Thaumatin was isolated as a sweet-tasting protein. Arabidopsis has over 20 Thaumatin-Like Protein (TLP)/Osmoti-Like Protein (OLP) genes that belong to the PR5 family. Although biotic stress-related ...functions of TLPs have been reported from transgenic lines expressing TLPs, it is nonetheless necessary to investigate genetic phenotypes produced by defects in the TLP genes. In this report, four TLP genes were selected based on sequence similarities (Thau1/2/3/4), and the corresponding mutant thau1/2/3/4 was examined for biotic and abiotic stress responses. The thau1/2/3/4 mutant showed increased susceptibility to the Pseudomonas syringae pv. tomato DC3000 infection, and reduced sensitivity to the ABA and drought stress treatments. Each of the four thaumatin genes showed different gene expression patterns for ABA treatment. Moreover, ABA-inductions of Thau1/2/3/4 were largely dependent on the intact ABA signaling pathway mediated by PYR/PYL receptors. Among the many ABA-responsive genes affected by the defects of Thau1/2/3/4, reduced expression of P5CS1 with decreased accumulation phenotype of prolines indicates that compromised proline synthesis may be associated with the stress phenotypes of thau1/2/3/4. Our data suggest that Thau1/2/3/4 have a function in both biotic stress and abiotic stress signal transduction through the regulation of proline synthesis.
●The quadruple mutant of 4 Thaumatin-like genes shows defects in the production of stress responses against ABA and pathogen.●The ABA-induction of Thaumatin-like genes requires the intact ABA signaling pathway.●The function of Thaumain-like genes is required for the production of proline biosynthesis.
Summary
The signal transduction pathway governed by the phytohormone abscisic acid (ABA) regulates not only abiotic stress responses but also early developmental programs such as seed dormancy, ...germination and seedling growth in response to environmental signals. Optimal plant growth and development depend on the integration of environmental stimuli and intrinsic developmental programs. Here, we show that the homeodomain transcription factors BLH1 and KNAT3, previously implicated in embryo sac development, have additional functions in ABA‐mediated seed dormancy and early seedling development. The ABA‐dependent induction of BLH1 and KNAT3 expression required the presence of functional PYR/PYL/RCAR receptors. The blh1 and knat3 mutants were less sensitive than the wild‐type to ABA or salinity exposure during seed germination and early seedling development. In contrast, BLH1 over‐expressing lines were hypersensitive to ABA and salinity, and exhibited increased expression of ABA‐responsive genes, such as ABI3 and ABI5. BLH1 interacted with KNAT3 and enhanced the retention of KNAT3 in the nucleus. BLH1 and KNAT3 synergistically increased the ABA responses by binding to and subsequently activating the ABI3 promoter. Taken together, we propose that BLH1 and KNAT3 together modulate seed germination and early seedling development by directly regulating ABI3 expression.
Plants have evolutionarily established resistance responses to a variety of abiotic stress conditions, in which ABA mediates the integrated regulation of these stress responses. Numerous proteins ...function at the transcription level or at the protein level when contributing to controls of the ABA signaling process. Although osmotin is identified as a salt-inducible protein, its function in the abiotic stress response is yet to be elucidated. To examine the role of Arabidopsis OSMOTIN 34 (OSM34) in the ABA signaling pathway, a deletion mutant osm34 generated by a CRISPR/Cas9 system and the double mutant osm34 osml (osmotin 34-like) were analyzed for various ABA responses. Both osm34 and osm34 osml showed reduced levels of ABA responses in seeds and leaves. Moreover, proline level and expression of the proline biosynthesis gene P5CS1 was significantly reduced in osm34 osml. Interestingly, OSM34 binds to SKP2A, an F-Box protein whose transcription is induced by ABA. The protein stability of OSM34 was determined to be under the control of the 26S proteasome. In conclusion, our data suggest that OSM34 functions as a positive regulator in the generation of ABA responses and is under post-translational control.
When plants are subjected to unfavorable environmental conditions, overall gene expression in stressed cells is altered from a programmed pattern for normal development to an adaptive pattern for ...survival. Rapid changes in plant gene expression include production of stress responsive proteins for protection as well as reduction of irrelevant proteins to minimize energy consumption during growth. In addition to the many established mechanisms known to modulate gene expression in eukaryotes, a novel strategy involving tRNA-derived fragments (tRFs) was recently reported to control gene expression. In animals, tRFs are shown to play a certain role in infected or cancer cells. However, tRFs are expected to function in the regulation of gene expression against abiotic stress conditions in plants. Moreover, the underlying mechanism linking up-regulation of tRFs under stress conditions with the stress tolerant response remains unknown. In this review, the biogenesis and putative function of diverse tRFs in abiotic stress signaling are discussed with a focus on tRFs as a transcriptional/post-transcriptional/translational regulator.
Summary
Insight into how plants simultaneously cope with multiple stresses, for example, when challenged with biotic stress from pathogen infection and abiotic stress from drought, is important both ...for understanding evolutionary trade‐offs and optimizing crop responses to these stresses. Mechanisms by which initial plant immune signaling antagonizes abscisic acid (ABA) signal transduction require further investigation. Using a chemical genetics approach, the small molecule 5‐(3,4‐dichlorophenyl)furan‐2‐yl‐piperidine‐1‐ylmethanethione (DFPM) has previously been identified due to its ability to suppress ABA signaling via plant immune signaling components. Here, we have used forward chemical genetics screening to identify DFPM‐insensitive loci by monitoring the activity of ABA‐inducible pRAB18::GFP in the presence of DFPM and ABA. The ability of DFPM to attenuate ABA signaling was reduced in rda mutants (resistant to DFPM inhibition of ABA signaling). One of the mutants, rda2, was mapped and is defective in a gene encoding a lectin receptor kinase. RDA2 functions in DFPM‐mediated inhibition of ABA‐mediated reporter expression. RDA2 is required for DFPM‐mediated activation of immune signaling, including phosphorylation of mitogen‐activated protein kinase (MAPK) 3 (MPK3) and MPK6, and induction of immunity marker genes. Our study identifies a previously uncharacterized receptor kinase gene that is important for DFPM‐mediated immune signaling and inhibition of ABA signaling. We demonstrate that the lectin receptor kinase RDA2 is essential for perceiving the DFPM signal and activating MAPKs, and that MKK4 and MKK5 are required for DFPM interference with ABA signal transduction.
Significance Statement
By activating plant immune signaling, the synthetic small molecule 5‐(3,4‐dichlorophenyl)furan‐2‐yl‐piperidine‐1‐ylmethanethione (DFPM) inhibits signaling by the drought‐response hormone abscisic acid (ABA). DFPM thus provides a powerful tool for dissecting mechanisms that enable initial biotic signals to interfere with ABA signal transduction. We have used DFPM to identify, by a forward chemical genetics screen, a lectin receptor kinase that is essential to this process.
Stomatal pores are formed by pairs of specialized epidermal guard cells and serve as major gateways for both CO(2) influx into plants from the atmosphere and transpirational water loss of plants. ...Because they regulate stomatal pore apertures via integration of both endogenous hormonal stimuli and environmental signals, guard cells have been highly developed as a model system to dissect the dynamics and mechanisms of plant-cell signaling. The stress hormone ABA and elevated levels of CO(2) activate complex signaling pathways in guard cells that are mediated by kinases/phosphatases, secondary messengers, and ion channel regulation. Recent research in guard cells has led to a new hypothesis for how plants achieve specificity in intracellular calcium signaling: CO(2) and ABA enhance (prime) the calcium sensitivity of downstream calcium-signaling mechanisms. Recent progress in identification of early stomatal signaling components are reviewed here, including ABA receptors and CO(2)-binding response proteins, as well as systems approaches that advance our understanding of guard cell-signaling mechanisms.
Most eukaryotic genes undergo various post-transcriptional processing events before being translated into proteins. Alternative splicing (AS) is one such event and is an essential mechanism in ...post-transcriptional gene regulation that allows multiple mRNA variants to be expressed from a single pre-mRNA, thereby expending the functional capacity of a gene as well as the organismal complexity. With the advancement of next-generation sequencing technologies, extensive transcriptomic resources in plant species have determined crucial roles of AS in the regulation of developmental processes and adaption to environmental stresses. We review here recent studies of AS events and splicing factors that specifically affect abiotic-stress tolerance in crop plants, including other agricultural traits. Understanding how alternative splicing modulates plant development and abiotic-stress responses may provide new insights for improving the environmental fitness and productivity of crop plants.
The phytohormone abscisic acid (ABA) is a key regulator of plant growth and development as well as plant responses to situations of decreased water availability. Protein phosphatases type 2C (PP2Cs) ...from group A, which includes the ABI1/HAB1 and PP2CA branches, are key negative regulators of ABA signaling. Specifically, HAB1, ABI1, ABI2, and PP2CA have been shown to affect both seed and vegetative responses to ABA. To further understand their contribution to ABA signaling and to unravel possible genetic interactions and functional redundancy among them, we have generated different combinations of double and triple mutants impaired in these PP2Cs. Interestingly, hab1-1pp2ca-1 and abi1-2pp2ca-1 double mutants showed reduced water loss and enhanced resistance to drought stress, which further supports the role of PP2CA in vegetative responses to ABA. Two triple hab1-1abi1-2abi2-2 and hab1-1abi1-2pp2ca-1 mutants were generated, which showed an extreme response to exogenous ABA, impaired growth, and partial constitutive response to endogenous ABA. Thus, transcriptomic analysis revealed a partial up-regulation/down-regulation of a subset of ABA-responsive genes in both triple mutants in the absence of exogenous ABA. Comparison of ABA responses in the different pp2c mutants showed that a progressive increase in ABA sensitivity could be obtained through combined inactivation of these PP2Cs. These results indicate that ABA response is finely tuned by the integrated action of these genes, which is required to prevent a constitutive response to endogenous ABA that might have a deleterious effect on growth and development in the absence of environmental stress.
The small compound 5-(3,4-dichlorophenyl) furan-2-yl-piperidine-1-ylmethanethione (DFPM) inhibits ABA responses by activating effector-triggered immune signal transduction in Arabidopsis. In addition ...to the known function of DFPM as an antagonist of ABA signaling, DFPM causes accession-specific root growth arrest in Arabidopsis Columbia-0 via the TIR-NLR protein VICTR (VARIATION IN COMPOUND TRIGGERED ROOT growth response) in an EDS1/PAD4/RAR1/SGT1B-dependent manner. Although DFPM could control the specific steps of various cellular responses, the functional residues for the activity of DFPM or the existence of a stronger version of DFPM modification have not been characterized thoroughly. This study analyzed twenty-two DFPM derivatives during root growth arrest, inhibition of ABA signaling, and induction of biotic signal transduction to determine critical residues that confer the specific activity of DFPM. Furthermore, this study identified two more Arabidopsis accessions that generate significant root growth arrest in response to DFPM derivatives dependent on multiple amino acid polymorphisms in the coding region of VICTR. The isolation of novel compounds, such as DFPM-5, and specific amino acid polymorphisms critical for the compound-induced responses will help determine the detailed regulatory mechanism for how DFPM regulates abiotic and biotic stress signaling interactions.
Regulation of abscisic acid (ABA) signaling is crucial in balancing responses to abiotic stresses and retaining growth in planta. An ABA receptor (PYL/RCAR) and a protein phosphatase (PP2C), a ...co-receptor, form a complex upon binding to ABA. Previously we reported that the second and fourth positions in the VxGΦL motif of PP2Cs from
Oryza sativa
are critical in the interaction of PP2Cs with PYL/RCARs. Considering substantial effects of the VxGΦL motif on ABA signaling outputs, further comprehensive characterization of residues in the second and fourth positions are required. Here we surveyed the second and fourth positions of the VxGΦL motif by combination of biochemical, structural and physiological analyses. We found that the fourth position of the VxGΦL motif, highly conserved to small hydrophobic residues, was a key determinant of the OsPP2C50:OsPYL/RCAR interactions across subfamilies. Large hydrophobic or any hydrophilic residues in the fourth position abrogated ABA responsiveness. Analysis of crystal structures of OsPP2C50 mutants, S265L/I267V (“LV”), I267L (“SL”) and I267W (“SW”), in complex with ABA and OsPYL/RCAR3, along with energy calculation of the complexes, uncovered that a bulky hydrophobic residue in the fourth position of the VxGΦL motif pushed away side chains of nearby residues, conferring side-chain rotameric energy stress. Hydrophilic residues in this position imposed solvation energy stress to the PP2C:PYL/RCAR complex. Germination and gene expression analyses corroborated that OsPP2C50 AS and AK mutants modulated ABA responsiveness in
Arabidopsis
. Our results suggest that ABA responsiveness could be fine-tuned by the fourth position of the VxGΦL motif on PP2Cs.
Key message
We comprehensively surveyed the VxGΦL motif to find that the fourth position, highly conserved to small hydrophobic residues, was critical in regulating ABA responsiveness.
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