalinization Factor 1 (RALF1), physically interacts with C2 domain ABA-related (CAR) proteins to control the nano-organization of the PM. During this process, the RALF1-FER pathway upregulates CAR protein translation, and then more CAR proteins are recruited to the PM. This acts as a rapid feedforward loop that stabilizes the PM liquid-ordered phase. FER interacts with and phosphorylates CARs, thereby reducing their lipid-binding ability and breaking the feedback regulation at later time points. The formation of the flg22-induced FLS2-BAK1 immune complex, which depends on the integrity of FER-containing nanodomains, is impaired in fer and pentuple car14569 mutant. Together, we propose that the FER-CAR module controls the formation of PM nano-organization during RALF signaling through a self-contained amplifying loop including both positive and negative feedback.

Mapping QTL for Phenological and Grain-Related Traits in a Mapping Population Derived from High-Zinc-Biofortified Wheat.

Genomic regions governing days to heading (DH), days to maturity (DM), plant height (PH), thousand-kernel weight (TKW), and test weight (TW) were investigated in a set of 190 RILs derived from a cross between a widely cultivated wheat-variety, Kachu (DPW-621-50), and a high-zinc variety, Zinc-Shakti. The RIL population was genotyped using 909 DArTseq markers and phenotyped in three environments. The constructed genetic map had a total genetic length of 4665 cM, with an average marker density of 5.13 cM. A total of thirty-seven novel quantitative trait loci (QTL), including twelve for PH, six for DH, five for DM, eight for TKW and six for TW were identified. A set of 20 stable QTLs associated with the expression of DH, DM, PH, TKW, and TW were identified in two or more environments. Three novel pleiotropic genomic-regions harboring co-localized QTLs governing two or more traits were also identified. In silico analysis revealed that the DArTseq markers were located on important putative candidate genes such as MLO-like protein, Phytochrome, Zinc finger and RING-type, Cytochrome P450 and pentatricopeptide repeat, involved in the regulation of pollen maturity, the photoperiodic modulation of flowering-time, abiotic-stress tolerance, grain-filling duration, thousand-kernel weight, seed morphology, and plant growth and development. The identified novel QTLs, particularly stable and co-localized QTLs, will be validated to estimate their effects in different genetic backgrounds for subsequent use in marker-assisted selection (MAS).

The hidden power of secondary metabolites in plant-fungi interactions and sustainable phytoremediation.

The global environment is dominated by various small exotic substances, known as secondary metabolites, produced by plants and microorganisms. Plants and fungi are particularly plentiful sources of these molecules, whose physiological functions, in many cases, remain a mystery. Fungal secondary metabolites (SM) are a diverse group of substances that exhibit a wide range of chemical properties and generally fall into one of four main family groups: Terpenoids, polyketides, non-ribosomal peptides, or a combination of the latter two. They are incredibly varied in their functions and are often related to the increased fitness of the respective fungus in its environment, often competing with other microbes or interacting with plant species. Several of these metabolites have essential roles in the biological control of plant diseases by various beneficial microorganisms used for crop protection and biofertilization worldwide. Besides direct toxic effects against phytopathogens, natural metabolites can promote root and shoot development and/or disease resistance by activating host systemic defenses. The ability of these microorganisms to synthesize and store biologically active metabolites that are a potent source of novel natural compounds beneficial for agriculture is becoming a top priority for SM fungi research. In this review, we will discuss fungal-plant secondary metabolites with antifungal properties and the role of signaling molecules in induced and acquired systemic resistance activities. Additionally, fungal secondary metabolites mimic plant promotion molecules such as auxins, gibberellins, and abscisic acid, which modulate plant growth under biotic stress. Moreover, we will present a new trend regarding phytoremediation applications using fungal secondary metabolites to achieve sustainable food production and microbial diversity in an eco-friendly environment.

Fatty acid amide hydrolase and 9-lipoxygenase modulate cotton seedling growth by ethanolamide oxylipin levels.

Polyunsaturated N-acylethanolamines (NAEs) can be hydrolyzed by fatty acid amide hydrolase (FAAH) or oxidized by lipoxygenase (LOX). In Arabidopsis (Arabidopsis thaliana), the 9-LOX product of linoleoylethanolamide, namely, 9-hydroxy linoleoylethanolamide (9-NAE-HOD), is reported to negatively regulate seedling development during secondary dormancy. In upland cotton (Gossypium hirsutum L.), six putative FAAH genes (from two diverged groups) and six potential 9-LOX genes are present; however, their involvement in 9-NAE-HOD metabolism and its regulation of seedling development remain unexplored. Here, we report that in cotton plants, two specific FAAH isoforms (GhFAAH Ib and GhFAAH IIb) are needed for hydrolysis of certain endogenous NAEs. Virus-induced gene silencing (VIGS) of either or both FAAHs led to reduced seedling growth and this coincided with reduced amidohydrolase activities and elevated quantities of endogenous 9-NAE-HOD. Transcripts of GhLOX21 were consistently elevated in FAAH-silenced tissues, and co-silencing of GhLOX21 and GhFAAH (Ib and/or IIb) led to reversal of seedling growth to normal levels (comparable with no silencing). This was concomitant with reductions in the levels of 9-NAE-HOD, but not of 13-NAE-HOD. Pharmacological experiments corroborated the genetic and biochemical evidence, demonstrating that direct application of 9-NAE-HOD, but not 13-NAE-HOD or their corresponding free fatty acid oxylipins, inhibited the growth of cotton seedlings. Additionally, VIGS of GhLOX21 in cotton lines overexpressing AtFAAH exhibited enhanced growth and no detectable 9-NAE-HOD. Altogether, we conclude that the growth of cotton seedlings involves fine-tuning of 9-NAE-HOD levels via FAAH-mediated hydrolysis and LOX-mediated production, expanding the mechanistic understanding of plant growth modulation by NAE oxylipins to a perennial crop species.

Abscisic acid and its role in the modulation of plant growth, development, and yield stability.

Abscisic acid (ABA) is known to confer stress tolerance; however, at elevated levels it impairs plant growth under prolonged stress. Paradoxically, at its basal level, ABA plays many vital roles in promoting plant growth and development, including modulation of tillering, flowering, and seed development, as well as seed maturation. In this review, we provide insight into novel discoveries of ABA fluxes, ABA signaling responses, and their impact on yield stability. We discuss ABA homeostasis implicated under pre- and postanthesis drought and its impact on productive tillers, grain number determination, and seed development to address yield stability in cereal crops while considering the new knowledge that emerged from the model plant systems.

Role of endophytic bacteria in salinity stress amelioration by physiological and molecular mechanisms of defense: A comprehensive review

• In drylands, salinity stress reduces production and crop yield. • CRISPR CAS/Cas9, miRNAs, CAM pathways and plant breeding used to cope with the drastic effects of salt stress but costly on ground levels. • Plants that have been inoculated with Endophytes have a higher resistance to salinity. • By inducing systematic resistance, endophytes were able to remove saline stress. • Resistant halotolerant endophytes that have a longer shelf life need to be develop. Climate change is a major concern for sustainable agriculture in the twenty-first century, as it has an impact on crop production and soil fertility, which may increase the risk of famine. Of the array of issues pertaining to climate change, salt stress is one of the most significant factors affecting crop production all over the world. Plants undergo different morphological, physio-chemical, and molecular adaptations to deal with salinity stress. However, several mitigation strategies are also used to cope with the drastic effects of salt stress. Microbial-based solutions, in particular, are highly desirable in sustainable agriculture as they provide a natural, cost-effective, and environmentally safe approach for improving plant growth and yield. Endophytic bacteria not only preserve soil fertility but also boost plant growth under salt stress situations. These bacteria mitigate salt stress by lowering the synthesis of reactive oxygen species (ROS) and facilitating nutrient availability. Moreover, the endophytic bacteria also regulate the expression of genes responsible for producing various phytohormones, antioxidant enzymes, siderophores, volatile organic compounds, and ROS-scavenging enzymes, and other substances. The current research extensively explored the potential pathways involved in plant growth modulation and salinity stress mitigation by endophytic bacteria. Bacterial endophytes as a plant's second genome might be a natural strategy for improving a plant's growth and yield under salt stress conditions.

Bacillus: a eco-friendly source for plant development and sanity

Bacillus are non-pathogenic gram-positive bacteria capable of producing resistant spores. They have several beneficial characteristics to crop production, such as increased plant growth, resistance to abiotic/biotic stresses, nutritional improvement, and potential for bioremediation of contaminated soils. The use of microorganisms in agriculture has increased due to the reduction in the use of agrochemicals, and sustainable production. Therefore, the present study was based on bibliographical research on the current state of the art of biotechnological prospecting and obtaining commercial products of Bacillus for the agricultural sector. The search was conducted through the Google Academic platform limiting the search to the years 2015 to 2020. Papers that explained in vitro or in vivo prospecting methodologies of Bacillus with promoter or protective activity of plants and those that described microbial inoculants with this genus were selected. Different species of Bacillus can modulate plant growth producing plant hormones. Molecular biology tools such as DNA sequencing and PCR are applied to the study of genes involved in plant growth modulation by Bacillus such as AcPho, ipdC and asbA. For the elaboration of agricultural bioproducts, vegetative structures or endospores are used, under an optimal concentration of 1 x 108 CFU/mL. In the face of species diversity, many have not yet been studied and are promising to become bioproducts. This fact is enhanced by the immeasurable applicability of Bacillus.

Cellobiose elicits immunity in lettuce conferring resistance to Botrytis cinerea.

Cellobiose is the primary product of cellulose hydrolysis and is expected to function as a type of pathogen/damage-associated molecular pattern in evoking plant innate immunity. In this study, cellobiose was demonstrated to be a positive regulator in the immune response of lettuce, but halted autoimmunity when lettuce was exposed to concentrations of cellobiose >60 mg l-1. When lettuce plants were infected by Botrytis cinerea, cellobiose endowed plants with enhanced pre-invasion resistance by activating high β-1,3-glucanase and antioxidative enzyme activities at the initial stage of pathogen infection. Cellobiose-activated core regulatory factors such as EDS1, PTI6, and WRKY70, as well as salicylic acid signaling, played an indispensable role in modulating plant growth-defense trade-offs. Transcriptomics data further suggested that the cellobiose-activated plant-pathogen pathways are involved in microbe/pathogen-associated molecular pattern-triggered immune responses. Genes encoding receptor-like kinases, transcription factors, and redox homeostasis, phytohormone signal transduction, and pathogenesis-related proteins were also up- or down-regulated by cellobiose. Taken together, the findings of this study demonstrated that cellobiose serves as an elicitor to directly activate disease-resistance-related cellular functions. In addition, multiple genes have been identified as potential modulators of the cellobiose-induced immune response, which could aid understanding of underlying molecular events.

Red and Blue Light Differently Influence Actinidia chinensis Performance and Its Interaction with Pseudomonas syringae pv. Actinidiae.

Light composition modulates plant growth and defenses, thus influencing plant-pathogen interactions. We investigated the effects of different light-emitting diode (LED) red (R) (665 nm) and blue (B) (470 nm) light combinations on Actinidia chinensis performance by evaluating biometric parameters, chlorophyll a fluorescence, gas exchange and photosynthesis-related gene expression. Moreover, the influence of light on the infection by Pseudomonas syringae pv. actinidiae (Psa), the etiological agent of bacterial canker of kiwifruit, was investigated. Our study shows that 50%R-50%B (50R) and 25%R-75%B (25R) lead to the highest PSII efficiency and photosynthetic rate, but are the least effective in controlling the endophytic colonization of the host by Psa. Monochromatic red light severely reduced ΦPSII, ETR, Pn, TSS and photosynthesis-related genes expression, and both monochromatic lights lead to a reduction of DW and pigments content. Monochromatic blue light was the only treatment significantly reducing disease symptoms but did not reduce bacterial endophytic population. Our results suggest that monochromatic blue light reduces infection primarily by modulating Psa virulence more than host plant defenses.

Endophytic microbes modulate plant responses to abiotic stresses: a review

Many groups of microorganisms have been studied for their benefits towards humankind due to their capacity to produce natural compounds that can be valorized in many economic sectors such as agriculture. Due to the extensive use of chemicals pesticides and fertilizers, current agriculture systems facing several major problems such as emergence of resistant in pathogens and pests, soil infertility and bioaccumulation of toxic residues in the environment and particularly in foods which negatively affects human health. The use of natural products harmless to plants, humans and biodegradable constitute a promising way to overcome these problems. Modern agriculture systems are moving toward the use of beneficial microorganisms isolated from the soil, plant surfaces and inside tissues for developing eco-friendly products such as biofertilizers and biopesticides. Recent literatures show that colonization of plants by endophytes is the rule in nature and endophyte-free plant is a rare exception. Endophytes are microbes living inside plant tissues and supporting them in growth and development, as well as stresses tolerance without causing any apparent disease symptom. Abiotic stresses have a great impact on growth, production and health of plants. Many literatures show the role of endophytes in abiotic stress tolerance as well as mechanisms involved to cope with these constraints via the induction of stress-related genes and molecules. This review provides a summary of literature on how endophytes modulate plant growth and responses to abiotic stresses which may help to better understand their role in plant adaptation to environmental constraints and valorize their use in agriculture.

Effect of Silver Nanoparticles Synthesized by ‘Green’ Methods on the Growth of in vitro Culture of Betula pendula L. whole Plants

Background: Metal nanoparticles, such as silver nanoparticles obtained by “green” nanosynthesis, have been increasingly used in research and practice in recent years due to their high biocompatibility and low toxicity. It is important to understand how green nanoparticles have regulatory effects on all groups of living systems, including plants. One of the key questions is how silver nanoparticles obtained by green methods modify plant growth in various cultivation and biotechnological systems, such as in vitro culture. Objective: The aim of this study was to establish how in vitro culture of birch plants (Betula pendula Roth) reacts to different levels of silver nanoparticles synthesized by green methods (based on plant extracts) and chemical approaches. Methods: The paper examined the nodal segments of silver birch Betula pendula Roth grown on Woody Plant Medium (WPM) with the addition of silver nanoparticles (0.3-300 mg L-1). After 30 days of cultivation in an in vitro environment, the growth of shoots and roots was measured. Silver nanoparticles were synthesized using L-ascorbic acid (reducing agent) and polyvinylpyrrolidone (PVP; stabilizer), as well as with needle extract (as a reducing agent and stabilizer). Results: Chemical nanosynthesis based on PVP and L-ascorbate, as well as green nanosynthesis using extract of spruce needles made it possible to obtain spherical nanoparticles with similar physical parameters. Low levels of AgNPs (0.3-10 mg L-1) synthesized by chemical techniques (PVP and L-ascorbate) stimulated the growth of birch shoots. In this case, the maximum stimulating effect on shoot growth was found at 10 mg of L-1 AgNPs (250-300% stimulation compared to the control). Under higher levels of nanoparticles (30-300 mg L-1), the stimulating effect decreased. Concentrations over 300 mg of L-1 inhibited the growth of birch plants. Very similar effects were observed in roots. In experiments with nanoparticles synthesized using spruce needle extract, it was shown that low concentrations of AgNPs (0.3 and 1 mg L-1) did not cause a significant change in the size of birch shoots and roots. At the same time, higher levels of silver nanoparticles (3-300 mg L-1) significantly stimulated growth. Conclusion: The present study demonstrates the production of stable silver nanoparticles based on PVP and L-ascorbic acid, as well as an extract of Betula pendula needles. The resulting nanoparticles have a uniform shape and distribution. The presence of AgNP (1-300 mg L-1) in the nutrient media has a stimulating effect on Betula pendula shoot and root growth.

A Functional Genomics View of Gibberellin Metabolism in the Cnidarian Symbiont Breviolum minutum.

Dinoflagellate inhabitants of the reef-building corals exchange nutrients and signals with host cells, which often benefit the growth of both partners. Phytohormones serve as central hubs for signal integration between symbiotic microbes and their hosts, allowing appropriate modulation of plant growth and defense in response to various stresses. However, the presence and function of phytohormones in photosynthetic dinoflagellates and their function in the holobionts remain elusive. We hypothesized that endosymbiotic dinoflagellates may produce and employ phytohormones for stress responses. Using the endosymbiont of reef corals Breviolum minutum as model, this study aims to exam whether the alga employ analogous signaling systems by an integrated multiomics approach. We show that key gibberellin (GA) biosynthetic genes are widely present in the genomes of the selected dinoflagellate algae. The non-13-hydroxylation pathway is the predominant route for GA biosynthesis and the multifunctional GA dioxygenase in B. minutum has distinct substrate preference from high plants. GA biosynthesis is modulated by the investigated bleaching-stimulating stresses at both transcriptional and metabolic levels and the exogenously applied GAs improve the thermal tolerance of the dinoflagellate. Our results demonstrate the innate ability of a selected Symbiodiniaceae to produce the important phytohormone and the active involvement of GAs in the coordination and the integration of the stress response.

The effects of genetic distance, nutrient conditions, and recognition ways on outcomes of kin recognition in Glechoma longituba.

Kin recognition might help plants decrease competitive cost and improve inclusive fitness with close genes; thus it might interact with environmental factors to affect communities. Whether and how various factors, such as the genetic distance of neighbors, environmental stressors, or the way a plant recognizes its neighbors, might modify plant growth strategies remains unclear. To answer these questions, we conducted experiments in which ramets of a clonal plant, Glechoma longituba, were grown adjacent to different genetically related neighbors (clone kin / close kin / distant kin) in different nutrient conditions (high / medium / low), or with only root exudates from pre-treatment in culture solution. By comparing competitive traits, we found that: (1) kin recognition in G. longituba was enhanced with closer genetic distance; (2) the outcomes of kin recognition were influenced by the extent of nutrient shortage; (3) kin recognition helped to alleviate the nutrient shortage effect; (4) kin recognition via root exudates affected only below-ground growth. Our results provide new insights on the potential for manipulating the outcome of kin recognition by altering neighbor genetic distance, nutrient conditions and recognition ways. Moreover, kin recognition can help plants mitigate the effects of nutrient shortage, with potential implications in agricultural research.

Genome-Wide Expression Profiling Analysis of Kiwifruit GolS and RFS Genes and Identification of AcRFS4 Function in Raffinose Accumulation.

The raffinose synthetase (RFS) and galactinol synthase (GolS) are two critical enzymes for raffinose biosynthesis, which play an important role in modulating plant growth and in response to a variety of biotic or abiotic stresses. Here, we comprehensively analyzed the RFS and GolS gene families and their involvement in abiotic and biotic stresses responses at the genome-wide scale in kiwifruit. A total of 22 GolS and 24 RFS genes were identified in Actinidia chinensis and Actinidia eriantha genomes. Phylogenetic analysis showed that the GolS and RFS genes were clustered into four and six groups, respectively. Transcriptomic analysis revealed that abiotic stresses strongly induced some crucial genes members including AcGolS1/2/4/8 and AcRFS2/4/8/11 and their expression levels were further confirmed by qRT-PCR. The GUS staining of AcRFS4Pro::GUS transgenic plants revealed that the transcriptionlevel of AcRFS4 was significantly increased by salt stress. Overexpression of AcRFS4 in Arabidopsis demonstrated that this gene enhanced the raffinose accumulation and the tolerance to salt stress. The co-expression networks analysis of hub transcription factors targeting key AcRFS4 genes indicated that there was a strong correlation between AcNAC30 and AcRFS4 expression under salt stress. Furthermore, the yeast one-hybrid assays showed that AcNAC30 could bind the AcRFS4 promoter directly. These results may provide insights into the evolutionary and functional mechanisms of GolS and RFS genes in kiwifruit.

Synergism of endophytic Bacillus subtilis and Klebsiella aerogenes modulates plant growth and bacoside biosynthesis in Bacopa monnieri.

Bacopa monnieri is the main source of pharmaceutically important bacosides; however, the low content of these molecules in planta remains a limiting factor for fulfilling the industrial requirement. The accumulation of secondary metabolites can be enhanced in plants upon inoculation with endophytes. In this study, we isolated and analyzed the culturable endophytes associated with different plant parts. By analyzing their impact on plant growth parameters (in vitro and in vivo) and Bacoside A content, we found few candidates which increased bacoside accumulation significantly. Finally, two promising endophytes namely Bacillus subtilis (OK070745) and Klebsiella aerogenes (OK070774) were co-cultivated with B. monnieri cuttings singly and in combination mode to clarify their effect on bacoside biosynthesis and their accumulation in B. monnieri shoot. Consortium-inoculated plants significantly enhanced the plant biomass and Bacoside A content with respect to single inoculation. The results of real-time quantitative (RT-PCR) revealed significant accumulation of bacoside biosynthetic pathway transcripts (HMGCR, PMVK, FDPS, SQS, and β-AS) in the case of plants inoculated with microbial combination, while the single inoculation of B. subtilis diverted the plant’s machinery toward the synthesis of phenylpropanoid genes like CCR, CAD, CHS, and HST. In addition, higher expression of MYB 2 and WRKY 1 transcription factors in combinational treatment points out their probable role in better physiological and developmental processes. Altogether, this is the first study on B. monnieri-endophyte interaction showing improvement in the accumulation of bacoside A by modulating various genes of metabolic pathway and thus suggests an effective “green approach” for augmenting in planta production of pharmaceutically important bacosides.

Genome-Wide Survey and Expression Analyses of Hexokinase Family in Poplar (Populus trichocarpa)

Hexokinase (HXK) family proteins exert critical roles in catalyzing hexose phosphorylation, sugar sensing, and modulation of plant growth and stress adaptation. Nevertheless, a large amount remains unknown about the molecular profile of HXK enzymes in Populus trichocarpa, a woody model tree species. A genome-wide survey of HXK-encoding genes, including phylogenies, genomic structures, exon/intron organization, chromosomal distribution, and conserved features, was conducted, identifying six putative HXK isogenes (PtHXK1-6) in the Populus genome. The evolutionary tree demonstrated that 135 homologous HXKs between 17 plant species were categorized into four major subfamilies (type A, B, C, and D), clustering one plastidic (PtHXK3) and five mitochondrial PtHXKs grouped into type A and B, respectively. The in silico deduction prompted the presence of the conserved sugar-binding core (motif 4), phosphorylation sites (motif 2 and 3), and adenosine-binding domains (motif 7). The transcriptomic sequencing (RNA-seq) and the quantitative real-time PCR (qRT-PCR) assays revealed that three isogenes (PtHXK2, 3, and 6) were abundantly expressed in leaves, stems, and roots, while others appeared to be dominantly expressed in the reproductive tissues. Under the stress exposure, PtHXK2 and 6 displayed a significant induction upon the pathogenic fungi (Fusarium solani) infection and marked promotions by glucose feeding in roots. In contrast, the PtHXK3 and 6 are ABA-responsive genes, following a dose-dependent manner. The comprehensive analyses of the genomic patterns and expression profiling provide theoretical clues and lay a foundation for unraveling the physiological and signaling roles underlying the fine-tuned PtHXKs responding to diverse stressors.

Genome-wide identification and characterization of the HD-Zip gene family and expression analysis in response to stress in Rehmannia glutinosa Libosch

ABSTRACT The HD-Zip family of transcription factors is unique to the plant kingdom, and play roles in modulation of plant growth and response to environmental stresses. R. glutinosa is an important Chinese medicinal material. Its yield and quality are susceptible to various stresses. The HD-Zip transcription factors is unique to the plant, and roles in modulation of plant growth and response to environmental stresses. However, there is no relevant research on the HD-ZIP of R. glutinosa. In this study, 92 HD-Zip transcription factors were identified in R. glutinosa, and denominated as RgHDZ1-RgHDZ92. Members of RgHDZ were classified into four groups (HD-ZipI-IV) based on the phylogenetic relationship of Arabidopsis HD-Zip proteins, and each group contains 38, 18, 17, and 19 members, respectively. Expression analyses of RgHDZ genes based on transcriptome data showed that the expression of these genes could be induced by the endophytic fungus of R. glutinosa. Additionally, we showed that RgHDZ genes were differentially expressed in response to drought, waterlogging, temperature, and salinity treatments. This study provides important information for different expression patterns of stress-responsive HD-Zip and may contribute to the better understanding of the different responses of plants to biotic and abiotic stresses, and provide a molecular basis for the cultivation of resistant varieties of R. glutinosa.

Effects of Volatile Organic Compounds on Biofilms and Swimming Motility of Agrobacterium tumefaciens.

Volatile organic compounds (VOCs) emitted by bacteria play an important role in the interaction between microorganisms and other organisms. They can inhibit the growth of phytopathogenic microorganisms, modulate plant growth, and serve as infochemicals. Here, we investigated the effects of ketones, alcohols, and terpenes on the colony biofilms of plant pathogenic Agrobacterium tumefaciens strains and swimming motility, which can play an important role in the formation of biofilms. It was shown that 2-octanone had the greatest inhibitory effect on biofilm formation, acting in a small amount (38.7 g/m3). Ketone 2-butanone and unsaturated ketone β-ionone reduced the formation of biofilms at higher doses (145.2–580.6 and 387.1–1548.3 g/m3, respectively, up to 2.5–5 times). Isoamyl alcohol and 2-phenylethanol decreased the formation of biofilms at doses of 88.7 and 122.9 g/m3 by 1.7 and 5 times, respectively, with an increased effect at 177.4 and 245.9 g/m3, respectively. The agrobacteria cells in mature biofilms were more resistant to the action of ketones and alcohols. These VOCs also suppressed the swimming motility of agrobacteria; the radius of swimming zones decreased ~from 2 to 5 times. Terpenes (−)-limonene and (+)-α-pinene had no significant influence on the colony biofilms and swimming motility at the doses used. The results obtained represent new information about the effect of VOCs on biofilms and the motility of bacteria.

Siderophores, a potential phosphate solubilizer from the endophyte Streptomyces sp. CoT10, improved phosphorus mobilization for host plant growth and rhizosphere modulation

Available phosphorus (AP) deficiency in soil is an important limiting factor in agricultural and forestry production. Thus, microbes with high P mobilization capacity are of great concern, especially for acidic soil where most P is fixed by Fe. Camellia oleifera is a typical acidic soil–planted oil crop with a high status in forestry economic systems in China. In this study, Streptomyces sp. CoT10 was screened and identified from C. oleifera endophytes. CoT10 could effectively mobilize different P resources, particularly showing a high solubility of 72.49 mg L−1 for FePO4, and was prominent in the production of different siderophores. Here, we initially assumed and confirmed that the Fe–P mobilization function of CoT10 was directly mediated by its siderophores. Application of CoT10 in C. oleifera could benefit P fraction transformation by mobilizing insoluble P and Fe, thus improving 15.35% AP content in soil and promoting plant growth with high P and Fe acquisition. In addition, CoT10 inoculation improved microbial diversity, with the proportions of some dominant groups, such as Actinobacteria, Proteobacteria, and Firmicutes, obviously enriched by 21.32%, 7.93%, and 38.95%, respectively. In addition, redundancy analysis (RDA), network analysis and functional prediction indicated that CoT10 inoculation improved the microbial interactions in C. oleifera rhizosphere soil and balanced the soil microbial P- and Fe-related functional roles. The results of Streptomyces sp. CoT10 and its siderophores provide a valuable approach to regulate P mobilization in iron-rich soil for the sustainable and eco-friendly development of plant-related industries.