Gibberellin Production Research Articles

Gibberellin-Dependent Pulp Pigmentation in CPPU-Induced Parthenocarpic Melon Fruit: Insights from Metabolome and Transcriptome Analysis

The plant growth regulator N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) is applied to induce parthenocarpic fruit setting in melon (Cucumis melo L.) production. However, CPPU-induced fruits frequently exhibit a decline in quality attributes, such as sucrose, aroma, and pigmentation, the mechanisms underlying these changes remain largely unclear. This research assessed the effects of CPPU application on carotenoid biosynthesis in the pulp during melon fruit development, aiming to elucidate the underlying mechanisms. Transcriptome and metabolome analyses were employed to examine changes in pigment and hormone levels in melon fruit at various developmental stages following CPPU treatment. The results indicated that CPPU application for fruit setting significantly reduced β-carotene content in the fruit pulp compared to fruits resulting from artificial pollination. Transcriptome analysis revealed a decrease in the expression of carotenoid biosynthesis genes (e.g., PSY1/2, Z-ISO, and LYCB), while the expression of catabolic enzyme genes (e.g., NCED5/6, NXS, and CCD4) were up-regulated following CPPU application. Metabolome analysis showed a decrease in gibberellin production during the development of CPPU-induced fruits compared to pollinated samples. Furthermore, exogenous gibberellin application recovered the pigment defects in the CPPU-induced parthenocarpic fruits. This study provides novel insights into how CPPU-induced parthenocarpy affects melon pulp pigmentation during development, offering valuable theoretical foundations for improving fruit set management in melon cultivation.

Is Pseudofrankia, the non-nitrogen-fixing and/or non-nodulating actinorhizal nodule dweller, mutualistic or parasitic? Insights from genome-predictive analysis.

This study re-evaluates Pseudofrankia strains, traditionally regarded as parasitic dwellers of actinorhizal root nodules due to their inability to fix nitrogen (Fix -) and/or nodulate (Nod -), as potential plant growth-promoting bacteria (PGPB). We compared plant growth-promoting traits (PGPTs) between Pseudofrankia strains, including one newly sequenced strain BMG5.37 in this study and typical (Fix + /Nod +) Frankia, Protofrankia, and Parafrankia, as well as non-frankia actinorhizal species Nocardia and Micromonospora, and the phytopathogenic Streptomyces. Although lacking nitrogen-fixing genes typically found in mutualistic Frankiaceae strains, Pseudofrankia may compensate through predicted pathways for denitrification and nitrate utilization. Functional profiling suggests potential for phosphorus solubilization, gibberellin production, and vitamin metabolism, as well as bioremediation of pollutants. Pseudofrankia strains are predicted to show moderate resistance to heavy metals, with a stronger tolerance to arsenic and tellurium compared to Frankia. Furthermore, they are anticipated to exhibit significant biotic and abiotic stress resistance, including oxidative and osmotic stress. Predictive data also indicate that Pseudofrankia strains may have root colonization abilities and may play a role in plant signaling and phytohormone production, particularly in auxin and gibberellin pathways. Secretion systems, especially CE-Type VI, are predicted to be highly developed in Pseudofrankia, suggesting potential for effective plant interactions. These findings position Pseudofrankia strains as promising candidates for plant growth promotion, although experimental validation and the integration of transcriptomic or proteomic data are needed to confirm these predictions.

Regulatory Mechanism of Exogenous ABA on Gibberellin Signaling and Antioxidant Responses in Rhododendron chrysanthum Pall. Under UV-B Stress.

In the present work, we examined the effects of exogenous abscisic acid (ABA) under ultraviolet B (UV-B) exposure on gibberellin (GA) production, signaling, and antioxidant-related genes in Rhododendron chrysanthum Pall (R. chrysanthum). Using transcriptomics, acetylated proteomics, and widely targeted metabolomics, the effects of UV-B stress on R. chrysanthum and the regulatory effects of exogenous ABA on it were revealed from multiple perspectives. The findings revealed that R. chrysanthum's antioxidant enzyme genes were differentially expressed by UV-B radiation and were substantially enriched in the glutathione metabolic pathway. Exogenous ABA supplementation boosted plant resistance to UV-B damage and further enhanced the expression of antioxidant enzyme genes. Furthermore, under UV-B stress, glutathione reductase, glutathione peroxidase, and L-ascorbate peroxidase were found to be the primary antioxidant enzymes controlled by exogenous ABA. In addition, gibberellin content was altered due to UV-B and exogenous ABA treatments, with greater effects on GA3 and GA53. The acetylation proteomics study's outcomes disclosed that the three main oxidative enzymes' acetylation modifications were dramatically changed during UV-B exposure, which may have an impact on the antioxidant enzymes' functions and activities. The protective impact of exogenous ABA and gibberellin on R. chrysanthum's photosynthetic system was further established by measuring the parameters of chlorophyll fluorescence. This research offers a theoretical foundation for the development of breeding highly resistant plant varieties as well as fresh insights into how hormone levels and antioxidant systems are regulated by plants in response to UV-B damage.

Biochemical and Molecular Identification of Azospirillum brasilense Bacteria and Evaluation of Their Efficiency in Producing Hormones, Dissolving Phosphorus, and Fixing Nitrogen

The study aimed to isolate A.brasilense bacteria from the soil of the rhizosphere of different plants and different locations in Al-Diwaniyah Governorate. They were identified in two ways. The first was the routine method, which included studying the microscopic and cultural characteristics and biochemical tests of the isolates. The second method was molecular, using polymerase chain reaction (PCR) technology and using primers. It also included testing the efficiency of these isolates in dissolving tricalcium phosphate (TCP) on Pikovskaya agar medium, fixing nitrogen in the liquid nutrient medium (N.B), and measuring the amount of hormone production using an HPLC device. The results of isolation and regular and molecular identification the presence of ten isolates of bacteria bearing the characteristics of A. brasilense bacteria, out of fifteen local bacterial isolates, took the following symbols and sequences (Az2, Az3, Az5, Az6, Az7, Az9, Az11, Az12, Az13, Az14), as the results showed confirmation of the identification of the bacterial isolates identified by biochemical tests. Using a specialized primer to amplify the 462bp fragment of the 16S ribosomal RNA gene, the results of testing the efficiency of the bacteria in dissolving phosphate (TCP) showed that the isolate (Az13) outperformed the highest value in its effectiveness in dissolving metallic phosphorus through the diameter of the clear zone around the colony, which was effective in dissolving phosphate of up to 3.89 mm. As for the nitrogen fixation efficiency test, the isolate (Az3) excelled in the amount of fixed nitrogen reaching 12.44 mg.L-1. As for the amount of its production of growth regulators for Auxins, Gibberellins, and Cytokinins, the isolate (Az3) recorded the highest value in the amount of Auxins production ( Indol-3-acetic acid) its concentration reached 34.4 µg.ml-1, and as for the production of the hormone Gibberellins (GA3), the isolate (Az3) recorded the highest value amounting to 34.7 µg.ml-1, as for the production of the hormone Cytokinins (CK), The isolate (Az11) recorded the highest value, amounting to 28.8 µg.ml-1.

The SINA1-BSD1 Module Regulates Vegetative Growth Involving Gibberellin Biosynthesis in Tomato.

In plants, vegetative growth is controlled by synergistic and/or antagonistic effects of many regulatory factors. Here, the authors demonstrate that the ubiquitin ligase seven in absentia1 (SINA1) mammalian BTF2-like transcription factors, Drosophila synapse-associated proteins, and yeast DOS2-like proteins (BSD1) function as a regulatory module to control vegetative growth in tomato via regulation of the production of plant growth hormone gibberellin (GA). SINA1 negatively regulates the protein level of BSD1 through ubiquitin-proteasome-mediated degradation, and the transgenic tomato over-expressing SINA1 (SINA1-OX) resembles the dwarfism phenotype of the BSD1-knockout (BSD1-KO) tomato plant. BSD1 directly activates expression of the BSD1-regulated gene 1 (BRG1) via binding to a novel core BBS (standing for BSD1 binding site) binding motif in the BRG1 promoter. Knockout of BRG1 (BRG1-KO) in tomato also results in a dwarfism phenotype, suggesting BRG1 plays a positive role in vegetative growth as BSD1 does. Significantly, GA contents are attenuated in transgenic SINA1-OX, BSD1-KO, and BRG1-KO plants exhibiting dwarfism phenotype and exogenous application of bioactive GA3 restores their vegetative growth. Moreover, BRG1 is required for the expression of multiple GA biosynthesis genes and BSD1 activates three GA biosynthesis genes promoting GA production. Thus, this study suggests that the SINA1-BSD1 module controls vegetative growth via direct and indirect regulation of GA biosynthesis in tomato.

GhHAM regulates GoPGF-dependent gland development and contributes to broad-spectrum pest resistance in cotton.

Cotton is a globally cultivated crop, producing 87% of the natural fiber used in the global textile industry. The pigment glands, unique to cotton and its relatives, serve as a defense structure against pests and pathogens. However, the molecular mechanism underlying gland formation and the specific role of pigment glands in cotton's pest defense are still not well understood. In this study, we cloned a gland-related transcription factor GhHAM and generated the GhHAM knockout mutant using CRISPR/Cas9. Phenotypic observations, transcriptome analysis, and promoter-binding experiments revealed that GhHAM binds to the promoter of GoPGF, regulating pigment gland formation in cotton's multiple organs via the GoPGF-GhJUB1 module. The knockout of GhHAM significantly reduced gossypol production and increased cotton's susceptibility to pests in the field. Feeding assays demonstrated that more than 80% of the cotton bollworm larvae preferred ghham over the wild type. Furthermore, the ghham mutants displayed shorter cell length and decreased gibberellins (GA) production in the stem. Exogenous application of GA3 restored stem cell elongation but not gland formation, thereby indicating that GhHAM controls gland morphogenesis independently of GA. Our study sheds light on the functional differentiation of HAM proteins among plant species, highlights the significant role of pigment glands in influencing pest feeding preference, and provides a theoretical basis for breeding pest-resistant cotton varieties to address the challenges posed by frequent outbreaks of pests.

Rhizobacteria Bacillus spp. mitigate osmotic stress and improve seed germination in mustard by regulating osmolyte and plant hormone signaling.

Drought, a widespread abiotic stressor, exerts a profound impact on agriculture, impeding germination and plant growth, and reducing crop yields. In the present investigation, the osmotolerant rhizobacteria Bacillus casamancensis strain MKS-6 and Bacillus sp. strain MRD-17 were assessed for their effects on molecular processes involved in mustard germination under osmotic stress conditions. Enhancement in germination was evidenced by improved germination percentages, plumule and radicle lengths, and seedling vigor upon rhizobacterial inoculation under no stress and osmotic stress conditions. Under osmotic stress, rhizobacteria stimulated the production of gibberellins and reserve hydrolytic enzymes (lipases, isocitrate lyase, and malate synthase), bolstering germination. Furthermore, these rhizobacteria influenced the plant hormones such as gibberellins and abscisic acid (ABA), as well as signalling pathways, thereby promoting germination under osmotic stress. Reduced proline and glycine betaine accumulation, and down-regulation of transcription factors BjDREB1_2 and BjDREB2 (linked to ABA-independent signalling) in rhizobacteria-inoculated seedlings indicated that bacterial treatment mitigated water deficit stress during germination, independently of these pathways. Hence, the advantageous attributes exhibited by these rhizobacterial strains can be effectively harnessed to alleviate drought-induced stress in mustard crops, potentially through the development of targeted bio-formulations.

Production of Gibberellins via a Non-Natural Pathway Using Steviol as a Substrate.

Gibberellins (GAs) are plant hormones widely used in agriculture. At present, GAs are produced by fermentation of the fungus Fusarium fujikuroi. However, fungal growth is too slow, resulting in slow fungal fermentation and a low yield. Here, to develop an alternative production source of GAs, an artificial pathway was engineered in Escherichia coli. By selecting and combining enzymes derived from plants and bacteria, a novel 4-enzyme pathway was successfully constructed to produce GAs using steviol, a readily available and less valuable byproduct during enzymatic refining of rebaudioside A, as a feedstock. Whole-cell biotransformation with E. coli strain expressing the novel pathway produced 71.17 ± 2.00 mg/L GA1 and a trace amount of GA3 from steviol in 48 h. This report presents a significant advancement in the fast production of GAs and establishes a method for the metabolism of terpenoids to produce target products in microbial hosts.

Study on gibberellin and gibberellin-like substances from endophytes and their effect on maize plants

Plant growth promoting endophytes were isolated from the roots of rice, sugarcane, corn, maize, sunflower and chili. The biochemical characterization of those isolated endophytes was carried out according to Bergey's Manual of Determinative Bacteriology. The best gibberellin production of all isolates was found at the concentration of (55.12 ppm, 50 ppm, 38.06 ppm, 90.41 ppm, 58.65 ppm and 63.65 ppm, respectively) on the 12th day of the incubation period. Among all isolates, the A4 isolate produced more GA concentration (90.41 ppm) on the 12th day of the incubation period. In the maize seed germination test, A1, A4, A5 and A6 showed the best results. In the pot trial test, A4, A5 and A6 showed the best results in shoot length (37.5 cm, 35.4 cm and 36.9 cm per ten replicates, respectively). Among them, the A4 isolate was the best GA producing isolate for plant growth promoting activity in maize seedlings. It was found in an average shoot height of 37.5 cm; average shoot fresh weight of 56.7 g and an average shoot dry weight of 7.9 g per ten replicates after one month cultivation which was sprayed by A4 treatment, compared with an average shoot height of 27.80 g, an average shoot fresh weight of 25.08 g, an average shoot dry weight of 3.42 g which were sprayed by water treatment. The qualitative analysis of plant growth regulators (GAs) production of bacterial isolate A4 was determined by using TLC method and FTIR spectroscopy analysis. Chemical fertilizers should not be used not to harm effective endophytes.

Not All Acidovorax Are Created Equal: Gibberellin Biosynthesis in the Turfgrass Pathogen Acidovorax avenae subsp. avenae.

In recent years Acidovorax avenae subsp. avenae was identified as a major cause of bacterial etiolation and decline (BED) in turfgrasses and has become a growing economical concern for the turfgrass industry. The symptoms of BED resemble those of "bakanae," or foolish seedling disease, of rice (Oryzae sativa), in which the gibberellins produced by the infecting fungus, Fusarium fujikuroi, contribute to the symptom development. Additionally, an operon coding for the enzymes necessary for bacterial gibberellin production was recently characterized in plant-pathogenic bacteria belonging to the γ-proteobacteria. We therefore investigated whether this gibberellin operon might be present in A. avenae subsp. avenae. A homolog of the operon has been identified in two turfgrass-infecting A. avenae subsp. avenae phylogenetic groups but not in closely related phylogenetic groups or strains infecting other plants. Moreover, even within these two phylogenetic groups, the operon presence is not uniform. For that reason, the functionality of the operon was examined in one strain of each turfgrass-infecting phylogenetic group (A. avenae subsp. avenae strains KL3 and MD5). All nine operon genes were functionally characterized through heterologous expression in Escherichia coli and enzymatic activities were analyzed by liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry. All enzymes were functional in both investigated strains, thus demonstrating the ability of phytopathogenic β-proteobacteria to produce biologically active GA4. This additional gibberellin produced by A. avenae subsp. avenae could disrupt phytohormonal balance and be a leading factor contributing to the pathogenicity on turf grasses. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Endophytic bacteria improve jute growth through induction of phytohormones-related gene expression

Plants coexist with complex populations of microorganisms, including Plant Growth-Promoting Rhizobacteria (PGPR). PGPR bacteria help in plant development by secreting numerous plan growth-promoting compounds like IAA, gibberellin, siderophore, and cytokinin. They also provide resistance to plants against different pathogens. Jute fibre is the second most important fibre next to cotton, obtained from the bark of plant through microbial retting process. Hence, increased plant growth means increased bark i.e., increased fibre. This study aims to identify the molecular, physiological and growth promotion characteristics of non-rhizobial bacterial specie from the surface-sterilized root of healthy and biotic stressed (nematode-infested) jute (Corchorus capsularis; Corchorus olitorius and an advanced variety of C. olitorius, Robi-1). We have identified 62 culturable bacterial isolates from healthy and nematode-infected jute plant using bacterial 16S rDNA sequencing. All the isolates were distributed to Bacillus, Staphylococcus and Ensifer genera, respectively. B. cereus, S. hominis and a consortium increased the growth phenotype (Root length, shoot length, germination rate, root and shoot biomass) of C. capsularis (CVL-1), C. olitorius (O-9897), and an advanced variety of C. olitorius (Robi-1), respectively. Increased expression (qRT-PCR analysis) of growth hormones GA-20 and GA-03 oxidase corroborates plant growth induction by increased production of the growth hormone gibberellin. Taken together, our results suggest that plant-growth promotion by endophytic bacteria may involve the increased expression of growth hormone gibberellin and nutrient uptake. B. cereus and S. hominis having plant growth-promoting traits could be useful in sustainable agriculture practice.

Screening of endophytic Bacteria from stress-tolerating plants for abiotic stress tolerance and plant growth-promoting properties: Identification of potential strains for bioremediation and crop enhancement

Enhancing plant productivity and fortifying defense mechanisms against biotic and abiotic stresses is crucial for sustainable agriculture. To achieve this, researchers have investigated the use of endophytic bacteria as a viable alternative to chemical fertilizers and pesticides. In this study, 50 endophytic microbes were isolated from stress-tolerant parts of different plants, including Lantana camara, Phoenix dactylifera, Hemerocallis fulva, Salvia rosmarinus, Commiphora wightii, and Abutilon indicum. These microbes were evaluated for their tolerance to abiotic stresses and ability to promote plant growth. Among the isolates, R1L2 and A2L2L2 exhibited the highest tolerance to salt stress, withstanding up to 16% NaCl. DL2R2, R1L2, and A1S1S were the most tolerant to lead stress, tolerating up to 6% w/v lead. For cadmium stress, R1L2, DL3R2, and DP1L1L1 showed the highest tolerance, enduring up to 6% w/v cadmium. The isolates were also assessed for their plant growth-promoting (PGP) activities, including the production of IAA, Gibberellin, Cytokinin, HCN, siderophore, phosphate solubilization, and nitrogen fixation. All isolates were positive for nitrogen fixation attribute. However, under specific stress conditions, all isolates showed negative results for HCN production, siderophore production, or inorganic phosphate solubilization. Isolates A1S1S and DL3R2 demonstrated positive results for producing phytohormones such as IAA, Gibberellin, and Cytokinin. Through phenotypic and biochemical characteristics, as well as 16S rDNA gene sequencing, isolate A1S1S was identified as Pelomonas aquatic (accession no. OP984335), and isolate DL3R2 was identified as Solibacillus silvestris (accession no. OP854919). These findings suggest that the endophytic strains Pelomonas aquatic and Solibacillus silvestris have potential applications as multi-stress reducers, bioremediation agents, and crop growth promoters in essential crops.

Elicitation of Bacillus cereus-Amazcala (B.c-A) with SiO2 Nanoparticles Improves Its Role as a Plant Growth-Promoting Bacteria (PGPB) in Chili Pepper Plants.

Agriculture needs to decrease the use of agrochemicals due to their high toxicity and adopt new strategies to achieve sustainable food production. Therefore, nanoparticles (NPs) and plant growth-promoting bacteria (PGPB) have been proposed as viable strategies to obtain better crop yields with less environmental impact. Here, we describe the effect of silica nanoparticles (SiO2-NPs) on survival, antioxidant enzymatic activity, phosphate solubilization capacity, and gibberellin production of Bacillus cereus-Amazcala (B.c-A). Moreover, the effect of the co-application of SiO2-NPs and B.c-A on seed germination, physiological characteristics, and antioxidant enzymatic activity of chili pepper plants was investigated under greenhouse conditions. The results indicated that SiO2-NPs at 100 ppm enhanced the role of B.c-A as PGPB by increasing its phosphate solubilization capacity and the production of GA7. Moreover, B.c-A catalase (CAT) and superoxide dismutase (SOD) activities were increased with SiO2-NPs 100 ppm treatment, indicating that SiO2-NPs act as a eustressor, inducing defense-related responses. The co-application of SiO2-NPs 100 ppm and B.c-A improved chili pepper growth. There was an increase in seed germination percentage, plant height, number of leaves, and number and yield of fruits. There was also an increase in CAT and PAL activities in chili pepper plants, indicating that bacteria-NP treatment induces plant immunity.

Effects of Trichoderma atroviride SG3403 and Bacillus subtilis 22 on the Biocontrol of Wheat Head Blight.

Wheat head blight caused by Fusarium graminearum is one of the major wheat diseases in the world; therefore, it is very significant to develop an effective and environmentally friendly microbial fungicide against it. Trichoderma atroviride and Bacillus subtilis are widely applied biocontrol microorganisms with separate advantages; however, little work has been conducted for synergistically elevating the effects of biocontrol and plant promotion through the co-cultivation of the two microorganisms. Our study demonstrated that T. atroviride SG3403 is compatible with B. subtilis 22. The co-culture metabolites contained a group of antagonistic compounds which were able to inhibit F. graminearum growth and increase the activities of pathogen G protein and mitogen-activated protein kinase (MAPK) as compared with axenic culture metabolites. Additionally, the co-culture metabolites enabled us to more significantly decrease the production of gibberellin (GA), deoxynivalenol (DON), and zearalenone (ZEN) from F. graminearum, which disorganized the subcellular structure, particularly the cytoplasm of F. graminearum hyphae, relative to the axenically cultured metabolites. Furthermore, the seed-coating agent made by the co-culture had significant effects against F. graminearum infection by triggering the expression of host plant defensive genes, including PR1, PR3, PR4, PR5, ACS, and SOD. It is suggested that jasmonic acid and ethylene (JA/ET) signaling might dominate wheat's induced systemic resistance (ISR) against wheat head blight. A dry, powdered bio-seed coating agent containing the co-culture mixtures was confirmed to be a bioavailable formulation that can be applied to control wheat head blight. Taken together, the co-culture's metabolites or the metabolites and living cells might provide a basis for the further development of a new kind of microbial bio-fungicide in the future.

Anthracnose of Onion (Allium cepa L.): A Twister Disease

The onion (Allium cepa L.) is a lucrative and high-value vegetable–spice crop in India, but it is sensitive to several of diseases caused by fungi, bacteria, viruses, and nematodes, of which a fungal disease, anthracnose, caused by Colletotrichum spp., is a major issue for both onion producers and researchers since it severely affects the bulb production. Twister disease is currently one of the most common problems in onion production, particularly in humid regions, and it reduces productivity while also lowering the value and profitability. Twister disease is visualised by white or pale-yellow water-soaked oval depressed lesions on leaf blades, which are the first symptoms. Lesions expand as the disease advances, and numerous black-coloured, slightly elevated structures/fruiting bodies appear in the middle area, arranged in concentric rings. Curling, twisting, chlorosis of the leaves, and aberrant extension of the neck or pseudo-stem occurs, followed by rotting of the bulb. In an unmanaged crop, an excess gibberellin production by Colletotrichum gloeosporioides and Gibberella moniliformis is suspected to induce twisting and aberrant neck elongation, which will ruin onion productivity. It is difficult and environmentally unfriendly to control these infections. Since, to the best of our knowledge, this is the first review on onion anthracnose, we tried to consolidate information. This review updates our knowledge of the pathogen, including the disease cycle, infection pathways, and disease management techniques. As a result, growers will be benefit from the application of cultural, biological, and chemical measures and the use of resistant varieties.

Production of the plant hormone gibberellin by rhizobia increases host legume nodule size.

Plant-associated microbes have evolved the ability to independently produce gibberellin (GA) phytohormones as a mechanism to influence their host. Indeed, GA was first discovered as a metabolite from the fungal rice pathogen Gibberella fujikuroi, which uses it as a virulence factor. Though some bacterial plant pathogens similarly use GA to promote infection, symbiotic nitrogen-fixing bacteria (rhizobia), which inhabit the root nodules of legumes, also can produce GA, suggesting a role in symbiosis. The bacterial GA biosynthetic operon has been identified, but in rhizobia this typically no longer encodes the final metabolic gene (cyp115), so that these symbionts can only produce the penultimate intermediate GA9. Here, we demonstrate that soybean (Glycine max) expresses functional GA 3-oxidases (GA3ox) within its nodules, which have the capability to convert GA9 produced by the enclosed rhizobial symbiont Bradyrhizobium diazoefficiens to bioactive GA4. This rhizobia-derived GA is demonstrated to cause an increase in nodule size and decrease in the number of nodules. The increase in individual nodule size correlates to greater numbers of bacterial progeny within a nodule, thereby providing a selective advantage to rhizobia that produce GA during the rhizobia-legume symbiosis. The expression of GA3ox in nodules and resultant nodulation effects of the GA product suggests that soybean has co-opted control of bioactive GA production, and thus nodule size, for its own benefit. Thus, our results suggest rhizobial GA biosynthesis has coevolved with host plant metabolism for cooperative production of a phytohormone that influences nodulation in a mutually beneficial manner.

Phytohormone biosynthetic potential of different Rhizobium species

Plants may not have optimum growth hormone production potential under suboptimal growth and environmental conditions. The exogenous application of microbes is a potential and economical source of plant hormones. A laboratory trial was performed to evaluate the hormone biosynthesis potential of several soil microbes. Rhizobium sp. (Rhizobium trifolii, Rhizobium etli, Rhizobium meliloti, Rhizobium ciceri, Azorhizobium caulinodans, Bradyrhizobium japonicum, Rhizobium vulgaris, and Rhizobium phaseoli) were isolated from root nodules of various legumes and were biochemically characterized. Absorption spectroscopy (535, 254 and 665 nm λ) was used to quantify indole acetic acid (IAA), gibberellin and cytokinin production of different Rhizobium species. B3 isolate of Rhizobium trifolii had yielded (14.54 and 21.37 µg mL-1) IAA equivalents without and with L-tryptophan (L-TRP) supplement, that was statistically at par with same species while significantly greater than other Rhizobium isolates. Gibberellin production was found statistically non-significant in all isolates. Rhizobium phaseoli (Vp1) yielded 1.68 µg mL-1 cytokinin that was at par with the same species isolates and with Rhizobium trifolii but was critically greater in amount than other species. It was concluded that Rhizobium plays a vital role in plant growth and development can produce auxin and gibberellins, but some could produce cytokinin. Keywords: Phytohormone, Biosynthesis, IAA, PGPR, Auxin, Gibberellins, Cytokinin

Sequencing of non-virulent strains of Fusarium fujikuroi reveals genes putatively involved in bakanae disease of rice

Bakanae, one of the most important diseases of rice, is caused by the fungal pathogen Fusarium fujikuroi. The elongation of internodes is the most common symptom induced by the pathogen, and it is related to the production of gibberellins. Despite this, the pathogenicity mechanism of F. fujikuroi is still not completely clear, and there are some strains inducing stunting instead of elongation. Even if there are relatively many genomes of F. fujikuroi strains available in online databases, none of them belongs to an isolate of proven non-virulence, and therefore there has been no comparative genomics study conducted between virulent and non-virulent strains. In the present work, the genomes of non-virulent strain SG4 and scarcely virulent strain C2S were compared to the ones of 12 available virulent isolates. Genes present in the majority of available virulent strains, but not in the non-virulent one, underwent functional annotation with multiple tools, and their expression level during rice infection was checked using pre-existing data. Nine genes putatively related to pathogenicity in F. fujikuroi were identified throughout comparative and functional analyses. Among these, many are involved in the degradation of plant cell wall, which is poorly studied in F. fujikuroi-rice interactions. Three of them were validated through qPCR, showing higher expression in the virulent strain and low to no expression in the low virulent and non virulent strains during rice infection. This work helps to clarify the mechanisms of pathogenicity of F. fujikuroi on rice.

Phytohormone Production Profiles in Trichoderma Species and Their Relationship to Wheat Plant Responses to Water Stress.

The production of eight phytohormones by Trichoderma species is described, as well as the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) activity, which diverts the ethylene biosynthetic pathway in plants. The use of the Trichoderma strains T. virens T49, T. longibrachiatum T68, T. spirale T75 and T. harzianum T115 served to demonstrate the diverse production of the phytohormones gibberellins (GA) GA1 and GA4, abscisic acid (ABA), salicylic acid (SA), auxin (indole-3-acetic acid: IAA) and the cytokinins (CK) dihydrozeatin (DHZ), isopenteniladenine (iP) and trans-zeatin (tZ) in this genus. Such production is dependent on strain and/or culture medium. These four strains showed different degrees of wheat root colonization. Fresh and dry weights, conductance, H2O2 content and antioxidant activities such as superoxide dismutase, peroxidase and catalase were analyzed, under optimal irrigation and water stress conditions, on 30-days-old wheat plants treated with four-day-old Trichoderma cultures, obtained from potato dextrose broth (PDB) and PDB-tryptophan (Trp). The application of Trichoderma PDB cultures to wheat plants could be linked to the plants’ ability to adapt the antioxidant machinery and to tolerate water stress. Plants treated with PDB cultures of T49 and T115 had the significantly highest weights under water stress. Compared to controls, treatments with strains T68 and T75, with constrained GA1 and GA4 production, resulted in smaller plants regardless of fungal growth medium and irrigation regime.

Molecular phylogeny, pathogenic variability and phytohormone production of Fusarium species associated with bakanae disease of rice in temperate agro-ecosystems

Bakanae is the emerging disease threating the rice cultivation globally. Yield reduction of 4-70% is recorded in different parts of the world. A total of 119 Fusarium isolates were collected from rice plants at different geographical locations and seeds of different rice cultivars. The isolates were evaluated for morphological, biochemical and pathogenic diversity. The amplification of TEF-1α gene was carried out for exploring the species spectrum associated with the cultivated and pre-released rice varieties. The production of gibberellin varied from 0.53 to 2.26µg/25ml, while as that of Indole acetic acid varied from 0.60 to 3.15µg/25ml among the Fusarium isolates. The phylogenetic analysis identified 5 different species of the genus Fusarium viz. Fusarium fujikuroi, F. proliferatum, F. equiseti, F.oxysporum and F. persicinum after nucleotide blasting in NCBI. Only two Fusarium spp. F. fujikuroi and F. proliferatum were found to be pathogenic under virulence assays of the isolates. The isolates showed a considerable variation in morphological and pathogenic characters. The isolates were divided into different groups based on morphology and pathogenicity tests. The isolates showed a considerable variation in morphology, phytohormone profile and virulence indicative of population diversity. Three species F. equiseti, F.oxysporum and F. persicinum which have not been reported as pathogens of rice in India were found to be associated with bakanae disease of rice, however their pathogenicity could not be established.