Root exudates and rhizosphere microbiota in responding to long-term continuous cropping of tobacco.

Soil sickness a severe problem in tobacco production, leading to soil-borne diseases and reduce in tobacco yield. This occurs as a result of the interaction between root exudates and rhizosphere microorganisms, which is however, little studied until now. By combining the field investigation and pot experiment, we found the output yield consistently decreased during the first 10 years of continuous cropping in a tobacco field, but increased at the 15th year (15Y). The root exudate and rhizosphere bacterial community was further analyzed to reveal the underlying mechanism of the suppressive soil formation. Root exudate of 15Y tobacco enriched in amino acids and derivatives, while depleted in the typical autotoxins including phenolic acids and alkaloids. This was correlated to the low microbial diversity in 15Y, but also the changes in community composition and topological properties of the co-occurrence network. Especially, the reduced autotoxins were associated with low Actinobacteria abundance, low network complexity and high network modularity, which significantly correlated with the recovered output yield in 15Y. This study revealed the coevolution of rhizosphere microbiota and root exudate as the soil domesticated by continuous cropping of tobacco, and indicated a potential role of the autotoxins and theirs effect on the microbial community in the formation of suppressive soil.

Hydrolysis of riboflavins in root exudates under iron deficiency and alkaline stress.

Riboflavins are secreted under iron deficiency as a part of the iron acquisition Strategy I, mainly when the external pH is acidic. In plants growing under Fe-deficiency and alkaline conditions, riboflavins have been reported to accumulate inside the roots, with very low or negligible secretion. However, the fact that riboflavins may undergo hydrolysis under alkaline conditions has been so far disregarded. In this paper, we report the presence of riboflavin derivatives and products of their alkaline hydrolysis (lumichrome, lumiflavin and carboxymethylflavin) in nutrient solutions of Cucumis sativus plants grown under different iron regimes (soluble Fe-EDDHA in the nutrient solution, total absence of iron in the nutrient solution, or two different doses of FeSO4 supplied as a foliar spray), either cultivated in slightly acidic (pH 6) or alkaline (pH 8.8, 10 mM bicarbonate) nutrient solutions. The results show that root synthesis and exudation of riboflavins is controlled by shoot iron status, and that exuded riboflavins undergo hydrolysis, especially at alkaline pH, with lumichrome being the main product of hydrolysis.

The dissipation of organophosphate esters mediated by ryegrass root exudate oxalic acid in soil: Analysis of enzymes activities, microorganism.

Complex rhizoremediation is the main mechanism of phytoremediation in organic-contaminated soil. Low molecular weight organic acids (LMWOAs) in root exudates have been shown to increase the bioavailability of contaminants and are essential for promoting the dissipation of contaminants. The effects of root exudates on the dissipation of organophosphate esters (OPEs) in soil are unclear. Consequently, we studied the combined effects of root exudates, soil enzymes and microorganisms on OPEs (tri (1-chloro-2-propyl) phosphate (TCPP) and triphenyl phosphate (TPP)) dissipation through pot experiments. Oxalic acid (OA) was confirmed to be the main component of LMWOAs in root exudates of ryegrass. The existence of OA increased the dissipation rate of OPEs by 6.04%-25.50%. Catalase and dehydrogenase activities were firstly activated and then inhibited in soil. While, urease activity was activated and alkaline phosphatase activity was inhibited during the exposure period. More bacteria enrichment (e.g., Sphingomonas, Pseudomonas, Flavisolibacter, Pontibacter, Methylophilus and Massilia) improved the biodegradation of OPEs. In addition, the transformation paths of OPEs hydrolysis and methylation under the action of root exudates were observed. This study provided theoretical insights into reducing the pollution risk of OPEs in the soil.

Nitrogen and Nod factor signaling determine Lotus japonicus root exudate composition and bacterial assembly.

Symbiosis with soil-dwelling bacteria that fix atmospheric nitrogen allows legume plants to grow in nitrogen-depleted soil. Symbiosis impacts the assembly of root microbiota, but it is unknown how the interaction between the legume host and rhizobia impacts the remaining microbiota and whether it depends on nitrogen nutrition. Here, we use plant and bacterial mutants to address the role of Nod factor signaling on Lotus japonicus root microbiota assembly. We find that Nod factors are produced by symbionts to activate Nod factor signaling in the host and that this modulates the root exudate profile and the assembly of a symbiotic root microbiota. Lotus plants with different symbiotic abilities, grown in unfertilized or nitrate-supplemented soils, display three nitrogen-dependent nutritional states: starved, symbiotic, or inorganic. We find that root and rhizosphere microbiomes associated with these states differ in composition and connectivity, demonstrating that symbiosis and inorganic nitrogen impact the legume root microbiota differently. Finally, we demonstrate that selected bacterial genera characterizing state-dependent microbiomes have a high level of accurate prediction.

The genotype of barley cultivars influences multiple aspects of their associated microbiota via differential root exudate secretion.

Plant-associated microbes play vital roles in promoting plant growth and health, with plants secreting root exudates into the rhizosphere to attract beneficial microbes. Exudate composition defines the nature of microbial recruitment, with different plant species attracting distinct microbiota to enable optimal adaptation to the soil environment. To more closely examine the relationship between plant genotype and microbial recruitment, we analysed the rhizosphere microbiomes of landrace (Chevallier) and modern (NFC Tipple) barley (Hordeum vulgare) cultivars. Distinct differences were observed between the plant-associated microbiomes of the 2 cultivars, with the plant-growth promoting rhizobacterial genus Pseudomonas substantially more abundant in the Tipple rhizosphere. Striking differences were also observed between the phenotypes of recruited Pseudomonas populations, alongside distinct genotypic clustering by cultivar. Cultivar-driven Pseudomonas selection was driven by root exudate composition, with the greater abundance of hexose sugars secreted from Tipple roots attracting microbes better adapted to growth on these metabolites and vice versa. Cultivar-driven selection also operates at the molecular level, with both gene expression and the abundance of ecologically relevant loci differing between Tipple and Chevallier Pseudomonas isolates. Finally, cultivar-driven selection is important for plant health, with both cultivars showing a distinct preference for microbes selected by their genetic siblings in rhizosphere transplantation assays.

Impacts of continuous cropping on the rhizospheric and endospheric microbial communities and root exudates of Astragalus mongholicus.

Astragalus mongholicus is a medicinal plant that is known to decrease in quality in response to continuous cropping. However, the differences in the root-associated microbiome and root exudates in the rhizosphere soil that may lead to these decreases are barely under studies. We investigated the plant biomass production, root-associated microbiota, and root exudates of A. mongholicus grown in two different fields: virgin soil (Field I) and in a long-term continuous cropping field (Field II). Virgin soil is soil that has never been cultivated for A. mongholicus. Plant physiological measurements showed reduced fresh and dry weight of A. mongholicus under continuous cropping conditions (i.e. Field II). High-throughput sequencing of the fungal and bacterial communities revealed differences in fungal diversity between samples from the two fields, including enrichment of potentially pathogenic fungi in the roots of A. mongholicus grown in Field II. Metabolomic analysis yielded 20 compounds in A. mongholicus root exudates that differed in relative abundance between rhizosphere samples from the two fields. Four of these metabolites (2-aminophenol, quinic acid, tartaric acid, and maleamate) inhibited the growth of A. mongholicus, the soil-borne pathogen Fusarium oxysporum, or both. This comprehensive analysis enhances our understanding of the A. mongholicus microbiome, root exudates, and interactions between the two in response to continuous cropping. These results offer new information for future design of effective, economical approaches to achieving food security.

Plant seedlings of peas, tomatoes, and cucumbers exude compounds that are needed for growth and chemoattraction of Rhizobium leguminosarum bv. viciae 3841 and Azospirillum brasilense Sp7.

This study characterizes seedling exudates of peas, tomatoes, and cucumbers at the level of chemical composition and functionality. A plant experiment confirmed that Rhizobium leguminosarum bv. viciae 3841 enhanced growth of pea shoots, while Azospirillum brasilense Sp7 supported growth of pea, tomato, and cucumber roots. Chemical analysis of exudates after 1 day of seedling incubation in water yielded differences between the exudates of the three plants. Most remarkably, cucumber seedling exudate did not contain detectable sugars. All exudates contained amino acids, nucleobases/nucleosides, and organic acids, among other compounds. Cucumber seedling exudate contained reduced glutathione. Migration on semi solid agar plates containing individual exudate compounds as putative chemoattractants revealed that R. leguminosarum bv. viciae was more selective than A. brasilense, which migrated towards any of the compounds tested. Migration on semi solid agar plates containing 1:1 dilutions of seedling exudate was observed for each of the combinations of bacteria and exudates tested. Likewise, R. leguminosarum bv. viciae and A. brasilense grew on each of the three seedling exudates, though at varying growth rates. We conclude that the seedling exudates of peas, tomatoes, and cucumbers contain everything that is needed for their symbiotic bacteria to migrate and grow on.

Elucidating the significant roles of root exudates in organic pollutant biotransformation within the rhizosphere.

Biotransformation of organic pollutants is crucial for the dissipation of environmental pollutants. While the roles of microorganisms have been extensively studied, the significant contribution of various root exudates are still not very well understood. Through plant growth experiment, coupled with gas and liquid chromatography-mass spectrometry methods, this study examined the effect of the presence of M. sativa on microbial-associated biochemical transformation of petroleum hydrocarbons. The results of this study revealed that the concentration of exudates within the soil matrix is a function of proximity to root surfaces. Similarly, biodegradation was found to correlate with distance from roots, ranging from ≥ 90% within the rhizosphere to < 50% in bulk soil and unplanted control soil. Most importantly, for the first time in a study of an entire petroleum distillate, this study revealed a statistically significant negative correlation between root exudate concentration and residual total petroleum hydrocarbons. While not all the compounds that may influence biodegradation are derived from roots, the results of this study show that the presence of plant can significantly influence biodegradation of hydrocarbon pollutants through such root exudation as organic acids, amino acids, soluble sugars and terpenoids. Therefore, root exudates, including secondary metabolites, offer great prospects for biotechnological applications in the remediation of organic pollutants, including recalcitrant ones.

Harnessing root exudates for plant microbiome engineering and stress resistance in plants.

A wide range of abiotic and biotic stresses adversely affect plant's growth and production. Under stress, one of the main responses of plants is the modulation of exudates excreted in the rhizosphere, which consequently leads to alterations in the resident microbiota. Thus, the exudates discharged into the rhizospheric environment play a preponderant role in the association and formation of plant-microbe interactions. In this review, we aimed to provide a synthesis of the latest and most pertinent literature on the diverse biochemical and structural compositions of plant root exudates. Also, this work investigates into their multifaceted role in microbial nutrition and intricate signaling processes within the rhizosphere, which includes quorum-sensing molecules. Specifically, it explores the contributions of low molecular weight compounds, such as carbohydrates, phenolics, organic acids, amino acids, and secondary metabolites, as well as the significance of high molecular weight compounds, including proteins and polysaccharides. It also discusses the state-of-the-art omics strategies that unveil the vital role of root exudates in plant-microbiome interactions, including defense against pathogens like nematodes and fungi. We propose multiple challenges and perspectives, including exploiting plant root exudates for host-mediated microbiome engineering. In this discourse, root exudates and their derived interactions with the rhizospheric microbiota should receive greater attention due to their positive influence on plant health and stress mitigation.

Listening to plant's Esperanto via root exudates: reprogramming the functional expression of plant growth-promoting rhizobacteria.

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.

The core metabolome and root exudation dynamics of three phylogenetically distinct plant species.

Root exudates are plant-derived, exported metabolites likely shaping root-associated microbiomes by acting as nutrients and signals. However, root exudation dynamics are unclear and thus also, if changes in exudation are reflected in changes in microbiome structure. Here, we assess commonalities and differences between exudates of different plant species, diurnal exudation dynamics, as well as the accompanying methodological aspects of exudate sampling. We find that exudates should be collected for hours rather than days as many metabolite abundances saturate over time. Plant growth in sterile, nonsterile, or sugar-supplemented environments significantly alters exudate profiles. A comparison of Arabidopsis thaliana, Brachypodium distachyon, and Medicago truncatula shoot, root, and root exudate metabolite profiles reveals clear differences between these species, but also a core metabolome for tissues and exudates. Exudate profiles also exhibit a diurnal signature. These findings add to the methodological and conceptual groundwork for future exudate studies to improve understanding of plant-microbe interactions.

Plant growth strategy determines the magnitude and direction of drought-induced changes in root exudates in subtropical forests.

Root exudates are an important pathway for plant-microbial interactions and are highly sensitive to climate change. However, how extreme drought affects root exudates and the main components, as well as species-specific differences in response magnitude and direction, are poorly understood. In this study, root exudation rates of total carbon (C) and its components (e.g., sugar, organic acid, and amino acid) were measured under the control and extreme drought treatments (i.e., 70% throughfall reduction) by in situ collection of four tree species with different growth rates in a subtropical forest. We also quantified soil properties, root morphological traits, and mycorrhizal infection rates to examine the driving factors underlying variations in root exudation. Our results showed that extreme drought significantly decreased root exudation rates of total C, sugar, and amino acid by 17.8%, 30.8%, and 35.0%, respectively, but increased root exudation rate of organic acid by 38.6%, which were largely associated with drought-induced changes in tree growth rates, root morphological traits, and mycorrhizal infection rates. Specifically, trees with relatively high growth rates were more responsive to drought for root exudation rates compared with those with relatively low growth rates, which were closely related to root morphological traits and mycorrhizal infection rates. These findings highlight the importance of plant growth strategy in mediating drought-induced changes in root exudation rates. The coordinations among root exudation rates, root morphological traits, and mycorrhizal symbioses in response to drought could be incorporated into land surface models to improve the prediction of climate change impacts on rhizosphere C dynamics in forest ecosystems.

Wild Wheat Rhizosphere-Associated Plant Growth-Promoting Bacteria Exudates: Effect on Root Development in Modern Wheat and Composition.

Diazotrophic bacteria isolated from the rhizosphere of a wild wheat ancestor, grown from its refuge area in the Fertile Crescent, were found to be efficient Plant Growth-Promoting Rhizobacteria (PGPR), upon interaction with an elite wheat cultivar. In nitrogen-starved plants, they increased the amount of nitrogen in the seed crop (per plant) by about twofold. A bacterial growth medium was developed to investigate the effects of bacterial exudates on root development in the elite cultivar, and to analyze the exo-metabolomes and exo-proteomes. Altered root development was observed, with distinct responses depending on the strain, for instance, with respect to root hair development. A first conclusion from these results is that the ability of wheat to establish effective beneficial interactions with PGPRs does not appear to have undergone systematic deep reprogramming during domestication. Exo-metabolome analysis revealed a complex set of secondary metabolites, including nutrient ion chelators, cyclopeptides that could act as phytohormone mimetics, and quorum sensing molecules having inter-kingdom signaling properties. The exo-proteome-comprised strain-specific enzymes, and structural proteins belonging to outer-membrane vesicles, are likely to sequester metabolites in their lumen. Thus, the methodological processes we have developed to collect and analyze bacterial exudates have revealed that PGPRs constitutively exude a highly complex set of metabolites; this is likely to allow numerous mechanisms to simultaneously contribute to plant growth promotion, and thereby to also broaden the spectra of plant genotypes (species and accessions/cultivars) with which beneficial interactions can occur.

In Situ Detection of Amino Acids from Bacterial Biofilms and Plant Root Exudates by Liquid Microjunction Surface-Sampling Probe Mass Spectrometry.

The plant rhizosphere is a complex and dynamic chemical environment where the exchange of molecular signals between plants, microbes, and fungi drives the development of the entire biological system. Exogenous compounds in the rhizosphere are known to affect plant-microbe organization, interactions between organisms, and ultimately, growth and survivability. The function of exogenous compounds in the rhizosphere is still under much investigation, specifically with respect to their roles in plant growth and development, the assembly of the associated microbial community, and the spatiotemporal distribution of molecular components. A major challenge for spatiotemporal measurements is developing a nondisruptive and nondestructive technique capable of analyzing the exogenous compounds contained within the environment. A methodology using liquid microjunction-surface sampling probe-mass spectrometry (LMJ-SSP-MS) and microfluidic devices with attached microporous membranes was developed for in situ, spatiotemporal measurement of amino acids (AAs) from bacterial biofilms and plant roots. Exuded arginine was measured from a living Pantoea YR343 biofilm, which resulted in a chemical image indicative of biofilm growth within the device. Spot sampling along the roots of Populus trichocarpa with the LMJ-SSP-MS resulted in the detection of 15 AAs. Variation in AA concentrations across the root system was observed, indicating that exudation is not homogeneous and may be linked to local rhizosphere architecture and different biological processes along the root.

Time point- and plant part-specific changes in phloem exudate metabolites of leaves and ears of wheat in response to drought and effects on aphids.

Alterations in the frequency and intensity of drought events are expected due to climate change and might have consequences for plant metabolism and the development of plant antagonists. In this study, the responses of spring wheat (Triticum aestivum) and one of its major pests, the aphid Sitobion avenae, to different drought regimes were investigated, considering different time points and plant parts. Plants were kept well-watered or subjected to either continuous or pulsed drought. Phloem exudates were collected twice from leaves and once from ears during the growth period and concentrations of amino acids, organic acids and sugars were determined. Population growth and survival of the aphid S. avenae were monitored on these plant parts. Relative concentrations of metabolites in the phloem exudates varied with the time point, the plant part as well as the irrigation regime. Pronounced increases in relative concentrations were found for proline, especially in pulsed drought-stressed plants. Moreover, relative concentrations of sucrose were lower in phloem exudates of ears than in those of leaves. The population growth and survival of aphids were decreased on plants subjected to drought and populations grew twice as large on ears compared to leaves. Our study revealed that changes in irrigation frequency and intensity modulate plant-aphid interactions. These effects may at least partly be mediated by changes in the metabolic composition of the phloem sap.

Microbial consortium inoculant increases pasture grasses yield in low-phosphorus soil by influencing root morphology, rhizosphere carboxylate exudation and mycorrhizal colonisation.

BACKGROUND: Pasture farming in south-western Australia is challenged by nutrient-poor soils. We assessed the impact of microbial consortium inoculant (MI) and rock mineral fertiliser (MF) on growth, nutrient uptake, root morphology, rhizosphere carboxylate exudation and mycorrhizal colonisation in three pasture grasses - tall fescue (Festuca arundinacea L.), veldt grass (Ehrharta calycina Sm.) and tall wheatgrass (Thinopyrum ponticum L.) grown in low-phosphorus (P) sandy soil in a glasshouse for 30 and 60 days after sowing (DAS). RESULTS: Veldt grass produced the highest specific root length and smallest average root diameter in both growth periods, and had similar shoot weight, root surface area and fine root length (except at 30 DAS) to tall fescue. Compared with the control, MI alone or combined with MF significantly increased shoot and root biomass (except root biomass at 30 DAS), likely due to the significant increases in root surface area and fine root length. Plants supplied with MI + MF had higher shoot N and P contents than those in the MI and the control treatments at 60 DAS. Malate, citrate and trans-aconitate were the major rhizosphere carboxylates exuded at both 30 and 60 DAS. Malate exudation varied among species and treatments in both growth periods, but citrate exudation was consistently higher in the low-P treatments (control and MI) than the MF and MI + MF treatments. CONCLUSION: Microbial consortium inoculant can positively influence pasture production in low-P soil by increasing root surface area and fine root length, whereas exudation of nutrient-mobilising carboxylates (citrate) is dependent more on soil P supply than microbial consortium inoculant. © 2021 Society of Chemical Industry.

Surfactin Stimulated by Pectin Molecular Patterns and Root Exudates Acts as a Key Driver of the Bacillus-Plant Mutualistic Interaction.

Bacillus velezensis is considered as a model species belonging to the so-called Bacillus subtilis complex that evolved typically to dwell in the soil rhizosphere niche and establish an intimate association with plant roots. This bacterium provides protection to its natural host against diseases and represents one of the most promising biocontrol agents. However, the molecular basis of the cross talk that this bacterium establishes with its natural host has been poorly investigated. We show here that these plant-associated bacteria have evolved a polymer-sensing system to perceive their host and that, in response, they increase the production of the surfactin-type lipopeptide. Furthermore, we demonstrate that surfactin synthesis is favored upon growth on root exudates and that this lipopeptide is a key component used by the bacterium to optimize biofilm formation, motility, and early root colonization. In this specific nutritional context, the bacterium also modulates qualitatively the pattern of surfactin homologues coproduced in planta and forms mainly variants that are the most active at triggering plant immunity. Surfactin represents a shared good as it reinforces the defensive capacity of the host. IMPORTANCE Within the plant-associated microbiome, some bacterial species are of particular interest due to the disease protective effect they provide via direct pathogen suppression and/or stimulation of host immunity. While these biocontrol mechanisms are quite well characterized, we still poorly understand the molecular basis of the cross talk these beneficial bacteria initiate with their host. Here, we show that the model species Bacillus velezensis stimulates the production of the surfactin lipopeptide upon sensing pectin as a cell surface molecular pattern and upon feeding on root exudates. Surfactin favors bacterial rhizosphere fitness on one hand and primes the plant immune system on the other hand. Our data therefore illustrate how both partners use this multifunctional compound as a unique shared good to sustain a mutualistic interaction.

Manipulating exudate composition from root apices shapes the microbiome throughout the root system.

Certain soil microorganisms can improve plant growth, and practices that encourage their proliferation around the roots can boost production and reduce reliance on agrochemicals. The beneficial effects of the microbial inoculants currently used in agriculture are inconsistent or short-lived because their persistence in soil and on roots is often poor. A complementary approach could use root exudates to recruit beneficial microbes directly from the soil and encourage inoculant proliferation. However, it is unclear whether the release of common organic metabolites can alter the root microbiome in a consistent manner and if so, how those changes vary throughout the whole root system. In this study, we altered the expression of transporters from the ALUMINUM-ACTIVATED MALATE TRANSPORTER and the MULTIDRUG AND TOXIC COMPOUND EXTRUSION families in rice (Oryza sativa L.) and wheat (Triticum aestivum L.) and tested how the subsequent release of their substrates (simple organic anions, including malate, citrate, and γ-amino butyric acid) from root apices affected the root microbiomes. We demonstrate that these exudate compounds, separately and in combination, significantly altered microbiome composition throughout the root system. However, the root type (seminal or nodal), position along the roots (apex or base), and soil type had a greater influence on microbiome structure than the exudates. These results reveal that the root microbiomes of important cereal species can be manipulated by altering the composition of root exudates, and support ongoing attempts to improve plant production by manipulating the root microbiome.

Decoupling of Plant Growth and Accumulation of Biologically Active Compounds in Leaves, Roots, and Root Exudates of Hypericum perforatum L. by the Combination of Jasmonate and Far-Red Lighting.

The plant hormone jasmonic acid (JA) fine tunes the growth-defense dilemma by inhibiting plant growth and stimulating the accumulation of secondary compounds. We investigated the interactions between JA and phytochrome B signaling on growth and the accumulation of selected secondary metabolites in Hypericum perforatum L., a medically important plant, by spraying plants with methyl jasmonate (MeJA) and by adding far-red (FR) lighting. MeJA inhibited plant growth, decreased fructose concentration, and enhanced the accumulation of most secondary metabolites. FR enhanced plant growth and starch accumulation and did not decrease the accumulation of most secondary metabolites. MeJA and FR acted mostly independently with no observable interactions on plant growth or secondary metabolite levels. The accumulation of different compounds (e.g., hypericin, flavonols, flavan-3-ols, and phenolic acid) in shoots, roots, and root exudates showed different responses to the two treatments. These findings indicate that the relationship between growth and secondary compound accumulation is specific and depends on the classes of compounds and/or their organ location. The combined application of MeJA and FR enhanced the accumulation of most secondary compounds without compromising plant growth. Thus, the negative correlations between biomass and the content of secondary compounds predicted by the growth-defense dilemma were overcome.

Dehydrin MsDHN1 improves aluminum tolerance of alfalfa (Medicago sativa L.) by affecting oxalate exudation from root tips.

A SK3 -type dehydrin MsDHN1 was cloned from alfalfa (Medicago sativa L.). Its function and gene regulatory pathways were studied via overexpression and suppression of MsDHN1 in alfalfa seedlings or hairy roots. The results showed that MsDHN1 is a typical intrinsically disordered protein that exists in the form of monomers and homodimers in alfalfa. The plant growth rates increased as a result of MsDHN1 overexpression (MsDHN1-OE) and decreased upon MsDHN1 suppression (MsDHN1-RNAi) in seedlings or hairy roots of alfalfa compared with the wild-type or the vector line under Al stress. MsDHN1 interacting with aquaporin (AQP) MsPIP2;1 and MsTIP1;1 positively affected oxalate secretion from root tips and Al accumulation in root tips. MsABF2 was proven to be an upstream transcription factor of MsDHN1 and activated MsDHN1 expression by binding to the ABRE element of the MsDHN1 promoter. The transcriptional regulation of MsABF2 on MsDHN1 was dependent on the abscisic acid signaling pathway. These results indicate that MsDHN1 can increase alfalfa tolerance to Al stress via increasing oxalate secretion from root tips, which may involve in the interaction of MsDHN1 with two AQP.