Rice calcium/calmodulin-dependent protein kinase directly phosphorylates a mitogen-activated protein kinase kinase to regulate abscisic acid responses

Genome-wide screening of mitogen-activated protein kinase (MAPK) gene family and expression profile under heavy metal stress in Solanum lycopersicum

MAPKs are one of the essential signal transduction complexes which are responsible for the perception of abiotic stress and for the producing of related transcripts for responding to abiotic stress. For systematical analyzes of the mitogen-activated protein (MAP) kinase gene families and their expression profiles in Solanum lycopersicum L. exposed to diverse heavy metal stresses, 17 SlMAPK genes were studied in comparison with their 159 orthologs from various plant species. The result of phylogenetic analysis revealed that SlMAPKs were divided into four different subgroups (A, B, C, and D) based on their nucleic acid and protein sequence alignments. SlMAPKs including A, B and C group had lower molecular weights and more hydrophobic structures than D group SlMAPKs, while possible extra phosphorylation sites predicted in D-group SLMAPKs. 24 cis regulating elements such as Box 4, TATA-box, ABRE and CAAT-box were detected in their upstream parts of DNA sequences. Also, it was determined that SlMAPKs show interactions with important proteins such as Guanine nucleotide-binding protein beta subunit, heterotrimeric G-protein, protein phosphatase 2C and HY5. The results from our gene expression analyzes, significant increases were found in the expressions of the selected SLMAPK gene with applications of a range of increasing heavy metal concentrations (e.g., by the application of the 400 mM Ni + Pb exposure, a 16-fold increase in the expression of SlMAPK gene was noted). Overall, SlMAPK genes and proteins known were re-evaluated, and the SlMAPKs interactions with some other important proteins were observed. Also, some predictions about the extra phosphorylation sites of SlMAPKs having effects on their functions were done. In addition, the expression levels of SlMAPK genes were monitored under different levels of heavy metal stress exposures.

Agave macroacantha Transcriptome Reveals Candidate CNGC Genes Responsive to Cold Stress in Agave

Agave, with its unique appearance and ability to produce hard fibers, holds high economic value. However, low temperatures during winter can restrict its growth and even damage the leaves, causing a loss of ornamental appeal or affecting the fiber quality. Conversely, the plant cyclic nucleotide-gated channel (CNGC) family plays an important role in the growth and development of plants and the response to stress. Studying the CNGC family genes is of great importance for analyzing the mechanism by which agave responds to cold stress. This research conducted a transcriptomic analysis of the ornamental plant Agave macroacantha. Through assembly via Illumina sequencing, 119,911 transcripts were obtained, including 78,083 unigenes. In total, 6, 10, 11, and 13 CNGC genes were successfully identified from A. macroacantha, Agave. H11648, Agave. deserti, and Agave. tequilana, respectively. These CNGC genes could be divided into four groups (I, II, III, and IV), and group IV could be divided into two subgroups (IV-A and IV-B). The relative expression levels were quantified by qRT-PCR assays, which revealed that AhCNGC4.1 was significantly upregulated after cold treatment and Ca(NO3)2 treatment, suggesting its importance in cold stress and calcium signaling. Additionally, the Y2H assay has preliminarily identified interacting proteins of AhCNGC4.1, including AhCML19 and AhCBSX3. This study has established a completely new transcriptome dataset of A. macroacantha for the first time, enriching the bioinformatics of agave's transcriptome. The identified CNGC genes are of great significance for understanding the evolution of agave species. The cloned CNGC genes, expression pattern analysis, and protein interaction results laid a foundation for future research related to the molecular functions of agave CNGC genes in cold tolerance.

The OsMAPK6-OsWRKY72 module positively regulates rice leaf angle through brassinosteroid signals

Leaf angle is a major agronomic trait that determines plant architecture, which directly affects rice planting density, photosynthetic efficiency, and yield. The plant phytohormones brassinosteroids (BRs) and the MAPK signaling cascade are known to play crucial roles in regulating leaf angle, but the underlying molecular mechanisms are not fully understood. Here, we report a rice WRKY family transcription factor gene, OsWRKY72, which positively regulates leaf angle by affecting lamina joint development and BR signaling. Phenotypic analysis showed that oswrky72 mutants have smaller leaf angles and exhibit insensitivity to exogenous BRs, whereas OsWRKY72 overexpression lines show enlarged leaf angles and are hypersensitive to exogenous BRs. Histological sections revealed that the change in leaf inclination is due to asymmetric cell proliferation and growth at the lamina joint. Further investigation showed that OsWRKY72 binds directly to the promoter region of BR receptor kinase (OsBRI1), a key gene in the BR signaling pathway, and activates its expression to positively regulate rice BR signaling. In addition, we discovered that OsWRKY72 interacts with and is phosphorylated by OsMAPK6, and this phosphorylation event can enhance OsWRKY72 activity in promoting OsBRI1 expression. Genetic evidence confirmed that OsMAPK6, OsWRKY72, and OsBRI1 function in a common pathway to regulate leaf angle. Collectively, our findings clarify the critical role of the OsWRKY72 transcription factor in regulating rice leaf angle. These results provide valuable insights into the molecular regulatory networks that govern plant architecture in rice.

Soybean mitogen-activated protein kinase GmMPK6 enhances drought tolerance

Soybeans are a critical crop that provides both protein and oil. In response to environmental stresses, mitogen-activated protein kinases (MPKs) play a key role in transmitting stress signals to the nucleus to initiate stress-responsive actions. Drought stress reduces plant development and productivity but the specific MPK responsible for drought stress responses has not been previously identified. In this study, we demonstrate that GmMPK6, a soybean MPK, responds to drought stress and enhances drought tolerance. GmMPK6 is activated in drought conditions through post-translational modifications. Inhibition of GmMPK6 activity leads to reduced drought resistance and a decrease in GmRD19A expression. Additionally, GmMPK6 activation is modulated by calcium signaling, highlighting GmMPK6 as a positive regulator of drought stress resistance in soybean. This study presents the first report of an MPK conferring drought tolerance in soybean.

MAPKKK28 functions upstream of the MKK1-MPK1 cascade to regulate abscisic acid responses in rice

The mitogen-activated protein kinase (MAPK) cascade (MAPKKK-MAPKK-MAPK) plays a critical role in biotic and abiotic stress responses and abscisic acid (ABA) signalling. A previous study has shown that the ABA-activated MKK1-MPK1 cascade is essential in regulating ABA response and stress tolerance in rice. However, the specific MAPKKK upstream of the MKK1-MPK1 cascade in ABA signalling remains unknown. Here, we identified that MAPKKK28, a previously uncharacterized member of the rice MEKK family, is involved in regulating ABA responses, including seed germination, root growth, stomatal closure, and the tolerance to oxidative stress and osmotic stress. We found that MAPKKK28 directly interacts with and phosphorylates MKK1. Further analysis indicated that the activation of both MKK1 and MPK1 depends on MAPKKK28 in ABA signalling. Genetic analysis revealed that MAPKKK28 functions upstream of the MKK1-MPK1 cascade to positively regulate ABA responses and enhance tolerance to oxidative and osmotic stress. These results not only reveal a new complete MAPK cascade in plants but also uncover its importance in ABA signalling.

Abscisic acid-induced H2O2 production positively regulates the activity of SAPK8/9/10 through oxidation of the type one protein phosphatase OsPP47

Subclass III sucrose nonfermenting1-related protein kinase 2s (SnRK2s) are positive regulators of abscisic acid (ABA) signaling and abiotic stress responses. However, the underlying activation mechanisms of osmotic stress/ABA-activated protein kinase 8/9/10 (SAPK8/9/10) of rice (Oryza sativa) subclass III SnRK2s in ABA signaling remain to be elucidated. In this study, we employed biochemical, molecular biology, cell biology, and genetic approaches to identify the molecular mechanism by which OsPP47, a type one protein phosphatase in rice, regulates SAPK8/9/10 activity in ABA signaling. We found that OsPP47 not only physically interacted with SAPK8/9/10 but also interacted with ABA receptors PYLs. OsPP47 negatively regulated ABA sensitivity in seed germination and root growth. In the absence of ABA, OsPP47 directly inactivated SAPK8/9/10 by dephosphorylation. In the presence of ABA, ABA-bound OsPYL2 formed complexes with OsPP47 and inhibited its phosphatase activity, partially releasing the inhibition of SAPK8/9/10. SAPK8/9/10-mediated H2O2 production inhibited OsPP47 activity by oxidizing Cys-116 and Cys-256 to form OsPP47 oligomers, resulting in not only preventing the OsPP47-SAPK8/9/10 interaction but also blocking the inhibition of SAPK8/9/10 activity by OsPP47. Our results reveal novel pathways for the inhibition of SAPK8/9/10 in the basal state and for the activation of SAPK8/9/10 induced by ABA in rice.

Growth and protein response of rice plant with plant growth-promoting rhizobacteria inoculations under salt stress conditions

Soil salinity has been one of the significant barriers to improving rice production and quality. According to reports, Bacillus spp. can be utilized to boost plant development in saline soil, although the molecular mechanisms behind the interaction of microbes towards salt stress are not fully known. Variations in rice plant protein expression in response to salt stress and plant growth-promoting rhizobacteria (PGPR) inoculations were investigated using a proteomic method and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Findings revealed that 54 salt-responsive proteins were identified by mass spectrometry analysis (LC-MS/MS) with the Bacillus spp. interaction, and the proteins were functionally classified as gene ontology. The initial study showed that all proteins were labeled by mass spectrometry analysis (LC-MS/MS) with Bacillus spp. interaction; the proteins were functionally classified into six groups. Approximately 18 identified proteins (up-regulated, 13; down-regulated, 5) were involved in the photosynthetic process. An increase in the expression of eight up-regulated and two down-regulated proteins in protein synthesis known as chaperones, such as the 60 kDa chaperonin, the 70 kDa heat shock protein BIP, and calreticulin, was involved in rice plant stress tolerance. Several proteins involved in protein metabolism and signaling pathways also experienced significant changes in their expression. The results revealed that phytohormones regulated the manifestation of various chaperones and protein abundance and that protein synthesis played a significant role in regulating salt stress. This study also described how chaperones regulate rice salt stress, their different subcellular localizations, and the activity of chaperones.

Hydrogen peroxide positively regulates ABA signaling via oxidative modification of the C2H2-type zinc finger protein ZFP36 in rice

The rice zinc finger protein ZFP36 serves as a pivotal regulator of the hydrogen peroxide (H2O2) signaling pathway in response to abscisic acid (ABA). Its role is crucial for integrating H2O2 signals with the plant defense mechanisms against water deficit and oxidative stress. However, it remains unclear whether ZFP36 directly modulates ABA-induced H2O2 signaling. This study explored the effects of oxidative post-translational modifications (OxiPTMs) on ZFP36 in rice, with an emphasis on the H2O2-induced oxidation through its cysteine (Cys) residues. We found that ZFP36 undergoes oxidative modification as a target of H2O2 in the presence of ABA, specifically at Cys32. Employing quantitative detection and fluorescence assays, we observed that ZFP36 oxidation enhances the expression and activity of genes encoding protective antioxidant enzymes. Moreover, our investigation into the thioredoxin (Trx) and glutaredoxin (Grx) families revealed that OsTrxh1 facilitates the reduction of oxidized ZFP36. Genetic evidence indicates that ZFP36 positively influences rice resilience to oxidative and water stress, while OsTrxh1 exerts an opposing effect. These insights reveal a distinctive pathway for plant cells to perceive ABA-induced H2O2 signaling, advance our comprehension of H2O2 signaling dynamics, and ABA-related plant responses, and lay a vital groundwork for enhancing crop stress tolerance.

GmANKTM21 Positively Regulates Drought Tolerance and Enhanced Stomatal Response through the MAPK Signaling Pathway in Soybean

Drought stress is one of the significant abiotic stresses that limit soybean (Glycine max [L.] Merr.) growth and production. Ankyrin repeat (ANK) proteins, being highly conserved, occupy a pivotal role in diverse biological processes. ANK genes were classified into nine subfamilies according to conserved domains in the soybean genome. However, the function of ANK-TM subfamily proteins (Ankyrin repeat proteins with a transmembrane domain) in the abiotic-stress response to soybean remains poorly understood. In this study, we first demonstrated the subcellular localization of GmANKTM21 in the cell membrane and nucleus. Drought stress-induced mRNA levels of GmANKTM21, which encodes proteins belonging to the ANK-TM subfamily, Transgenic 35S:GmANKTM21 soybean improved drought tolerance at the germination and seedling stages, with higher stomatal closure in soybean, lower water loss, lower malondialdehyde (MDA) content, and less reactive oxygen species (ROS) production compared with the wild-type soybean (Dongnong50). RNA-sequencing (RNA-seq) and RT-qPCR analysis of differentially expressed transcripts in overexpression of GmANKTM21 further identified potential downstream genes, including GmSPK2, GmSPK4, and GmCYP707A1, which showed higher expression in transgenic soybean, than those in wild-type soybean and KEGG enrichment analysis showed that MAPK signaling pathways were mostly enriched in GmANKTM21 overexpressing soybean plants under drought stress conditions. Therefore, we demonstrate that GmANKTM21 plays an important role in tolerance to drought stress in soybeans.

Gene-edited protein kinases and phosphatases in molecular plant breeding

Protein phosphorylation, the most common and essential post-translational modification, belongs to crucial regulatory mechanisms in plants, affecting their metabolism, intracellular transport, cytoarchitecture, cell division, growth, development, and interactions with the environment. Protein kinases and phosphatases, two important families of enzymes optimally regulating phosphorylation, have now become important targets for gene editing in crops. We review progress on gene-edited protein kinases and phosphatases in crops using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9). We also provide guidance for computational prediction of alterations and/or changes in function, activity, and binding of protein kinases and phosphatases as consequences of CRISPR/Cas9-based gene editing with its possible application in modern crop molecular breeding towards sustainable agriculture.

Modulation of plant immunity and biotic interactions under phosphate deficiency

Phosphorus (P) is an essential macronutrient for plant life and growth. P is primarily acquired in the form of inorganic phosphate (Pi) from soil. To cope with Pi deficiency, plants have evolved an elaborate system to improve Pi acquisition and utilization through an array of developmental and physiological changes, termed Pi starvation response (PSR). Plants also assemble and manage mutualistic microbes to enhance Pi uptake, through integrating PSR and immunity signaling. A trade-off between plant growth and defense favors the notion that plants lower a cellular state of immunity to accommodate host-beneficial microbes for nutrition and growth at the cost of infection risk. However, the existing data indicate that plants selectively activate defense responses against pathogens, but do not or less against non-pathogens, even under nutrient deficiency. In this review, we highlight recent advances in the principles and mechanisms with which plants balance immunity and growth-related processes to optimize their adaptation to Pi deficiency.

Zinc oxide nanoparticles influence on plant tolerance to salinity stress: insights into physiological, biochemical, and molecular responses

A slight variation in ecological milieu of plants, like drought, heavy metal toxicity, abrupt changes in temperature, flood, and salt stress disturbs the usual homeostasis or metabolism in plants. Among these stresses, salinity stress is particularly detrimental to the plants, leading to toxic effects and reduce crop productivity. In a saline environment, the accumulation of sodium and chloride ions up to toxic levels significantly correlates with intracellular osmotic pressure, and can result in morphological, physiological, and molecular alterations in plants. Increased soil salinity triggers salt stress signals that activate various cellular-subcellular mechanisms in plants to enable their survival in saline conditions. Plants can adapt saline conditions by maintaining ion homeostasis, activating osmotic stress pathways, modulating phytohormone signaling, regulating cytoskeleton dynamics, and maintaining cell wall integrity. To address ionic toxicity, researchers from diverse disciplines have explored novel approaches to support plant growth and enhance their resilience. One such approach is the application of nanoparticles as a foliar spray or seed priming agents positively improve the crop quality and yield by activating germination enzymes, maintaining reactive oxygen species homeostasis, promoting synthesis of compatible solutes, stimulating antioxidant defense mechanisms, and facilitating the formation of aquaporins in seeds and root cells for efficient water absorption under various abiotic stresses. Thus, the assessment mainly targets to provide an outline of the impact of salinity stress on plant metabolism and the resistance strategies employed by plants. Additionally, the review also summarized recent research efforts exploring the innovative applications of zinc oxide nanoparticles for reducing salt stress at biochemical, physiological, and molecular levels.

A B-box transcription factor OsBBX17 regulates saline-alkaline tolerance through the MAPK cascade pathway in rice

Rice OsBBX17 encodes a B-box zinc finger transcription factor in which the N-terminal B-box structural domain interacts with OsMPK1. In addition, it directly binds to the G-box of OsHAK2 and OsHAK7 promoters and represses their transcription. Under saline-alkaline conditions, the expression of OsBBX17 was inhibited. Meanwhile, activation of the OsMPK1-mediated mitogen-activated protein kinase cascade pathway caused OsMPK1 to interact with OsBBX17 and phosphorylate OsBBX17 at the Thr-95 site. It reduced OsBBX17 DNA-binding activity and enhanced saline-alkaline tolerance by deregulating transcriptional repression of OsHAK2 and OsHAK7. Genetic assays showed that the osbbx17-KO had an excellent saline-alkaline tolerance, whereas the opposite was in OsBBX17-OE. In addition, overexpression of OsMPK1 significantly improved saline-alkaline tolerance, but knockout of OsMPK1 caused an increased sensitivity. Further overexpression of OsBBX17 in the osmpk1-KO caused extreme saline-alkaline sensitivity, even a quick death. OsBBX17 was validated in saline-alkaline tolerance from two independent aspects, transcriptional level and post-translational protein modification, unveiling a mechanistic framework by which OsMPK1-mediated phosphorylation of OsBBX17 regulates the transcription of OsHAK2 and OsHAK7 to enhance the Na+ /K+ homeostasis, which partially explains light on the molecular mechanisms of rice responds to saline-alkaline stress via B-box transcription factors for the genetic engineering of saline-alkaline tolerant crops.

The chromatin remodeller MdRAD5B enhances drought tolerance by coupling MdLHP1-mediated H3K27me3 in apple

RAD5B belongs to the Rad5/16-like group of the SNF2 family, which often functions in chromatin remodelling. However, whether RAD5B is involved in chromatin remodelling, histone modification, and drought stress tolerance is largely unclear. We identified a drought-inducible chromatin remodeler, MdRAD5B, which positively regulates apple drought tolerance. Transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) analysis showed that MdRAD5B affects the expression of 466 drought-responsive genes through its chromatin remodelling function in response to drought stress. In addition, MdRAD5B interacts with and degrades MdLHP1, a crucial regulator of histone H3 trimethylation at K27 (H3K27me3), through the ubiquitin-independent 20S proteasome. Chromatin immunoprecipitation-sequencing (ChIP-seq) analysis revealed that MdRAD5B modulates the H3K27me3 deposition of 615 genes in response to drought stress. Genetic interaction analysis showed that MdRAD5B mediates the H3K27me3 deposition of drought-responsive genes through MdLHP1, which causes their expression changes under drought stress. Our results unravelled a dual function of MdRAD5B in gene expression modulation in apple in response to drought, that is, via the regulation of chromatin remodelling and H3K27me3.

Basic helix-loop-helix transcription factor OsbHLH110 positively regulates abscisic acid biosynthesis and salinity tolerance in rice

Salinity is a significant abiotic stress factor affecting plant growth, consequently reducing crop yield. Abscisic acid (ABA), a well-known phytohormone, is crucial in conferring resistance to abiotic stress, thus, understanding the mechanisms underlying ABA biosynthesis is crucial. In rice (Oryza sativa L.), OsABA2, a short-chain dehydrogenase protein, has a pivotal role in modulating ABA biosynthesis and salt tolerance by undergoing phosphorylation at Ser197 through mitogen-activated protein kinase OsMPK1. However, the interaction between OsABA2 and other proteins in regulating ABA biosynthesis remains unclear. We employed OsABA2 as a bait in yeast two-hybrid screening: a basic helix-loop-helix transcription factor interacting with OsABA2, named OsbHLH110, was identified. Our results showed that firefly luciferase complementary imaging, pull-down, and co-immunoprecipitation assays validated the interaction between OsbHLH110 and OsABA2, affirming their interaction in vivo and in vitro. Moreover, the expression of OsbHLH110 significantly increases in response to salt and ABA treatments. Additionally, OsbHLH110 can directly bind to the G-box element in the OsABA2 promoter. This binding enhances luciferase activity controlled by the OsABA2 promoter, thereby increasing the expression of the OsABA2 gene and content of the OsABA2 protein, resulting in an increase in ABA content. OsABA2 enhanced the interaction between OsbHLH110 and OsABA2 promoter. This collaborative effect enhanced the regulation of ABA biosynthesis. Subsequent genetic analysis demonstrated that OsbHLH110 improved the tolerance of rice to salt stress.

OsMKK1 is a novel element that positively regulates the Xa21-mediated resistance response to Xanthomonas oryzae pv. oryzae in rice

KEY MESSAGE

OsMKK1, a MAPK gene, positively regulates rice Xa21-mediated resistance response and also plays roles in normal growth and development process of rice. The mitogen-activated protein kinase (MAPK) cascade was highly conserved among eukaryotes, which played crucial roles in plant responses to pathogen infection. Bacterial blight is the most devastating bacterial disease. Xa21 confers broad-spectrum resistance to Xanthomonas oryzae pv. Oryzae (Xoo). This study identified that the transcription level of OsMKK1 was up-regulated in resistant response against Xoo, thus overexpression (OsMKK1-OX) and RNA interference (OsMKK1-RNAi) transgenic rice lines under the background of Xa21 was constructed. Compared with recipient control plants 4021, the OsMKK1-OX lines significantly enhanced disease resistance to Xoo, on the contrary, the resistance of OsMKK1-RNAi lines was weakened, demonstrated that OsMKK1 played a positive role in Xa21-mediated disease resistance pathway. A number of pathogenesis-related proteins, including PR1A, PR2 and PR10A showed enhanced expression in OsMKK1-OX lines, supported that these PR genes may be regulated by OsMKK1 to participate in the defense responses. In addition, the agronomic traits of OsMKK1 transgenic plants were affected. Overall, these results revealed the role of OsMKK1 in Xa21-mediated resistance against Xoo and in the normal growth and development process in rice.

Genome-Wide Association Study of Seed Morphology Traits in Senegalese Sorghum Cultivars

Sorghum is considered the fifth most important crop in the world. Despite the potential value of Senegalese germplasm for various traits, such as resistance to fungal diseases, there is limited information on the study of sorghum seed morphology. In this study, 162 Senegalese germplasms were evaluated for seed area size, length, width, length-to-width ratio, perimeter, circularity, the distance between the intersection of length & width (IS) and center of gravity (CG), and seed darkness and brightness by scanning and analyzing morphology-related traits with SmartGrain software at the USDA-ARS Plant Science Research Unit. Correlations between seed morphology-related traits and traits associated with anthracnose and head smut resistance were analyzed. Lastly, genome-wide association studies were performed on phenotypic data collected from over 16,000 seeds and 193,727 publicly available single nucleotide polymorphisms (SNPs). Several significant SNPs were found and mapped to the reference sorghum genome to uncover multiple candidate genes potentially associated with seed morphology. The results indicate clear correlations among seed morphology-related traits and potential associations between seed morphology and the defense response of sorghum. GWAS analysis listed candidate genes associated with seed morphologies that can be used for sorghum breeding in the future.

Phosphorylation of OsRbohB by the protein kinase OsDMI3 promotes H2O2 production to potentiate ABA responses in rice

In rice, the Ca²⁺/calmodulin-dependent protein kinase OsDMI3 is an important positive regulator of abscisic acid (ABA) signaling. In ABA signaling, H₂O₂ is required for ABA-induced activation of OsDMI3, which in turn increase H₂O₂ production. However, how OsDMI3 regulates H₂O₂ production in ABA signaling remains unknown. Here we show that OsRbohB is the main NADPH oxidase involved in ABA-induced H₂O₂ production and ABA-mediated physiological responses. OsDMI3 directly interacts with and phosphorylates OsRbohB at Ser-191, which is OsDMI3-mediated site-specific phosphorylation in ABA signaling. Further analyses revealed that OsDMI3-mediated OsRbohB Ser-191 phosphorylation positively regulates the activity of NADPH oxidase and the production of H₂O₂ in ABA signaling, thereby enhancing the sensitivity of seed germination and root growth to ABA and plant tolerance to water stress and oxidative stress. Moreover, we discovered that the OsDMI3-mediated OsRbohB phosphorylation and H₂O₂ production is dependent on the sucrose non-fermenting 1-related protein kinases SAPK8/9/10, which phosphorylate OsRbohB at Ser-140 in ABA signaling. Taken together, these results not only reveal an important regulatory mechanism that directly activates Rboh for ABA-induced H₂O₂ production but also uncover the importance of this regulatory mechanism in ABA signaling.

Kinase MxMPK4-1 and calmodulin-binding protein MxIQM3 enhance apple root acidification during Fe deficiency

Iron (Fe) deficiency is a long-standing issue in plant mineral nutrition. Ca2+ signals and the mitogen-activated protein kinase (MAPK) cascade are frequently activated in parallel to perceive external cues, but their interplay under Fe deficiency stress remains largely unclear. Here, the kinase MxMPK4-1, which is induced during the response to Fe deficiency stress in apple rootstock Malus xiaojinensis, cooperates with IQ-motif containing protein3 (MxIQM3). MxIQM3 gene expression, protein abundance, and phosphorylation level increased under Fe deficiency stress. The overexpression of MxIQM3 in apple calli and rootstocks mitigated the Fe deficiency phenotype and improved stress tolerance, whereas RNA interference or silencing of MxIQM3 in apple calli and rootstocks, respectively, worsened the phenotype and reduced tolerance to Fe deficiency. MxMPK4-1 interacted with MxIQM3 and subsequently phosphorylated MxIQM3 at Ser393, and co-expression of MxMPK4-1 and MxIQM3 in apple calli and rootstocks enhanced Fe deficiency responses. Furthermore, MxIQM3 interacted with the central-loop region of the plasma membrane (PM) H+-ATPase MxHA2. Phospho-mimicking mutation of MxIQM3 at Ser393 inhibited binding to MxHA2, but phospho-abolishing mutation promoted interaction with both the central-loop and C terminus of MxHA2, demonstrating phosphorylation of MxIQM3 caused dissociation from MxHA2 and therefore increased H+ secretion. Moreover, Ca2+/MxCAM7 (Calmodulin7) regulated the MxMPK4-1-MxIQM3 module in response to Fe deficiency stress. Overall, our results demonstrate that MxMPK4-1-MxIQM3 forms a functional complex and positively regulates PM H+-ATPase activity in Fe deficiency responses, revealing a versatile mechanism of Ca2+/MxCAM7 signaling and MAPK cascade under Fe deficiency stress.

The UDP-glucuronic acid decarboxylase OsUXS3 regulates Na+ ion toxicity tolerance under salt stress by interacting with OsCATs in rice

Overly Na⁺ ion in soil caused by salt stress has a significant negative impact on the growth and production of crops, especially rice (Oryza sativa L.). Therefore, it is vital for us to clarify how salt stress tolerance in rice is caused by Na⁺ ion toxicity. The UDP-glucuronic acid decarboxylase (UXS) is a critical enzyme in the biosynthesis of UDP-xylose, which is the key substrate of cytoderm synthesis in plants. In this study, we found that OsUXS3, a rice UXS, is a positive regulator to regulate Na⁺ ion toxicity under salt stress by interacting with OsCATs (Oryza sativa catalase; OsCAT). The expression of OsUXS3 was significantly up-regulated under NaCl and NaHCO₃ treatments of rice seedlings. Meanwhile, by the genetic and biochemical evidence, knockout of OsUXS3 significantly increased reactive oxygen species (ROS) levels and decreased CAT activity under NaCl and NaHCO₃ treatments in tissue. Furthermore, knockout of OsUXS3 caused excessive accumulation of Na ⁺ ion and rapid loss of K⁺ ion and disrupts Na⁺/K⁺ homeostasis under NaCl and NaHCO₃ treatments. Based on the results above, we can conclude that OsUXS3 might regulate CAT activity by interacting with OsCATs, which is not only characterized for the first time but also regulating Na⁺/K⁺ homeostasis, positively regulating the Na⁺ ion toxicity tolerance under salt stress in rice.

Life cycle and reproduction dynamics of Bangiales in response to environmental stresses

Red algae of the order Bangiales are notable for exhibiting flexible promotion of sexual and asexual reproductive processes by environmental stresses. This flexibility indicates that a trade-off between vegetative growth and reproduction occurs in response to environmental stresses that influence the timing of phase transition within the life cycle. Despite their high phylogenetic divergence, both filamentous and foliose red alga in the order Bangiales exhibit a haploid-diploid life cycle, with a haploid leafy or filamentous gametophyte (thallus) and a diploid filamentous sporophyte (conchocelis). Unlike haploid-diploid life cycles in other orders, the gametophyte in Bangiales is generated independently of meiosis; the regulation of this generation transition is not fully understood. Based on transcriptome and gene expression analyses, the originally proposed biphasic model for alternation of generations in Bangiales was recently updated to include a third stage. Along with the haploid gametophyte and diploid sporophyte, the triphasic framework recognizes a diploid conchosporophyte-a conchosporangium generated on the conchocelis-phase and previously considered to be part of the sporophyte. In addition to this sexual life cycle, some Bangiales species have an asexual life cycle in which vegetative cells of the thallus develop into haploid asexual spores, which are then released from the thallus to produce clonal thalli. Here, we summarize the current knowledge of the triphasic life cycle and life cycle trade-off in Neopyropia yezoensis and 'Bangia' sp. as model organisms for the Bangiales.

CaM/CaMKII mediates activation and proliferation of hepatic stellate cells regulated by ASIC1a

The activation of hepatic stellate cells (HSCs) is closely related to hepatic fibrosis and plays a key role in its occurrence and development. In the damaged liver, inhibition of the activation, proliferation, and clearance of HSCs is an important therapeutic strategy. However, the mechanism underlying the activation of HSCs is not completely clear. Acid-sensitive ion channel 1a (ASIC1a) is a cation channel activated by extracellular acid, which is responsible for the transport of Ca²⁺ and Na⁺ and participates in the activation of HSCs and the occurrence and development of many inflammatory diseases, suggesting that ASIC1a plays an important role in liver fibrosis. A previous study by the project team found that when the membrane channel protein ASIC1a was opened, intracellular Ca²⁺ levels increased, the expression of CaM/CaMKII in HSCs was high, and HSC was activated and proliferated. Therefore, we established an SD rat model of hepatic fibrosis and induced HSC-T6 activation by stimulating ASIC1a with acid in vitro. In vivo, CCl₄ was used to induce liver fibrosis in rats, and different doses of KN93 (0.5, 1, and 2 mg/kg/d) and colchicine (0.1 mg/kg/d) were administered. Eight weeks later, the activities of ALT and AST in serum were measured and hematoxylin-eosin and Masson staining in liver tissue, and immunohistochemistry analysis were performed in SD rats. The expressions of ASIC1a, α-SMA, Collagen-1, CaM, and CaMKII were detected. In vitro, we activated HSC-T6 cells by stimulating ASIC1a with acid. The results showed that inhibition of ASIC1a could improve acid-induced HSCs activation. In addition, CaM/CaMKII was expressed in HSC of rats with hepatic fibrosis regulated by ASIC1a. After blocking or silencing the expression of CaMKII, the fibrosis marker protein can be down-regulated. KN93 also reduced inflammation and improved the activation, proliferation and fibrosis of HSC. In summary, we concluded that CaM/CaMKII participates in ASIC1a regulation of the proliferation and activation of HSC and promotes the occurrence of liver fibrosis.

Calcium/calmodulin-mediated microbial symbiotic interactions in plants

Cytoplasmic calcium (Ca²⁺) transients and nuclear Ca²⁺ oscillations act as hubs during root nodulation and arbuscular mycorrhizal symbioses. Plants perceive bacterial Nod factors or fungal signals to induce the Ca²⁺ oscillation in the nucleus of root hair cells, and subsequently activate calmodulin (CaM) and Ca²⁺/CaM-dependent protein kinase (CCaMK). Ca²⁺ and CaM-bound CCaMK phosphorylate transcription factors then initiate down-stream signaling events. In addition, distinct Ca²⁺ signatures are activated at different symbiotic stages: microbial colonization and infection; nodule formation; and mycorrhizal development. Ca²⁺ acts as a key signal that regulates a complex interplay of downstream responses in many biological processes. This short review focuses on advances in Ca²⁺ signaling-regulated symbiotic events. It is meant to be an introduction to readers in and outside the field of bacterial and fungal symbioses. We summarize the molecular mechanisms underlying Ca²⁺/CaM-mediated signaling in fine-tuning both local and systemic symbiotic events.

OsDMI3-mediated OsUXS3 phosphorylation improves oxidative stress tolerance by modulating OsCATB protein abundance in rice

Calcium (Ca²⁺ )/calmodulin (CaM)-dependent protein kinase (CCaMK) is an important positive regulator of antioxidant defenses and tolerance against oxidative stress. However, the underlying molecular mechanisms are largely unknown. Here, we report that the rice (Oryza sativa) CCaMK (OsDMI3) physically interacts with and phosphorylates OsUXS3, a cytosol-localized UDP-xylose synthase. Genetic and biochemical evidence demonstrated that OsUXS3 acts downstream of OsDMI3 to enhance the oxidative stress tolerance conferred by higher catalase (CAT) activity. Indeed, OsUXS3 interacted with CAT isozyme B (OsCATB), and this interaction was required to increase OsCATB protein abundance under oxidative stress conditions. Furthermore, we showed that OsDMI3 phosphorylates OsUXS3 on residue Ser-245, thereby further promoting the interaction between OsUXS3 and OsCATB. Our results indicate that OsDMI3 promotes the association of OsUXS3 with OsCATB to enhance CAT activity under oxidative stress. These findings reveal OsUXS3 as a direct target of OsDMI3 and demonstrate its involvement in antioxidant defense.

Phosphorylation of MdERF17 by MdMPK4 promotes apple fruit peel degreening during light/dark transitions

As apple fruits (Malus domestica) mature, they accumulate anthocyanins concomitantly with losing chlorophyll (Chl); however, the molecular pathways and events that coordinate Chl degradation and fruit coloration have not been elucidated. We showed previously that the transcription factor ETHYLENE RESPONSE FACTOR17 (MdERF17) modulates Chl degradation in apple fruit peels and that variation in the pattern of MdERF17 serine (Ser) residues is responsible for differences in its transcriptional regulatory activity. Here, we report that MdERF17 interacts with and is phosphorylated by MAP KINASE4 (MdMPK4-14G). Phosphorylation of MdERF17 at residue Thr67 by MdMPK4-14G is necessary for its transcriptional regulatory activity and its regulation of Chl degradation. We also show that MdERF17 mutants with different numbers of Ser repeat insertions exhibit altered phosphorylation profiles, with more repeats increasing its interaction with MdMPK4. MdMPK4-14G can be activated by exposure to darkness and is involved in the dark-induced degreening of fruit peels. We also demonstrate that greater phosphorylation of MdERF17 by MdMPK4-14G is responsible for the regulation of Chl degradation during light/dark transitions. Overall, our findings reveal the mechanism by which MdMPK4 controls fruit peel coloration.

Identification of candidate genes involved in salt stress response at germination and seedling stages by QTL mapping in upland cotton

Salinity is a major abiotic stress at critical stages of seed germination and seedling establishment. Germination rate (GR) and field emergence rate (FER) are the key traits that determine the basic number of plants stand under field conditions. To explore molecular mechanisms in upland cotton under salt stress, a population of 177 recombinant inbred lines, and their parents were evaluated for seed germination traits (GP, germination potential; GR; FW, fresh weight; DW, dry weight; GL, germinal length) and seedling traits (FER; SH, seedling height; NL, number of main stem leaves) in 2016–2018. Based on the linkage map contained 2,859 single nucleotide polymorphism and simple sequence repeat markers, traits under salt stress (E1) and normal conditions (E2), and in the converted relative index (R-value) dataset of 3 years’ trials were used to map quantitative trait loci (QTL). A total of 3 QTL and 2 clusters were detected as salt-tolerant QTL. Three QTL (qGR-Chr4-3, qFER-Chr12-3, and qFER-Chr15-1) were detected under salt stress conditions and R-value dataset, which explained variance of phenotype 9.62–13.67%, and 4.2–4.72%, 4.75–8.96%, respectively. Two clusters (Loci-Chr4-2 and Loci-Chr5-4) harboring the QTL for 4 germination traits (GR, FER, GL, and NL) and 6 seedling traits (GR, FER, DW, FW, SH, and NL) were detected related under salt stress. A total of 691 genes were found in the candidate QTL or clusters. Among them, 4 genes (Gh_A04G1106, Gh_A05G3246, Gh_A05G3177, and Gh_A05G3266) showed expression differences between salt-sensitive and -tolerant lines under salt stress conditions, and were assigned as candidate genes in response to salt stress. The consistent salt-tolerance QTL identified in both germination and seedling stages will facilitate novel insights into effective utilization of cotton genetic resources.

Integrated Analysis of Physiological, mRNA Sequencing, and miRNA Sequencing Data Reveals a Specific Mechanism for the Response to Continuous Cropping Obstacles in Pogostemon cablin Roots

Pogostemon cablin (patchouli) is a commercially important medicinal and industrial crop grown worldwide for its medicinal and aromatic properties. Patchoulol and pogostone, derived from the essential oil of patchouli, are considered valuable components in the cosmetic and pharmaceutical industries. Due to its high application value in the clinic and industry, the demand for patchouli is constantly growing. Unfortunately, patchouli cultivation has suffered due to severe continuous cropping obstacles, resulting in a significant decline in yield and quality. Moreover, the physiological and transcriptional changes in patchouli in response to continuous cropping obstacles remain unclear. This has greatly restricted the development of the patchouli industry. To explore the mechanism underlying the rapid response of patchouli roots to continuous cropping stress, integrated analysis of the transcriptome and miRNA profiles of patchouli roots under continuous and noncontinuous cropping conditions in different growth periods was conducted using RNA sequencing (RNA-seq) and miRNA-seq and complemented with physiological data. The physiological and biochemical results showed that continuous cropping significantly inhibited root growth, decreased root activity, and increased the activity of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and the levels of osmoregulators (malondialdehyde, soluble protein, soluble sugar, and proline). Subsequently, we found 4,238, 3,494, and 7,290 upregulated and 4,176, 3,202, and 8,599 downregulated differentially expressed genes (DEGs) in the three growth periods of continuously cropped patchouli, many of which were associated with primary carbon and nitrogen metabolism, defense responses, secondary metabolite biosynthesis, and transcription factors. Based on miRNA-seq, 927 known miRNAs and 130 novel miRNAs were identified, among which 67 differentially expressed miRNAs (DEMIs) belonging to 24 miRNA families were induced or repressed by continuous cropping. By combining transcriptome and miRNA profiling, we obtained 47 miRNA-target gene pairs, consisting of 18 DEMIs and 43 DEGs, that likely play important roles in the continuous cropping response of patchouli. The information provided in this study will contribute to clarifying the intricate mechanism underlying the patchouli response to continuous cropping obstacles. In addition, the candidate miRNAs and genes can provide a new strategy for breeding continuous cropping-tolerant patchouli.

Regulatory Mechanisms of Mitogen-Activated Protein Kinase Cascades in Plants: More than Sequential Phosphorylation

Mitogen-activated protein kinase (MAPK) cascades play crucial roles in almost all biological processes in plants. They transduce extracellular cues into cells, typically through linear and sequential phosphorylation and activation of members of the signaling cascades. However, accumulating data suggest various regulatory mechanisms of plant MAPK cascades in addition to the traditional phosphorylation pathway, in concert with their large numbers and coordinated roles in plant responses to complex ectocytic signals. Here, we highlight recent studies that describe the uncanonical mechanism of regulation of MAPK cascades, regarding the activation of each tier of the signaling cascades. More particularly, we discuss the unusual role for MAPK kinase kinases (MAPKKKs) in the regulation of MAPK cascades, as accumulating data suggest the non-MAPKKK function of many MAPKKKs. In addition, future work on the biochemical activation of MAPK members that needs attention will be discussed.

Plant Salinity Stress Response and Nano-Enabled Plant Salt Tolerance

The area of salinized land is gradually expanding cross the globe. Salt stress seriously reduces the yield and quality of crops and endangers food supply to meet the demand of the increased population. The mechanisms underlying nano-enabled plant tolerance were discussed, including (1) maintaining ROS homeostasis, (2) improving plant's ability to exclude Na+ and to retain K+, (3) improving the production of nitric oxide, (4) increasing α-amylase activities to increase soluble sugar content, and (5) decreasing lipoxygenase activities to reduce membrane oxidative damage. The possible commonly employed mechanisms such as alleviating oxidative stress damage and maintaining ion homeostasis were highlighted. Further, the possible role of phytohormones and the molecular mechanisms in nano-enabled plant salt tolerance were discussed. Overall, this review paper aims to help the researchers from different field such as plant science and nanoscience to better understand possible new approaches to address salinity issues in agriculture.

GR24-mediated enhancement of salt tolerance and roles of H2O2 and Ca2+ in regulating this enhancement in cucumber

This study investigated the regulation of the exogenous strigolactone (SL) analog GR24 in enhancing the salt tolerance and the effects of calcium ion (Ca2+) and hydrogen peroxide (H2O2) on GR24's regulation effects in cucumber. The seedlings were sprayed with (1) distilled water (CK), (2) NaCl, (3) GR24, then NaCl, (4) GR24, then H2O2 scavenger, then NaCl, and (5) GR24, then Ca2+ blocker, then NaCl. The second true leaf was selected for biochemical assays. Under the salt stress, the exogenous GR24 maintained the ion balance, increased the activity of antioxidant enzymes, reduced the membrane lipid peroxidation, and increased the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), accompanied by a decrease in relative conductivity, an increase in the proline content, and elevated gene expression levels of antioxidant enzymes, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, calcium-dependent protein kinases (CDPKs), salt overly sensitive SOS1, CBL-interacting protein kinase 2 (CIPK2), and calcineurin B-like protein 3 (CBL3). Such protective effects triggered by GR24 were attenuated or almost abolished by ethylene glycol tetraacetic acid (EGTA), lanthanum chloride (LaCl3, Ca2+ channel blocker), diphenyleneiodonium (DPI, NADPH oxidase inhibitor), and dimethylthiourea (DMTU, hydroxyl radical scavenger). Our data suggest that exogenous GR24 is highly effective in alleviating salt-induced damages via modulating antioxidant capabilities and improving ionic homeostasis and osmotic balance and that H2O2 and Ca2+ are required for GR24-mediated enhancement of salt tolerance.

Phosphorylation of OsABA2 at Ser197 by OsMPK1 regulates abscisic acid biosynthesis in rice

The mitogen-activated protein kinase OsMPK1 is involved in abscisic acid (ABA) biosynthesis in rice (Oryza sativa L.). However, the underlying molecular mechanisms of OsMPK1 in regulating ABA biosynthesis are poorly understood. Here, by using yeast two-hybrid assay and firefly luciferase complementary imaging assay, we show that OsMPK1 physically interact with a short-chain dehydrogenase protein OsABA2. However, OsMPK5, a homolog of OsMPK1, does not interact with OsABA2. Further, OsMPK1 can phosphorylate OsABA2^S197 in vitro. Phosphorylation at the position of OsABA2^S197 does not affect its subcellular localization, but enhances the stability of OsABA2 protein. We also found that OsABA2 has feedback regulation on OsMPK1 kinase activity. Further research reveals that OsMPK1 and OsABA2 coordinately regulate the biosynthesis of ABA, and phosphorylation of OsABA2 at Ser197 by OsMPK1 plays a crucial role in regulating the biosynthesis of ABA. Finally, genetic analysis showed that OsABA2 can enhance the sensitivity of rice to ABA and the tolerance of rice to drought and salt stress.

An ABA Functional Analogue B2 Enhanced Salt Tolerance by Inducing the Root Elongation and Reducing Peroxidation Damage in Maize Seedlings

Salt stress negatively affects maize growth and yield. Application of plant growth regulator is an effective way to improve crop salt tolerance, therefore reducing yield loss by salt stress. Here, we used a novel plant growth regulator B2, which is a functional analogue of ABA. With the aim to determine whether B2 alleviates salt stress on maize, we studied its function under hydroponic conditions. When the second leaf was fully developed, it was pretreated with 100 µM ABA, 0.01 µM B2, 0.1 µM B2, and 1 µM B2, independently. After 5 days treatment, NaCl was added into the nutrient solution for salt stress. Our results showed that B2 could enhance salt tolerance in maize, especially when the concentration was 1.0 µMol·L⁻¹. Exogenous application of B2 significantly enhanced root growth, and the root/shoot ratio increased by 7.6% after 6 days treatment under salt stress. Compared with control, the ABA level also decreased by 31% after 6 days, which might have resulted in the root development. What is more, B2 maintained higher photosynthetic capacity in maize leaves under salt stress conditions and increased the activity of antioxidant enzymes and decreased the generation rate of reactive oxygen species by 16.48%. On the other hand, B2 can enhance its water absorption ability by increasing the expression of aquaporin genes ZmPIP1-1 and ZmPIP1-5. In conclusion, the novel plant growth regulator B2 can effectively improve the salt tolerance in maize.

The rice Raf-like MAPKKK OsILA1 confers broad-spectrum resistance to bacterial blight by suppressing the OsMAPKK4-OsMAPK6 cascade

Mitogen-activated protein kinase kinase kinase (MAPKKK) are the first components of MAPK cascades, which play pivotal roles in signaling during plant development and physiological processes. The genome of rice encodes 75 MAPKKKs, of which 43 are Raf-like MAPKKKs. The functions and action modes of most of the Raf-like MAPKKKs, whether they function as bona fide MAPKKKs and which are their downstream MAPKKs, are largely unknown. Here, we identified the osmapkkk43 mutant, which conferred broad-spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo), the destructive bacterial pathogen of rice. Oryza sativa (Os)MAPKKK43 encoding a Raf-like MAPKKK was previously known as Increased Leaf Angle 1 (OsILA1). Genetic analysis indicated that OsILA1 functioned as a negative regulator and acted upstream of the OsMAPKK4-OsMAPK6 cascade in rice-Xoo interactions. Unlike classical MAPKKKs, OsILA1 mainly phosphorylated the threonine 34 site at the N-terminal domain of OsMAPKK4, which possibly influenced the stability of OsMAPKK4. The N-terminal domain of OsILA1 is required for its homodimer formation and its full phosphorylation capacity. Taken together, our findings reveal that OsILA1 acts as a negative regulator of the OsMAPKK4-OsMAPK6 cascade and is involved in rice-Xoo interactions.

CDPKs: The critical decoders of calcium signal at various stages of malaria parasite development

Calcium ions are used as important signals during various physiological processes. In malaria parasites, Plasmodium spp., calcium dependent protein kinases (CDPKs) have acquired the unique ability to sense and transduce calcium signals at various critical steps during the lifecycle, either through phosphorylation of downstream substrates or mediating formation of high molecular weight protein complexes. Calcium signaling cascades establish important crosstalk events with signaling pathways mediated by other secondary messengers such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). CDPKs play critical roles at various important physiological steps during parasite development in vertebrates and mosquitoes. They are also important for transmission of the parasite between the two hosts. Combined with the fact that CDPKs are not present in humans, they continue to be pursued as important targets for development of anti-malarial drugs.