Effects of Abscisic Acid and Salicylic Acid on Gene Expression in the Antiviral RNA Silencing Pathway in Arabidopsis.
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ABSTRACT:
SUBMITTER: Alazem M
PROVIDER: S-EPMC6566719 | biostudies-literature | 2019 May
REPOSITORIES: biostudies-literature
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Project description:BackgroundBrassinosteroids (BRs) play crucial roles in plant development and also promote tolerance to a range of abiotic stresses. Although much has been learned about their roles in plant development, the mechanisms by which BRs control plant stress responses and regulate stress-responsive gene expression are not fully known. Since BR interacts with other plant hormones, it is likely that the stress tolerance conferring ability of BR lies in part in its interactions with other stress hormones.ResultsUsing a collection of Arabidopsis mutants that are either deficient in or insensitive to abscisic acid (ABA), ethylene (ET), jasmonic acid (JA) and salicylic acid (SA), we studied the effects of 24-epibrassinloide (EBR) on basic thermotolerance and salt tolerance of these mutants. The positive impact of EBR on thermotolerance in proportion to wild type was evident in all mutants studied, with the exception of the SA-insensitive npr1-1 mutant. EBR could rescue the ET-insensitive ein2 mutant from its hypersensitivity to salt stress-induced inhibition of seed germination, but remained ineffective in increasing the survival of eto1-1 (ET-overproducer) and npr1-1 seedlings on salt. The positive effect of EBR was significantly greater in the ABA-deficient aba1-1 mutant as compared to wild type, indicating that ABA masks BR effects in plant stress responses. Treatment with EBR increased expression of various hormone marker genes in both wild type and mutant seedlings, although to different levels.ConclusionsThese results together indicate that the redox-sensitive protein NPR1 (NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1), a master regulator of SA-mediated defense genes, is likely a critical component of EBR-mediated increase in thermotolerance and salt tolerance, but it is not required for EBR-mediated induction of PR-1 (PATHOGENESIS-RELATED1) gene expression; that BR exerts anti-stress effects independently as well as through interactions with other hormones; that ABA inhibits BR effects during stress; and that BR shares transcriptional targets with other hormones.
| S-EPMC3095295 | biostudies-literature
Project description:BACKGROUND: Verticillium longisporum is a soil-borne vascular pathogen infecting cruciferous hosts such as oilseed rape. Quantitative disease resistance (QDR) is the major control means, but its molecular basis is poorly understood so far. Quantitative trait locus (QTL) mapping was performed using a new (Bur×Ler) recombinant inbred line (RIL) population of Arabidopsis thaliana. Phytohormone measurements and analyses in defined mutants and near-isogenic lines (NILs) were used to identify genes and signalling pathways that underlie different resistance QTL. RESULTS: QTL for resistance to V. longisporum-induced stunting, systemic colonization by the fungus and for V. longisporum-induced chlorosis were identified. Stunting resistance QTL were contributed by both parents. The strongest stunting resistance QTL was shown to be identical with Erecta. A functional Erecta pathway, which was present in Bur, conferred partial resistance to V. longisporum-induced stunting. Bur showed severe stunting susceptibility in winter. Three stunting resistance QTL of Ler origin, two co-localising with wall-associated kinase-like (Wakl)-genes, were detected in winter. Furthermore, Bur showed a much stronger induction of salicylic acid (SA) by V. longisporum than Ler. Systemic colonization was controlled independently of stunting. The vec1 QTL on chromosome 2 had the strongest effect on systemic colonization. The same chromosomal region controlled the level of abscisic acid (ABA) and jasmonic acid (JA) in response to V. longisporum: The level of ABA was higher in colonization-susceptible Ler than in colonization-resistant Bur after V. longisporum infection. JA was down-regulated in Bur after infection, but not in Ler. These differences were also demonstrated in NILs, varying only in the region containing vec1. All phytohormone responses were shown to be independent of Erecta. CONCLUSIONS: Signalling systems with a hitherto unknown role in the QDR of A. thaliana against V. longisporum were identified: Erecta mediated resistance against V. longisporum-induced stunting. Independent of Erecta, stunting was caused in a light-dependent manner with possible participation of SA and Wakl genes. ABA and JA showed a genotype-specific response that corresponded with systemic colonization by the fungus. Understanding the biological basis of phenotypic variation in A. thaliana with respect to V. longisporum resistance will provide new approaches for implementing durable resistance in cruciferous crops.
| S-EPMC4021371 | biostudies-literature
Project description:Cucumber mosaic virus (CMV) encodes the 2b protein, which plays a role in local and systemic virus movement, symptom induction and suppression of RNA silencing. It also disrupts signalling regulated by salicylic acid and jasmonic acid. CMV induced an increase in tolerance to drought in Arabidopsis thaliana. This was caused by the 2b protein, as transgenic plants expressing this viral factor showed increased drought tolerance, but plants infected with CMV?2b, a viral mutant lacking the 2b gene, did not. The silencing effector ARGONAUTE1 (AGO1) controls a microRNA-mediated drought tolerance mechanism and, in this study, we noted that plants (dcl2/3/4 triple mutants) lacking functional short-interfering RNA-mediated silencing were also drought tolerant. However, drought tolerance engendered by CMV may be independent of the silencing suppressor activity of the 2b protein. Although CMV infection did not alter the accumulation of the drought response hormone abscisic acid (ABA), 2b-transgenic and ago1-mutant seeds were hypersensitive to ABA-mediated inhibition of germination. However, the induction of ABA-regulated genes in 2b-transgenic and CMV-infected plants was inhibited more strongly than in ago1-mutant plants. The virus engenders drought tolerance by altering the characteristics of the roots and not of the aerial tissues as, compared with the leaves of silencing mutants, leaves excised from CMV-infected or 2b-transgenic plants showed greater stomatal permeability and lost water more rapidly. This further indicates that CMV-induced drought tolerance is not mediated via a change in the silencing-regulated drought response mechanism. Under natural conditions, virus-induced drought tolerance may serve viruses by aiding susceptible hosts to survive periods of environmental stress.
| S-EPMC6638696 | biostudies-literature
Project description:BackgroundSalicylic acid (SA) is one of the plant hormones, which plays crucial roles in signaling transduction in plant growth, disease resistance, and leaf senescence. Arabidopsis (Arabidopsis thaliana) SA 3-hydroxylase (S3H) and 5-hydroxylase (S5H) are key enzymes which maintain SA homeostasis by catalyzing SA to 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, respectively.ResultsSA deficient transgenic Arabidopsis lines were generated by introducing two binary vectors S5Hpro::EGFP-S3H and 35Spro::EGFP-S3H respectively, in which the expression of S3H is under the control of the S5H promoter or CaMV 35S promoter. Compared with the constitutive expression of S3H gene under the control of 35S promoter, the S3H gene under the native S5H promoter is activated by endogenous SA and results in a dynamic control of SA catabolism in a feedback mode. The SA accumulation, growth, leaf senescence, and pathogen resistance of the S5Hpro::GFP-S3H transgenic plants were investigated in parallel with NahG transgenic plants. The SA levels in the S5Hpro::EGFP-S3H transgenic plants were similar to or slightly lower than those of NahG transgenic Arabidopsis and resulted in SA deficient phenotypes. The low-SA trait of the S5Hpro::EGFP-S3H transgenic lines was inherited stably in the later generations.ConclusionsCompared with NahG transgenic lines producing by-product catechol, S5Hpro::EGFP-S3H transgenic lines reduce SA levels by converting SA to a native product 2,3-DHBA for catabolism. Together, we provide new SA-deficient germplasms for the investigations of SA signaling in plant development, leaf senescence, and disease resistance.
| S-EPMC9238041 | biostudies-literature
Project description:The interplay between abscisic acid (ABA) and salicylic acid (SA) influences plant responses to various (a)biotic stresses; however, the underlying mechanism for this crosstalk is largely unknown. Here, we report that type 2C protein phosphatases (PP2Cs), some of which are negative regulators of ABA signaling, bind SA. SA binding suppressed the ABA-enhanced interaction between these PP2Cs and various ABA receptors belonging to the PYR/PYL/RCAR protein family. Additionally, SA suppressed ABA-enhanced degradation of PP2Cs and ABA-induced stabilization of SnRK2s. Supporting SA's role as a negative regulator of ABA signaling, exogenous SA suppressed ABA-induced gene expression, whereas the SA-deficient sid2-1 mutant displayed heightened PP2C degradation and hypersensitivity to ABA-induced suppression of seed germination. Together, these results suggest a new molecular mechanism through which SA antagonizes ABA signaling. A better understanding of the crosstalk between these hormones is important for improving the sustainability of agriculture in the face of climate change.
| S-EPMC6508495 | biostudies-literature
Project description:Stem cells are essential for the development and organ regeneration of multicellular organisms, so their infection by pathogenic viruses must be prevented. Accordingly, mammalian stem cells are highly resistant to viral infection due to dedicated antiviral pathways including RNA interference (RNAi). In plants, a small group of stem cells harbored within the shoot apical meristem generate all postembryonic above-ground tissues, including the germline cells. Many viruses do not proliferate in these cells, yet the molecular bases of this exclusion remain only partially understood. Here, we show that a plant-encoded RNA-dependent RNA polymerase, after activation by the plant hormone salicylic acid, amplifies antiviral RNAi in infected tissues. This provides stem cells with RNA-based virus sequence information, which prevents virus proliferation. Furthermore, we find RNAi to be necessary for stem cell exclusion of several unrelated RNA viruses, despite their ability to efficiently suppress RNAi in the rest of the plant. This work elucidates a molecular pathway of great biological and economic relevance and lays the foundations for our future understanding of the unique systems underlying stem cell immunity.
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Project description:Plant RNA silencing machinery enlists four primary classes of proteins to achieve sequence-specific regulation of gene expression and mount an antiviral defense. These include Dicer-like ribonucleases (DCLs), Argonaute proteins (AGOs), dsRNA-binding proteins (DRBs), and RNA-dependent RNA polymerases (RDRs). Although at least four distinct endogenous RNA silencing pathways have been thoroughly characterized, a detailed understanding of the antiviral RNA silencing pathway is just emerging. In this report, we have examined the role of four DCLs, two AGOs, one DRB, and one RDR in controlling viral RNA accumulation in infected Arabidopsis plants by using a mutant virus lacking its silencing suppressor. Our results show that all four DCLs contribute to antiviral RNA silencing. We confirm previous reports implicating both DCL4 and DCL2 in this process and establish a minor role for DCL3. Surprisingly, we found that DCL1 represses antiviral RNA silencing through negatively regulating the expression of DCL4 and DCL3. We also implicate DRB4 in antiviral RNA silencing. Finally, we show that both AGO1 and AGO7 function to ensure efficient clearance of viral RNAs and establish that AGO1 is capable of targeting viral RNAs with more compact structures, whereas AGO7 and RDR6 favor less structured RNA targets. Our results resolve several key steps in the antiviral RNA silencing pathway and provide a basis for further in-depth analysis.
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Project description:Abscisic acid (ABA) hydroxylation is an important pathway for ABA inactivation and homeostasis maintenance. Here, we discover a new downstream catabolite of neophaseic acid (neoPA) in the ABA 9'-hydroxyl pathway and identify it as epi-neodihydrophaseic acid (epi-neoDPA) by comparing its accurate mass, retention time, and MSn spectra with those of our chemically synthesized epi-neoDPA. Analyses of Arabidopsis seed germination and ABA-related gene expression reveal that neoPA rather than epi-neoDPA possesses ABA-like hormonal activity. In vitro enzyme activity tests of prokaryotic recombinant protein reveal that NeoPAR1 (neoPA reductase 1) identified from Arabidopsis converts neoPA into epi-neoDPA. Site-directed mutation at Tyr163 in the conserved motif of NeoPAR1 abolishes the catalytic activity of NeoPAR1. Accelerated seed germination was observed in NeoPAR1 knockdown and knockout mutants, whereas retarded seed germination and the accumulation of epi-neoDPA and ABA were observed in NeoPAR1 overexpression lines, suggesting that NeoPAR1 is involved in seed germination and maintenance of ABA homeostasis.
| S-EPMC9482987 | biostudies-literature
Project description:The aim of this study was to characterize hormonal crosstalk with the sugar signaling and metabolic pathway based on a time course analysis of drought intensity. Drought intensity-responsive changes in the assimilation of newly fixed carbon (C) into soluble sugar, the content of sugar and starch, and expression of genes involved in carbohydrate metabolism were interpreted as being linked to endogenous abscisic acid (ABA) and salicylic acid (SA) levels and their signaling genes. The ABA and SA levels in the drought-stressed leaves increased together during the early drought period (days 0-6), and additional ABA accumulation occurred with depressed SA during the late period (days 6-14). Although drought treatment decreased the assimilation of newly fixed C into soluble sugar, representing a 59.9%, 33.1%, and 62.9% reduction in 13C-glucose, 13C-fructose, and 13C-sucrose on day 14, respectively, the drought-responsive accumulation of soluble sugars was significant. During the early period, the drought-responsive accumulation of hexose and sucrose was concurrent with the upregulated expression of hexokinase 1 (HXK1), which, in turn, occurred parallel to the upregulation of ABA synthesis gene 9-sis-epoxycarotenoid dioxygenase (NCED3) and SA-related genes (isochorismate synthase 1 (ICS1) and non-expressor of pathogenesis-related gene (NPR1)). During the late period, hexose accumulation, sucrose phloem loading, and starch degradation were dominant, with a highly enhanced expression of the starch degradation-related genes β-amylase 1 (BAM1) and α-amylase 3 (AMY3), which were concomitant with the parallel enhancement of sucrose non-fermenting-1 (Snf1)-related protein kinase 2 (SnRK2).2 and ABA-responsive element binding 2 (AREB2) expression in an ABA-dependent manner. These results indicate that the drought-responsive accumulation of sugars (especially SA-mediated sucrose accumulation) is part of the acclamatory process during the early period. Conversely, ABA-responsive hexose accumulation and sucrose phloem loading represent severe drought symptoms during the late drought period.
| S-EPMC8004980 | biostudies-literature
Project description:The plant hormone salicylic acid (SA) plays critical roles in plant defense, stress responses, and senescence. Although SA biosynthesis is well understood, the pathways by which SA is catabolized remain elusive. Here we report the identification and characterization of an SA 3-hydroxylase (S3H) involved in SA catabolism during leaf senescence. S3H is associated with senescence and is inducible by SA and is thus a key part of a negative feedback regulation system of SA levels during senescence. The enzyme converts SA (with a Km of 58.29 µM) to both 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-DHBA in vitro but only 2,3-DHBA in vivo. The s3h knockout mutants fail to produce 2,3-DHBA sugar conjugates, accumulate very high levels of SA and its sugar conjugates, and exhibit a precocious senescence phenotype. Conversely, the gain-of-function lines contain high levels of 2,3-DHBA sugar conjugates and extremely low levels of SA and its sugar conjugates and display a significantly extended leaf longevity. This research reveals an elegant SA catabolic mechanism by which plants regulate SA levels by converting it to 2,3-DHBA to prevent SA overaccumulation. The research also provides strong molecular genetic evidence for an important role of SA in regulating the onset and rate of leaf senescence.
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