The Mg-chelatase H subunit is an abscisic acid receptor

Appropriate induction of TOC1 ensures optimal MYB44 expression in ABA signaling and stress response in Arabidopsis

Plants possess the remarkable ability to integrate the circadian clock with various signalling pathways, enabling them to quickly detect and react to both external and internal stress signals. However, the interplay between the circadian clock and biological processes in orchestrating responses to environmental stresses remains poorly understood. TOC1, a core component of the plant circadian clock, plays a vital role in maintaining circadian rhythmicity and participating in plant defences. Here, our study reveals a direct interaction between TOC1 and the promoter region of MYB44, a key gene involved in plant defence. TOC1 rhythmically represses MYB44 expression, thereby ensuring elevated MYB44 expression at dawn to help the plant in coping with lowest temperatures during diurnal cycles. Additionally, both TOC1 and MYB44 can be induced by cold stress in an Abscisic acid (ABA)-dependent and independent manner. TOC1 demonstrates a rapid induction in response to lower temperatures compared to ABA treatment, suggesting timely flexible regulation of TOC1-MYB44 regulatory module by the circadian clock in ensuring a proper response to diverse stresses and maintaining a balance between normal physiological processes and energy-consuming stress responses. Our study elucidates the role of TOC1 in effectively modulating expression of MYB44, providing insights into the regulatory network connecting the circadian clock, ABA signalling, and stress-responsive genes.

Chemical Driving the Subtype Selectivity of Phytohormone Receptors Is Beneficial for Crop Productivity

Chemicals that modulate phytohormones serve as a research tool in plant science and as products to improve crop productivity. Subtype selectivity refers to a ligand to selectively bind to specific subtypes of a receptor rather than binding to all possible subtypes indiscriminately. It allows for precise and specific control of cellular functions and is widely used in medicine. However, subtype selectivity is rarely mentioned in the realm of plant science, and it requires integrated knowledge from chemistry and biology, including structural features of small molecules as ligands, the redundancy of target proteins, and the response of signaling factors. Here, we present a comprehensive review and evaluation of phytohormone receptor subtype selectivity, leveraging the chemical characteristics of phytohormones and their analogues as clues. This work endeavors to provide a valuable research strategy that integrates knowledge from chemistry and biology to advance research efforts geared toward enhancing crop productivity.

Discovering novel targets of abscisic acid using computational approaches

Abscisic acid (ABA) is a crucial plant hormone that is naturally produced in various mammalian tissues and holds significant potential as a therapeutic molecule in humans. ABA is selected for this study due to its known roles in essential human metabolic processes, such as glucose homeostasis, immune responses, cardiovascular system, and inflammation regulation. Despite its known importance, the molecular mechanism underlying ABA's action remain largely unexplored. This study employed computational techniques to identify potential human ABA receptors. We screened 64 candidate molecules using online servers and performed molecular docking to assess binding affinity and interaction types with ABA. The stability and dynamics of the best complexes were investigated using molecular dynamics simulation over a 100 ns time period. Root mean square fluctuations (RMSF), root mean square deviation (RMSD), solvent-accessible surface area (SASA), radius of gyration (Rg), free energy landscape (FEL), and principal component analysis (PCA) were analyzed. Next, the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method was employed to calculate the binding energies of the complexes based on the simulated data. Our study successfully pinpointed four key receptors responsible for ABA signaling (androgen receptor, glucocorticoid receptor, mineralocorticoid receptor, and retinoic acid receptor beta) that have a strong affinity for binding with ABA and remained structurally stable throughout the simulations. The simulations with Hydralazine as an unrelated ligand were conducted to validate the specificity of the identified receptors for ABA. The findings of this study can contribute to further experimental validation and a better understanding of how ABA functions in humans.

Integrating the multiple functions of CHLH into chloroplast-derived signaling fundamental to plant development and adaptation as well as fruit ripening

Chlorophyll (Chl)-mediated oxygenic photosynthesis sustains life on Earth. Greening leaves play fundamental roles in plant growth and crop yield, correlating with the idea that more Chls lead to better adaptation. However, they face significant challenges from various unfavorable environments. Chl biosynthesis hinges on the first committed step, which involves inserting Mg2+ into protoporphyrin. This step is facilitated by the H subunit of magnesium chelatase (CHLH) and features a conserved mechanism from cyanobacteria to plants. For better adaptation to fluctuating land environments, especially drought, CHLH evolves multiple biological functions, including Chl biosynthesis, retrograde signaling, and abscisic acid (ABA) responses. Additionally, it integrates into various chloroplast-derived signaling pathways, encompassing both retrograde signaling and hormonal signaling. The former comprises ROS (reactive oxygen species), heme, GUN (genomes uncoupled), MEcPP (methylerythritol cyclodiphosphate), β-CC (β-cyclocitral), and PAP (3'-phosphoadenosine-5'-phosphate). The latter involves phytohormones like ABA, ethylene, auxin, cytokinin, gibberellin, strigolactone, brassinolide, salicylic acid, and jasmonic acid. Together, these elements create a coordinated regulatory network tailored to plant development and adaptation. An intriguing example is how drought-mediated improvement of fruit quality provides insights into chloroplast-derived signaling, aiding the shift from vegetative to reproductive growth. In this context, we explore the integration of CHLH's multifaceted roles into chloroplast-derived signaling, which lays the foundation for plant development and adaptation, as well as fruit ripening and quality. In the future, manipulating chloroplast-derived signaling may offer a promising avenue to enhance crop yield and quality through the homeostasis, function, and regulation of Chls.

Coordination of m6A mRNA Methylation and Gene Transcriptome in Sugarcane Response to Drought Stress

The N6-methyladenosine (m6A) methylation of mRNA is involved in biological processes essential for plant growth. To explore the m6A modification of sugarcane and reveal its regulatory function, methylated RNA immunoprecipitation sequencing (MeRIP-seq) was used to construct the m6A map of sugarcane. In this study, m6A sites of sugarcane transcriptome were significantly enriched around the stop codon and within 3'-untranslated regions (3'UTR). Gene ontology (GO) analysis showed that the m6A modification genes are associated with metabolic biosynthesis. In addition, the m6A modification of drought-resistant transcript mRNA increased significantly under drought (DR) treatment, resulting in enhanced mRNA stability, which is involved in regulating sugarcane drought resistance. GO and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment results showed that differentially methylated peak (DMP) modification of differentially expressed genes (DEGs) in DR were particularly associated with abscisic acid (ABA) biosynthesis. The upregulated genes were significantly enriched in the ABA metabolism, ethylene response, fatty acid metabolism, and negative regulation of the abscisic acid activation signaling pathway. These findings provide a basis and resource for sugarcane RNA epigenetic studies and further increase our knowledge of the functions of m6A modifications in RNA under abiotic stress.

A clathrin-related protein FaRRP1/SCD2 integrates ABA trafficking and signaling to regulate strawberry fruit ripening

Abscisic acid (ABA) is a critical regulator for nonclimacteric fruit ripening such as in the model plant of strawberry (Fragaria × ananassa). Although FaRRP1 is proposed to participate in clathrin-mediated endocytosis of ABA, its action molecular mechanisms in ABA signaling are not fully understood. Here, using our isolated FaRRP1 (ripening-regulation protein) and candidate ABA receptor FaPYL2 and FaABAR from strawberry fruit, a series of silico and molecular interaction analyses demonstrate that they all bind to ABA, and FaRRP1 binds both FaPYL2 and FaABAR; by contrast, the binding affinity of FaRRP1 to FaPYL2 is relatively higher. Interestingly, the binding of FaRRP1 to FaPYL2 and FaABAR affects the perception affinity to ABA. Furthermore, exogenous ABA application and FaRRP1 transgenic analyses confirm that FaRRP1 participates in clathrin-mediated endocytosis and vesicle transport. Importantly, FaRRP1, FaPYL2, and FaABAR all trigger the initiation of strawberry fruit ripening at physiological and molecular levels. In conclusion, FaRRP1 not only binds to ABA but also affects the binding affinity of FaPYL2 and FaABAR to ABA, thus promoting strawberry fruit ripening. Our findings provide novel insights into the role of FaRRP1 in ABA trafficking and signaling, at least in strawberry, a model plant for nonclimacteric fruit ripening.

Expression of the Arabidopsis Mg-chelatase H subunit alleviates iron deficiency-induced stress in transgenic rice

The most common symptom of iron (Fe) deficiency in plants is leaf chlorosis caused by impairment of chlorophyll biosynthesis. Magnesium (Mg)-chelatase H subunit (CHLH) is a key component in both chlorophyll biosynthesis and plastid signaling, but its role in Fe deficiency is poorly understood. Heterologous expression of the Arabidopsis thaliana Mg-chelatase H subunit gene (AtCHLH) increased Mg-chelatase activity by up to 6-fold and abundance of its product, Mg-protoporphyrin IX (Mg-Proto IX), by 60-75% in transgenic rice (Oryza sativa) seedlings compared to wild-type (WT) controls. Noticeably, the transgenic seedlings showed alleviation of Fe deficiency symptoms, as evidenced by their less pronounced leaf chlorosis and lower declines in shoot growth, chlorophyll contents, and photosynthetic efficiency, as indicated by F _v/F _m and electron transport rate, compared to those in WT seedlings under Fe deficiency. Porphyrin metabolism was differentially regulated by Fe deficiency between WT and transgenic seedlings, particularly with a higher level of Mg-Proto IX in transgenic lines, showing that overexpression of AtCHLH reprograms porphyrin metabolism in transgenic rice. Leaves of Fe-deficient transgenic seedlings exhibited greater upregulation of deoxymugineic acid biosynthesis-related genes (i.e., NAS, NAS2, and NAAT1), YSL2 transporter gene, and Fe-related transcription factor genes IRO2 and IDEF2 than those of WT, which may also partly contribute to alleviating Fe deficiency. Although AtCHLH was postulated to act as a receptor for abscisic acid (ABA), exogenous ABA did not alter the phenotypes of Fe-deficient WT or transgenic seedlings. Our study demonstrates that modulation of porphyrin biosynthesis through expression of AtCHLH in transgenic rice alleviates Fe deficiency-induced stress, suggesting a possible role for CHLH in Fe deficiency responses.

Jasmonate perception: Ligand-receptor interaction, regulation, and evolution

Phytohormones integrate external environmental and developmental signals with internal cellular responses for plant survival and multiplication in changing surroundings. Jasmonate (JA), which might originate from prokaryotes and benefit plant terrestrial adaptation, is a vital phytohormone that regulates diverse developmental processes and defense responses against various environmental stresses. In this review, we first provide an overview of ligand-receptor binding techniques used for the characterization of phytohormone-receptor interactions, then introduce the identification of the receptor COI1 and active JA molecules, and finally summarize recent advances on the regulation of JA perception and its evolution.

Fine mapping and identifying candidate gene of Y underlying yellow peel in Cucurbita pepo

As a conspicuous trait, peel color is one of the most important characteristics that affects commodity quality and consumer preferences. The locus Y underlying yellow peel in Cucurbita pepo (zucchini) was first reported in 1922; however, its molecular mechanism is still unknown. In this study, a genetic analysis revealed that yellow peel is controlled by a single dominant genetic factor. Furthermore, Y was mapped in a ~170 kb region on chromosome 10 by bulked segregated analysis (BSA) and fine mapping in F₂ and BC₁ segregating populations. The candidate region harbors fifteen annotated genes, among which Cp4.1LG10g11560 (CpCHLH) is regarded as a promising candidate gene. CpCHLH encodes a magnesium chelatase H subunit involved in chlorophyll biosynthesis, and its mutation can result in a reduction in chlorophyll content and yellow phenotype. Interestingly, a large fragment (~15 kb) duplication containing incomplete CpCHLH was inserted in the candidate interval, resulting in two reformed CpCHLH proteins in the yellow parental line. It is most likely that the reformed CpCHLH proteins act as a malfunctional competitor of the normal CpCHLH protein to interrupt the formation of chlorophyll. Overall, the isolation of Y will shed light on the molecular mechanism of the peel color regulation of zucchini and lay a foundation for breeding.

Activated abscisic acid pathway and C4 pathway, inhibited cell cycle progression, responses of Ulva prolifera to short term high temperature elucidated by multi-omics

The annual outbreak of green tides since 2007 has destroyed coastal waters' ecological environment and caused substantial economic losses. Ulva prolifera, known as the dominant species of green tides, is influenced by temperatures. Omics-based technology was used to analyze U. prolifera under 12 h of treatment at 30 °C in the work. High temperature has the following advantages, e.g., activating the abscisic acid signaling pathway, improving the heat tolerance of U. prolifera, up-regulating metabolites such as glycolipids, glyceroyl, and glutamic acid to maintain the stability and fluidity of cells, and reducing the stimulatory effect of external stress on cells. The key genes and proteins of the tricarboxylic acid cycle, glycolysis, and pentose phosphorylation pathways were inhibited; however, the key enzyme pyruvate phospho-dikinase of the C4 pathway was up-regulated. The C4 pathway was activated in U. prolifera in response to high-temperature stress and may play a key role in photosynthesis. Besides, U. prolifera metabolizing amino acids was active. High temperature inhibited genes and proteins related to DNA replication and cell cycle in the transcriptome and proteome as well as the growth and reproduction of U. prolifera.

Dynamic regulation of DNA methylation and histone modifications in response to abiotic stresses in plants

DNA methylation and histone modification are evolutionarily conserved epigenetic modifications that are crucial for the expression regulation of abiotic stress-responsive genes in plants. Dynamic changes in gene expression levels can result from changes in DNA methylation and histone modifications. In the last two decades, how epigenetic machinery regulates abiotic stress responses in plants has been extensively studied. Here, based on recent publications, we review how DNA methylation and histone modifications impact gene expression regulation in response to abiotic stresses such as drought, abscisic acid, high salt, extreme temperature, nutrient deficiency or toxicity, and ultraviolet B exposure. We also review the roles of epigenetic mechanisms in the formation of transgenerational stress memory. We posit that a better understanding of the epigenetic underpinnings of abiotic stress responses in plants may facilitate the design of more stress-resistant or -resilient crops, which is essential for coping with global warming and extreme environments.

A mutation in SlCHLH encoding a magnesium chelatase H subunit is involved in the formation of yellow stigma in tomato (Solanum lycopersicum L.)

Chlorophylls are ubiquitous pigments responsible for the green color in plants. Changes in the chlorophyll content have a significant impact on photosynthesis, plant growth and development. In this study, we used a yellow stigma mutant (ys) generated from a green stigma tomato WT by using ethylmethylsulfone (EMS)-induced mutagenesis. Compared with WT, the stigma of ys shows low chlorophyll content and impaired chloroplast ultrastructure. Through map-based cloning, the ys gene is localized to a 100 kb region on chromosome 4 between dCAPS596 and dCAPS606. Gene expression analysis and nonsynonymous SNP determination identified the Solyc04g015750, as the potential candidate gene, which encodes a magnesium chelatase H subunit (CHLH). In ys mutant, a single base C to T substitution in the SlCHLH gene results in the conversion of Serine into Leucine (Ser92Leu) at the N-terminal region. The functional complementation test shows that the SlCHLH from WT can rescue the green stigma phenotype of ys. In contrast, knockdown of SlCHLH in green stigma tomato AC, observed the yellow stigma phenotype at the stigma development stage. Overexpression of the mutant gene Slys in green stigma tomato AC results in the light green stigma. These results indicate that the mutation of the N-terminal S92 to Leu in SlCHLH is the main reason for the formation of the yellow stigma phenotype. Characterization of the ys mutant enriches the current knowledge of the tomato chlorophyll mutant library and provides a novel and effective tool for understanding the function of CHLH in tomato.

Transcriptome analysis of response strategy in Hemerocallis fulva under drought stress

BACKGROUND

Hemerocallis fulva is an important ground cover plant widely used in urban greening. The analysis of the molecular mechanism underlying the drought response of H. fulva can lay a foundation for improving its adaptability and expanding its planting area.

OBJECTIVE

To reveal the drought response mechanisms of H. fulva, identify candidate unigenes associated with drought response, and lay a foundation for further unigenes functional study and drought resistance improvement of H. fulva via genetic engineering.

METHODS

RNA was isolated from H. fulva under different experimental conditions. De novo transcriptomic analysis of the samples was performed to screen drought response unigenes. The transcriptional changes of candidate drought response unigenes were verified by quantitative real-time PCR.

RESULTS

The differentially expressed unigenes and their functions were analyzed after H. fulva treated by PEG-simulated drought stress and rewatering. The candidate unigenes, associated with H. fulva drought response, were identified after transcriptome analysis. Then, the transcription level of drought response unigenes of H. fulva under different conditions was further verified. Abscisic acid, protein phosphorylation, sterol biosynthesis and ion transport were involved in drought response with quick restore in H. fulva. The response unigenes, involved in hormone (ABA, JA, CK and GA) signaling pathways, defense response, high light response, karrikin response and leaf shaping, can maintain at changed expression levels even after stress withdraw.

CONCLUSION

Hemerocallis fulva has unique drought response mechanism. Negative regulation mechanism may play more important roles in drought response of H. fulva. The analysis of candidate unigenes, associated with drought response, lays a foundation for further drought resistance improvement of H. fulva.

The protein kinase FvRIPK1 regulates plant morphogenesis by ABA signaling using seed genetic transformation in strawberry

A strawberry RIPK1, a leu-rich repeat receptor-like protein kinase, is previously demonstrated to be involved in fruit ripening as a positive regulator; however, its role in vegetable growth remains unknown. Here, based on our first establishment of Agrobacterium-mediated transformation of germinating seeds in diploid strawberry by FvCHLH/FvABAR, a reporter gene that functioned in chlorophyll biosynthesis, we got FvRIPK1-RNAi mutants. Downregulation of FvRIPK1 inhibited plant morphogenesis, showing curled leaves; also, this silencing significantly reduced FvABAR and FvABI1 transcripts and promoted FvABI4, FvSnRK2.2, and FvSnRK2.6 transcripts. Interestingly, the downregulation of the FvCHLH/ABAR expression could not affect FvRIPK1 transcripts but remarkably reduced FvABI1 transcripts and promoted FvABI4, FvSnRK2.2, and FvSnRK2.6 transcripts in the contrast of the non-transgenic plants to the FvCHLH/FvABAR-RNAi plants, in which chlorophyll contents were not affected but had abscisic acid (ABA) response in stomata movement and drought stress. The distinct expression level of FvABI1 and FvABI4, together with the similar expression level of FvSnRK2.2 and FvSnRK2.6 in the FvRIPK1- and FvABAR/CHLH-RNAi plants, suggested that FvRIPK1 regulated plant morphogenesis probably by ABA signaling. In addition, FvRIPK1 interacted with FvSnRK2.6 and phosphorylated each other, thus forming the FvRIPK1-FvSnRK2.6 complex. In conclusion, our results provide new insights into the molecular mechanism of FvRIPK1 in plant growth.

The key clock component ZEITLUPE (ZTL) negatively regulates ABA signaling by degradation of CHLH in Arabidopsis

Ubiquitination-mediated protein degradation plays important roles in ABA signal transduction and delivering responses to chloroplast stress signals in plants, but additional E3 ligases of protein ubiquitination remain to be identified to understand the complex signaling network. Here we reported that ZEITLUPE (ZTL), an F-box protein, negatively regulates abscisic acid (ABA) signaling during ABA-inhibited early seedling growth and ABA-induced stomatal closure in Arabidopsis thaliana. Using molecular biology and biochemistry approaches, we demonstrated that ZTL interacts with and ubiquitinates its substrate, CHLH/ABAR (Mg-chelatase H subunit/putative ABA receptor), to modulate CHLH stability via the 26S proteasome pathway. CHLH acts genetically downstream of ZTL in ABA and drought stress signaling. Interestingly, ABA conversely induces ZTL phosphorylation, and high levels of ABA also induce CHLH proteasomal degradation, implying that phosphorylated ZTL protein may enhance the affinity to CHLH, leading to the increased degradation of CHLH after ABA treatment. Taken together, our results revealed a possible mechanism of reciprocal regulation between ABA signaling and the circadian clock, which is thought to be essential for plant fitness and survival.

Genomic insights of the WRKY genes in kenaf (Hibiscus cannabinus L.) reveal that HcWRKY44 improves the plant's tolerance to the salinity stress

The WRKY transcription factors (TFs) are among the most diverse TF families of plants. They are implicated in various processes related to plant growth and stress response. Kenaf (Hibiscus cannabinus L.), an important fiber crop, has many applications, including the phytoremediation of saline-alkaline soil. However, the roles of WRKY TFs in kenaf are rarely studied. In the present study, 46 kenaf WRKY genes were genome-widely identified and characterized by gene structure, phylogeny and expression pattern analysis. Furthermore, the HcWRKY44 gene was functionally characterized in Arabidopsis under salinity and drought stresses. HcWRKY44 is a nuclear-localized protein that is positively induced by salinity and drought, with roots showing maximum accumulation of its transcripts. Under NaCl and abscisic acid (ABA) stress conditions, plants overexpressing HcWRKY44 had higher germination rates, better root growth and increased survival than control plants; however, it did not improve the ability to withstand drought stress. Moreover, ABA signaling genes (ABI1, ABI2, and ABI5), ABA-responsive genes (ABF4, RD29B, COR15A, COR47, and RD22), stress-related genes (STZ, P5CS, and KIN1), and ionic homeostasis-related genes (SOS1, AHA1, AHA2, and HKT1) were positively induced in HcWRKY44 transgenic plants under NaCl treatment. These results suggest that HcWRKY44 improved plant's tolerance to salt stress but not osmotic stress through an ABA-mediated pathway. In summary, this study provides provided comprehensive information about HcWRKY genes and revealed that HcWRKY44 is involved in salinity tolerance and ABA signaling.

PtoNF-YC9-SRMT-PtoRD26 module regulates the high saline tolerance of a triploid poplar

BACKGROUND

Sensing and responding to stresses determine the tolerance of plants to adverse environments. The triploid Chinese white poplar is widely cultivated in North China because of its adaptation to a wide range of habitats including highly saline ones. However, its triploid genome complicates any detailed investigation of the molecular mechanisms underlying its adaptations.

RESULTS

We report a haplotype-resolved genome of this triploid poplar and characterize, using reverse genetics and biochemical approaches, a MYB gene, SALT RESPONSIVE MYB TRANSCRIPTION FACTOR (SRMT), which combines NUCLEAR FACTOR Y SUBUNIT C 9 (PtoNF-YC9) and RESPONSIVE TO DESICCATION 26 (PtoRD26), to regulate an ABA-dependent salt-stress response signaling. We reveal that the salt-inducible PtoRD26 is dependent on ABA signaling. We demonstrate that ABA or salt drives PtoNF-YC9 shuttling into the nucleus where it interacts with SRMT, resulting in the rapid expression of PtoRD26 which in turn directly regulates SRMT. This positive feedback loop of SRMT-PtoRD26 can rapidly amplify salt-stress signaling. Interference with either component of this regulatory module reduces the salt tolerance of this triploid poplar.

CONCLUSION

Our findings reveal a novel ABA-dependent salt-responsive mechanism, which is mediated by the PtoNF-YC9-SRMT-PtoRD26 module that confers salt tolerance to this triploid poplar. These genes may therefore also serve as potential and important modification targets in breeding programs.

Characterization of Organellar-Specific ABA Responses during Environmental Stresses in Tobacco Cells and Arabidopsis Plants

Abscisic acid (ABA) is a critical phytohormone involved in multifaceted processes in plant metabolism and growth under both stressed and nonstressed conditions. Its accumulation in various tissues and cells has long been established as a biomarker for plant stress responses. To date, a comprehensive understanding of ABA distribution and dynamics at subcellular resolution in response to environmental cues is still lacking. Here, we modified the previously developed ABA sensor ABAleon2.1_Tao3 (Tao3) and targeted it to different organelles including the endoplasmic reticulum (ER), chloroplast/plastid, and nucleus through the addition of corresponding signal peptides. Together with the cytosolic Tao3, we show distinct ABA distribution patterns in different tobacco cells with the chloroplast showing a lower level of ABA in both cell types. In a tobacco mesophyll cell, organellar ABA displayed specific alterations depending on osmotic stimulus, with ABA levels being generally enhanced under a lower and higher concentration of salt and mannitol treatment, respectively. In Arabidopsis roots, cells from both the meristem and elongation zone accumulated ABA considerably in the cytoplasm upon mannitol treatment, while the plastid and nuclear ABA was generally reduced dependent upon specific cell types. In Arabidopsis leaf tissue, subcellular ABA seemed to be less responsive when stressed, with notable increases of ER ABA in epidermal cells and a reduction of nuclear ABA in guard cells. Together, our results present a detailed characterization of stimulus-dependent cell type-specific organellar ABA responses in tobacco and Arabidopsis plants, supporting a highly coordinated regulatory network for mediating subcellular ABA homeostasis during plant adaptation processes.

Chlorophyll decomposition is accelerated in banana leaves after the long-term magnesium deficiency according to transcriptome analysis

Magnesium (Mg) is an essential macronutrient for plant growth and development. Physiological and transcriptome analyses were conducted to elucidate the adaptive mechanisms to long-term Mg deficiency (MD) in banana seedlings at the 6-leaf stage. Banana seedlings were irrigated with a Mg-free nutrient solution for 42 days, and a mock control was treated with an optimum Mg supply. Leaf edge chlorosis was observed on the 9th leaf, which gradually turned yellow from the edge to the interior region. Accordingly, the total chlorophyll content was reduced by 47.1%, 47.4%, and 53.8% in the interior, center and edge regions, respectively, and the net photosynthetic rate was significantly decreased in the 9th leaf. Transcriptome analysis revealed that MD induced 9,314, 7,425 and 5,716 differentially expressed genes (DEGs) in the interior, center and edge regions, respectively. Of these, the chlorophyll metabolism pathway was preferentially enriched according to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The expression levels of the five candidate genes in leaves were consistent with what is expected during chlorophyll metabolism. Our results suggest that changes in the expression of genes related to chlorophyll synthesis and decomposition result in the yellowing of banana seedling leaves, and these results are helpful for understanding the banana response mechanism to long-term MD.

Environment-mediated mutagenetic interference on genetic stabilization and circadian rhythm in plants

Many mortal organisms on this planet have developed the potential to merge all internal as well as external environmental cues to regulate various processes running inside organisms and in turn make them adaptive to the environment through the circadian clock. This moving rotator controls processes like activation of hormonal, metabolic, or defense pathways, initiation of flowering at an accurate period, and developmental processes in plants to ensure their stability in the environment. All these processes that are under the control of this rotating wheel can be changed either by external environmental factors or by an unpredictable phenomenon called mutation that can be generated by either physical mutagens, chemical mutagens, or by internal genetic interruption during metabolic processes, which alters normal functionality of organisms like innate immune responses, entrainment of the clock, biomass reduction, chlorophyll formation, and hormonal signaling, despite its fewer positive roles in plants like changing plant type, loss of vernalization treatment to make them survivable in different latitudes, and defense responses during stress. In addition, with mutation, overexpression of gene components sometimes supresses mutation effect and promote normal circadian genes abundance in the cell, while sometimes it affects circadian functionality by generating arrhythmicity and shows that not only mutation but overexpression also effects normal functional activities of plant. Therefore, this review mainly summarizes the role of each circadian clock genes in regulating rhythmicity, and shows that how circadian outputs are controlled by mutations as well as overexpression phenomenon.

PYR/PYL/RCAR Receptors Play a Vital Role in the Abscisic-Acid-Dependent Responses of Plants to External or Internal Stimuli

Abscisic acid (ABA) is a phytohormone that plays a key role in regulating several developmental processes as well as in response to stressful conditions such as drought. Activation of the ABA signaling cascade allows the induction of an appropriate physiological response. The basic components of the ABA signaling pathway have been recognized and characterized in recent years. Pyrabactin resistance, pyrabactin resistance-like, and the regulatory component of ABA receptors (PYR/PYL/RCAR) are the major components responsible for the regulation of the ABA signaling pathway. Here, we review recent findings concerning the PYR/PYL/RCAR receptor structure, function, and interaction with other components of the ABA signaling pathway as well as the termination mechanism of ABA signals in plant cells. Since ABA is one of the basic elements related to abiotic stress, which is increasingly common in the era of climate changes, understanding the perception and transduction of the signal related to this phytohormone is of paramount importance in further increasing crop tolerance to various stress factors.

Fine Mapping and Characterization of a Major Gene Responsible for Chlorophyll Biosynthesis in Brassica napus L

Rapeseed (Brassica napus L.) is mainly used for oil production and industrial purposes. A high photosynthetic efficiency is the premise of a high yield capable of meeting people’s various demands. Chlorophyll-deficient mutants are ideal materials for studying chlorophyll biosynthesis and photosynthesis. In a previous study, we obtained the mutant yl1 for leaf yellowing throughout the growth period by ethyl methanesulfonate mutagenesis of B. napus. A genetic analysis showed that the yl1 chlorophyll-deficient phenotype was controlled by one incompletely dominant gene, which was mapped on chromosome A03 by a quantitative trait loci sequencing analysis and designated as BnA03.Chd in this study. We constructed an F2 population containing 5256 individuals to clone BnA03.Chd. Finally, BnA03.Chd was fine-mapped to a 304.7 kb interval of the B. napus ‘ZS11’ genome containing 58 annotated genes. Functional annotation, transcriptome, and sequence variation analyses confirmed that BnaA03g0054400ZS, a homolog of AT5G13630, was the most likely candidate gene. BnaA03g0054400ZS encodes the H subunit of Mg-chelatase. A sequence analysis revealed a single-nucleotide polymorphism (SNP), causing an amino-acid substitution from glutamic acid to lysine (Glu1349Lys). In addition, the molecular marker BnaYL1 was developed based on the SNP of BnA03.Chd, which perfectly cosegregated with the chlorophyll-deficient phenotype in two different F2 populations. Our results provide insight into the molecular mechanism underlying chlorophyll synthesis in B. napus.

Dynamic physiological and transcriptome changes reveal a potential relationship between the circadian clock and salt stress response in Ulmus pumila

Despite the important role the circadian clock plays in numerous critical physiological responses in plants, such as hypocotyl elongation, leaf movement, stomatal opening, flowering, and stress responses, there have been no investigations into the effect of the circadian clock on physiological and transcriptional networks under salt stress. Ulmus pumila L. has been reported to tolerate 100-150 mM NaCl treatment. We measured the diurnal variation in photosynthesis and chlorophyll fluorescence parameters and performed a time-course transcriptome analysis of 2-years-old U. pumila seedlings under salt treatment to dissect the physiological regulation and potential relationship between the circadian network and the salt stress response. Seedlings in 150 mM NaCl treatment exhibited salt-induced physiological enhancement compared to the control group. A total of 7009 differentially expressed unigenes (DEGs) were identified under salt stress, of which 16 DEGs were identified as circadian rhythm-related DEGs (crDEGs). Further analysis of dynamic expression changes revealed that DEGs involved in four crucial pathways-photosynthesis, thiamine metabolism, abscisic acid synthesis and metabolism, and the hormone-MAPK signal crosstalk pathway-are closely related to the circadian clock. Finally, we constructed a co-expression network between the circadian clock and these four crucial pathways. Our results help shed light on the molecular link between the circadian network and salt stress tolerance in U. pumila.

Abscisic Acid: Role in Fruit Development and Ripening

Abscisic acid (ABA) is a plant growth regulator known for its functions, especially in seed maturation, seed dormancy, adaptive responses to biotic and abiotic stresses, and leaf and bud abscission. ABA activity is governed by multiple regulatory pathways that control ABA biosynthesis, signal transduction, and transport. The transport of the ABA signaling molecule occurs from the shoot (site of synthesis) to the fruit (site of action), where ABA receptors decode information as fruit maturation begins and is significantly promoted. The maximum amount of ABA is exported by the phloem from developing fruits during seed formation and initiation of fruit expansion. In the later stages of fruit ripening, ABA export from the phloem decreases significantly, leading to an accumulation of ABA in ripening fruit. Fruit growth, ripening, and senescence are under the control of ABA, and the mechanisms governing these processes are still unfolding. During the fruit ripening phase, interactions between ABA and ethylene are found in both climacteric and non-climacteric fruits. It is clear that ABA regulates ethylene biosynthesis and signaling during fruit ripening, but the molecular mechanism controlling the interaction between ABA and ethylene has not yet been discovered. The effects of ABA and ethylene on fruit ripening are synergistic, and the interaction of ABA with other plant hormones is an essential determinant of fruit growth and ripening. Reaction and biosynthetic mechanisms, signal transduction, and recognition of ABA receptors in fruits need to be elucidated by a more thorough study to understand the role of ABA in fruit ripening. Genetic modifications of ABA signaling can be used in commercial applications to increase fruit yield and quality. This review discusses the mechanism of ABA biosynthesis, its translocation, and signaling pathways, as well as the recent findings on ABA function in fruit development and ripening.

Integrated morpho-biochemical and transcriptome analyses reveal multidimensional response of upland cotton (Gossypium hirsutum L.) to low temperature stress during seedling establishment

Cotton is a tropical/subtropical crop and is innately susceptible to cold. Using an approach that integrates morphological, biochemical, and transcriptome analyses, the study aimed to understand the molecular underpinnings of phenotypic adjustments in cotton seedlings under cold stress. Exposure of six cotton accessions to 15°C during the seedling stage significantly reduced chlorophyll content, stomatal conductance, plant height, and biomass, but increased malondialdehyde and proline production. Comparative transcriptome profiling of the cold-sensitive accession SA 3781 grown under low and normal temperatures showed the upregulation of genes related to the production of reactive oxygen species (ROS) under cold stress. Despite a similar upregulation of genes encoding metabolites that can scavenge ROS and provide osmoprotection for the cell, the stressed plants still exhibited oxidative stress in terms of lipid peroxidation. This may be due in part to the upregulation of abscisic acid synthesis genes and downregulation of chlorophyll synthesis genes effecting lower stomatal conductance and chlorophyll contents, respectively. Additionally, stomatal closure which is required to avoid the cooling effect and dehydration under cold conditions may have contributed in reducing the net photosynthetic rates in plants exposed to low temperature. These findings provide an insight into the expression of key genes regulating the phenotypic changes observed in cotton in response to cold stress.

Genome-Wide Association Studies of Soybean Yield-Related Hyperspectral Reflectance Bands Using Machine Learning-Mediated Data Integration Methods

In conjunction with big data analysis methods, plant omics technologies have provided scientists with cost-effective and promising tools for discovering genetic architectures of complex agronomic traits using large breeding populations. In recent years, there has been significant progress in plant phenomics and genomics approaches for generating reliable large datasets. However, selecting an appropriate data integration and analysis method to improve the efficiency of phenome-phenome and phenome-genome association studies is still a bottleneck. This study proposes a hyperspectral wide association study (HypWAS) approach as a phenome-phenome association analysis through a hierarchical data integration strategy to estimate the prediction power of hyperspectral reflectance bands in predicting soybean seed yield. Using HypWAS, five important hyperspectral reflectance bands in visible, red-edge, and near-infrared regions were identified significantly associated with seed yield. The phenome-genome association analysis of each tested hyperspectral reflectance band was performed using two conventional genome-wide association studies (GWAS) methods and a machine learning mediated GWAS based on the support vector regression (SVR) method. Using SVR-mediated GWAS, more relevant QTL with the physiological background of the tested hyperspectral reflectance bands were detected, supported by the functional annotation of candidate gene analyses. The results of this study have indicated the advantages of using hierarchical data integration strategy and advanced mathematical methods coupled with phenome-phenome and phenome-genome association analyses for a better understanding of the biology and genetic backgrounds of hyperspectral reflectance bands affecting soybean yield formation. The identified yield-related hyperspectral reflectance bands using HypWAS can be used as indirect selection criteria for selecting superior genotypes with improved yield genetic gains in large breeding populations.

WRKY Transcription Factor Response to High-Temperature Stress

Plant growth and development are closely related to the environment, and high-temperature stress is an important environmental factor that affects these processes. WRKY transcription factors (TFs) play important roles in plant responses to high-temperature stress. WRKY TFs can bind to the W-box cis-acting elements of target gene promoters, thereby regulating the expression of multiple types of target genes and participating in multiple signaling pathways in plants. A number of studies have shown the important biological functions and working mechanisms of WRKY TFs in plant responses to high temperature. However, there are few reviews that summarize the research progress on this topic. To fully understand the role of WRKY TFs in the response to high temperature, this paper reviews the structure and regulatory mechanism of WRKY TFs, as well as the related signaling pathways that regulate plant growth under high-temperature stress, which have been described in recent years, and this paper provides references for the further exploration of the molecular mechanisms underlying plant tolerance to high temperature.

O-fucosylation of CPN20 by SPINDLY Derepresses Abscisic Acid Signaling During Seed Germination and Seedling Development

SPINDLY is involved in some aspects of plant development. However, the nature of this protein as an O-fucosyltransferase was recently discovered. In this study, we show that SPINDLY (SPY) interacts with CPN20 in yeast two-hybrid and split-luc assays, and the interaction is promoted by ABA. CPN20 is a chloroplast-localized co-chaperonin that negatively regulates ABAR-mediated ABA signaling. By using Electron Transfer Dissociation-MS/MS analysis, two O-fucosylation sites, e.g., 116th and 119th threonines, were detected in ectopically expressed CPN20 in mammalian cells and in Arabidopsis. The O-fucosylation at both threonine residues was confirmed by in vitro peptide O-fucosylation assay. We further show that CPN20 accumulates in the chloroplast of spy mutants, suggesting that SPY negatively regulates CPN20 localization in the chloroplast. In vivo protein degradation assay along with CPN20 localization behavior suggest that import of CPN20 into the chloroplast is negatively regulated by SPY. Genetic analysis shows that ABA insensitive phenotypes of spy-3 in terms of seed germination and early seedling development are partially suppressed by the cpn20 mutation, suggesting that CPN20 acts downstream of SPY in this ABA signaling pathway and that there may exist other pathways in parallel with CPN20. Collectively, the above data support the notion that the O-fucosylation of CPN20 by SPY fine-tunes ABA signaling in Arabidopsis.

An Update on Crop ABA Receptors

The hormone abscisic acid (ABA) orchestrates the plant stress response and regulates sophisticated metabolic and physiological mechanisms essential for survival in a changing environment. Plant ABA receptors were described more than 10 years ago, and a considerable amount of information is available for the model plant Arabidopsis thaliana. Unfortunately, this knowledge is still very limited in crops that hold the key to feeding a growing population. In this review, we summarize genomic, genetic and structural data obtained in crop ABA receptors. We also provide an update on ABA perception in major food crops, highlighting specific and common features of crop ABA receptors.

Connecting Chlorophyll Metabolism with Accumulation of the Photosynthetic Apparatus

Chlorophyll (Chl) is indispensable for photosynthesis. In association with Chl-binding proteins (CBPs), it is responsible for light absorption, excitation energy transfer, and charge separation within the photosynthetic complexes. By contrast, photoexcitation of free Chl and its metabolic intermediates generates hazardous reactive oxygen species (ROS). While antagonistic activities of Chl synthesis and catabolism have been mostly elucidated, the tight synchronization of these metabolic activities with the formation and dismantling of the photosynthetic complexes is poorly understood. Recently, a set of auxiliary factors were identified to adjust metabolic activities and provide accurate amounts of Chl for pigment-protein complexes. Here, we review current knowledge of post-translational coordination of Chl formation, breakdown, and turnover with the assembly and disassembly of various CBPs and highlight future research perspectives.

Quantitative Proteomics Reveals the Dynamic Regulation of the Tomato Proteome in Response to Phytophthora infestans

Late blight (LB) disease is a major threat to potato and tomato production. It is caused by the hemibiotrophic pathogen, Phytophthora infestans. P. infestans can destroy all of the major organs in plants of susceptible crops and result in a total loss of productivity. At the early pathogenesis stage, this hemibiotrophic oomycete pathogen causes an asymptomatic biotrophic infection in hosts, which then progresses to a necrotrophic phase at the later infection stage. In this study, to examine how the tomato proteome is regulated by P. infestans at different stages of pathogenesis, a data-independent acquisition (DIA) proteomics approach was used to trace the dynamics of the protein regulation. A comprehensive picture of the regulation of tomato proteins functioning in the immunity, signaling, defense, and metabolism pathways at different stages of P. infestans infection is revealed. Among the regulated proteins, several involved in mediating plant defense responses were found to be differentially regulated at the transcriptional or translational levels across different pathogenesis phases. This study increases understanding of the pathogenesis of P. infestans in tomato and also identifies key transcriptional and translational events possibly targeted by the pathogen during different phases of its life cycle, thus providing novel insights for developing a new strategy towards better control of LB disease in tomato.

Smart glass impacts stomatal sensitivity of greenhouse Capsicum through altered light

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of Capsicum plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (gs) or maximal (gmax) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K+ and Cl- efflux, and Ca2+ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m-2 s-1) and high PAR (1500 µmol m-2 s-1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect gs in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of Capsicum to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO2 assimilation.

Root endophytic fungus Serendipita indica modulates barley leaf blade proteome by increasing the abundance of photosynthetic proteins in response to salinity

AIMS

The present study aimed at analysing the proteome pattern of the leaf blade of barley (Hordeum vulgare L.) in Serendipita indica-colonised plants to decipher the molecular mechanism of S. indica-mediated salt stress. This work is aligned with our previous research on barley leaf sheath to study proteomic pattern variability in leaf blade and sheath of barley plant in response to salinity and S. indica inoculation.

METHODS AND RESULTS

The experiment was conducted using a completely randomised factorial design with four replications and two treatments: salinity (0 and 300 mmol l^-1 NaCl) and fungus (noninoculated and S. indica-inoculated). The leaf blades of the salt-treated S. indica-colonised and noninoculated plants were harvested after 2 weeks of salt treatment for the physiological and proteomic analyses. After exposure to 300 mmol l^-1 NaCl, shoot dry matter production in noninoculated control plants decreased 84% which was about twofold higher than inoculated plants with S. indica. However, the accumulation of sodium in the shoot of S. indica-inoculated plants was significantly lower than the control plants. Analysis of the proteome profile revealed a high number of significantly up-regulated proteins involved in photosynthesis (26 out of 42 identified proteins).

CONCLUSIONS

The results demonstrated how the enhanced plant growth and salt stress resistance induced by S. indica was positively associated with the up-regulation of several proteins involved in photosynthesis and carbohydrate metabolism. In fact, S. indica improved photosynthesis in order to reach the best possible performance of the host plant under salt stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

Current research provides new insight into the mechanism applied by S. indica in reducing the negative impacts of salt stress in barley at physiological and molecular levels.

The PalWRKY77 transcription factor negatively regulates salt tolerance and abscisic acid signaling in Populus

High salinity, one of the most widespread abiotic stresses, inhibits photosynthesis, reduces vegetation growth, blocks respiration and disrupts metabolism in plants. In order to survive their long-term lifecycle, trees, such as Populus species, recruit the abscisic acid (ABA) signaling pathway to adapt to a saline environment. However, the molecular mechanism behind the ABA-mediated salt stress response in woody plants remains elusive. We have isolated a WRKY transcription factor gene, PalWRKY77, from Populus alba var. pyramidalis (poplar), the expression of which is repressed by salt stress. PalWRKY77 decreases salt tolerance in poplar. Furthermore, PalWRKY77 negatively regulated ABA-responsive genes and relieved ABA-mediated growth inhibition, indicating that PalWRKY77 is a repressor of the ABA response. In vivo and in vitro assays revealed that PalWRKY77 targets the ABA- and salt-induced PalNAC002 and PalRD26 genes by binding to the W-boxes in their promoters. In addition, overexpression of both PalNAC002 and PalRD26 could elevate salt tolerance in transgenic poplars. These findings reveal a novel negative regulation mechanism for the ABA signaling pathway mediated by PalWRKY77 that results in more sensitivity to salt stress in poplar. This deepens our understanding of the complex responses of woody species to salt stress.

Arabidopsis exoribonuclease USB1 interacts with the PPR-domain protein SOAR1 to negatively regulate abscisic acid signaling

Signaling by the phytohormone abscisic acid (ABA) involves pre-mRNA splicing, a key process of post-transcriptional regulation of gene expression. However, the regulatory mechanism of alternative pre-mRNA splicing in ABA signaling remains largely unknown. We previously identified a pentatricopeptide repeat protein SOAR1 (suppressor of the ABAR-overexpressor 1) as a crucial player downstream of ABAR (putative ABA receptor) in ABA signaling. In this study, we identified a SOAR1 interaction partner USB1, which is an exoribonuclease catalyzing U6 production for spliceosome assembly. We reveal that together USB1 and SOAR1 negatively regulate ABA signaling in early seedling development. USB1 and SOAR1 are both required for the splicing of transcripts of numerous genes, including those involved in ABA signaling pathways, suggesting that USB1 and SOAR1 collaborate to regulate ABA signaling by affecting spliceosome assembly. These findings provide important new insights into the mechanistic control of alternative pre-mRNA splicing in the regulation of ABA-mediated plant responses to environmental cues.

A Clathrin-Related Protein, SCD2/RRP1, Participates in Abscisic Acid Signaling in Arabidopsis

Abscisic acid (ABA) plays important roles in many aspects of plant growth and development, and responses to diverse stresses. Although much progress has been made in understanding the molecular mechanisms of ABA homoeostasis and signaling, the mechanism by which plant cells integrate ABA trafficking and signaling to regulate plant developmental processes is poorly understood. In this study, we used Arabidopsis STOMATAL CYTOKINESIS DEFECTIVE 2/RIPENING-REGULATED PROTEIN 1 (SCD2/RRP1) mutants and overexpression plants, in combination with transcriptome and protein-interaction assays, to investigate SCD2/RRP1 involvement in the integration of ABA trafficking and signaling in seed germination and seedling growth. Manipulation of SCD2/RRP1 expression affected ABA sensitivity in seed germination and seedling growth, as well as transcription of several ABA transporter genes and ABA content. RNA-sequencing analysis of Arabidopsis transgenic mutants suggested that SCD2/RRP1 was associated with ABA signaling via a type 2C protein phosphatase (PP2C) protein. The N- and C-terminal regions of SCD2/RRP1 separately interacted with both PYRABACTIN RESISTANCE 1 (PYR1) and ABA INSENSITIVE 1 (ABI1) on the plasma membrane, and SCD2/RRP1 acted genetically upstream of ABI1. Interestingly, ABA inhibited the interaction of SCD2/RRP1 with ABI1, but did not affect the interaction of SCD2/RRP1 with PYR1. These results suggested that in Arabidopsis SCD2/RRP1participates in early seed development and growth potentially through clathrin-mediated endocytosis- and clathrin-coated vesicle-mediated ABA trafficking and signaling. These findings provide insight into the mechanism by which cells regulate plant developmental processes through ABA.

Post-translational coordination of chlorophyll biosynthesis and breakdown by BCMs maintains chlorophyll homeostasis during leaf development

Chlorophyll is indispensable for life on Earth. Dynamic control of chlorophyll level, determined by the relative rates of chlorophyll anabolism and catabolism, ensures optimal photosynthesis and plant fitness. How plants post-translationally coordinate these two antagonistic pathways during their lifespan remains enigmatic. Here, we show that two Arabidopsis paralogs of BALANCE of CHLOROPHYLL METABOLISM (BCM) act as functionally conserved scaffold proteins to regulate the trade-off between chlorophyll synthesis and breakdown. During early leaf development, BCM1 interacts with GENOMES UNCOUPLED 4 to stimulate Mg-chelatase activity, thus optimizing chlorophyll synthesis. Meanwhile, BCM1’s interaction with Mg-dechelatase promotes degradation of the latter, thereby preventing chlorophyll degradation. At the onset of leaf senescence, BCM2 is up-regulated relative to BCM1, and plays a conserved role in attenuating chlorophyll degradation. These results support a model in which post-translational regulators promote chlorophyll homeostasis by adjusting the balance between chlorophyll biosynthesis and breakdown during leaf development.

Plants regulate chlorophyll levels to optimise photosynthesis. Here Wang et al. describe two paralogous thylakoid proteins, BCM1 and BCM2, which stimulate chlorophyll biosynthesis and attenuate chlorophyll degradation respectively through interaction with the Mg-chelatase-stimulating factor GUN4 and Mg-dechelatase isoform SGR1.

Ionomic and metabolomic analyses reveal the resistance response mechanism to saline-alkali stress in Malus halliana seedlings

Saline-alkali stress is a major abiotic stress limiting plant growth. The selection of saline-alkali-tolerant rootstock is an effective strategy to reduce salinization-alkalization influence in apple production. M. halliana is a highly saline-alkali-resistant apple rootstock in northwestern China. However, few metabolic response studies have been conducted on this species. In plants under saline-alkali stress, the uptake of K, Mg and Zn in M. halliana leaves were inhibited, whereas the absorption of Fe²⁺, Cu²⁺ or Mn²⁺ were increased. Metabolic analysis revealed 140 differentially expressed metabolites, which were mainly involved in alkaloid biosynthesis, phenylalanine biosynthesis, ATP-binding cassette (ABC) transporters, and mineral absorption. Especially, the expression of sucrose, amino acids, alkaloids, flavonoids and carotenoids were significantly upregulated under saline-alkali stress. qRT-PCR analysis demonstrated that NHX8 and ZTP1 involved in Na⁺ and Fe²⁺ transport were upregulated, while AKT1, MRS2-4 and ZTP29 involved in K⁺, Mg²⁺ and Zn²⁺ transport were downregulated, respectively. ANT, ATP2A, CALM and SOS2 are involved in Ca²⁺ signal transduction, and ABCB1, ABCC10 and NatA are key transporters that maintain ionic homeostasis. M. halliana regulates Na⁺/K⁺ homeostasis by mediating Ca²⁺ signalling and ABC transporters. The accumulation of metabolites contributes to improving the saline-alkali resistance of M. halliana because of the scavenging of ROS. An increase in pheophorbide a content in porphyrin and chlorophyll metabolism leads to leaf senescence in M. halliana leaves, which contributes to a reduction in stress-induced injury. These findings provide important insights into the saline-alkali tolerance mechanism in apple, which also provides an important starting point for future research.

The Role of ROS Homeostasis in ABA-Induced Guard Cell Signaling

The hormonal and environmental regulation of stomatal aperture is mediated by a complex signaling pathway found within the guard cells that surround stomata. Abscisic acid (ABA) induces stomatal closure in response to drought stress by binding to its guard cell localized receptor, initiating a signaling cascade that includes synthesis of reactive oxygen species (ROS). Genetic evidence in Arabidopsis indicates that ROS produced by plasma membrane respiratory burst oxidase homolog (RBOH) enzymes RBOHD and RBOHF modulate guard cell signaling and stomatal closure. However, ABA-induced ROS accumulates in many locations such as the cytoplasm, chloroplasts, nucleus, and endomembranes, some of which do not coincide with plasma membrane localized RBOHs. ABA-induced guard cell ROS accumulation has distinct spatial and temporal patterns that drive stomatal closure. Productive ROS signaling requires both rapid increases in ROS, as well as the ability of cells to prevent ROS from reaching damaging levels through synthesis of antioxidants, including flavonols. The relationship between locations of ROS accumulation and ABA signaling and the role of enzymatic and small molecule ROS scavengers in maintaining ROS homeostasis in guard cells are summarized in this review. Understanding the mechanisms of ROS production and homeostasis and the role of ROS in guard cell signaling can provide a better understanding of plant response to stress and could provide an avenue for the development of crop plants with increased stress tolerance.

The Arabidopsis kinase-associated protein phosphatase KAPP, interacting with protein kinases SnRK2.2/2.3/2.6, negatively regulates abscisic acid signaling

KEY MESSAGE

The kinase-associated protein phosphatase, KAPP, is negatively involved in abscisic acid (ABA) signaling. KAPP interacts physically with SnRK2.2, SnRK2.3 and SnRK2.6, and functionally acts upstream of SnRK2.2 and SnRK2.3. The kinase-associated protein phosphatase (KAPP) has been reported to be involved in the regulation of many developmental and signaling events, but it remains unknown whether KAPP is involved in ABA signaling. Here, we report that KAPP is negatively involved in ABA-mediated seed germination and early seedling growth in Arabidopsis thaliana. The two loss-of-function mutants of KAPP, kapp-1 and kapp-2, exhibit increased ABA sensitivity in ABA-induced seed germination inhibition and post-germination growth arrest. The three closely-related protein kinase, (SNF1)-related protein kinase SnRK2.2, SnRK2.3 and SnRK2.6, which play critical roles in ABA signaling, interact and co-localize with KAPP. Genetic evidence showed that the ABA-hypersensitive phenotypes caused by KAPP mutation were suppressed by the double mutation of SnRK2.2 and SnRK2.3, indicating that KAPP functions upstream of SnRK2.2 and SnRK2.3 in ABA signaling. RNA-sequencing analysis revealed that KAPP mutation affects expression of multiple ABA-responsive genes. These results demonstrated that KAPP is negatively involved in plant response to ABA, which help to understand the complicated ABA signaling mechanism.

Plant responses to fungal volatiles involve global posttranslational thiol redox proteome changes that affect photosynthesis

Microorganisms produce volatile compounds (VCs) that promote plant growth and photosynthesis through complex mechanisms involving cytokinin (CK) and abscisic acid (ABA). We hypothesized that plants' responses to microbial VCs involve posttranslational modifications of the thiol redox proteome through action of plastidial NADPH-dependent thioredoxin reductase C (NTRC), which regulates chloroplast redox status via its functional relationship with 2-Cys peroxiredoxins. To test this hypothesis, we analysed developmental, metabolic, hormonal, genetic, and redox proteomic responses of wild-type (WT) plants and a NTRC knockout mutant (ntrc) to VCs emitted by the phytopathogen Alternaria alternata. Fungal VC-promoted growth, changes in root architecture, shifts in expression of VC-responsive CK- and ABA-regulated genes, and increases in photosynthetic capacity were substantially weaker in ntrc plants than in WT plants. As in WT plants, fungal VCs strongly promoted growth, chlorophyll accumulation, and photosynthesis in ntrc-Δ2cp plants with reduced 2-Cys peroxiredoxin expression. OxiTRAQ-based quantitative and site-specific redox proteomic analyses revealed that VCs promote global reduction of the thiol redox proteome (especially of photosynthesis-related proteins) of WT leaves but its oxidation in ntrc leaves. Our findings show that NTRC is an important mediator of plant responses to microbial VCs through mechanisms involving global thiol redox proteome changes that affect photosynthesis.

Arabidopsis translation initiation factors eIFiso4G1/2 link repression of mRNA cap-binding complex eIFiso4F assembly with RNA-binding protein SOAR1-mediated ABA signaling

The translation initiation factor eIF4E-binding protein-mediated regulation of protein translation by interfering with assembly of mRNA cap-binding complex eIF4F is well described in mammalian and yeast cells. However, it remains unknown whether a signaling regulator or pathway interacts directly with any translation initiation factor to modulate assembly of eIF4F in plant cells. Here, we report that the two isoforms of Arabidopsis eIF4G, eIFiso4G1 and eIFiso4G2, interact with a cytoplasmic-nuclear dual-localized pentatricopeptide repeat protein SOAR1 to regulate abscisic acid (ABA) signaling. SOAR1 inhibits interactions of eIFiso4E, eIF4Es, eIF4A1, eIF4B2 and poly(A)-binding protein PAB6 with eIFiso4G1 and eIFiso4G2, thereby inhibiting eIFiso4F/mixed eIF4F assembly and repressing translation initiation. SOAR1 binds mRNA of a key ABA-responsive gene ABI5 and cooperates with eIFiso4G1/2 to repress translation of ABI5. The binding of SOAR1 to ABI5 mRNA is likely to inhibit the interaction of SOAR1 with eIFiso4G1/2, suggesting a regulatory loop. Our findings identify a novel translation initiation repressor interfering with cap-binding complex assembly, and establish a link between cap-binding complex assembly and ABA signaling.

The Roles of GmERF135 in Improving Salt Tolerance and Decreasing ABA Sensitivity in Soybean

Abscisic acid (ABA) mediates various abiotic stress responses, and ethylene responsive factors (ERFs) play vital role in resisting stresses, but the interaction of these molecular mechanisms remains elusive. In this study, we identified an ABA-induced soybean ERF gene GmERF135 that was highly up-regulated by ethylene (ET), drought, salt, and low temperature treatments. Subcellular localization assay showed that the GmERF135 protein was targeted to the nucleus. Promoter cis-acting elements analysis suggested that numerous potential stress responsive cis-elements were distributed in the promoter region of GmERF135, including ABA-, light-, ET-, gibberellin (GA)-, and methyl jasmonate (MeJA)-responsive elements. Overexpression of GmERF135 in Arabidopsis enhanced tolerance to drought and salt conditions. In addition, GmERF135 promoted the growth of transgenic hairy roots under salt and exogenous ABA conditions. These results suggest that soybean GmERF135 may participate in both ABA and ET signaling pathways to regulate the responses to multiple stresses.

Recent Advances in Hormonal Regulation and Cross-Talk during Non-Climacteric Fruit Development and Ripening

Fleshy fruits are characterized by having a developmentally and genetically controlled, highly intricate ripening process, leading to dramatic modifications in fruit size, texture, color, flavor, and aroma. Climacteric fruits such as tomato, pear, banana, and melon show a ripening-associated increase in respiration and ethylene production and these processes are well-documented. In contrast, the hormonal mechanism of fruit development and ripening in non-climacteric fruit, such as strawberry, grape, raspberry, and citrus, is not well characterized. However, recent studies have shown that non-climacteric fruit development and ripening, involves the coordinated action of different hormones, such as abscisic acid (ABA), auxin, gibberellins, ethylene, and others. In this review, we discuss and evaluate the recent research findings concerning the hormonal regulation of non-climacteric fruit development and ripening and their cross-talk by taking grape, strawberry, and raspberry as reference fruit species.

Fruit ripening: the role of hormones, cell wall modifications, and their relationship with pathogens

Fruits result from complex biological processes that begin soon after fertilization. Among these processes are cell division and expansion, accumulation of secondary metabolites, and an increase in carbohydrate biosynthesis. Later fruit ripening is accomplished by chlorophyll degradation and cell wall lysis. Fruit maturation is an essential step to optimize seed dispersal, and is controlled by a complex network of transcription factors and genetic regulators that are strongly influenced by phytohormones. Abscisic acid (ABA) and ethylene are the major regulators of ripening and senescence in both dry and fleshy fruits, as demonstrated by numerous ripening-defective mutants, effects of exogenous hormone application, and transcriptome analyses. While ethylene is the best characterized player in the final step of a fruit's life, ABA also has a key regulatory role, promoting ethylene production and acting as a stress-related hormone in response to drought and pathogen attack. In this review, we focus on the role of ABA and ethylene in relation to the interconnected biotic and abiotic phenomena that affect ripening and senescence. We integrate and discuss the most recent data available regarding these biological processes, which are crucial for post-harvest fruit conservation and for food safety.

Biogenic Synthesis and Spatial Distribution of Endogenous Phytohormones and Ginsenosides Provide Insights on Their Intrinsic Relevance in Panax ginseng

Ginseng, the root and rhizome of Panax ginseng C. A. Mey., is a well-known and valuable traditional Chinese medicine. The pharmacological activities of ginseng are mainly attributed to the presence of ginsenosides, which are considered to be critical biomarkers for evaluating ginseng quality. The biosynthesis of triterpenes, which serve defensive functions in plants, is regulated by endogenous phytohormones that play key roles in growth and defense of plant populations. However, the role of major hormones that are closely related to secondary metabolism pathways in P. ginseng is poorly understood. To gain insight into their potential correlation, we performed a spatial synthesis analysis and studied the distribution of endogenous phytohormones and ginsenosides in different tissue regions of the entire P. ginseng plant. Gibberellins are growth hormones that accumulate in the fiber root. In contrast, abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA), which are considered stress hormones, were predominantly found in the leaf and leaf peduncle. We observed a tissue-specific distribution of phytohormones consistent with the expression of genes involved in hormone biosynthesis that influenced ginsenoside synthesis and distribution. The aim of this study was to investigate the role of different endogenous phytohormones on triterpene metabolites in ginseng innate immunity.

Molecular Mechanism for the Regulation of ABA Homeostasis During Plant Development and Stress Responses

The plant hormone abscisic acid (ABA) play essential roles in numerous physiological processes such as seed dormancy, seed germination, seeding growth and responses to biotic and abiotic stresses. Such biological processes are tightly controlled by a complicated regulatory network including ABA homoeostasis, signal transduction as well as cross-talking among other signaling pathways. It is known that ABA homoeostasis modulated by its production, inactivation, and transport pathways is considered to be of great importance for plant development and stress responses. Most of the enzymes and transporters involved in ABA homoeostasis have been largely characterized and they all work synergistically to maintain ABA level in plants. Increasing evidence have suggested that transcriptional regulation of the genes involved in either ABA production or ABA inactivation plays vital roles in ABA homoeostasis. In addition to transcription factors, such progress is also regulated by microRNAs and newly characterized root to shoot mobile peptide-receptor like kinase (RLKs) mediated long-distance signal transduction. Thus, ABA contents are always kept in a dynamic balance. In this review, we survey recent research on ABA production, inactivation and transport pathways, and summarize some latest findings about the mechanisms that regulate ABA homoeostasis.

Multi-gene co-expression can improve comprehensive resistance to multiple abiotic stresses in Brassica napus L

Rapeseed (Brassica napus L.) is an important oil crop worldwide. For current B. napus production, it is urgent to develop new varieties with higher seed productivity and increased stress tolerance for better adaptation to the abiotic stresses as a result of global climate change. Genetic engineering, to some extent, can overcome the limitations of genetic exchange in conventional breeding. Consequently, it considered as an effective method for improving modern crop breeding for B. napus. Since crop stress resistance is a polygenic complex trait, only by multi-gene synergistic effects can effectively achieve the comprehensive stress resistance of crops. Hence, in the present study, five stress resistance genes, NCED3, ABAR, CBF3, LOS5, and ICE1 were transferred into B. napus. Compared with wildtype (WT) plants, the multi-gene transformants K15 exhibited pronounced growth advantage under both normal growth and stress conditions. Additionally, K15 plants also showed significantly higher resistance response to multiple stresses at seed germination and seedling stages than WT plants. Furthermore, K15 plants had significantly higher leaf temperature and significantly lower stomatal aperture and water loss rate than WT plants, which indicated that the water-holding capacity of K15 plants was significantly superior to that of WT plants after stress treatment. In addition, K15 plants had significantly higher abscisic acid (ABA) content and significantly lower malondialdehyde (MDA) content than WT plants. In conclusion, the above results suggested that multi-gene co-expression could rapidly trigger plant stress resistance, reduce the stress injury on plants and synergistically improve the comprehensive resistance of B. napus.

Transcriptome characterization of moso bamboo (Phyllostachys edulis) seedlings in response to exogenous gibberellin applications

BACKGROUND

Moso bamboo (Phyllostachys edulis) is a well-known bamboo species of high economic value in the textile industry due to its rapid growth. Phytohormones, which are master regulators of growth and development, serve as important endogenous signals. However, the mechanisms through which phytohormones regulate growth in moso bamboo remain unknown to date.

RESULTS

Here, we reported that exogenous gibberellins (GA) applications resulted in a significantly increased internode length and lignin condensation. Transcriptome sequencing revealed that photosynthesis-related genes were enriched in the GA-repressed gene class, which was consistent with the decrease in leaf chlorophyll concentrations and the lower rate of photosynthesis following GA treatment. Exogenous GA applications on seedlings are relatively easy to perform, thus we used 4-week-old whole seedlings of bamboo for GA- treatment followed by high throughput sequencing. In this study, we identified 932 cis-nature antisense transcripts (cis-NATs), and 22,196 alternative splicing (AS) events in total. Among them, 42 cis-nature antisense transcripts (cis-NATs) and 442 AS events were differentially expressed upon exposure to exogenous GA3, suggesting that post-transcriptional regulation might be also involved in the GA3 response. Targets of differential expression of cis-NATs included genes involved in hormone receptor, photosynthesis and cell wall biogenesis. For example, LAC4 and its corresponding cis-NATs were GA3-induced, and may be involved in the accumulation of lignin, thus affecting cell wall composition.

CONCLUSIONS

This study provides novel insights illustrating how GA alters post-transcriptional regulation and will shed light on the underlying mechanism of growth modulated by GA in moso bamboo.

Arabidopsis IQM4, a Novel Calmodulin-Binding Protein, Is Involved With Seed Dormancy and Germination in Arabidopsis

Seed dormancy and germination are regulated by complex mechanisms controlled by diverse hormones and environmental cues. Abscisic acid (ABA) promotes seed dormancy and inhibits seed germination and post-germination growth. Calmodulin (CaM) signals are involved with the inhibition of ABA during seed germination and seedling growth. In this study, we showed that Arabidopsis thaliana IQM4 could bind with calmodulin 5 (CaM5) both in vitro and in vivo, and that the interaction was the Ca2+-independent type. The IQM4 protein was localized in the chloroplast and the IQM4 gene was expressed in most tissues, especially the embryo and germinated seedlings. The T-DNA insertion mutants of IQM4 exhibited the reduced primary seed dormancy and lower ABA levels compared with wild type seeds. Moreover, IQM4 plays key roles in modulating the responses to ABA, salt, and osmotic stress during seed germination and post-germination growth. T-DNA insertion mutants exhibited ABA-insensitive and salt-hypersensitive phenotypes during seed germination and post-germination growth, whereas IQM4-overexpressing lines had ABA- and osmotic-hypersensitive, and salt-insensitive phenotypes. Gene expression analyses showed that mutation of IQM4 inhibited the expression of ABA biosynthetic genes NCED6 and NCED9, and seed maturation regulators LEC1, LEC2, ABI3, and ABI5 during the silique development, as well as promoted the expression of WRKY40 and inhibited that of ABI5 in ABA-regulated seed germination. These observations suggest that IQM4 is a novel Ca2+-independent CaM-binding protein, which is positively involved with seed dormancy and germination in Arabidopsis.