MAPK cascades and major abiotic stresses

Insight into the transcriptional regulation of key genes involved in proline metabolism in plants under osmotic stress

Proline biosynthesis and catabolism pathways are executed by powerful action of specific enzymes that are subjected to environmental fluctuations at the transcriptional level. Previous researches have demonstrated that osmotic stress-induced upstream events can affect the expression of proline metabolism-related genes, which results in adjustable free proline accumulation to protect plant cells from severe damage. Here, we mainly describe the mechanisms for how some key factors, such as transcription factors, ABA (abscisic acid), Ca2+, MAPK cascades, CK (cytokinin) and phospholipase, in a phosphorylated manner, vividly function in the transcriptional regulation of proline metabolism under osmotic stress. These mechanisms reveal that sustaining of proline homeostasis is an efficient way for plants to adapt to osmotic stress.

Harnessing the power of genomics to develop climate-smart crop varieties: A comprehensive review

Abiotic stresses arising as consequences of climate change pose a serious threat to agricultural productivity on a global scale. Most cultivated crop varieties exhibit susceptibility to such environmental pressures as drought, salinity, and waterlogging. Addressing these abiotic stresses through agronomic means is not only financially burdensome but also often impractical, particularly in the case of abiotic stresses like heat stress. Cultivating resilient varieties that can withstand such pressures emerges as an economically feasible strategy to mitigate these challenges. Nevertheless, the development of stress-tolerant cultivars is hindered by the intricate nature of abiotic stress tolerance, often characterized by low heritability values. Compounding this complexity is the dynamic and multifaceted nature of these stresses, which impede conventional breeding efforts, rendering them painstakingly slow. The identification of molecular markers has emerged as a pivotal advancement in this arena. By pinpointing genomic regions associated with tolerance to abiotic stresses, these markers serve as effective tools for selection and trait introgression. In the post-genomic era, the proliferation of high-density SNP markers has revolutionized breeding strategies. Genomic selection, leveraging these markers, has become the method of choice for addressing polygenic traits with low heritability, such as abiotic stress tolerance. With the functional characterization of many genes being done, precise manipulation through genome editing techniques is gaining significant traction. This review delves into the application of molecular markers in breeding stress-tolerant crop varieties, alongside role of recent genomic techniques in enhancing abiotic stress tolerance. It also explores success stories and identifies potential targets for marker-assisted selection.

Novel Ser74 of NF-κB/IκBα phosphorylated by MAPK/ERK regulates temperature adaptation in oysters

Phosphorylation of Ser32 and Ser36 controls the degradation of IκBα is the conserved cascade mechanisms of immune core signaling pathway, NF-κB pathway in metazoans, but it's response to abiotic stress and the presence of novel phosphorylation mechanisms in other species remain unclear. Herein, we reported a novel heat-induced phosphorylation site (Ser74) at oysters' major IκBα, which independently regulated ubiquitination-proteasome degradation without the requirement of phosphorylation at S32 and S36. And this site was phosphorylated by ERK/MAPK pathway, which then promoted REL nuclear translocation to activate cell survival related genes to defend heat-stress. The MAPK-NF-κB cascade exhibited divergent thermal responses and adaptation patterns between two congeneric oyster species with differential habitat temperatures, indicating its involvement in shaping temperature adaptation. This study demonstrated that the existence of complex and unique phosphorylation-mediated signaling transduction mechanism in marine invertebrates, and expanded our understanding of the evolution and function of established classical pathway crosstalk mechanisms.

Antioxidant activity and comparative RNA-seq analysis support mitigating effects of an algae-based biostimulant on drought stress in tomato plants

Drought is a significant global environmental stress. Biostimulants offer a sustainable solution to enhance crop tolerance and mitigate productivity losses. This study assessed the impact of foliar application of ERANTHIS®, a biostimulant derived from the algae Ascophyllum nodosum and Laminaria digitata and yeast extracts, on tomato plants under mild water stress. Evaluations were conducted at 5 and 24 hours after the third treatment. Under optimal water conditions, the biostimulant showed a priming effect, with an early increase of stress markers and a timing-specific modulation of ROS non enzymatic and enzymatic ROS scavenging activities. Under drought stress, the biostimulant later decreased stress markers, by aligning the majority of analyzed ROS scavengers closer to levels in well-irrigated plants. Transcriptome analysis using RNA-seq data revealed differentially expressed genes (DEGs) and multivariate data highlighted groups of co-regulated genes (k-means clustering). Genes involved in water channel activity, transcription regulator activity, and oxidoreductase activity were significantly modulated. Cluster analysis identified distinct gene clusters influenced by the biostimulant under optimal conditions, including early responses (cell wall modification, hormone signaling) and late responses (RNA modification, nutrient uptake process). Under water stress, early responses involved actin filament organization and MAPK signaling, while late responses were related to plasma membrane components and cell wall organization. This study, integrating biochemical and transcriptomic data, provides a comprehensive understanding of how a biostimulant primes plants under optimal conditions and mitigates water stress effects, offering valuable insights for sustainable agriculture.

Genome editing prospects for heat stress tolerance in cereal crops

The world population is steadily growing, exerting increasing pressure to feed in the future, which would need additional production of major crops. Challenges associated with changing and unpredicted climate (such as heat waves) are causing global food security threats. Cereal crops are a staple food for a large portion of the world's population. They are mostly affected by these environmentally generated abiotic stresses. Therefore, it is imperative to develop climate-resilient cultivars to support the sustainable production of main cereal crops (Rice, wheat, and maize). Among these stresses, heat stress causes significant losses to major cereals. These issues can be solved by comprehending the molecular mechanisms of heat stress and creating heat-tolerant varieties. Different breeding and biotechnology techniques in the last decade have been employed to develop heat-stress-tolerant varieties. However, these time-consuming techniques often lack the pace required for varietal improvement in climate change scenarios. Genome editing technologies offer precise alteration in the crop genome for developing stress-resistant cultivars. CRISPR/Cas9 (Clustered regularly interspaced short palindromic repeat/Cas9), one such genome editing platform, recently got scientists' attention due to its easy procedures. It is a powerful tool for functional genomics as well as crop breeding. This review will focus on the molecular mechanism of heat stress and different targets that can be altered using CRISPR/Cas genome editing tools to generate climate-smart cereal crops. Further, heat stress signaling and essential players have been highlighted to provide a comprehensive overview of the topic.

Variations in Citations Across Databases: Implications for Journal Impact Factors

The Journal Impact Factor (JIF) is a widely used metric for ranking journals based on the number of citations garnered by papers published over a specific timeframe. To assess the accuracy of JIF values, I compared citation counts for 30 of my own publications across six major bibliography databases: CrossRef, Web of Science, Publisher records, Google Scholar, PubMed and Scopus. The analysis revealed noteworthy variations in citation counts, ranging from 10% to over 50% between the lowest and highest citation counts. Google Scholar records the highest citation numbers, while PubMed reported the lowest. Notably, Web of Science, whose citation data are used in JIF calculations, tend to underestimate citation counts compared to other databases. These observations raise concerns about the accuracy of JIF calculation based on Web of Science's citation data. The real JIF values for most journals would differ from those annually reported by Clarivate's journal citation reports (JCR). These citation discrepancies underscore the importance of comprehensive data collection and the necessity to include additional citation sources. Not because a paper is cited in one journal rather than another should it have a less or more citation weight. Ultimately, one citation remains one citation, regardless of its origin. Clarivate Analytics may thus need to consider integrating all citation sources for more accurate JIF values. Alternatively, Google Scholar could potentially develop its own journal or citation impact based on its extensive journal citation records. However, while making adjustments to how the Journal Impact Factor is calculated can make it more mathematically precise, it doesn't address the fundamental biases built into the metric. Even with refinements, the Journal Impact Factor will remain skewed due to how it's defined and used.

SlWRKY81 regulates Spd synthesis and Na+/K+ homeostasis through interaction with SlJAZ1 mediated JA pathway to improve tomato saline-alkali resistance

Saline-alkali stress is an important abiotic stress factor affecting tomato (Solanum lycopersicum L.) plant growth. Although the involvement of the tomato SlWRKY gene family in responses to saline-alkali stress has been well established, the mechanism underlying resistance to saline-alkali stress remains unclear. In this study, we investigated the role of SlWRKY81 in conferring saline-alkali stress resistance by using overexpression and knockout tomato seedlings obtained via genetic modification. We demonstrated that SlWRKY81 improves the ability of tomato to withstand saline-alkali stress by enhancing antioxidant capacity, root activity, and proline content while reducing malondialdehyde levels. Saline-alkali stress induces an increase in jasmonic acid (JA) content in tomato seedlings, and the SlWRKY81 promoter responds to JA signaling, leading to an increase in SlWRKY81 expression. Furthermore, the interaction between SlJAZ1 and SlWRKY81 represses the expression of SlWRKY81. SlWRKY81 binds to W-box motifs in the promoter regions of SlSPDS2 and SlNHX4, thereby positively regulating their expression. This regulation results in increased spermidine (Spd) content and enhanced potassium (K+) absorption and sodium (Na+) efflux, which contribute to the resistance of tomato to saline-alkali stress. However, JA and SlJAZ1 exhibit antagonistic effects. Elevated JA content reduces the inhibitory effect of SlJAZ1 on SlWRKY81, leading to the release of additional SlWRKY81 protein and further augmenting the resistance of tomato to saline-alkali stress. In summary, the modulation of Spd synthesis and Na+/K+ homeostasis mediated by the interaction between SlWRKY81 and SlJAZ1 represents a novel pathway underlying tomato response to saline-alkali stress.

Soybean MKK2 establishes intricate signalling pathways to regulate soybean response to cyst nematode infection

Mitogen-activated protein kinase (MPK) cascades play central signalling roles in plant immunity and stress response. The soybean orthologue of MPK kinase2 (GmMKK2) was recently identified as a potential signalling node whose expression is upregulated in the feeding site induced by soybean cyst nematode (SCN, Heterodera glycines). To investigate the role of GmMKK2 in soybean-SCN interactions, we overexpressed a catabolically inactive variant referred to as kinase-dead variant (KD-GmMKK2) using transgenic hairy roots. KD-GmMKK2 overexpression caused significant reduction in soybean susceptibility to SCN, while overexpression of the wild-type variant (WT-GmMKK2) exhibited no effect on susceptibility. Transcriptome analysis indicated that KD-GmMKK2 overexpressing plants are primed for SCN resistance via constitutive activation of defence signalling, particularly those related to chitin, respiratory burst, hydrogen peroxide and salicylic acid. Phosphoproteomic profiling of the WT-GmMKK2 and KD-GmMKK2 root samples upon SCN infection resulted in the identification of 391 potential targets of GmMKK2. These targets are involved in a broad range of biological processes, including defence signalling, vesicle fusion, chromatin remodelling and nuclear organization among others. Furthermore, GmMKK2 mediates phosphorylation of numerous transcriptional and translational regulators, pointing to the presence of signalling shortcuts besides the canonical MAPK cascades to initiate downstream signalling that eventually regulates gene expression and translation initiation. Finally, the functional requirement of specific phosphorylation sites for soybean response to SCN infection was validated by overexpressing phospho-mimic and phospho-dead variants of two differentially phosphorylated proteins SUN1 and IDD4. Together, our analyses identify GmMKK2 impacts on signalling modules that regulate soybean response to SCN infection.

TaMAPK3 phosphorylates TaCBF and TaICE and plays a negative role in wheat freezing tolerance

Freezing temperature during overwintering often kills plants; plants have thus, developed a defense mechanism called 'cold acclimation', in which a number of genes are involved in increasing cell protection and gene expression. Mitogen-activated protein kinase (MAPK) controls proteins' activities by phosphorylation and is involved in numerous metabolic pathways. In this study, we identified the protein interaction between TaMAPK3 and the proteins in the cold response pathway, ICE41, ICE87, and CBFIVd-D9. The subcellular localization and bimolecular fluorescence complement (BiFC) assays revealed that these proteins interact in the nucleus or in the plasma membrane. Furthermore, MAPK3-mediated phosphorylation of ICE41, ICE87, and CBFIVd-D9 was verified using an in vitro phosphorylation assay. TaMAPK3-overexpressing transgenic Brachypodium showed a lower survival rate upon freezing stress and lower proline content during cold acclimation, compared to wild-type plants. Furthermore, cold response gene expression analysis revealed that the expression of these genes was suppressed in the transgenic lines under cold treatment. It was further elucidated that MAPK3 mediates the degradation of ICE and CBF proteins, which implies the negative impact of MAPK3 on the freezing tolerance of plants. This study will help to elucidate the molecular mechanisms of cold tolerance and the activity of MAPK3 in wheat.

StMAPK10 gene functional identification and analysis in drought resistance of potato crop (Solanum tuberosum L.)

All over the world, potato (Solanum tuberosum L.) production is constrained by several biotic and abiotic factors. Many techniques and mechanisms have been used to overcome these hurdles and increase food for the rising population. In crop plants, the mitogen-activated protein kinase (MAPK) cascade, a significant regulator of the MAPK pathway under various biotic and abiotic stress conditions, is one of the targets to increase productivity. MAPK plays a significant role under drought stress in potato. However, the function of MAPK in drought resistance in potato is poorly understood. In this study, we wanted to identify the function of StMAPK10 in the drought resistance in potato. StMAPK10 was up-regulated under drought conditions and dynamically modulated by abiotic stresses. Over-expression and down-regulation of StMAPK10 revealed that StMAPK10 stimulated potato growth under drought conditions, as demonstrated by changes in SOD, CAT, and POD activity, as well as H2O2, proline, and MDA content. StMAPK10 up-regulation exaggerated the drought resistance of the potato plant by uplifting antioxidant activities and photosynthetic indices. Overexpressed-StMAPK10 potato lines showed highly significant results for physiological and photosynthetic indices in response to drought stress, while knockdown expression showed opposite outcomes. Additionally, subcellular localization and phenotypic analysis of transgenic and non-transgenic plants substantiated the role of the increased expression of StMAPK10 against drought stress. The results could provide novel insights into the functionality of StMAPK10 in drought responses and conceivable mechanisms.

Salicylic acid treatment and overexpression of a novel polyamine transporter gene for astaxanthin production in Phaffia rhodozyma

Phaffia rhodozyma represents an excellent microbial resource for astaxanthin production. However, the yeast's low astaxanthin productivity poses challenges in scaling up industrial production. Although P. rhodozyma originates from plant material, and phytohormones have demonstrated their effectiveness in stimulating microbial production, there has been limited research on the effects and mechanisms of phytohormones on astaxanthin biosynthesis in P. rhodozyma. In this study, the addition of exogenous salicylic acid (SA) at a concentration as low as 0.5 mg/L significantly enhanced biomass, astaxanthin content, and yield by 20.8%, 95.8% and 135.3% in P. rhodozyma, respectively. Moreover, transcriptomic analysis showed that SA had discernible impact on the gene expression profile of P. rhodozyma cells. Differentially expressed genes (DEGs) in P. rhodozyma cells between the SA-treated and SA-free groups were identified. These genes played crucial roles in various aspects of astaxanthin and its competitive metabolites synthesis, material supply, biomolecule metabolite and transportation, anti-stress response, and global signal transductions. This study proposes a regulatory mechanism for astaxanthin synthesis induced by SA, encompassing the perception and transduction of SA signal, transcription factor-mediated gene expression regulation, and cellular stress responses to SA. Notably, the polyamine transporter gene (PT), identified as an upregulated DEG, was overexpressed in P. rhodozyma to obtain the transformant Prh-PT-006. The biomass, astaxanthin content and yield in this engineered strain could reach 6.6 g/L, 0.35 mg/g DCW and 2.3 mg/L, 24.5%, 143.1% and 199.0% higher than the wild strain at the SA-free condition, respectively. These findings provide valuable insights into potential targets for genetic engineering aimed at achieving high astaxanthin yields, and such advancements hold promise for expediting the industrialization of microbial astaxanthin production.

Regulation of photosynthesis by mitogen-activated protein kinase in rice: antagonistic adjustment by OsMPK3 and OsMPK6

Photosynthesis is the basis of almost all life on earth and is the main component of crop yield that contributes to the carbohydrate partitioning to the grains. Maintaining the photosynthetic efficiency of plants in challenging environmental conditions by regulating the associated factors is a potential research arena which will help in the improvement of crop yield. Phosphorylation is known to play a pivotal role in the regulation of photosynthesis. Mitogen Activated Protein Kinases (MAPKs) cascade although known to regulate a diverse range of processes does not have any exact reported function in the regulation of photosynthesis. To elucidate the regulatory role of MAPKs in photosynthesis we investigated the changes in net photosynthesis rate and related parameters in DEX inducible over-expressing (OE) lines of two members of MAPK gene family namely, OsMPK3 and OsMPK6 in rice. Interestingly, significant changes were found in net photosynthesis rate and related physiological parameters in OsMPK3 and OsMPK6-OE lines compared to its wild-type relatives. OsMPK3 and OsMPK6 have regulatory effects on nuclear-encoded photosynthetic genes. Untargeted metabolite profiling reveals a higher accumulation of sugars and their derivatives in MPK6 overexpressing plants and a lower accumulation of sugars and organic acids in MPK3 overexpressing plants. The accumulation of amino acids was found in abundance in both MPK3 and MPK6 overexpressing plants. Understanding the effects of MPK3 and MPK6 on the CO2 assimilation of rice plants under normal growth conditions, will help in devising strategies that can be extended for crop improvement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01383-9.

Banana MKK1 modulates fruit ripening via the MKK1-MPK6-3/11-4-bZIP21 module

The mitogen-activated protein kinase (MAPK) cascade consisting of MKKK, MKK, and MPK plays an indispensable role in various plant physiological processes. Previously, we showed that phosphorylation of MabZIP21 by MaMPK6-3 is involved in banana fruit ripening, but the regulatory mechanism by which MKK controls banana fruit ripening remains unclear. Here, ripening-induced MaMKK1 from banana fruit is characterized, and transiently overexpressing and silencing of MaMKK1 in banana fruit accelerates and inhibits fruit ripening, respectively, possibly by influencing phosphorylation and activity of MPK. MaMKK1 interacts with and phosphorylates MaMPK6-3 and MaMPK11-4 mainly at the pTEpY residues, resulting in MPK activation. MaMPK11-4 phosphorylates MabZIP21 to elevate its transcriptional activation ability. Transgenic tomato fruit expressing MabZIP21 ripen quickly with a concomitant increase in MabZIP21 phosphorylation. Additionally, MabZIP21 activates MaMPK11-4 and MaMKK1 transcription to form a regulatory feedback loop. Collectively, here we report a regulatory pathway of the MaMPK6-3/11-4-MabZIP21 module in controlling banana fruit ripening.

How Plants Tolerate Salt Stress

Soil salinization inhibits plant growth and seriously restricts food security and agricultural development. Excessive salt can cause ionic stress, osmotic stress, and ultimately oxidative stress in plants. Plants exclude excess salt from their cells to help maintain ionic homeostasis and stimulate phytohormone signaling pathways, thereby balancing growth and stress tolerance to enhance their survival. Continuous innovations in scientific research techniques have allowed great strides in understanding how plants actively resist salt stress. Here, we briefly summarize recent achievements in elucidating ionic homeostasis, osmotic stress regulation, oxidative stress regulation, and plant hormonal responses under salt stress. Such achievements lay the foundation for a comprehensive understanding of plant salt-tolerance mechanisms.

Foliar Spraying of NaHS Alleviates Cucumber Salt Stress by Maintaining N+/K+ Balance and Activating Salt Tolerance Signaling Pathways

Hydrogen sulfide (H₂S) is involved in the regulation of plant salt stress as a potential signaling molecule. This work investigated the effect of H₂S on cucumber growth, photosynthesis, antioxidation, ion balance, and other salt tolerance pathways. The plant height, stem diameter, leaf area and photosynthesis of cucumber seedlings were significantly inhibited by 50 mmol·L^-1 NaCl. Moreover, NaCl treatment induced superoxide anion (O₂^·-) and Na⁺ accumulation and affected the absorption of other mineral ions. On the contrary, exogenous spraying of 200 μmol·L^-1 sodium hydrosulfide (NaHS) maintained the growth of cucumber seedlings, increased photosynthesis, enhanced the ascorbate-glutathione cycle (AsA-GSH), and promoted the absorption of mineral ions under salt stress. Meanwhile, NaHS upregulated SOS1, SOS2, SOS3, NHX1, and AKT1 genes to maintain Na⁺/K⁺ balance and increased the relative expression of MAPK3, MAPK4, MAPK6, and MAPK9 genes to enhance salt tolerance. These positive effects of H₂S could be reversed by 150 mmol·L^-1 propargylglycine (PAG, a specific inhibitor of H₂S biosynthesis). These results indicated that H₂S could mitigate salt damage in cucumber, mainly by improving photosynthesis, enhancing the AsA-GSH cycle, reducing the Na⁺/K⁺ ratio, and inducing the SOS pathway and MAPK pathway.

Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Functional Characterization of Two Cell Wall Integrity Pathway Components of the MAPK Cascade in Phomopsis longicolla

The pathogenic fungus Phomopsis longicolla causes numerous plant diseases, such as Phomopsis seed decay, pod and stem blight, and stem canker, which seriously affect the yield and quality of soybean production worldwide. Because of a lack of technology for efficient manipulation of genes for functional genomics, understanding of P. longicolla pathogenesis is limited. Here, we developed an efficient polyethylene glycol-mediated protoplast transformation system in P. longicolla that we used to characterize the functions of two genes involved in the cell wall integrity (CWI) pathway of the mitogen-activated protein kinase (MAPK) cascade, including PlMkk1, which encodes MAPK kinase, and its downstream gene PlSlt2, which encodes MAPK. Both gene knockout mutants ΔPlMkk1 and ΔPlSlt2 displayed a reduced growth rate, fragile aerial hyphae, abnormal polarized growth and pigmentation, defects in sporulation, inadequate CWI, enhanced sensitivity to abiotic stress agents, and significant deficiencies in virulence, although there were some differences in degree. The results suggest that PlMkk1 and PlSlt2 are crucial for a series of growth and development processes as well as pathogenicity. The developed transformation system will be a useful tool for additional gene function research and will aid in the elucidation of the pathogenic mechanisms of P. longicolla. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Knocking Out the Transcription Factor OsNAC092 Promoted Rice Drought Tolerance

Environmental drought stress threatens rice production. Previous studies have reported that related NAC (NAM, ATAF1/2, and CUC) transcription factors play an important role in drought stress. Herein, we identified and characterized OsNAC092, encoding an NAC transcription factor that is highly expressed and induced during drought tolerance. OsNAC092 knockout lines created using the clustered regularly interspaced palindromic repeats (CRISPR)-associated protein 9 (Cas9) system exhibited increased drought resistance in rice. RNA sequencing showed that the knockout of OsNAC092 caused a global expression change, and differential gene expression is chiefly associated with "response to light stimulus," "MAPK signaling pathway," "plant hormone signal transduction," "response to oxidative stress," "photosynthesis," and "water deprivation." In addition, the antioxidants and enzyme activities of the redox response were significantly increased. OsNAC092 mutant rice exhibited a higher ability to scavenge more ROS and maintained a high GSH/GSSG ratio and redox level under drought stress, which could protect cells from oxidant stress, revealing the importance of OsNAC092 in the rice's response to abiotic stress. Functional analysis of OsNAC092 will be useful to explore many rice resistance genes in molecular breeding to aid in the development of modern agriculture.

Arbuscular mycorrhizal fungi enhance photosynthesis and drought tolerance by regulating MAPK genes expressions of Populus simonii × P. nigra

Arbuscular mycorrhizal fungi (AMF) promote plants to absorb more water and nutrients and improve their stress resistance. As the main signal transducer, the mitogen-activated protein kinase (MAPK) cascade plays a vital role in drought stress. However, how the MAPK family genes of mycorrhizal plants respond to stress is still not clear. Our study analyzed physiological indexes and expression profiles of MAPK family genes of Populus simonii × P. nigra under two inoculation treatments (inoculated with or without Rhizophagus irregularis) and two water conditions (well-watered or drought stress). The results showed that the stronger photosynthesis of mycorrhizal plants may be mediated by MAPK genes induced by AMF. Mycorrhizal plants showed lower oxidative damage and drought sensitivity. Mycorrhiza downregulated the expression of PsnMAPK7-2, PsnMAPK16-1, PsnMAPK19-2, and PsnMAPK20-2 which negatively regulate drought tolerance and induced specific PsnMAPKs in roots which activate transcription factors to regulate downstream gene expressions, enhancing drought tolerance. This is the first time to identify part of the MAPK gene family of P. simonii × P. nigra at the genome level and study MAPK genes in mycorrhizal forest trees. This is helpful to understand the function of the MAPK gene family in response to drought of mycorrhizal plants and lays a foundation for afforestation by using mycorrhizal saplings.

TaMPK2B, a member of the MAPK family in T. aestivum, enhances plant low-Pi stress tolerance through modulating physiological processes associated with phosphorus starvation defensiveness

The mitogen-activated protein kinase (MAPK) cascades are present in plant species and modulate plant growth and stress responses. This study characterizes TaMPK2B, a MAPK family gene in T. aestivum that regulates plant adaptation to low-Pi stress. TaMPK2B harbors the conserved domains involving protein phosphorylation and protein-protein interaction. A yeast two-hybrid assay reveals an interaction between TaMPK2B and TaMPKK2 and between the latter and TaMPKKK;A, suggesting that all comprise a MAPK signaling cascade TaMPKKK;A-TaMPKK2-TaMPK2B. TaMPK2B expression levels were elevated in roots and leaves under a Pi starvation (PS) condition. Additionally, the induced TaMPK2B transcripts under PS in tissues were gradually restored following the Pi normal recovery condition. TaMPK2B overexpression conferred on plants improved PS adaptation; the tobacco lines with TaMPK2B overexpression enhanced the plant's dry mass production, Pi uptake capacity, root system architecture (RSA) establishment, and ROS homeostasis relative to wild type under PS treatment. Moreover, the transcripts of genes in phosphate transporter (PT), PIN-FORMED, and antioxidant enzyme (AE) families, including NtPT3 and NtPT4, NtPIN9, and NtMnSOD1 and NtPOD1;7, were elevated in Pi-deprived lines overexpressing TaMPK2B. Transgene analyses validated their functions in regulating Pi uptake, RSA establishment, and AE activities of plants treated by PS. These results suggest that TaMPK2B-mediated plant PS adaptation is correlated with the modified transcription of distinct PT, PIN, and AE genes. Our investigation suggests that TaMPK2B is one of the crucial regulators in plant low-Pi adaptation by improving Pi uptake, RSA formation, and ROS homeostasis via transcriptionally regulating genes associated with the above physiological processes.

MxMPK4-1 phosphorylates NADPH oxidase to trigger the MxMPK6-2-MxbHLH104 pathway mediated Fe deficiency responses in apple

Iron (Fe) deficiency is a nutritional stress in plants that commonly occurs in alkaline and calcareous soils. Mitogen-activated protein kinases (MPKs), the terminal player of MAPK cascade, are involved in distinct physiological processes. Once plants suffer from Fe deficiency stress, the mechanism of MPK function remains unclear owing to limited study on the MPK networks including substrate proteins and downstream pathways. Here, the MAP kinase MPK4-1 was induced in roots of Fe efficient apple rootstock Malus xiaojinensis but not in Fe inefficient rootstock Malus baccata under Fe deficiency conditions. Overexpression of MxMPK4-1 in apple calli and apple roots enhanced the responses to Fe deficiency. We found that MxMPK4-1 interacted with NADPH oxidases (NOX)-respiratory burst oxidase homologs MxRBOHD1 and MxRBOHD2, which positively regulated responses to Fe deficiency. Moreover, MxMPK4-1 phosphorylated the C terminus of MxRBOHD2 at Ser797 and Ser906 and positively and negatively regulated NOX activity through these phospho-sites, respectively. When compared with apple calli that overexpressed MxRBOHD2, the coexpression of MxMPK4-1 and MxRBOHD2 prominently enhanced the Fe deficiency responses. We also demonstrated that hydrogen peroxide derived from MxMPK4-1-MxRBOHD2 regulated the MxMPK6-2-MxbHLH104 pathway, illuminating a systematic network that involves different MPK proteins in M. xiaojinensis under Fe deficiency stress.

Potential application of TurboID-based proximity labeling in studying the protein interaction network in plant response to abiotic stress

Abiotic stresses are major environmental conditions that reduce plant growth, productivity and quality. Protein-protein interaction (PPI) approaches can be used to screen stress-responsive proteins and reveal the mechanisms of protein response to various abiotic stresses. Biotin-based proximity labeling (PL) is a recently developed technique to label proximal proteins of a target protein. TurboID, a biotin ligase produced by directed evolution, has the advantages of non-toxicity, time-saving and high catalytic efficiency compared to other classic protein-labeling enzymes. TurboID-based PL has been successfully applied in animal, microorganism and plant systems, particularly to screen transient or weak protein interactions, and detect spatially or temporally restricted local proteomes in living cells. This review concludes classic PPI approaches in plant response to abiotic stresses and their limitations for identifying complex network of regulatory proteins of plant abiotic stresses, and introduces the working mechanism of TurboID-based PL, as well as its feasibility and advantages in plant abiotic stress research. We hope the information summarized in this article can serve as technical references for further understanding the regulation of plant adaptation to abiotic stress at the protein level.

Transcriptomic and physiological responses of contrasting maize genotypes to drought stress

Drought is a significant environmental stress factor that adversely affects maize productivity. However, many details regarding the molecular mechanisms of maize against drought are still unclear. In this study, leaf transcriptomics and physiological traits of two maize genotypes with differing drought resistance were analyzed. Transcriptome sequencing identified 8985 and 7305 differentially expressed genes (DEGs) in SD902 and SD609, respectively. Functional analysis suggested that numerous genes are highly involved in oxidative defense, protein modification, photosynthesis, phytohormone response, MAPK signaling, and transcription factors (TFs). Compared to SD902, SD609 had a higher expression of DEGs related to antioxidant enzymes, photosynthetic electron transport, heat shock proteins, and indole-3-acetic acid (IAA) signaling under drought conditions, which might contribute to its tolerance mechanisms to drought. Stress-induced TFs may play a crucial regulatory role in genotypic differences. Moreover, the physiological changes and gene expression abundance determined using quantitative reverse transcription polymerase chain reaction were consistent with the RNA sequencing data. The study results suggest that the higher drought tolerance of SD609 than SD902 can be attributed to stronger stress defense capabilities, IAA signal transduction, and more stable photosynthesis. Our findings provide new insights into the molecular mechanisms of maize against drought stress, and the candidate genes identified may be used in breeding drought-tolerant maize cultivars.

Reproductive-Stage Heat Stress in Cereals: Impact, Plant Responses and Strategies for Tolerance Improvement

Reproductive-stage heat stress (RSHS) poses a major constraint to cereal crop production by damaging main plant reproductive structures and hampering reproductive processes, including pollen and stigma viability, pollination, fertilization, grain setting and grain filling. Despite this well-recognized fact, research on crop heat stress (HS) is relatively recent compared to other abiotic stresses, such as drought and salinity, and in particular, RSHS studies in cereals are considerably few in comparison with seedling-stage and vegetative-stage-centered studies. Meanwhile, climate change-exacerbated HS, independently or synergistically with drought, will have huge implications on crop performance and future global food security. Fortunately, due to their sedentary nature, crop plants have evolved complex and diverse transient and long-term mechanisms to perceive, transduce, respond and adapt to HS at the molecular, cell, physiological and whole plant levels. Therefore, uncovering the molecular and physiological mechanisms governing plant response and tolerance to RSHS facilitates the designing of effective strategies to improve HS tolerance in cereal crops. In this review, we update our understanding of several aspects of RSHS in cereals, particularly impacts on physiological processes and yield; HS signal perception and transduction; and transcriptional regulation by heat shock factors and heat stress-responsive genes. We also discuss the epigenetic, post-translational modification and HS memory mechanisms modulating plant HS tolerance. Moreover, we offer a critical set of strategies (encompassing genomics and plant breeding, transgenesis, omics and agronomy) that could accelerate the development of RSHS-resilient cereal crop cultivars. We underline that a judicious combination of all of these strategies offers the best foot forward in RSHS tolerance improvement in cereals. Further, we highlight critical shortcomings to RSHS tolerance investigations in cereals and propositions for their circumvention, as well as some knowledge gaps, which should guide future research priorities. Overall, our review furthers our understanding of HS tolerance in plants and supports the rational designing of RSHS-tolerant cereal crop cultivars for the warming climate.

Transcriptomic and Metabolomic Analysis of Seedling-Stage Soybean Responses to PEG-Simulated Drought Stress

Soybean is an important crop grown worldwide, and drought stress seriously affects the yield and quality of soybean. Therefore, it is necessary to elucidate the molecular mechanisms underlying soybean resistance to drought stress. In this study, RNA-seq technology and ultra-performance liquid chromatography-tandem mass spectrometry were used to analyze the transcriptome and metabolome changes in soybean leaves at the seedling stage under drought stress. The results showed that there were 4790 and 3483 DEGs (differentially expressed genes) and 156 and 124 DAMs (differentially expressed metabolites), respectively, in the HN65CK vs. HN65S0 and HN44CK vs. HN44S0 comparison groups. Comprehensive analysis of transcriptomic and metabolomic data reveals metabolic regulation of seedling soybean in response to drought stress. Some candidate genes such as LOC100802571, LOC100814585, LOC100777350 and LOC100787920, LOC100800547, and LOC100785313 showed different expression trends between the two cultivars, which may cause differences in drought resistance. Secondly, a large number of flavonoids were identified, and the expression of Monohydroxy-trimethoxyflavone-O-(6″-malonyl)glucoside was upregulated between the two varieties. Finally, several key candidate genes and metabolites involved in isoflavone biosynthesis and the TCA cycle were identified, suggesting that these metabolic pathways play important roles in soybean response to drought. Our study deepens the understanding of soybean drought resistance mechanisms and provides references for soybean drought resistance breeding.

Transcriptomic Analysis of Mature Transgenic Poplar Expressing the Transcription Factor JERF36 Gene in Two Different Environments

During the last several decades, a number of transgenic or genetically modified tree varieties with enhanced characteristics and new traits have been produced. These trees have become associated with generally unsubstantiated concerns over health and environmental safety. We conducted transcriptome sequencing of transgenic Populus alba × P. berolinensis expressing the transcription factor JERF36 gene (ABJ01) and the non-transgenic progenitor line (9#) to compare the transcriptional changes in the apical buds. We found that 0.77% and 1.31% of the total expressed genes were significant differentially expressed in ABJ01 at the Daqing and Qiqihar sites, respectively. Among them, 30%–50% of the DEGs contained cis-elements recognized by JERF36. Approximately 5% of the total number of expressed genes showed significant differential expression between Daqing and Qiqihar in both ABJ01 and 9#. 10 DEGs resulting from foreign gene introduction, 394 DEGs that resulted solely from the environmental differences, and 47 DEGs that resulted from the combination of foreign gene introduction and the environment were identified. The number of DEGs resulting from environmental factors was significantly greater than that resulting from foreign gene introduction, and the combined effect of the environmental effects with foreign gene introduction was significantly greater than resulting from the introduction of JERF36 alone. GO and KEGG annotation showed that the DEGs mainly participate in the photosynthesis, oxidative phosphorylation, plant hormone signaling, ribosome, endocytosis, and plant-pathogen interaction pathways, which play important roles in the responses to biotic and abiotic stresses ins plant. To enhance its adaptability to salt-alkali stress, the transgenic poplar line may regulate the expression of genes that participate in the photosynthesis, oxidative phosphorylation, MAPK, and plant hormone signaling pathways. The crosstalk between biotic and abiotic stress responses by plant hormones may improve the ability of both transgenic and non-transgenic poplars to defend against pathogens. The results of our study provide a basis for further studies on the molecular mechanisms behind improved stress resistance and the unexpected effects of transgenic gene expression in poplars, which will be significant for improving the biosafety evaluation of transgenic trees and accelerating the breeding of new varieties of forest trees resistant to environmental stresses.

Physiological Responses to Drought, Salinity, and Heat Stress in Plants: A Review

On the world stage, the increase in temperatures due to global warming is already a reality that has become one of the main challenges faced by the scientific community. Since agriculture is highly dependent on climatic conditions, it may suffer a great impact in the short term if no measures are taken to adapt and mitigate the agricultural system. Plant responses to abiotic stresses have been the subject of research by numerous groups worldwide. Initially, these studies were concentrated on model plants, and, later, they expanded their studies in several economically important crops such as rice, corn, soybeans, coffee, and others. However, agronomic evaluations for the launching of cultivars and the classical genetic improvement process focus, above all, on productivity, historically leaving factors such as tolerance to abiotic stresses in the background. Considering the importance of the impact that abiotic stresses can have on agriculture in the short term, new strategies are currently being sought and adopted in breeding programs to understand the physiological, biochemical, and molecular responses to environmental disturbances in plants of agronomic interest, thus ensuring the world food security. Moreover, integration of these approaches is bringing new insights on breeding. We will discuss how water deficit, high temperatures, and salinity exert effects on plants.

Comprehensive analysis of MAPK cascade genes in sorghum (Sorghum bicolor L.) reveals SbMPK14 as a potential target for drought sensitivity regulation

The mitogen-activated protein kinase (MAPK) cascade plays a crucial role in regulating many important biological processes in plants. Here, we identified and characterized eight MAPKK and 49 MAPKKK genes in sorghum and analyzed their differential expression under drought treatment; we also characterized 16 sorghum MAPK genes. RNA-seq analysis revealed that 10 MAPK cascade genes were involved in drought stress response at the transcriptome level in sorghum. Overexpression of SbMPK14 in Arabidopsis and maize resulted in hypersensitivity to drought by promoting water loss, indicating that SbMPK14 functions as a negative regulator of the drought response. Subsequent transcriptome analysis and qRT-PCR verification of maize SbMPK14 overexpression lines revealed that SbMPK14 likely increases plant drought sensitivity by suppressing the activity of specific ERF and WRKY transcription factors. This comprehensive study provides valuable insight into the mechanistic basis of MAPK cascade gene function and their responses to drought in sorghum.

De novo and comparative transcriptomic analysis explain morphological differences in Panax notoginseng taproots

Background

Panax notoginseng (Burk.) F. H. Chen (PN) belonging to the genus Panax of family Araliaceae is widely used in traditional Chinese medicine to treat various diseases. PN taproot, as the most vital organ for the accumulation of bioactive components, presents a variable morphology (oval or long), even within the same environment. However, no related studies have yet explained the molecular mechanism of phenotypic differences. To investigate the cause of differences in the taproot phenotype, de novo and comparative transcriptomic analysis on PN taproot was performed.

Results

A total of 133,730,886 and 114,761,595 paired-end clean reads were obtained based on high-throughput sequencing from oval and long taproot samples, respectively. 121,955 unigenes with contig N50 = 1,774 bp were generated by using the de novo assembly transcriptome, 63,133 annotations were obtained with the BLAST. And then, 42 genes belong to class III peroxidase (PRX) gene family, 8 genes belong to L-Ascorbate peroxidase (APX) gene family, and 55 genes belong to a series of mitogen-activated protein kinase (MAPK) gene family were identified based on integrated annotation results. Differentially expressed genes analysis indicated substantial up-regulation of PnAPX3 and PnPRX45, which are related to reactive oxygen species metabolism, and the PnMPK3 gene, which is related to cell proliferation and plant root development, in long taproots compared with that in oval taproots. Furthermore, the determination results of real-time quantitative PCR, enzyme activity, and H₂O₂ content verified transcriptomic analysis results.

Conclusion

These results collectively demonstrate that reactive oxygen species (ROS) metabolism and the PnMPK3 gene may play vital roles in regulating the taproot phenotype of PN. This study provides further insights into the genetic mechanisms of phenotypic differences in other species of the genus Panax.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08283-w.

The involvement of gaseous signaling molecules in plant MAPK cascades: function and signal transduction

This review describes the interaction of gaseous signaling molecules and MAPK cascade components, which further reveals the specific mechanism of the crosstalk between MAPK cascade components and gaseous signaling molecules. Plants have evolved complex and sophisticated mitogen-activated protein kinase (MAPK) signaling cascades that are engaged in response to environmental stress. There is currently compelling experimental evidence that gaseous signaling molecules are involved in MAPK cascades. During stress, nitric oxide (NO) activates MAPK cascades to transmit stimulus signals, and MAPK cascades also regulate NO biosynthesis to mediate NO-dependent physiological processes. Activated MAPK cascades lead to phosphorylation of specific sites of aminocyclopropane carboxylic acid synthase to regulate the ethylene biosynthesis-signaling pathway. Hydrogen sulfide functions upstream of MAPKs and regulates the MAPK signaling pathway at the transcriptional level. Here, we describe the function and signal transduction of gaseous signaling molecules involved in MAPK cascades and focus on introducing and discussing the recent data obtained in this field concerning the interaction of gaseous signaling molecules and MAPK cascades. In addition, this article outlines the direction and challenges of future work and further reveals the specific mechanism of the crosstalk between MAPK cascade components and gaseous signaling molecules.

In-silico genome wide analysis of Mitogen activated protein kinase kinase kinase gene family in C. sinensis

Mitogen activated protein kinase kinase kinase (MAPKKK) form the upstream component of MAPK cascade. It is well characterized in several plants such as Arabidopsis and rice however the knowledge about MAPKKKs in tea plant is largely unknown. In the present study, MAPKKK genes of tea were obtained through a genome wide search using Arabidopsis thaliana as the reference genome. Among 59 candidate MAPKKK genes in tea, 17 genes were MEKK-like, 31 genes were Raf-like and 11 genes were ZIK- like. Additionally, phylogenetic relationships were established along with structural analysis, which includes gene structure, its location as well as conserved motifs, cis-acting regulatory elements and functional domain signatures that were systematically examined. Also, on the basis of one orthologous gene found between tea and Arabidopsis, functional interaction was carried out in C. sinensis based on an Arabidopsis association model. The expressional profiles indicated major involvement of MAPKKK genes from tea in response to various abiotic stress factors. Taken together, this study provides the targets for additional inclusive identification, functional study, and provides comprehensive knowledge for a better understanding of the MAPKKK cascade regulatory network in C. sinensis.

Role of copper in the enhancement of astaxanthin and lipid coaccumulation in Haematococcus pluvialis exposed to abiotic stress conditions

This study investigated the effects of copper (Cu) on astaxanthin and lipid biological synthesis in unicellular alga Haematococcus pluvialis under high-light (HL) and nitrogen-deficiency (ND) conditions. During a 15-day cultivation period, the astaxanthin and lipid contents reached the peak values (3.32% and 47.72%) under 6 μM Cu treatment, which were increased by 66.87% and 34.99% compared to nontreated group, respectively. The application of Cu also increased the transcriptional expression of biosynthesis genes and antioxidant enzyme-related genes, as well as increased the intracellular calcium (Ca²⁺) level but led to a decrease in reactive oxygen species (ROS) levels. Additionally, Cu treatment induced the activation of calcium-dependent protein kinases (CDPKs) and mitogen-activated protein kinases (MAPKs). This approach simultaneously facilitated astaxanthin and lipid production, and the role of Cu were elucidated on the regulation of signal transduction (e.g., Ca²⁺, CDPK, MAPK and ROS) in the carotenogenesis and lipogenesis in H. pluvialis.

Isotopically Dimethyl Labeling-Based Quantitative Proteomic Analysis of Phosphoproteomes of Soybean Cultivars

Isotopically dimethyl labeling was applied in a quantitative post-translational modification (PTM) proteomic study of phosphoproteomic changes in the drought responses of two contrasting soybean cultivars. A total of 9457 phosphopeptides were identified subsequently, corresponding to 4571 phosphoprotein groups and 3889 leading phosphoproteins, which contained nine kinase families consisting of 279 kinases. These phosphoproteins contained a total of 8087 phosphosites, 6106 of which were newly identified and constituted 54% of the current soybean phosphosite repository. These phosphosites were converted into the highly conserved kinase docking sites by bioinformatics analysis, which predicted six kinase families that matched with those newly found nine kinase families. The overly post-translationally modified proteins (OPP) occupies 2.1% of these leading phosphoproteins. Most of these OPPs are photoreceptors, mRNA-, histone-, and phospholipid-binding proteins, as well as protein kinase/phosphatases. The subgroup population distribution of phosphoproteins over the number of phosphosites of phosphoproteins follows the exponential decay law, Y = 4.13e-0.098X - 0.04. Out of 218 significantly regulated unique phosphopeptide groups, 188 phosphoproteins were regulated by the drought-tolerant cultivar under the water loss condition. These significantly regulated phosphoproteins (SRP) are mainly enriched in the biological functions of water transport and deprivation, methionine metabolic processes, photosynthesis/light reaction, and response to cadmium ion, osmotic stress, and ABA response. Seventeen and 15 SRPs are protein kinases/phosphatases and transcription factors, respectively. Bioinformatics analysis again revealed that three members of the calcium dependent protein kinase family (CAMK family), GmSRK2I, GmCIPK25, and GmAKINβ1 kinases, constitute a phosphor-relay-mediated signal transduction network, regulating ion channel activities and many nuclear events in this drought-tolerant cultivar, which presumably contributes to the development of the soybean drought tolerance under water deprivation process.

Molecular cloning and sequence analysis of a mitogen-activated protein kinase gene in the Antarctic yeast Rhodotorula mucilaginosa AN5

BACKGROUND

The mitogen-activated protein kinase (MAPK) cascades play important roles in various signaling transduction networks of biotic and abiotic stress responses. However, MAPK signaling pathways in cold-active yeast Rhodotorula mucilaginosa have not been reported comprehensively.

METHODS AND RESULTS

In the present study, MAPK gene (RmMAPK) was first cloned and characterized from Antarctic sea ice yeast R. mucilaginosa AN5. The full length of the RmMAPK gene is 1086 bp and encodes a 361 amino acids protein with a predicted molecular mass of 40.9 kDa and a pI of 5.25. The RmMAPK contains 11 MAPK conserved subdomains and the phosphorylation motif TGY located in the activation loop of the kinase. Quantitative real-time PCR and western blot assay revealed that the expression and phosphorylation level of RmMAPK up-regulated rapidly and significantly when yeast cells were subjected to low temperature (4 °C), high salinity (120‰ NaCl) and heavy metal (2 mmol/L CuCl₂).

CONCLUSIONS

All data suggested that the MAPK cascades might act as a key function in response to extreme stresses, such as low temperature, high salinity and heavy metal.

Plant Responses to Abiotic Stresses and Rhizobacterial Biostimulants: Metabolomics and Epigenetics Perspectives

In response to abiotic stresses, plants mount comprehensive stress-specific responses which mediate signal transduction cascades, transcription of relevant responsive genes and the accumulation of numerous different stress-specific transcripts and metabolites, as well as coordinated stress-specific biochemical and physiological readjustments. These natural mechanisms employed by plants are however not always sufficient to ensure plant survival under abiotic stress conditions. Biostimulants such as plant growth-promoting rhizobacteria (PGPR) formulation are emerging as novel strategies for improving crop quality, yield and resilience against adverse environmental conditions. However, to successfully formulate these microbial-based biostimulants and design efficient application programs, the understanding of molecular and physiological mechanisms that govern biostimulant-plant interactions is imperatively required. Systems biology approaches, such as metabolomics, can unravel insights on the complex network of plant-PGPR interactions allowing for the identification of molecular targets responsible for improved growth and crop quality. Thus, this review highlights the current models on plant defence responses to abiotic stresses, from perception to the activation of cellular and molecular events. It further highlights the current knowledge on the application of microbial biostimulants and the use of epigenetics and metabolomics approaches to elucidate mechanisms of action of microbial biostimulants.

AtPFA-DSP3, an atypical dual-specificity protein tyrosine phosphatase, affects salt stress response by modulating MPK3 and MPK6 activity

Protein phosphorylation, especially serine/threonine and tyrosine phosphorylation, plays significant roles in signalling during plant growth and development as well as plant responses to biotic or abiotic stresses. Dual-specificity protein tyrosine phosphatases dephosphorylate components of these signalling pathways. Here, we report that an atypical dual-specificity protein tyrosine phosphatase, AtPFA-DSP3 (DSP3), negatively affects the response of plants to high-salt conditions. A DSP3 loss-of-function mutant showed reduced sensitivity to salt treatment. DSP3 was primarily localized in nuclei and was degraded during salt treatment. Compared to wild type, the level of ROS was lower in the dsp3 mutant and higher in plants ectopically expressing DSP3, indicating that higher DSP3 level was associated with increased ROS production. DSP3 interacted with and dephosphorylated MPK3 and MPK6. Genetic analyses of a dsp3mpk3 double mutant revealed that DSP3's effect on salt stress depends on MPK3. Moreover, the phosphatase activity of DSP3 was required for its role in salt signalling. These results indicate that DSP3 is a negative regulator of salt responses in Arabidopsis by directly modulating the accumulation of phosphorylated MPK3 and MPK6.

Regulation of Plant Responses to Salt Stress

Salt stress is a major environmental stress that affects plant growth and development. Plants are sessile and thus have to develop suitable mechanisms to adapt to high-salt environments. Salt stress increases the intracellular osmotic pressure and can cause the accumulation of sodium to toxic levels. Thus, in response to salt stress signals, plants adapt via various mechanisms, including regulating ion homeostasis, activating the osmotic stress pathway, mediating plant hormone signaling, and regulating cytoskeleton dynamics and the cell wall composition. Unraveling the mechanisms underlying these physiological and biochemical responses to salt stress could provide valuable strategies to improve agricultural crop yields. In this review, we summarize recent developments in our understanding of the regulation of plant salt stress.

Rice Transcription Factor OsWRKY55 Is Involved in the Drought Response and Regulation of Plant Growth

WRKY transcription factors (TFs) have been reported to respond to biotic and abiotic stresses and regulate plant growth and development. However, the molecular mechanisms of WRKY TFs involved in drought stress and regulating plant height in rice remain largely unknown. In this study, we found that transgenic rice lines overexpressing OsWRKY55 (OsWRKY55-OE) exhibited reduced drought resistance. The OsWRKY55-OE lines showed faster water loss and greater accumulation of hydrogen peroxide (H₂O₂) and superoxide radical (O₂^−·) compared to wild-type (WT) plants under drought conditions. OsWRKY55 was expressed in various tissues and was induced by drought and abscisic acid (ABA) treatments. Through yeast two-hybrid assays, we found that OsWRKY55 interacted with four mitogen-activated protein kinases (MAPKs) that could be induced by drought, including OsMPK7, OsMPK9, OsMPK20-1, and OsMPK20-4. The activation effects of the four OsMPKs on OsWRKY55 transcriptional activity were demonstrated by a GAL4-dependent chimeric transactivation assay in rice protoplasts. Furthermore, OsWRKY55 was able to reduce plant height under normal conditions by decreasing the cell size. In addition, based on a dual luciferase reporter assay, OsWRKY55 was shown to bind to the promoter of OsAP2-39 through a yeast one-hybrid assay and positively regulate OsAP2-39 expression. These results suggest that OsWRKY55 plays a critical role in responses to drought stress and the regulation of plant height in rice, further providing valuable information for crop improvement.

Natural population re-sequencing detects the genetic basis of local adaptation to low temperature in a woody plant

Total of 14 SNPs associated with overwintering-related traits and 75 selective regions were detected. Important candidate genes were identified and a possible network of cold-stress responses in woody plants was proposed. Local adaptation to low temperature is essential for woody plants to against changeable climate and safely survive the winter. To uncover the specific molecular mechanism of low temperature adaptation in woody plants, we sequenced 134 core individuals selected from 494 paper mulberry (Broussonetia papyrifera), which naturally distributed in different climate zones and latitudes. The population structure analysis, PCA analysis and neighbor-joining tree analysis indicated that the individuals were classified into three clusters, which showed forceful geographic distribution patterns because of the adaptation to local climate. Using two overwintering phenotypic data collected at high latitudes of 40°N and one bioclimatic variable, genome-phenotype and genome-environment associations, and genome-wide scans were performed. We detected 75 selective regions which possibly undergone temperature selection and identified 14 trait-associated SNPs that corresponded to 16 candidate genes (including LRR-RLK, PP2A, BCS1, etc.). Meanwhile, low temperature adaptation was also supported by other three trait-associated SNPs which exhibiting significant differences in overwintering traits between alleles within three geographic groups. To sum up, a possible network of cold signal perception and responses in woody plants were proposed, including important genes that have been confirmed in previous studies while others could be key potential candidates of woody plants. Overall, our results highlighted the specific and complex molecular mechanism of low temperature adaptation and overwintering of woody plants.

Identification and characterisation of cold stress-related proteins in Oryza rufipogon at the seedling stage using label-free quantitative proteomic analysis

In this study, label-free quantitative proteomics were used to study cold stress-related proteins in Dongxiang wild rice (Oryza rufipogon Griff., DWR) and cold sensitive cultivated rice 'Xieqingzao B'(Oryza sativa L. ssp. indica cv., XB). The results demonstrated the presence of 101 and 216 differentially expressed proteins (DEPs) were detected in DWR and XB, respectively, after cold stress. Bioinformatics analysis showed that DWR and XB differed significantly in their ability to scavenge reactive oxygen species (ROS) and regulate energy metabolism. Of the 101 DEPs of DWR, 46 DEPs related to differential expressed genes were also detected by transcriptome analysis. And 13 out of 101 DEPs were located in previous cold related quantitative trait loci (QTL). Quantitative real-time PCR analysis indicated that protein expression and transcription patterns were not similar in XB and DWR. Protein-protein interaction (PPI) network was constituted using the DEPs of DWR and XB, and the following three centre proteins were identified: Q8H3I3, Q9LDN2, and Q2QXR8. Next, we selected a centre protein and two of the 37 DEPs with high levels of differential expression (fold change ≥ 2) were used for cloning and prokaryotic expression. We found that Q5Z9Q8 could significantly improve the cold tolerance of Escherichia coli.

Characterizing the putative mitogen-activated protein kinase (MAPK) and their protective role in oxidative stress tolerance and carbon assimilation in wheat under terminal heat stress

Wheat, being sensitive to terminal heat, causes drastic reduction in grain quality and yield. MAPK cascade regulates the network of defense mechanism operated inside plant system. Here, we have identified 21 novel MAPKs through gel-based proteomics and RNA-seq data analysis. Based on digital gene expression, two transcripts (transcript_2834 and transcript_8242) showing homology with MAPK were cloned and characterized from wheat (acc. nos. MK854806 and KT835664). Transcript_2834 was cloned in pET28a vector and recombinant MAPK protein of ∼40.3 kDa was isolated and characterized to have very high in-vitro kinase activity under HS. Native MAPK showed positive correlation with the expression of TFs, HSPs, genes linked with antioxidant enzyme (SOD, CAT, GPX), photosynthesis and starch biosynthesis pathways in wheat under HS. Wheat cv. HD3086 (thermotolerant) having higher expression and activity of MAPK under HS showed significant increase in accumulation of proline, H2O2, starch, and granule integrity, compared with BT-Schomburgk (thermosusceptible).

Genome-Wide Identification and Analysis of MKK and MAPK Gene Families in Brassica Species and Response to Stress in Brassica napus

Mitogen-activated protein kinase (MAPK) cascades are common and conserved signal transduction pathways and play important roles in various biotic and abiotic stress responses and growth and developmental processes in plants. With the advancement of sequencing technology, more systematic genetic information is being explored. The work presented here focuses on two protein families in Brassica species: MAPK kinases (MKKs) and their phosphorylation substrates MAPKs. Forty-seven MKKs and ninety-two MAPKs were identified and extensively analyzed from two tetraploid (B. juncea and B. napus) and three diploid (B. nigra, B. oleracea, and B. rapa) Brassica species. Phylogenetic relationships clearly distinguished both MKK and MAPK families into four groups, labeled A–D, which were also supported by gene structure and conserved protein motif analysis. Furthermore, their spatial and temporal expression patterns and response to stresses (cold, drought, heat, and shading) were analyzed, indicating that BnaMKK and BnaMAPK transcript levels were generally modulated by growth, development, and stress signals. In addition, several protein interaction pairs between BnaMKKs and C group BnaMAPKs were detected by yeast two-hybrid assays, in which BnaMKK3 and BnaMKK9 showed strong interactions with BnaMAPK1/2/7, suggesting that interaction between BnaMKKs and C group BnaMAPKs play key roles in the crosstalk between growth and development processes and abiotic stresses. Taken together, our data provide a deeper foundation for the evolutionary and functional characterization of MKK and MAPK gene families in Brassica species, paving the way for unraveling the biological roles of these important signaling molecules in plants.

Phosphoproteomic analysis of lettuce (Lactuca sativa L.) reveals starch and sucrose metabolism functions during bolting induced by high temperature

High temperatures induce early bolting in lettuce (Lactuca sativa L.), which decreases both quality and production. However, knowledge of the molecular mechanism underlying high temperature promotes premature bolting is lacking. In this study, we compared lettuce during the bolting period induced by high temperatures (33/25 °C, day/night) to which raised under controlled temperatures (20/13 °C, day/night) using iTRAQ-based phosphoproteomic analysis. A total of 3,814 phosphorylation sites located on 1,766 phosphopeptides from 987 phosphoproteins were identified after high-temperature treatment,among which 217 phosphoproteins significantly changed their expression abundance (116 upregulated and 101 downregulated). Most phosphoproteins for which the abundance was altered were associated with the metabolic process, with the main molecular functions were catalytic activity and transporter activity. Regarding the functional pathway, starch and sucrose metabolism was the mainly enriched signaling pathways. Hence, high temperature influenced phosphoprotein activity, especially that associated with starch and sucrose metabolism. We suspected that the lettuce shorten its growth cycle and reduce vegetative growth owing to changes in the contents of starch and soluble sugar after high temperature stress, which then led to early bolting/flowering. These findings improve our understanding of the regulatory molecular mechanisms involved in lettuce bolting.

SMRT sequencing of a full-length transcriptome reveals transcript variants involved in C18 unsaturated fatty acid biosynthesis and metabolism pathways at chilling temperature in Pennisetum giganteum

Background

Pennisetum giganteum, an abundant, fast-growing perennial C₄ grass that belongs to the genus Pennisetum, family Poaceae, has been developed as a source of biomass for mushroom cultivation and production, as a source of forage for cattle and sheep, and as a tool to remedy soil erosion. However, having a chilling-sensitive nature, P. giganteum seedlings need to be protected while overwintering in most temperate climate regions.

Results

To elucidate the cold stress responses of P. giganteum, we carried out comprehensive full-length transcriptomes from leaf and root tissues under room temperature (RT) and chilling temperature (CT) using PacBio Iso-Seq long reads. We identified 196,124 and 140,766 full-length consensus transcripts in the RT and CT samples, respectively. We then systematically performed functional annotation, transcription factor identification, long non-coding RNAs (lncRNAs) prediction, and simple sequence repeat (SSR) analysis of those full-length transcriptomes. Isoform analysis revealed that alternative splicing events may be induced by cold stress in P. giganteum, and transcript variants may be involved in C18 unsaturated fatty acid biosynthesis and metabolism pathways at chilling temperature in P. giganteum. Furthermore, the fatty acid composition determination and gene expression level analysis supported that C18 unsaturated fatty acid biosynthesis and metabolism pathways may play roles during cold stress in P. giganteum.

Conclusions

We provide the first comprehensive full-length transcriptomic resource for the abundant and fast-growing perennial grass Pennisetum giganteum. Our results provide a useful transcriptomic resource for exploring the biological pathways involved in the cold stress responses of P. giganteum.

Banana MaBZR1/2 associate with MaMPK14 to modulate cell wall modifying genes during fruit ripening

Banana MaBZR1/2 interact with MaMPK14 to enhance the transcriptional inhibition of cell wall modifying genes including MaEXP2, MaPL2 and MaXET5. Fruit ripening and softening, the major attributes to perishability in fleshy fruits, are modulated by various plant hormones and gene expression. Banana MaBZR1/2, the central transcription factors of brassinosteroid (BR) signaling, mediate fruit ripening through regulation of ethylene biosynthesis, but their possible roles in fruit softening as well as the underlying mechanisms remain to be determined. In this work, we found that MaBZR1/2 directly bound to and repressed the promoters of several cell wall modifying genes such as MaEXP2, MaPL2 and MaXET5, whose transcripts were elevated concomitant with fruit ripening. Moreover, yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that MaBZR1/2 physically interacted with a mitogen-activated protein kinase MaMPK14, and this interaction strengthened the MaBZR1/2-mediated transcriptional inhibitory abilities. Collectively, our study provides insight into the mechanism of MaBZR1/2 contributing to fruit ripening and softening, which may have potential for banana molecular improvement.

Effects of maize organ-specific drought stress response on yields from transcriptome analysis

BACKGROUND

Drought is a serious causal factor of reduced crop yields than any other abiotic stresses. As one of the most widely distributed crops, maize plants frequently suffer from drought stress, which causes great losses in the final kernel yield. Drought stress response in plants showed tissue- and developmental stage-specific characteristics.

RESULTS

In this study, the ears at the V9 stage, kernels and ear leaf at the 5DAP (days after pollination) stage of maize were used for morphological, physiological and comparative transcriptomics analysis to understand the different features of "sink" or "source" organs and the effects on kernel yield under drought stress conditions. The ABA-, NAC-mediate signaling pathway, osmotic protective substance synthesis and protein folding response were identified as common drought stress response in the three organs. Tissue-specific drought stress responses and the regulators were identified, they were highly correlated with growth, physiological adaptation and yield loss under drought stress. For ears, drought stress inhibited ear elongation, led to the abnormal differentiation of the paired spikelet, and auxin signaling involved in the regulation of cell division and growth and primordium development changes. In the kernels, reduced kernel size caused by drought stress was observed, and the obvious differences of auxin, BR and cytokine signaling transduction appeared, which indicated the modification in carbohydrate metabolism, cell differentiation and growth retardation. For the ear leaf, dramatically and synergistically reduced the expression of photosynthesis genes were observed when suffered from drought stress, the ABA- and NAC- mediate signaling pathway played important roles in the regulation of photosynthesis.

CONCLUSIONS

Transcriptomic changes caused by drought were highly correlated with developmental and physiological adaptation, which was closely related to the final yield of maize, and a sketch of tissue- and developmental stage-specific responses to drought stress in maize was drafted.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

The Solanum chacoense Fertilization-Related Kinase 3 (ScFRK3) is involved in male and female gametophyte development

BACKGROUND

The Fertilization-related kinases (FRK) form a class that belongs to the MEKK subfamily of plant MAPKKKs. It was recently shown that FRK class kinases expanded during angiosperm evolution, reaching their maximum numbers in the lineage leading to solanaceous species and culminating in the Solanum genus where they account for more than 40% of the total MEKKs. The first members studied, ScFRK1 and ScFRK2 were shown to play a pivotal role in gametophyte development in the wild potato species Solanum chacoense.

RESULTS

ScFRK3 is also involved in gametophyte development. ScFRK3 is expressed in developing pollen and young ovules, reaching its highest level immediately after meiosis and during the mitosis steps in both gametophytes. Hence, three independent lines of ScFRK3 RNAi mutant plants showed decreased number of seeds per fruit. We also observed an important number of degenerated embryo sac in mature ovary. Analysis of ovule development showed that most embryo sac did not enter mitosis I in ScFRK3 RNAi mutant plants. Severe lethality was also observed during male gametophyte development, pollen being arrested before mitosis I, as observed in the female gametophyte. Obvious defects in vegetative organs were not observed, emphasizing the reproductive roles of the FRK class kinases. To isolate MAP kinases acting downstream of ScFRK3, a de novo S. chacoense transcriptome from male and female reproductive organs was assembled. Of the five ScMKKs and 16 ScMPKs retrieved, only the ScMKK3 interacted with ScFRK3, while only the ScMPK13 interacted with ScMKK3, leading to an apparent single three-tiered canonical MAP kinase cascade combination involving ScFRK3-ScMKK3-ScMPK13.

CONCLUSIONS

The ScFRK3 MAPKKK is involved in a signaling cascade that regulates both male and female gamete development, and most probably act upstream of ScMKK3 and ScMPK13.

A Förster resonance energy transfer sensor for live-cell imaging of mitogen-activated protein kinase activity in Arabidopsis

The catalytic activity of mitogen-activated protein kinases (MAPKs) is dynamically modified in plants. Since MAPKs have been shown to play important roles in a wide range of signaling pathways, the ability to monitor MAPK activity in living plant cells would be valuable. Here, we report the development of a genetically encoded MAPK activity sensor for use in Arabidopsis thaliana. The sensor is composed of yellow and blue fluorescent proteins, a phosphopeptide binding domain, a MAPK substrate domain and a flexible linker. Using in vitro testing, we demonstrated that phosphorylation causes an increase in the Förster resonance energy transfer (FRET) efficiency of the sensor. The FRET efficiency can therefore serve as a readout of kinase activity. We also produced transgenic Arabidopsis lines expressing this sensor of MAPK activity (SOMA) and performed live-cell imaging experiments using detached cotyledons. Treatment with NaCl, the synthetic flagellin peptide flg22 and chitin all led to rapid gains in FRET efficiency. Control lines expressing a version of SOMA in which the phosphosite was mutated to an alanine did not show any substantial changes in FRET. We also expressed the sensor in a conditional loss-of-function double-mutant line for the Arabidopsis MAPK genes MPK3 and MPK6. These experiments demonstrated that MPK3/6 are necessary for the NaCl-induced FRET gain of the sensor, while other MAPKs are probably contributing to the chitin and flg22-induced increases in FRET. Taken together, our results suggest that SOMA is able to dynamically report MAPK activity in living plant cells.