In Arabidopsis, photoperiodic flowering is controlled by the regulatory hub gene CONSTANS (CO), whereas floral organ senescence is regulated by the jasmonates (JAs). Because these processes are ...chronologically ordered, it remains unknown whether there are common regulators of both processes. In this study, we discovered that CO protein accumulates in Arabidopsis flowers after floral induction, and it displays a diurnal pattern in floral organs different from that in the leaves. We observed that altered CO expression could affect flower senescence and abscission by interfering with JA response, as shown by petal-specific transcriptomic analysis as well as CO overexpression in JA synthesis and signaling mutants. We found that CO has a ZIM (ZINC-FINGER INFLORESCENCE MERISTEM) like domain that mediates its interaction with the JA response repressor JAZ3 (jasmonate ZIM-domain 3). Their interaction inhibits the repressor activity of JAZ3, resulting in activation of downstream transcription factors involved in promoting flower senescence. Furthermore, we showed that CO, JAZ3, and the E3 ubiquitin ligase COI1 (Coronatine Insensitive 1) could form a protein complex in planta, which promotes the degradation of both CO and JAZ3 in the presence of JAs. Taken together, our results indicate that CO, a key regulator of photoperiodic flowering, is also involved in promoting flower senescence and abscission by augmenting JA signaling and response. We propose that coordinated recruitment of photoperiodic and JA signaling pathways could be an efficient way for plants to chronologically order floral processes and ensure the success of offspring production.
This study discovers that the flowering regulatory hub gene CONSTANS (CO) has a new role in Arabidopsis flowers: inducing senescence via jasmonate signaling. A newly defined ZIM-like domain in CO mediates its interaction with JAZ3 and this interaction inhibits the repressor activity of JAZ3 to promote JA-induced flower senescence. The study suggests that photoperiod signals may coordinate with hormone function to ensure the correct chronological order of flowering time and floral senescence programs.
Summary
Multidrug efflux pumps are ancient elements encoded in every genome, from bacteria to humans. In bacteria, in addition to antibiotics, efflux pumps extrude a wide range of substrates, ...including quorum sensing signals, bacterial metabolites, or plant‐produced compounds. This indicates that their original functions may differ from their recently acquired role in the extrusion of antibiotics during human infection. Concerning plant‐produced compounds, some of them are substrates and inducers of the same efflux pump, suggesting a coordinated plant/bacteria coevolution. Herein we analyse the ability of 1243 compounds from a Natural Product‐Like library to induce the expression of P. aeruginosa mexCD‐oprJ or mexAB‐oprM efflux pumps' encoding genes. We further characterized natural‐like compounds that do not trigger antibiotic resistance in P. aeruginosa and that act as virulence inhibitors, choosing those that were not only inducers but substrates of the same efflux pump. Four compounds impair swarming motility, exotoxin secretion through the Type 3 Secretion System (T3SS) and the ability to kill Caenorhabditis elegans, which might be explained by the downregulation of genes encoding flagellum and T3SS. Our results emphasize the possibility of discovering new anti‐virulence drugs by screening natural or natural‐like libraries for compounds that behave as both, inducers and substrates of efflux pumps.
(+)-7-iso-Jasmonoyl-L-isoleucine (JA-Ile) regulates developmental and stress responses in plants. Its perception involves the formation of a ternary complex with the F-box COI1 and a member of the ...JAZ family of co-repressors and leads to JAZ degradation. Coronatine (COR) is a bacterial phytotoxin that functionally mimics JA-Ile and interacts with the COI1-JAZ co-receptor with higher affinity than JA-Ile. On the basis of the co-receptor structure, we designed ligand derivatives that spatially impede the interaction of the co-receptor proteins and, therefore, should act as competitive antagonists. One derivative, coronatine-O-methyloxime (COR-MO), has strong activity in preventing the COI1-JAZ interaction, JAZ degradation and the effects of JA-Ile or COR on several JA-mediated responses in Arabidopsis thaliana. Moreover, it potentiates plant resistance, preventing the effect of bacterially produced COR during Pseudomonas syringae infections in different plant species. In addition to the utility of COR-MO for plant biology research, our results underscore its biotechnological potential for safer and sustainable agriculture.
A significant limitation of classical loss-of-function screens designed to dissect genetic pathways is that they rarely uncover genes that function redundantly, are compensated by alternative ...metabolic or regulatory circuits, or which have an additional role in early embryo or gametophyte development. Activation T-DNA tagging is one approach that has emerged in plants to help circumvent these potential problems. This technique utilises a T-DNA sequence that contains four tandem copies of the cauliflower mosaic virus (CaMV) 35S enhancer sequence. This element enhances the expression of neighbouring genes either side of the randomly integrated T-DNA tag, resulting in gain-of-function phenotypes. Activation tagging has identified a number of genes fundamental to plant development, metabolism and disease resistance in Arabidopsis. This review provides selected examples of these discoveries to highlight the utility of this technology. The recent development of activation tagging strategies for other model plant systems and the construction of new more sophisticated vectors for the generation of conditional alleles are also discussed. These recent advances have significantly expanded the horizons for gain-of-function genetics in plants.
Recent analyses on fungal jasmonic acid (JA)-containing metabolites suggest a mode-of-action of these naturally occurring compounds as inactive storage pools of JA. Plants and/or fungi can catabolize ...JA into the bioactive jasmonyl-isoleucine (JA-Ile) that in turn activates the JA-Ile-pathway in planta. To extend our knowledge on JA-derivates related to natural occurring JA conjugates, N-(-)-jasmonyl-S-tyrosin (JA-Tyr) and the ester JA-Sei between JA and seiridin, a fungal disubstituted furanone, were synthesized. The classical procedures for ester synthesis were applied for compound JA-Sei, while N-(-)-jasmonyl-S-tyrosin was synthesized with an optimized procedure. JA-Tyr and JA-Sei were characterized by spectroscopic method (essentially 1D and 2D NMR spectroscopy and ESI-MS) and their stereochemical composition was determined by means of HPLC and circular dichroism analysis. Finally, the activity of these JA-derivates was analyzed in planta. JA-Tyr and JA-Sei trigger JA-regulated plant responses, such as protein degradation and growth inhibition. These effects require the conversion of JA into JA-Ile and its recognition by the plant JA-Ile perception complex COI1-JAZ. Overall, these data suggest a mode-of-action of JA-Tyr and JA-Sei as inactive pool of JA that can be transformed into the bioactive JA-Ile to induce the canonical JA-Ile-pathway.
Display omitted
•Synthesis of N-(-)-jasmonyl-S-tyrosin (JA-Tyr) and seiridin jasmonate (JA-Sei).•Determination of the stereochemical composition by HPLC and CD of JA-Tyr and JA-Sei.•Activity of JA-Tyr and JA-Sei in planta. JA-Tyr and JA-Sei trigger JA-regulated plant responses.
In order to identify components of the defense signaling network engaged following attempted pathogen invasion, we generated a novel PR-1::luciferase (LUC) transgenic line that was deployed in an ...imaging-based screen to uncover defense-related mutants. The recessive mutant designated cir1 exhibited constitutive expression of salicylic acid (SA), jasmonic acid (JA)/ethylene, and reactive oxygen intermediate-dependent genes. Moreover, this mutation conferred resistance against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and a virulent oomycete pathogen Peronospora parasitica Noco2. Epistasis analyses were undertaken between cir1 and mutants that disrupt the SA (nprl, nahG), JA (jar1), and ethylene (ET) (ein2) signaling pathways. While resistance against both P. syringae pv. tomato DC3000 and Peronospora parasitica Noco2 was partially reduced by npr1, resistance against both of these pathogens was lost in an nahG genetic background. Hence, cirl-mediated resistance is established via NPR1-dependent and -independent signaling pathways and SA accumulation is essential for the function of both pathways. While jar1 and ein2 reduced resistance against P. syringae pv. tomato DC3000, these mutations appeared not to impact cir1-mediated resistance against Peronospora parasitica Noco2. Thus, JA and ET sensitivity are required for cir1-mediated resistance against P. syringae pv. tomato DC3000 but not Peronospora parasitica Noco2. Therefore, the cir1 mutation may define a negative regulator of disease resistance that operates upstream of SA, JA, and ET accumulation.
The life cycle of bacterial phytopathogens consists of a benign epiphytic phase, during which the bacteria grow in the soil or on the plant surface, and a virulent endophytic phase involving the ...penetration of host defenses and the colonization of plant tissues. Innovative strategies are urgently required to integrate copper treatments that control the epiphytic phase with complementary tools that control the virulent endophytic phase, thus reducing the quantity of chemicals applied to economically and ecologically acceptable levels. Such strategies include targeted treatments that weaken bacterial pathogens, particularly those inhibiting early infection steps rather than tackling established infections. This chapter describes a reporter gene-based chemical genomic high-throughput screen for the induction of bacterial virulence by plant molecules. Specifically, we describe a chemical genomic screening method to identify agonist and antagonist molecules for the induction of targeted bacterial virulence genes by plant extracts, focusing on the experimental controls required to avoid false positives and thus ensuring the results are reliable and reproducible.
Summary
Coronatine (
COR
) facilitates entry of bacteria into the plant apoplast by stimulating stomata opening.
COR
‐induced signaling events at stomata remain unclear. We found that the
COR
and ...jasmonate isoleucine (
JA
‐Ile) co‐receptor
JAZ
2 is constitutively expressed in guard cells and modulates stomatal dynamics during bacterial invasion
We analyzed tissue expression patterns of
At
JAZ
genes and measured stomata opening and pathogen resistance in loss‐ and gain‐of‐function mutants.
Arabidopsis
jaz2
mutants are partially impaired in pathogen‐induced stomatal closing and more susceptible to
Pseudomonas
. Gain‐of‐function mutations in
JAZ
2 prevent stomatal reopening by
COR
and are highly resistant to bacterial penetration. The
JAZ
2 targets
MYC
2,
MYC
3 and
MYC
4 directly regulate the expression of
ANAC
19,
ANAC
55
and
ANAC
72
to modulate stomata aperture. Due to the antagonistic interactions between the salicylic acid (
SA
) and
JA
defense pathways, efforts to increase resistance to biotrophs result in enhanced susceptibility to necrotrophs, and vice versa. Remarkably, dominant
jaz2Δjas
mutants are resistant to
Pseudomonas syringae
but retain unaltered resistance against necrotrophs.
Our results demonstrate the existence of a
COI
1‐
JAZ
2‐
MYC
2,3,4‐
ANAC
19,55,72 module responsible for the regulation of stomatal aperture that is hijacked by bacterial
COR
to promote infection. They also provide novel strategies for crop protection against biotrophs without compromising resistance to necrotrophs.
See also the Commentary on this article by
Wasternack,
213:
972–975
.
• Multidrug and toxic compound extrusion (MATE) proteins comprise the most recently identified family of multidrug transporters. In plants, the numbers of MATE proteins has undergone a remarkable ...expansion, underscoring the importance of these transporters within this kingdom. • Here, we describe the identification and characterization of Activated Disease Susceptibility 1 (ADS1) which encodes a putative MATE transport protein. An activation tagging screen uncovered the ads1‐Dominant (ads1‐D) mutant, which was subsequently characterized by molecular, genetic and biochemical approaches. • The ads1‐D mutant was compromised in both basal and nonhost resistance against microbial pathogens. Further, plant defence responses conferred by RPS4 were also disabled in ads1‐D plants. By contrast, depletion of ADS1 transcripts by RNA‐interference (RNAi) promoted basal disease resistance. Unexpectedly, ads1‐D plants were found to constitutively accumulate reactive oxygen intermediates (ROIs). However, analysis of ads1‐D Arabidopsis thaliana respiratory burst oxidase (atrboh) double and triple mutants indicated that an increase in ROIs did not impact ads1‐D‐mediated disease susceptibility. • Our findings imply that ADS1 negatively regulates the accumulation of the plant immune activator salicylic acid (SA) and cognate Pathogenesis‐Related 1 (PR1) gene expression. Collectively, these data highlight an important role for MATE proteins in the establishment of plant disease resistance.
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