Azospirillum: benefits that go far beyond biological nitrogen fixation
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Abstract:
The genus Azospirillum comprises plant-growth-promoting bacteria (PGPB), which have been broadly studied. The benefits to plants by inoculation with Azospirillum have been primarily attributed to its capacity to fix atmospheric nitrogen, but also to its capacity to synthesize phytohormones, in particular indole-3-acetic acid. Recently, an increasing number of studies has attributed an important role of Azospirillum in conferring to plants tolerance of abiotic and biotic stresses, which may be mediated by phytohormones acting as signaling molecules. Tolerance of biotic stresses is controlled by mechanisms of induced systemic resistance, mediated by increased levels of phytohormones in the jasmonic acid/ethylene pathway, independent of salicylic acid (SA), whereas in the systemic acquired resistance—a mechanism previously studied with phytopathogens—it is controlled by intermediate levels of SA. Both mechanisms are related to the NPR1 protein, acting as a co-activator in the induction of defense genes. Azospirillum can also promote plant growth by mechanisms of tolerance of abiotic stresses, named as induced systemic tolerance, mediated by antioxidants, osmotic adjustment, production of phytohormones, and defense strategies such as the expression of pathogenesis-related genes. The study of the mechanisms triggered by Azospirillum in plants can help in the search for more-sustainable agricultural practices and possibly reveal the use of PGPB as a major strategy to mitigate the effects of biotic and abiotic stresses on agricultural productivity.Keywords:
Jasmonic acid
Systemic Acquired Resistance
Jasmonic acid
Beet armyworm
Pseudomonas syringae
Systemic Acquired Resistance
Methyl jasmonate
Exigua
Pathogenesis-related protein
Jasmonate
Pieris rapae
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Root colonization by selected Trichoderma isolates can activate in the plant a systemic defense response that is effective against a broad-spectrum of plant pathogens. Diverse plant hormones play pivotal roles in the regulation of the defense signaling network that leads to the induction of systemic resistance triggered by beneficial organisms [induced systemic resistance (ISR)]. Among them, jasmonic acid (JA) and ethylene (ET) signaling pathways are generally essential for ISR. However, Trichoderma ISR (TISR) is believed to involve a wider variety of signaling routes, interconnected in a complex network of cross-communicating hormone pathways. Using tomato as a model, an integrative analysis of the main mechanisms involved in the systemic resistance induced by Trichoderma harzianum against the necrotrophic leaf pathogen Botrytis cinerea was performed. Root colonization by T. harzianum rendered the leaves more resistant to B. cinerea independently of major effects on plant nutrition. The analysis of disease development in shoots of tomato mutant lines impaired in the synthesis of the key defense-related hormones JA, ET, salicylic acid (SA), and abscisic acid (ABA), and the peptide prosystemin (PS) evidenced the requirement of intact JA, SA, and ABA signaling pathways for a functional TISR. Expression analysis of several hormone-related marker genes point to the role of priming for enhanced JA-dependent defense responses upon pathogen infection. Together, our results indicate that although TISR induced in tomato against necrotrophs is mainly based on boosted JA-dependent responses, the pathways regulated by the plant hormones SA- and ABA are also required for successful TISR development.
Jasmonic acid
Systemic Acquired Resistance
Jasmonate
Trichoderma harzianum
Trichoderma
Plant hormone
Biotic stress
Defence mechanisms
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Salicylic acid and jasmonic acid play an important role in plants coping with abiotic stresses. An experiment was conducted to examine the effect of salicylic acid and jasmonic acid on wheat under drought. Seeds were primed with jasmonic acid (100µM) and salicylic acid (10 Mm). Water stress was applied by withholding water and each treatment was replicated three times with a factorial block design. Application of Salicylic acid and Jasmonic acid mitigated drought effects in wheat. Results revealed that 100µM Jasmonic acid was more effective than 10 mM SA. Drought decreased germination by 26%, whereas application of Jasmonic acid and Salicylic acid ameliorated stress with the increase of germination by 27% and 21%, respectively. An increase in the shoot length of 23% and 20% was observed with Jasmonic acid and Salicylic acid, under drought conditions. The increase in water potential was 60% and 47% with JA and SA while the increase in proline and soluble sugar was 14% and 25% respectively. The application of Jasmonic acid and Salicylic acid has a potential to enhance the growth of wheat plants under drought.
Jasmonic acid
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Jasmonic acid
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Abstract To investigate the regulation of hydrogen peroxide (H2O2) in SA- and JA-dependent systemic defense pathways in tomato seedlings damaged by cotton bollworm. The lower two leaves of four-leaf tomato plant seedlings were treated with cotton bollworms. The upper leaves were then removed at various time points and assessed for systemic changes in H2O2 levels, enzyme activity and defense-related genes expression. Wild-type seedlings, def-5 mutant seedlings (deficient in JA accumulation) and transgenic nahG seedlings(deficient in SA content) were constructed at four-leaf stage. Wild-type plants were further treated with dimethylthiourea (DMTU) and 2,5-dihydroxycinnamic acid methyl ester (DHC). Bollworm feeding in the lower leaves induced rapid systemic accumulation of H2O2 in the upper leaves. H2O2 accumulation further increased activities for SA- and JA-dependent enzymes including proteinase inhibitors (PIs), pathogenesis-related gene 1 (PR-1), cathepsin D inhibitor (CDI), β-1,3-glucanse (BGL) and polyphenol oxidase (PPO). Furthermore, H2O2 accumulation enhanced mRNA expression of BGL-2, PR-1, PI, CDI and PPO genes. Suppression of H2O2 accumulation using H2O2 scavengers substantially diminished these effects. mRNA expression of PR-1 was not induced in transgenic nahG plants. SA- and JA-dependent signaling pathways are involved in the tomato systemic defense responses to herbivores, and that H2O2 generation is required for both systemic pathways.
Jasmonic acid
Peroxide
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Plant defence activators viz., benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester, β-aminobutyric acid and salicylic acid at 1 mM dosage were evaluated to manage Tilletia indica and cent percent protection was achieved under glass house conditions. Further, efforts were made to dissect expression pattern of pathogenesis-related genes which are downstream components of the systemic acquired resistance (SAR) pathway in response to primed compounds and T. indica infection, based on real-time polymerase chain reaction analysis of marker gene expression levels. Maximal accumulation of PDF1.2 transcripts followed by PR1 and PR5 in independently primed wheat spikes with all tested compounds at three days post-inoculation was observed. Additionally, plant defence activators primed the plant for a rapid and intense response to pathogen infection involving augmented activation of salicylic acid (SA) – and jasmonic acid (JA)/ethylene (ET)-mediated defence response and enhanced level of wheat protection. Therefore, the use of plant defence activators to induce SAR could be used as a management strategy for reducing the impact of T. indica for quality and nutritious wheat production.
Jasmonic acid
Systemic Acquired Resistance
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Phytohormones are not only instrumental in regulating developmental processes in plants but also play important roles for the plant's responses to biotic and abiotic stresses. In particular, abscisic acid, ethylene, jasmonic acid, and salicylic acid have been shown to possess crucial functions in mediating or orchestrating stress responses in plants. Here, we review the role of salicylic acid and jasmonic acid in pathogen defence responses with special emphasis on their function in the solanaceous plant potato.
Jasmonic acid
Biotic stress
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Jasmonic acid
Signalling
Systemic Acquired Resistance
Signalling pathways
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Jasmonic acid
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Trichoderma spp. are among the most widely used plant beneficial fungi in agriculture. Its interaction with the plant triggers resistance responses by the activation of Induced Systemic Resistance mediated by Jasmonic acid and Ethylene and/or Systemic Acquired Resistance, which involves Salicylic acid, with the consequent control of a wide range of plant parasites. However, the benefit they can confer to plants may be reduced or nullified by environmental conditions or fungal ecological fitness. A novel approach to enhance their effectiveness in plant defense is to combine them with bioactive molecules including plant-derived compounds. Here, we show that plant treatment with Trichoderma afroharzianum (strain T22) and Systemin, a tomato peptide active in triggering plant defense, confers protection against the fungal pathogens Fusarium oxysporum, Botrytis cinerea and the insect pest Tuta absoluta. The observed defensive response was associated with an increase of Jasmonic acid and related metabolites and a decrease of Salicylic acid.
Jasmonic acid
Trichoderma
Systemic Acquired Resistance
Plant disease
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