Abiotic stress
Ammonium (NH4+) and nitrate (NO3−) are major inorganic nitrogen (N) sources for plants. When serving as the sole or dominant N supply, NH4+ often causes root inhibition and shoot chlorosis in plants, known as ammonium toxicity. NO3− usually causes no toxicity and can mitigate ammonium toxicity even at low concentrations, referred to as nitrate-dependent alleviation of ammonium toxicity. Our previous studies indicated a NO3− efflux channel SLAH3 is involved in this process. However, whether additional components contribute to NO3−-mediated NH4+ detoxification is unknown. Previously, mutations in NO3− transporter NRT1.1 were shown to cause enhanced resistance to high concentrations of NH4+. Whereas, in this study, we found when the high-NH4+ medium was supplemented with low concentrations of NO3−, nrt1.1 mutant plants showed hyper-sensitive phenotype instead. Furthermore, mutation in NRT1.1 caused enhanced medium acidification under high-NH4+/low-NO3− condition, suggesting NRT1.1 regulates ammonium toxicity by facilitating H+ uptake. Moreover, NRT1.1 was shown to interact with SLAH3 to form a transporter-channel complex. Interestingly, SLAH3 appeared to affect NO3− influx while NRT1.1 influenced NO3− efflux, suggesting NRT1.1 and SLAH3 regulate each other at protein and/or gene expression levels. Our study thus revealed NRT1.1 and SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity through regulating NO3− transport and balancing rhizosphere acidification.
In eukaryotic cells, gene expression is greatly influenced by the dynamic chromatin environment. Epigenetic mechanisms, including covalent modifications to DNA and histone tails and the accessibility of chromatin, create various chromatin states for stress‐responsive gene expression that is important for adaptation to harsh environmental conditions. Recent studies have revealed that many epigenetic factors participate in abiotic stress responses, and various chromatin modifications are changed when plants are exposed to stressful environments. In this review, we summarize recent progress on the cross‐talk between abiotic stress response pathways and epigenetic regulatory pathways in plants. Our review focuses on epigenetic regulation of plant responses to extreme temperatures, drought, salinity, the stress hormone abscisic acid, nutrient limitations and ultraviolet stress, and on epigenetic mechanisms of stress memory.
The Na+/H+ antiporter SOS1 enhances the salinity tolerance of a number of plant species, but its involvement in the response to hypoxia is less well known. We presented chrysanthemum homologs CmSOS1 and CmRCD1 coordinately mediate waterlogging tolerance by maintaining membrane integrity and minimizing the level of reactive oxygen species.
Crop yield is sensitive to salt stresses, for which Calcineurin B‐like proteins (CBLs) are major response factors. This study shows that Arabidopsis CBL10, through protein S ‐acylation by protein S ‐acyl transferase10, targets to the vacuolar membrane to confer salt tolerance.
Drought is a major abiotic stress that limits plant growth and development. Adaptive mechanisms have evolved to mitigate drought stress, including the capacity to adjust water loss rate and to modify the morphology and structure of the epidermis. Here, we show that the expression of CmNF-YB8, encoding a nuclear factor Y (NF-Y) B-type subunit, is lower under drought conditions in chrysanthemum (Chrysanthemum morifolium). Transgenic chrysanthemum lines in which transcript levels of CmNF-YB8 were reduced by RNA interference (CmNF-YB8-RNAi) exhibited enhanced drought resistance relative to control lines, whereas lines overexpressing CmNF-YB8 (CmNF-YB8-OX) were less tolerant to drought. Compared to wild type (WT), CmNF-YB8-RNAi plants showed reduced stomatal opening and a thicker epidermal cuticle that correlated with their water loss rate. We also identified genes involved in stomatal adjustment (CBL-interacting protein kinase 6, CmCIPK6) and cuticle biosynthesis (CmSHN3) that are more highly expressed in CmNF-YB8-RNAi lines than in WT, CmCIPK6 being a direct downstream target of CmNF-YB8. Virus-induced gene silencing of CmCIPK6 or CmSHN3 in the CmNF-YB8-RNAi background abolished the effects of CmNF-YB8-RNAi on stomatal closure and cuticle deposition, respectively. CmNF-YB8 thus regulates CmCIPK6 and CmSHN3 expression to alter stomatal movement and cuticle thickness in the leaf epidermis, thereby affecting drought resistance.
Trehalose plays important roles in plant growth and stress responses and is synthesized from trehalose‐6‐phosphate by trehalose‐6‐phosphate phosphatase (TPP). Here, we show that trehalose and abscisic acid (ABA) have synergistic effects on root growth and stomatal closure. The Arabidopsis thaliana genome contains ten genes encoding TPPs and the expression level of one, TPPE, and trehalose contents increased in response to ABA. In the presence of ABA, the ABA‐responsive transcription factor ABA RESPONSE ELEMENT BINDING FACTOR2 (ABF2) directly binds to the TPPE promoter to activate its expression. Genetic analysis revealed that TPPE acts downstream of ABF2, which is supported by the findings that TPPE expression and trehalose content are reduced in the abf2 mutant and that a mutation in TPPE abolished the ABA‐sensitive root elongation phenotype of 35S:ABF2 plants. Reactive oxygen species (ROS) accumulation in response to ABA failed to occur in tppe mutant plants, suggesting that TPPE is involved in ABA‐controlled root elongation and stomatal movement by inducing ROS accumulation. This study uncovers a new branch of the ABA signaling pathway and provides a molecular basis for the role of trehalose in plant responses to abiotic stress.
In angiosperms, floral transition is a key developmental transition from the vegetative to reproductive growth, and requires precise regulation to maximize the reproductive success. A complex regulatory network governs this transition through integrating flowering pathways in response to multiple exogenous and endogenous cues. Phytohormones are essential for proper plant developmental regulation and have been extensively studied for their involvement in the floral transition. Among various phytohormones, gibberellin (GA) plays a major role in affecting flowering in the model plant Arabidopsis thaliana. The GA pathway interact with other flowering genetic pathways and phytohormone signaling pathways through either DELLA proteins or mediating GA homeostasis. In this review, we summarize the recent advances in understanding the mechanisms of DELLA‐mediated GA pathway in flowering time control in Arabidopsis, and discuss its possible link with other phytohormone pathways during the floral transition.
Cotton (Gossypium hirsutum L.) is a major crop and the main source of natural fiber worldwide. Because various abiotic and biotic stresses strongly influence cotton fiber yield and quality, improved stress resistance of this crop plant is urgently needed. In this study, we used Gateway technology to construct a normalized full‐length cDNA overexpressing (FOX) library from upland cotton cultivar ZM12 under various stress conditions. The library was transformed into Arabidopsis to produce a cotton‐FOX‐Arabidopsis library. Screening of this library yielded 6,830 transgenic Arabidopsis lines, of which 757 were selected for sequencing to ultimately obtain 659 cotton ESTs. GO and KEGG analyses mapped most of the cotton ESTs to plant biological process, cellular component, and molecular function categories. Next, 156 potential stress‐responsive cotton genes were identified from the cotton‐FOX‐Arabidopsis library under drought, salt, ABA, and other stress conditions. Four stress‐related genes identified from the library, designated as GhCAS , GhAPX , GhSDH , and GhPOD , were cloned from cotton complementary DNA, and their expression patterns under stress were analyzed. Phenotypic experiments indicated that overexpression of these cotton genes in Arabidopsis affected the response to abiotic stress. The method developed in this study lays a foundation for high‐throughput cloning and rapid identification of cotton functional genes.
Cuticular wax is a natural barrier on terrestrial plant organs, which protects plants from damages caused by a variety of stresses. Here, we report the identification and functional characterization of a cuticular‐wax‐related gene, Zea mays L. SEMI‐ROLLED LEAF 5 (ZmSRL5). The loss‐of‐function mutant srl5, which was created by a 3,745 bp insertion in the first intron that led to the premature transcript, exhibited abnormal wax crystal morphology and distribution, which, in turn, caused the pleiotropic phenotypes including increased chlorophyll leaching and water loss rate, decreased leaf temperature, sensitivity to drought, as well as semi‐rolled mature leaves. However, total wax amounts showed no significant difference between wild type and semi‐rolled leaf5 (srl5) mutant. The phenotype of srl5 was confirmed through the generation of two allelic mutants using CRISPR/Cas9. ZmSRL5 encodes a CASPARIAN‐STRIP‐MEMBRANE‐DOMAIN‐LIKE (CASPL) protein located in plasma membrane, and highly expressed in developing leaves. Further analysis showed that the expressions of the most wax related genes were not affected or slightly altered in srl5. This study, thus, primarily uncovers that ZmSRL5 is required for the structure formation of the cuticular wax and could increase the drought tolerance by maintaining the proper cuticular wax structure in maize.
In plants, submergence from flooding causes hypoxia, which impairs energy production and affects plant growth, productivity, and survival. In Arabidopsis, hypoxia induces nuclear localization of the group VII ethylene‐responsive transcription factor RELATED TO AP2.12 (RAP2.12), following its dissociation from the plasma membrane‐anchored ACYL‐COA BINDING PROTEIN1 (ACBP1) and ACBP2. Here, we show that polyunsaturated linolenoyl‐CoA (18:3‐CoA) regulates RAP2.12 release from the plasma membrane. Submergence caused a significant increase in 18:3‐CoA, but a significant decrease in 18:0‐, 18:1‐, and 18:2‐CoA. Application of 18:3‐CoA promoted nuclear accumulation of the green fluorescent protein (GFP) fusions RAP2.12‐GFP, HYPOXIA‐RESPONSIVE ERF1‐GFP, and RAP2.3‐GFP, and enhanced transcript levels of hypoxia‐responsive genes. Plants with decreased ACBP1 and ACBP2 (acbp1 ACBP2‐RNAi, produced by ACBP2 RNA interference in the acbp1 mutant) had reduced tolerance to hypoxia and impaired 18:3‐CoA‐induced expression of hypoxia‐related genes. In knockout mutants and overexpression lines of LONG‐CHAIN ACYL‐COA SYNTHASE2 (LACS2) and FATTY ACID DESATURASE 3 (FAD3), the acyl‐CoA pool size and 18:3‐CoA levels were closely related to ERF‐VII‐mediated signaling and hypoxia tolerance. These findings demonstrate that polyunsaturation of long‐chain acyl‐CoAs functions as important mechanism in the regulation of plant hypoxia signaling, by modulating ACBP–ERF‐VII dynamics.
The homeodomain‐leucine zipper (HD‐Zip) proteins play crucial roles in plant developmental and environmental responses. However, how they mediate gene expression to facilitate abiotic stress tolerance remains unknown. In the present study, we characterized BpHOX2 (encoding a HD‐Zip I family protein) from birch (Betula platyphylla). BpHOX2 is predominately expressed in mature stems and leaves, but expressed at a low level in apical buds and roots, suggesting that it has tissue‐specific characteristics. BpHOX2 expression was highly induced by osmotic and salt, but only slightly induced by abscisic acid. Overexpression of BpHOX2 markedly improved osmotic tolerance, while knockdown of BpHOX2 increased sensitivity to osmotic stress. BpHOX2 could induce the expression of pyrroline‐5‐carboxylate synthase, peroxidase, and superoxide dismutase genes to improve proline levels and the reactive oxygen species scavenging capability. Chromatin immunoprecipitation sequencing combined with RNA sequencing showed that BpHOX2 could bind to at least four cis‐acting elements, including dehydration‐responsive element “RCCGAC”, Myb‐p binding box “CCWACC,” and two novel cis‐acting elements with the sequences of “AAGAAG” and “TACGTG” (termed HBS1 and HBS2, respectively) to regulate gene expression. Our results suggested that BpHOX2 is a transcription factor that binds to different cis‐acting elements to regulate gene expression, ultimately improving osmotic tolerance in birch.
U‐box E3 ubiquitin ligases play important roles in the ubiquitin/26S proteasome machinery and in abiotic stress responses. TaPUB1‐overexpressing wheat (Triticum aestivum L.) were generated to evaluate its function in salt tolerance. These plants had more salt stress tolerance during seedling and flowering stages, whereas the TaPUB1‐RNA interference (RNAi)‐mediated knock‐down transgenic wheat showed more salt stress sensitivity than the wild type (WT). TaPUB1 overexpression upregulated the expression of genes related to ion channels and increased the net root Na+ efflux, but decreased the net K+ efflux and H+ influx, thereby maintaining a low cytosolic Na+/K+ ratio, compared with the WT. However, RNAi‐mediated knock‐down plants showed the opposite response to salt stress. TaPUB1 could induce the expression of some genes that improved the antioxidant capacity of plants under salt stress. TaPUB1 also interacted with TaMP (Triticum aestivum α‐mannosidase protein), a regulator playing an important role in salt response in yeast and in plants. Thus, low cytosolic Na+/K+ ratios and better antioxidant enzyme activities could be maintained in wheat with overexpression of TaPUB1 under salt stress. Therefore, we conclude that the U‐box E3 ubiquitin ligase TaPUB1 positively regulates salt stress tolerance in wheat.
BT2 is a BTB/TAZ domain protein with key roles in multiple stress responses and the plant development of Arabidopsis (Figueroa et al. 2005; Ren et al. 2007; Mandadi et al. 2009). Recent studies have demonstrated that apple MdBT2 functions as a negative regulator in diverse hormonal and environmental signal‐induced anthocyanin biosynthesis, suggesting that MdBT2 integrates stress signals and anthocyanin biosynthesis.
Endomembrane trafficking is a fundamental cellular process in all eukaryotic cells and its regulatory mechanisms have been extensively studied. In plants, the endomembrane trafficking system needs to be constantly adjusted to adapt to the ever‐changing environment. Evidence has accumulated supporting the idea that endomembrane trafficking is tightly linked to stress signaling pathways to meet the demands of rapid changes in cellular processes and to ensure the correct delivery of stress‐related cargo molecules. However, the underlying mechanisms remain unknown. In this review, we summarize the recent findings on the functional roles of both secretory trafficking and endocytic trafficking in different types of abiotic stresses. We also highlight and discuss the unique properties of specific regulatory molecules beyond their conventional functions in endosomal trafficking during plant growth under stress conditions.
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