Auxin Production Research Articles

Comparative Coexpression Analysis of Indole Synthase and Tryptophan Synthase A Reveals the Independent Production of Auxin via the Cytosolic Free Indole.

Indole synthase (INS), a homologous cytosolic enzyme of the plastidal tryptophan synthase A (TSA), has been reported as the first enzyme in the tryptophan-independent pathway of auxin synthesis. This suggestion was challenged as INS or its free indole product may interact with tryptophan synthase B (TSB) and, therefore, with the tryptophan-dependent pathway. Thus, the main aim of this research was to find out whether INS is involved in the tryptophan-dependent or independent pathway. The gene coexpression approach is widely recognized as an efficient tool to uncover functionally related genes. Coexpression data presented here were supported by both RNAseq and microarray platforms and, hence, considered reliable. Coexpression meta-analyses of Arabidopsis genome was implemented to compare between the coexpression of TSA and INS with all genes involved in the production of tryptophan via the chorismate pathway. Tryptophan synthase A was found to be coexpressed strongly with TSB1/2, anthranilate synthase A1/B1, phosphoribosyl anthranilate transferase1, as well as indole-3-glycerol phosphate synthase1. However, INS was not found to be coexpressed with any target genes suggesting that it may exclusively and independently be involved in the tryptophan-independent pathway. Additionally, annotation of examined genes as ubiquitous or differentially expressed were described and subunits-encoded genes available for the assembly of tryptophan and anthranilate synthase complex were suggested. The most probable TSB subunits expected to interact with TSA is TSB1 then TSB2. Whereas TSB3 is only used under limited hormone conditions to assemble tryptophan synthase complex, putative TSB4 is not expected to be involved in the plastidial synthesis of tryptophan in Arabidopsis.

Beneficial effects of selected rhizospheric and endophytic bacteria, inoculated individually or in combination, on non-native host plant development

Plant beneficial bacteria have been traditionally inoculated as unique strains, although combining bacteria with complementary traits could maximize their positive effect on plant growth and development. Our objective was to elaborate consortia from selected rhizospheric and endophytic bacteria with antifungal and plant growth promoting properties, and evaluate their beneficial effects on the growth of Physalis ixocarpa, an annual native Mexican species of horticultural importance. Bacterial strains were selected based on their antifungal activity against Fusarium spp. through in vitro antagonism assays. Characterization of the profile of volatile organic compounds (VOC) of newly-identified endophytic strains able to significantly inhibit Fusarium spp. evidenced the presence of sulfur compounds and ketones, reported for their antifungal activity. Seven bacterial strains were able to solubilize phosphate on NBRIP medium. Their capacity to promote the growth of A. thaliana in vitro was further tested. All stains stimulated the formation of lateral roots and root hairs, and enhanced A. thaliana biomass, most likely through auxin production. Twelve consortia were elaborated from rhizospheric and root endophytic bacteria, and the effects of consortia and individual strain inoculation on the growth and development of P. ixocarpa were evaluated in a greenhouse trial. Rhizobacterial strains A8a and 5911, and consortia formed by A8a + B3R7 and SO + B3R7 (all belonging to the Bacillus genus) showed the best results in terms of growth promotion and floral onset, with increases in plant height by up to 45% and flowering beginning 30 days before than in the Control. Our results confirm the potential of combining rhizospheric and endophytic bacteria with multiple beneficial traits for enhancing plant development and suggest that the most promising bacterial treatments could be applied to avocado trees, their natural host, to foster their productivity.

Improved growth and quality of saffron (Crocus sativus L.) in the field conditions through inoculation with selected native plant growth-promoting rhizobacteria (PGPR)

The use of bioresources such as bio-fertilizers especially those containing plant growth promoting rhizobacteria (PGPR), may be a strategy for sustainable agriculture that respects the environment while ensuring optimal plant growth. The objective of this study was to investigate the effects of selected PGPR strains on the growth, yield and quality of saffron. The bacteria tested were isolated from the saffron rhizosphere and selected for important plant beneficial activities (phosphate solubilization, siderophore, and auxin production). The best strains were identified by 16S rRNA gene sequence analysis. Strains S11P1 and S11A1a were identified as Rahnella aquatilis, while strain S12S4 belonged to the species Variovorax paradoxus. An inoculation field experiment was conducted in a 1575 m2 field area in Taliouine (Morocco). Four different inoculants were set-up: the three single selected strains and their mixture. Using the PGPR isolates as inoculum affects positively different saffron plant parameters, such as the number of leaves (28.87 ± 6.1 vs. 22.47 ± 8.19 for control treatment) and chlorophyll content. Underground parts, in particular, daughter corms production was significantly increased about 1.91 times more than the control. In addition, the quality of inoculated saffron was in accordance with the category I specifications (Crocin > 200, Picrocrocin > 70 and Safaranal >20). Overall these results bode well the possibility of using these rhizobacteria, and specially the treatment T2 (Rahnella aquatilis S11P1), as effective biofertilizers for saffron organic cultivation.

Potential of Halophytes-Associated Microbes for the Phytoremediation of Metal-Polluted Saline Soils

Saline ecosystems are often the target of spills and releases of pollutants such as metals, as many industrial companies settle in or around these areas. Metal pollution is a major threat for humans and ecosystems. In line with sustainable development, nature-based solutions and biological tools such as phytoremediation offer eco-friendly and low-cost solutions to remove metals or limit their spread in the environment. Many plant-growth-promoting (PGP) effects are frequently prospected in plant-associated microbes such as the production of auxins, siderophores, or extracellular polymeric substances to enhance phytoremediation. Halophytes are nowadays presented as good phytoremediators for metal-contaminated saline environments such as coastal regions, but little is known about the potential of their associated microbes in the bioaugmentation of this technique. Here, we review the studies that focused on halophytes-associated microbes and their plant-growth-promotion capacities. Moreover, we discuss the limitation and applicability of bioaugmented phytoremediation in saline ecosystems.

Strain Streptomyces sp. P-56 Produces Nonactin and Possesses Insecticidal, Acaricidal, Antimicrobial and Plant Growth-Promoting Traits

Streptomycetes produce a huge variety of bioactive metabolites, including antibiotics, enzyme inhibitors, pesticides and herbicides, which offer promise for applications in agriculture as plant protection and plant growth-promoting products. The aim of this report was to characterize the biological activities of strain Streptomyces sp. P-56, previously isolated from soil as an insecticidal bacterium. The metabolic complex was obtained from liquid culture of Streptomyces sp. P-56 as dried ethanol extract (DEE) and possessed insecticidal activity against vetch aphid (Medoura viciae Buckt.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), pea aphid (Acyrthosiphon pisum Harr.) and crescent-marked lily aphid (Neomyzus circumflexus Buckt.), as well as two-spotted spider mite (Tetranychus urticae). Insecticidal activity was associated with production of nonactin, which was purified and identified using HPLC-MS and crystallographic techniques. Strain Streptomyces sp. P-56 also showed antibacterial and antifungal activity against various phytopathogenic bacteria and fungi (mostly for Clavibacfer michiganense, Alternaria solani and Sclerotinia libertiana), and possessed a set of plant growth-promoting traits, such as auxin production, ACC deaminase and phosphate solubilization. The possibilities for using this strain as a biopesticide producer and/or biocontrol and a plant growth-promoting microorganism are discussed.

Mycobiota of Mexican Maize Landraces with Auxin-Producing Yeasts That Improve Plant Growth and Root Development.

Compared to agrochemicals, bioinoculants based on plant microbiomes are a sustainable option for increasing crop yields and soil fertility. From the Mexican maize landrace "Raza cónico" (red and blue varieties), we identified yeasts and evaluated in vitro their ability to promote plant growth. Auxin production was detected from yeast isolates and confirmed using Arabidopsis thaliana plants. Inoculation tests were performed on maize, and morphological parameters were measured. Eighty-seven yeast strains were obtained (50 from blue corn and 37 from red corn). These were associated with three families of Ascomycota (Dothideaceae, Debaryomycetaceae, and Metschnikowiaceae) and five families of Basidiomycota (Sporidiobolaceae, Filobasidiaceae, Piskurozymaceae, Tremellaceae, and Rhynchogastremataceae), and, in turn, distributed in 10 genera (Clavispora, Rhodotorula, Papiliotrema, Candida, Suhomyces, Soliccocozyma, Saitozyma Holtermaniella, Naganishia, and Aeurobasidium). We identified strains that solubilized phosphate and produced siderophores, proteases, pectinases, and cellulases but did not produce amylases. Solicoccozyma sp. RY31, C. lusitaniae Y11, R. glutinis Y23, and Naganishia sp. Y52 produced auxins from L-Trp (11.9-52 µg/mL) and root exudates (1.3-22.5 µg/mL). Furthermore, they stimulated the root development of A. thaliana. Inoculation of auxin-producing yeasts caused a 1.5-fold increase in maize plant height, fresh weight, and root length compared to uninoculated controls. Overall, maize landraces harbor plant growth-promoting yeasts and have the potential for use as agricultural biofertilizers.

Waste valorization as low-cost media engineering for auxin production from the newly isolated Streptomyces rubrogriseus AW22: Model development

Indole-3-acetic acid (IAA) represents a crucial phytohormone regulating specific tropic responses in plants and functions as a chemical signal between plant hosts and their symbionts. The Actinobacteria strain of AW22 with high IAA production ability was isolated in Algeria for the first time and was characterized as Streptomyces rubrogriseus through chemotaxonomic analysis and 16 S rDNA sequence alignment. The suitable medium for a maximum IAA yield was engineered in vitro and in silico using machine learning-assisted modeling. The primary low-cost feedstocks comprised various concentrations of spent coffee grounds (SCGs) and carob bean grounds (CBGs) extracts. Further, we combined the Box-Behnken design from response surface methodology (BBD-RSM) with artificial neural networks (ANNs) coupled with the genetic algorithm (GA). The critical process parameters screened via Plackett-Burman design (PBD) served as BBD and ANN-GA inputs, with IAA yield as the output variable. Analysis of the putative IAA using thin-layer chromatography (TLC) and (HPLC) revealed Rf values equal to 0.69 and a retention time of 3.711 min, equivalent to the authentic IAA. AW 22 achieved a maximum IAA yield of 188.290 ± 0.38 μg/mL using the process parameters generated by the ANN-GA model, consisting of L-Trp, 0.6%; SCG, 30%; T°, 25.8 °C; and pH 9, after eight days of incubation. An R2 of 99.98%, adding to an MSE of 1.86 × 10−5 at 129 epochs, postulated higher reliability of ANN-GA-approach in predicting responses, compared with BBD-RSM modeling exhibiting an R2 of 76.28%. The validation experiments resulted in a 4.55-fold and 4.46-fold increase in IAA secretion, corresponding to ANN-GA and BBD-RSM models, respectively, confirming the validity of both models.

Early Fruit Development Regulation-Related Genes Concordantly Expressed with TCP Transcription Factors in Tomato (Solanum lycopersicum).

The tomato (Solanum lycopersicum L.) is considered one of the most important vegetable crops globally, both agronomically and economically; however, its fruit development regulation network is still unclear. The transcription factors serve as master regulators, activating many genes and/or metabolic pathways throughout the entire plant life cycle. In this study, we identified the transcription factors that are coordinated with TCP gene family regulation in early fruit development by making use of the high-throughput sequencing of RNA (RNAseq) technique. A total of 23 TCP-encoding genes were found to be regulated at various stages during the growth of the fruit. The expression patterns of five TCPs were consistent with those of other transcription factors and genes. There are two unique subgroups of this larger family: class I and class II TCPs. Others were directly associated with the growth and/or ripening of fruit, while others were involved in the production of the hormone auxin. Moreover, it was discovered that TCP18 had an expression pattern that was similar to that of the ethylene-responsive transcription factor 4 (ERF4). Tomato fruit set and overall development are under the direction of a gene called auxin response factor 5 (ARF5). TCP15 revealed an expression that was in sync with this gene. This study provides insight into the potential processes that help in acquiring superior fruit qualities by accelerating fruit growth and ripening.

Optimization of the growth conditions through response surface methodology and metabolomics for maximizing the auxin production by Pantoea agglomerans C1.

The fermentative production of auxin/indole 3-acetate (IAA) using selected Pantoea agglomerans strains can be a promising approach to developing novel plant biostimulants for agriculture use. By integrating metabolomics and fermentation technologies, this study aimed to define the optimal culture conditions to obtain auxin/IAA-enriched plant postbiotics using P. agglomerans strain C1. Metabolomics analysis allowed us to demonstrate that the production of a selected. Array of compounds with plant growth-promoting- (IAA and hypoxanthine) and biocontrol activity (NS-5, cyclohexanone, homo-L-arginine, methyl hexadecenoic acid, and indole-3-carbinol) can be stimulated by cultivating this strain on minimal saline medium amended with sucrose as a carbon source. We applied a three-level-two-factor central composite design (CCD) based response surface methodology (RSM) to explore the impact of the independent variables (rotation speed and medium liquid-to-flask volume ratio) on the production of IAA and IAA precursors. The ANOVA component of the CCD indicated that all the process-independent variables investigated significantly impacted the auxin/IAA production by P. agglomerans strain C1. The optimum values of variables were a rotation speed of 180 rpm and a medium liquid-to-flask volume ratio of 1:10. Using the CCD-RSM method, we obtained a maximum indole auxin production of 208.3 ± 0.4 mg IAAequ/L, which was a 40% increase compared to the growth conditions used in previous studies. Targeted metabolomics allowed us to demonstrate that the IAA product selectivity and the accumulation of the IAA precursor indole-3-pyruvic acid were significantly affected by the increase in the rotation speed and the aeration efficiency.

Protist–Lactic Acid Bacteria Co-Culture as a Strategy to Bioaccumulate Polyunsaturated Fatty Acids in the Protist Aurantiochytrium sp. T66

Thraustochytrids are aquatic unicellular protists organisms that represent an important reservoir of a wide range of bioactive compounds, such as essential polyunsaturated fatty acids (PUFAs) such as arachidonic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), which are involved in the regulation of the immune system. In this study, we explore the use of co-cultures of Aurantiochytrium sp. and bacteria as a biotechnological tool capable of stimulating PUFA bioaccumulation. In particular, the co-culture of lactic acid bacteria and the protist Aurantiochytrium sp. T66 induce PUFA bioaccumulation, and the lipid profile was evaluated in cultures at different inoculation times, with two different strains of lactic acid bacteria capable of producing the tryptophan dependent auxins, and one strain of Azospirillum sp., as a reference for auxin production. Our results showed that the Lentilactobacillus kefiri K6.10 strain inoculated at 72 h gives the best PUFA content (30.89 mg g-1 biomass) measured at 144 h of culture, three times higher than the control (8.87 mg g-1 biomass). Co-culture can lead to the generation of complex biomasses with higher added value for developing aquafeed supplements.

Study of Phosphate Solubilizing Fluorescent Pseudomonas Recovered from Rhizosphere and Endorhizosphere of Aloe barbadensis (L.)

Phosphorus (P) is a key nutrient required by plants for their growth and development. A large part of applied phosphatic fertilizer becomes unavailable due to its fixation in soil. In rhizosphere, fluorescent Pseudomonads are instrumental in phosphate solubilization. We isolated Pseudomonads from the rhizosphere of Aloe barbadensis (L.), and screened them for their plant growth promoting ability such as - solubilization of phosphate, auxin production and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. A total of 307 fluorescent Pseudomonas were isolated and screened, of which, 24 isolates showed a strong phosphate solubilizing ability, ranging from 69.71 to 236.73 µg ml−1 . The Indole acetic acid (IAA) production by all 24 isolates varied from 28.44 to 151.99 µg ml−1. However, 17 isolates produced ACC-deaminase ranging from 8.19 to 10.27 µmol mg−1 h−1. Analyses of 16S rRNA gene and Pseudomonas-specific genes grouped the isolates in seven different species of fluorescent Pseudomonas. Genotypic analysis based on 16S rDNA-RFLP using restriction enzymes (HaeIII, AluI and MspI) and BOX-PCR generated unique genotype specific pattern. The results suggested that Pseudomonas diversity has no association with microenvironments and the sampling site of the plants. 16S rRNA gene-based diversity indices revealed great diversity among the fluorescent Pseudomonas recovered from the rhizospheric regions of the Aloe. Due to the above plant growth-promoting traits, fluorescent Pseudomonas can be exploited as bio-inoculants for crops, with minimal damage to the environment.

Co-Inoculation of Endophytes Bacillus siamensis TUR07-02b and Priestia megaterium SMBH14-02 Promotes Growth in Rice with Low Doses of Nitrogen Fertilizer.

Multiple biotic and abiotic factors influence rice cultivation. These factors limit productivity and yield, as well as an irrational use of agrochemicals in rice cultivation. A sustainable alternative is using selected growth-promoting microorganisms to increase nutritional efficiency. In the present study, the direct mechanisms of growth promotion in two strains of Bacillus, three strains of Priestia, and two strains of Burkholderia endophytes of rice were characterized. Bacillus siamensis TUR07-02b and Priestia megaterium SMBH14-02 were selected to promote Oryza sativa var's growth. "Bellavista" was used at different doses (50, 75, and 100%) of mineral nitrogen (N) using a randomized block design by quintuplicate. Both strains, SMBH14-02 and TUR07-02b, presented outstanding promoter characteristics, including auxin production (123.17 and 335.65 μg mL-1, respectively) and biological nitrogen fixation capacity. Similarly, B. siamensis TUR07-02b could solubilize phosphate-Ca (20.94 μg mL-1), cellulases, and pectinases. Under greenhouse conditions, co-inoculated plants receiving 75% of the total dose of mineral nitrogen showed increased agronomic parameters in relation to panicle length, grains per panicle, grain yield, and harvest index by 25.0, 30.7, 39.5, and 12.5%, respectively, compared to the 75% fertilized treatment without inoculation. The strains of B. siamensis TUR07-02b and P. megaterium SMBH14-02 are potential microbial resources in the formulation of new inoculants to reduce the use of nitrogenous fertilizers. Thus, agronomic validation of the inoculant consortium at the field level will be an essential step in providing an alternative for the sustainable management of rice cultivation and increased productivity of rice farmers in the San Martín region.

Draft Genome Sequences of Four Plant Growth-Promoting Rhizobacteria Isolated from Saffron (Crocus sativus L.) Rhizosphere in Morocco.

We report the draft genome sequences of plant growth-promoting Rahnella perminowiae strain S11P1, Variovorax sp. strain S12S4, and Pseudomonas sp. strains S11A4 and S11P7, which were isolated from saffron (Crocus sativus L.) rhizosphere. Several genes were predicted to be involved in auxin production, phosphate solubilization, and other specialized functions in plant growth and defense.

The auxin signaling pathway contributes to phosphorus-mediated zinc homeostasis in maize

Although the interaction between P and Zn has long been recognized in plants, the physiological and molecular mechanisms underlying P and Zn interactions are poorly understood. We show here that P supply decreases the Zn concentration in maize shoots and roots. Compared to +P + Zn (addition of both P and Zn), +P-Zn reduced and -P-Zn increased the total length of 1° lateral roots (LRs). Under +P + Zn, both P and Zn concentrations were lower in the sl1 mutant roots than in wild-type (WT) maize roots, and P accumulation did not reduce the Zn concentration in ll1 mutant roots. Transcriptome profiling showed that the auxin signaling pathway contributed to P-mediated Zn homeostasis in maize. Auxin production and distribution were altered by changes in P and Zn supply. Cytosolic Zn co-localized with auxin accumulation under +P + Zn. Exogenous application of 1-NAA and L-Kyn altered the P-mediated root system architecture (RSA) under Zn deficiency. -P-Zn repressed the expression of miR167. Overexpression of ZmMIR167b increased the lengths of 1° LRs and the concentrations of P and Zn in maize. These results indicate that auxin-dependent RSA is important for P-mediated Zn homeostasis in maize.HighlightAuxin-dependent RSA is important for P-mediated Zn homeostasis in maize.

Superior Antioxidant Capacity and Auxin Production Promote Seedling Formation of Rice Seeds under Submergence Stress

Rice (Oryza sativa L.) is one of the most significant food crops worldwide. Flooding can significantly impact the survival and emergence of rice seedlings in the direct planting form of rice, leading to a loss of production. This work investigated the critical phase of rice seed germination to the seedling establishment under submergence stress. It also explored the underlying physiological and molecular processes of shoot and root submergence tolerance. Physiological and transcriptomic analysis of flood-tolerant varieties (LS273) and non-flood-tolerant varieties (ZZ39) were performed. Under submergence stress, LS273 showed longer roots, taller shoots than ZZ39, and lower levels of malondialdehyde and GSSG, but a greater level of GSH/GSSG. In response to stress induced by submersion, LS273 produces more auxin than ZZ39. Within shoots, 4285 DEGs specific to LS273 and 4389 DEGs specifics to ZZ39 were found using the RNA-seq technique. There were 3983 specific DEGs in LS273 and 3292 specific DEGs in ZZ39 in the roots. Antioxidants and plant growth hormones were primarily mentioned in the annotations for these DEGs. Overall, our research provides a thorough foundation for investigating the molecular network underlying shoots’ and roots’ resistance to submergence stress in rice seedlings, leading us to hypothesize that the resistance of flood-tolerant rice may be attributed to high levels of oxidation resistance and auxin accumulation.

Increasing Plant Health using Plant Growth Regulator from Rice Rhizobacteria

Plant health is a very important factor in the agriculture system. The presence of plant hormones such as Auxin, gibberellic acid, and siderophores with variation numbers in the plant gives different effects on plant health. Related to the environment rich with rhizobacteria, they have a unique function because rhizobacteria can produce a chemical compound known as Plant Growth Promoting Rhizobacteria (PGPR). The purpose of the research is to study the production of auxin, gibberellic acid, and siderophore from rice rhizobacteria as the source of potential hormones for plant growth. Ten rhizobacteria isolates have been isolated from the rice rhizosphere. They are potential candidates as biofertilizers and biopesticide agents. The hormone production from each isolate was tested by spectrophotometric methods: Auxin at a wavelength of 535 nm with Salkowski's reagent, gibberellic acid at 254 nm, and siderophores at 560 nm with Hardaway's reagent. The results showed the highest auxin hormone was obtained from isolate 10 (3.374 ppm), the highest gibberellic acid from isolate 4 (3.960 ppm), and the highest siderophores hormone from isolate 2 (2.910 ppm). The conclusion of the research is, plant growth regulator from rice rhizobacteria has the potential increasing plant health.

PGPR Mediated Fe-Biofortification of T. aestivum L

Introduction: Due to the high prevalence of Fe deficiency in human populations, especially in developing nations, increasing Fe concentration in cereal crops is a major global challenge. Biofortification of cereals such as wheat with Fe is an attractive approach that can significantly compensate for Fe malnutritionand human health issues. Under nutrient imbalance circumstances, bio-fertilizers have been reported to play a vital role in plant development. Aims/Objectives: The current study was designed to evaluate the potential of PGPR to be used as bio-fertilizers and appraised their capability to enhance plant growth, quality and nutrient content, in combination with Fe treatment to combat malnutrition. Methodology: PGPR were screened for auxin producing ability and biochemically characterized for various growth promoting attributes. Fe in various combinations with PGPR was applied in soil and as foliar spray to the plants. Various growth and biochemical parameters were recorded. Wheat leaves were subjected to atomic absorption spectrometric (AAS) analysis. Results: Five bacteria with maximum auxin production potential were selected as bio-fertilizers. 36% improvement in fresh weight was recorded in Pseudomonas sp.(FS2) inoculations in the presence of 100µg/ml Fe under laboratory conditions, whereas, in wire house setup, plants supplemented with Jeotgalicoccus aerolatus (Tr3)exhibitedremarkable elevation in sugar content 298% with 100µg/ml foliar application of Fe. Data obtained from AAS showed that plants treated with Burkholderia cepacia (FS1) and Proteus mirabilis (Pc3) exhibited 2.17 and 2.28 ppm Fe content as a result of soil and foliar spray of 200µg/ml Fe respectively. Conclusion: Foliar application of Fe along with bio-fertilizers has proven to be a practical approach to improve grain quality and Fe content. Hence, biofortification of cereal crops with micronutrients and bio-fertilizers can assure a sustainable, eco-friendly and cost-effective solution to cure malnutrition and food security in developing countries.

Isolation and Characterization of Plant Growth promoting Rhizobacteria from Bamboo Rhizosphere and Their Role in Plant Growth Promotion

Plant growth-promoting rhizobacteria (PGPR) are a group of root-associated bacteria that intimately interact with the plant roots and consequently enhance growth by extemporising nutrient retrieval or phytohormone production. We isolated and screened indigenous phosphate solubilising and auxinproducing PGPR from bamboo rhizosphere. 66 soil samples from bamboo (Bambusa nutans subsp. cupulata, B. balcooa and B. tulda) rhizospheres were collected from Dhanusha, Mahottari and Sarlahi districts, Nepal. 120 isolates of PGPR were obtained by serial dilution method in (PVK) agar and Luria Bertani agar. 92 out of 120 isolates of PGPR with the ability to solubilise phosphate were selected based on the halo colony ratio in PVK agar medium and auxin production in Luria Bertani agar. Among them, six isolates having high phosphate solubilising index and high production capacity of indole-3-acetic acid were further screened. Biochemical analysis revealed that these isolates belonged to the genus Pseudomonas. Phosphate solubilising index and indole-3- acetic acid production by six isolates ranged from 4.19±0.8 to 7.65±1.3, and IAA production ranged from 72.93±0.2 to 82.48±0.9µg/ml respectively. These isolates significantly increased shoot length (13.26±0.56cm), shoot fresh weight (16.26±1.02mg), shoot dry weight (10.56±0.09mg), root length (4.9±0.5cm), root fresh weight (7.56±1.05mg), root dry weight (3.21±0.01mg), and chlorophyll ‘a’ and chlrophyll‘b’ and carotenoid (2.16±0.01mg/g, 1.19±0.06mg/g and 0.92±0.01mg/g respectively) of B. nutans subsp. cupulata seedlings. This study suggests that PGPR isolated from bamboo rhizosphere demonstrated outstanding contribution to the growth promotion of seedlings of B. nutans subsp. cupulata as compared to negative control.

Wheat genome architecture influences interactions with phytobeneficial microbial functional groups in the rhizosphere.

Wheat has undergone a complex evolutionary history, which led to allopolyploidization and the hexaploid bread wheat Triticum aestivum. However, the significance of wheat genomic architecture for beneficial plant-microbe interactions is poorly understood, especially from a functional standpoint. In this study, we tested the hypothesis that wheat genomic architecture was an overriding factor determining root recruitment of microorganisms with particular plant-beneficial traits. We chose five wheat species representing genomic profiles AA (Triticum urartu), BB {SS} (Aegilops speltoides), DD (Aegilops tauschii), AABB (Triticum dicoccon) and AABBDD (Triticum aestivum) and assessed by qPCR their ability to interact with free-nitrogen fixers, 1-aminocyclopropane-1-carboxylate deaminase producers, 2,4-diacetylphloroglucinol producers and auxin producers via the phenylpyruvate decarboxylase pathway, in combination with Illumina MiSeq metabarcoding analysis of N fixers (and of the total bacterial community). We found that the abundance of the microbial functional groups could fluctuate according to wheat genomic profile, as did the total bacterial abundance. N fixer diversity and total bacterial diversity were also influenced significantly by wheat genomic profile. Often, rather similar results were obtained for genomes DD (Ae. tauschii) and AABBDD (T. aestivum), pointing for the first time that the D genome could be particularly important for wheat-bacteria interactions. This article is protected by copyright. All rights reserved.

Molecular identification and characterization of phytobeneficial osmotolerant endophytic bacteria inhabiting root nodules of the Saharan tree Vachellia tortilis subsp. raddiana.

Nodular endophytes of drought-tolerant legumes are understudied. For this reason, we have isolated and studied non-symbiotic endophytic bacteria from nodules of Vachellia tortilis subsp. raddiana, a leguminous tree adapted to the harsh arid climate of Southern Morocco. Rep-PCR analysis followed by 16S rDNA sequencing revealed two main genera, Pseudomonas and Bacillus. Isolates responded variably to salt and water stresses, and mostly produced exopolysaccharides. Differences concerned also plant growth-promoting activities: phosphate, potassium, and zinc solubilization; biological nitrogen fixation; auxin, siderophore, ammonia, and HCN production; and ACC deaminase activity. Some strains exhibited antagonistic activities against phytopathogenic fungi (Fusarium oxysporum and Botrytis cinerea) and showed at least two enzymatic activities (cellulase, protease, chitinase). Four selected strains inoculated to vachellia plants under controlled conditions have shown significant positive impacts on plant growth parameters. These strains are promising bio-inoculants for vachellia plants to be used in reforestation programs in arid areas increasingly threatened by desertification.