Hormone-triggered activation of the jasmonate signaling pathway in Arabidopsis thaliana requires SCF(COI1)-mediated proteasome degradation of JAZ repressors. (-)-JA-L-Ile is the proposed bioactive ...hormone, and SCF(COI1) is its likely receptor. We found that the biological activity of (-)-JA-L-Ile is unexpectedly low compared to coronatine and the synthetic isomer (+)-JA-L-Ile, which suggests that the stereochemical orientation of the cyclopentanone-ring side chains greatly affects receptor binding. Detailed GC-MS and HPLC analyses showed that the (-)-JA-L-Ile preparations currently used in ligand binding studies contain small amounts of the C7 epimer (+)-7-iso-JA-L-Ile. Purification of each of these molecules demonstrated that pure (-)-JA-L-Ile is inactive and that the active hormone is (+)-7-iso-JA-L-Ile, which is also structurally more similar to coronatine. In addition, we show that pH changes promote conversion of (+)-7-iso-JA-L-Ile to the inactive (-)-JA-L-Ile form, thus providing a simple mechanism that can regulate hormone activity through epimerization.
Abstract
The majority of clinically used antibiotics originate from bacteria. As the need for new antibiotics grows, large-scale genome sequencing and mining approaches are being used to identify ...novel antibiotics. However, this task is hampered by the fact that many antibiotic biosynthetic clusters are not expressed under laboratory conditions. One strategy to overcome this limitation is the identification of signals that activate the expression of silent biosynthetic pathways. Here, we report the use of high-throughput screening to identify signals that control the biosynthesis of the acetyl-CoA carboxylase inhibitor antibiotic andrimid in the broad-range antibiotic-producing rhizobacterium Serratia plymuthica A153. We reveal that the pathway-specific transcriptional activator AdmX recognizes the auxin indole-3-acetic acid (IAA). IAA binding causes conformational changes in AdmX that result in the inhibition of the expression of the andrimid cluster and the suppression of antibiotic production. We also show that IAA synthesis by pathogenic and beneficial plant-associated bacteria inhibits andrimid production in A153. Because IAA is a signalling molecule that is present across all domains of life, this study highlights the importance of intra- and inter-kingdom signalling in the regulation of antibiotic synthesis. Our discovery unravels, for the first time, an IAA-dependent molecular mechanism for the regulation of antibiotic synthesis.
The jasmonate signaling pathway regulates development, growth, and defense responses in plants. Studies in the model eudicot, Arabidopsis thaliana, have identified the bioactive hormone ...(jasmonoyl-isoleucine JA-Ile) and its Coronatine Insensitive 1 (COI1)/Jasmonate-ZIM Domain (JAZ) co-receptor. In bryophytes, a conserved signaling pathway regulates similar responses but uses a different ligand, the JA-Ile precursor dinor-12-oxo-10,15(Z)-phytodienoic acid (dn-OPDA), to activate a conserved co-receptor. Jasmonate responses independent of JA-Ile and COI1, thought to be mediated by the cyclopentenone OPDA, have also been suggested, but experimental limitations in Arabidopsis have hindered attempts to uncouple OPDA and JA-Ile biosynthesis. Thus, a clear understanding of this pathway remains elusive. Here, we address the role of cyclopentenones in COI1-independent responses using the bryophyte Marchantia polymorpha, which is unable to synthesize JA-Ile but does accumulate OPDA and dn-OPDA. We demonstrate that OPDA and dn-OPDA activate a COI1-independent pathway that regulates plant thermotolerance genes, and consequently, treatment with these oxylipins protects plants against heat stress. Furthermore, we identify that these molecules signal through their electrophilic properties. By performing comparative analyses between M. polymorpha and two evolutionary distant species, A. thaliana and the charophyte alga Klebsormidium nitens, we demonstrate that this pathway is conserved in streptophyte plants and pre-dates the evolutionary appearance of the COI1-dependent jasmonate pathway, which later co-opted the pre-existing dn-OPDA as its ligand. Taken together, our data indicate that cyclopentenone-regulated COI1-independent signaling is an ancient conserved pathway, whose ancestral role was to protect plants against heat stress. This pathway was likely crucial for plants’ successful land colonization and will be critical for adaption to current climate warming.
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•OPDA and dn-OPDA activate plant thermotolerance genes in a COI1-independent manner•Treatment with these oxylipins protects plants against heat stress•These cyclopentenones activate this pathway through their electrophilic properties•This pathway is conserved in streptophytes and pre-dates COI1-dependent signaling
Monte, Kneeshaw, et al. identify a conserved COI1-independent role for electrophilic cyclopentenones in the regulation of thermotolerance in streptophyte plants. This role is ancient and preceded the emergence of COI1-dependent jasmonate signaling. Thus, an abiotic stress response pathway expanded to regulate biotic stress.
The fungal jasmonate lasiojasmonate A functions as a source of jasmonic acid that activates the JA-isoleucine pathway in Arabidopsis.
Abstract
Jasmonates are signaling compounds that regulate plant ...responses to stress. Jasmonic acid (JA) is the direct precursor of the bioactive plant hormone JA-isoleucine (JA-Ile), the ligand of the CORONATINE INSENSITIVE 1-jasmonate ZIM-domain (COI1-JAZ) co-receptor complex. JA, its methyl ester, and three furanonyl esters were recently isolated from the grapevine pathogen Lasiodiplodia mediterranea. The JA ester lasiojasmonate A (LasA) is the first reported naturally occurring JA-furanone, and its mode of action has not yet been elucidated. Here, we show that LasA activates many JA-regulated responses in planta, including protein degradation, gene expression, and physiological processes. These in vivo effects require LasA conversion into JA, formation of JA-Ile, and its recognition by the plant JA-Ile perception complex. These findings suggest a mode of action of the natural fungal LasA as an inactive JA pool that can be transformed into the bioactive JA-Ile form. We propose that fungal production of JA derivates such as LasA occurs at late infection stages to induce plant JA responses such as cell death, and can facilitate fungal infection.
Jasmonates (JAs) are essential hormones for plant defense and development. In spite of their importance, the molecular details of their signaling pathways remain largely unknown. A new family of ...regulators of JA signaling named JAZ, jasmonate ZIM-domain proteins, has recently been described. JAZ proteins repress of JA signaling and are targeted by the E3-ubiquitin ligase SCF
COI1 for proteasome degradation in response to JA. Hormone binding depends on a functional COI1 protein suggesting that COI1 is the JA receptor. MYC2, a positive regulator of JA-dependent responses, has been identified as a target of JAZ repressors. Interestingly, MYC2 and JAZ proteins are involved in a negative regulatory feedback loop, suggesting a model to explain how transcriptional reprogramming is turned on and off in response to JA. The discovery of JAZ repressors provides a new framework to understand JA-signaling pathways from hormonal perception to transcriptional activation.
Jasmonates are essential phytohormones for plant development and survival. However, the molecular details of their signalling pathway remain largely unknown. The identification more than a decade ago ...of COI1 as an F-box protein suggested the existence of a repressor of jasmonate responses that is targeted by the SCF(COI1) complex for proteasome degradation in response to jasmonate. Here we report the identification of JASMONATE-INSENSITIVE 3 (JAI3) and a family of related proteins named JAZ (jasmonate ZIM-domain), in Arabidopsis thaliana. Our results demonstrate that JAI3 and other JAZs are direct targets of the SCF(COI1) E3 ubiquitin ligase and jasmonate treatment induces their proteasome degradation. Moreover, JAI3 negatively regulates the key transcriptional activator of jasmonate responses, MYC2. The JAZ family therefore represents the molecular link between the two previously known steps in the jasmonate pathway. Furthermore, we demonstrate the existence of a regulatory feed-back loop involving MYC2 and JAZ proteins, which provides a mechanistic explanation for the pulsed response to jasmonate and the subsequent desensitization of the cell.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
Different plant species employ different jasmonates to activate a conserved signalling pathway in land plants, where (+)‐7‐iso‐JA‐Ile (JA‐Ile) is the ligand for the COI1/JAZ receptor in ...angiosperms and dn‐cis‐OPDA, dn‐iso‐OPDA and Δ4‐dn‐iso‐OPDA act as ligands in Marchantia polymorpha. In addition, some jasmonates play a COI1‐independent role.
To understand the distribution of bioactive jasmonates in the green lineage and how their biosynthetic pathways evolved, we performed phylogenetic analyses and systematic jasmonates profiling in representative species from different lineages.
We found that both OPDA and dn‐OPDA are ubiquitous in all tested land plants and present also in charophyte algae, underscoring their importance as ancestral signalling molecules. By contrast, JA‐Ile biosynthesis emerged within lycophytes coincident with the evolutionary appearance of JAR1 function.
We identified that the OPR3‐independent JA biosynthesis pathway is ancient and predates the evolutionary appearance of the OPR3‐dependent pathway. Moreover, we identified a negative correlation between dn‐iso‐OPDA and JA‐Ile in land plants, which supports that in bryophytes and lycophytes dn‐iso‐OPDA represents the analogous hormone to JA‐Ile in other vascular plants.
Reduction of the red/far-red (R/FR) light ratio that occurs in dense canopies promotes plant growth to outcompete neighbors but has a repressive effect on jasmonate (JA)-dependent defenses. The ...molecular mechanism underlying this trade-off is not well understood. We found that the JA-related transcription factors MYC2, MYC3, and MYC4 are short-lived proteins degraded by the proteasome, and stabilized by JA and light, in Arabidopsis thaliana. Dark and CONSTITUTIVE PHOTOMORPHOGENIC1 destabilize MYC2, MYC3, and MYC4, whereas R and blue (B) lights stabilize them through the activation of the corresponding photoreceptors. Consistently, phytochrome inactivation by monochromatic FR light or shade (FR-enriched light) destabilizes these three proteins and reduces their stabilization by JA. In contrast to MYCs, simulated shade conditions stabilize seven of their 10 JAZ repressors tested and reduce their degradation by JA. MYC2, MYC3, and MYC4 are required for JA-mediated defenses against the necrotrophic pathogen Botrytis cinerea and for the shade-triggered increased susceptibility, indicating that this negative effect of shade on defense is likely mediated by shade-triggered inactivation of MYC2, MYC3, and MYC4. The opposite regulation of protein stability of MYCs and JAZs by FR-enriched light help explain (on the molecular level) the long-standing observation that canopy shade represses JA-mediated defenses, facilitating reallocation of resources from defense to growth.
Hypoxic responses in plants involve Plant Cysteine Oxidases (PCOs). They catalyze the N-terminal cysteine oxidation of Ethylene Response Factors VII (ERF-VII) in an oxygen-dependent manner, leading ...to their degradation via the cysteine N-degron pathway (Cys-NDP) in normoxia. In hypoxia, PCO activity drops, leading to the stabilization of ERF-VIIs and subsequent hypoxic gene upregulation. Thus far, no chemicals have been described to specifically inhibit PCO enzymes. In this work, we devised an in vivo pipeline to discover Cys-NDP effector molecules. Budding yeast expressing AtPCO4 and plant-based ERF-VII reporters was deployed to screen a library of natural-like chemical scaffolds and was further combined with an Arabidopsis Cys-NDP reporter line. This strategy allowed us to identify three PCO inhibitors, two of which were shown to affect PCO activity in vitro. Application of these molecules to Arabidopsis seedlings led to an increase in ERF-VII stability, induction of anaerobic gene expression, and improvement of tolerance to anoxia. By combining a high-throughput heterologous platform and the plant model Arabidopsis, our synthetic pipeline provides a versatile system to study how the Cys-NDP is modulated. Its first application here led to the discovery of at least two hypoxia-mimicking molecules with the potential to impact plant tolerance to low oxygen stress.
Jasmonates (JAs) trigger an important transcriptional reprogramming of plant cells to modulate both basal development and stress responses. In spite of the importance of transcriptional regulation, ...only one transcription factor (TF), the Arabidopsis thaliana basic helix-loop-helix MYC2, has been described so far as a direct target of JAZ repressors. By means of yeast two-hybrid screening and tandem affinity purification strategies, we identified two previously unknown targets of JAZ repressors, the TFs MYC3 and MYC4, phylogenetically closely related to MYC2. We show that MYC3 and MYC4 interact in vitro and in vivo with JAZ repressors and also form homo-and heterodimers with MYC2 and among themselves. They both are nuclear proteins that bind DNA with sequence specificity similar to that of MYC2. Loss-of-function mutations in any of these two TFs impair full responsiveness to JA and enhance the JA insensitivity of myc2 mutants. Moreover, the triple mutant myc2 myc3 myc4 is as impaired as coi1-1 in the activation of several, but not all, JA-mediated responses such as the defense against bacterial pathogens and insect herbivory. Our results show that MYC3 and MYC4 are activators of JA-regulated programs that act additively with MYC2 to regulate specifically different subsets of the JA-dependent transcriptional response.
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