Histone deacetylase HDA710 controls salt tolerance by regulating ABA signaling in rice

Epigenetic arsenal for stress mitigation in plants

Plant's ability to perceive, respond to, and ultimately adapt to various stressors is a testament to their remarkable resilience. In response to stresses, plants activate a complex array of molecular and physiological mechanisms. These include the rapid activation of stress-responsive genes, the manufacturing of protective compounds, modulation of cellular processes and alterations in their growth and development patterns to enhance their chances of survival. Epigenetic mechanisms play a pivotal role in shaping the responses of plants to environmental stressors. This review explores the intricate interplay between epigenetic regulation and plant stress mitigation. We delve into the dynamic landscape of epigenetic modifications, highlighting their influence on gene expression and ultimately stress tolerance. This review assembles current research, shedding light on the promising strategies within plants' epigenetic arsenal to thrive amidst adverse conditions.

Histone deacetylase OsHDA716 represses rice chilling tolerance by deacetylating OsbZIP46 to reduce its transactivation function and protein stability

Low temperature is a major environmental factor limiting plant growth and crop production. Epigenetic regulation of gene expression is important for plant adaptation to environmental changes, whereas the epigenetic mechanism of cold signaling in rice (Oryza sativa) remains largely elusive. Here, we report that the histone deacetylase (HDAC) OsHDA716 represses rice cold tolerance by interacting with and deacetylating the transcription factor OsbZIP46. The loss-of-function mutants of OsHDA716 exhibit enhanced chilling tolerance, compared with the wild-type plants, while OsHDA716 overexpression plants show chilling hypersensitivity. On the contrary, OsbZIP46 confers chilling tolerance in rice through transcriptionally activating OsDREB1A and COLD1 to regulate cold-induced calcium influx and cytoplasmic calcium elevation. Mechanistic investigation showed that OsHDA716-mediated OsbZIP46 deacetylation in the DNA-binding domain reduces the DNA-binding ability and transcriptional activity as well as decreasing OsbZIP46 protein stability. Genetic evidence indicated that OsbZIP46 deacetylation mediated by OsHDA716 reduces rice chilling tolerance. Collectively, these findings reveal that the functional interplay between the chromatin regulator and transcription factor fine-tunes the cold response in plant and uncover a mechanism by which HDACs repress gene transcription through deacetylating nonhistone proteins and regulating their biochemical functions.

The role of priming and memory in rice environmental stress adaptation: Current knowledge and perspectives

Plant responses to abiotic stresses are dynamic, following the unpredictable changes of physical environmental parameters such as temperature, water and nutrients. Physiological and phenotypical responses to stress are intercalated by periods of recovery. An earlier stress can be remembered as 'stress memory' to mount a response within a generation or transgenerationally. The 'stress priming' phenomenon allows plants to respond quickly and more robustly to stressors to increase survival, and therefore has significant implications for agriculture. Although evidence for stress memory in various plant species is accumulating, understanding of the mechanisms implicated, especially for crops of agricultural interest, is in its infancy. Rice is a major food crop which is susceptible to abiotic stresses causing constraints on its cultivation and yield globally. Advancing the understanding of the stress response network will thus have a significant impact on rice sustainable production and global food security in the face of climate change. Therefore, this review highlights the effects of priming on rice abiotic stress tolerance and focuses on specific aspects of stress memory, its perpetuation and its regulation at epigenetic, transcriptional, metabolic as well as physiological levels. The open questions and future directions in this exciting research field are also laid out.

The rice LATE ELONGATED HYPOCOTYL enhances salt tolerance by regulating Na+/K+ homeostasis and ABA signalling

The circadian clock plays multiple functions in the regulation of plant growth, development and response to various abiotic stress. Here, we showed that the core oscillator component late elongated hypocotyl (LHY) was involved in rice response to salt stress. The mutations of OsLHY gene led to reduced salt tolerance in rice. Transcriptomic analyses revealed that the OsLHY gene regulates the expression of genes related to ion homeostasis and the abscisic acid (ABA) signalling pathway, including genes encoded High-affinity K+ transporters (OsHKTs) and the stress-activated protein kinases (OsSAPKs). We demonstrated that OsLHY directly binds the promoters of OsHKT1;1, OsHKT1;4 and OsSAPK9 to regulate their expression. Moreover, the ossapk9 mutants exhibited salt tolerance under salt stress. Taken together, our findings revealed that OsLHY integrates ion homeostasis and the ABA pathway to regulate salt tolerance in rice, providing insights into our understanding of how the circadian clock controls rice response to salt stress.

Histone deacetylase OsHDA706 orchestrates rice broad-spectrum antiviral immunity and is impeded by a viral effector

Lysine acetylation is a dynamic post-translational modification of proteins. Extensive studies have revealed that the acetylation modulated by histone acetyltransferases and histone deacetylases (HDACs) plays a crucial role in regulating protein function. However, there has been limited focus on how HDACs regulate jasmonic acid (JA) biosynthesis in plants. Here, we uncover that the protein stability of OsLOX14, a critical enzyme involved in JA biosynthesis, is regulated by a histone deacetylase, OsHDA706, and is hindered by a viral protein. Our results show that OsHDA706 deacetylates OsLOX14 and enhances the stability of OsLOX14, leading to JA accumulation and an improved broad-spectrum rice antiviral defense. Furthermore, we found that the viral protein P2, encoded by the destructive rice stripe virus, disrupts the association of OsHDA706-OsLOX14, promoting viral infection. Overall, our findings reveal how HDAC manipulates the interplay of deacetylation and protein stability of a JA biosynthetic enzyme to enhance plant antiviral responses.

Recent advancements in the role of histone acetylation dynamics to improve stress responses in plants

In eukaryotes, transcriptional regulation is determined by the DNA sequence and is facilitated through sophisticated and complex chromatin alterations and histone remodelling. Recent research has shown that the histone acetylation dynamic, an intermittent and reversible substitution, constitutes a prerequisite for chromatin modification. These changes in chromatin structure modulate genome-wide and specific changes in response to external and internal cues like cell differentiation, development, growth, light temperature, and biotic stresses. Histone acetylation dynamics also control the cell cycle. HATs and HDACs play a critical role in gene expression modulation during plant growth and response to environmental circumstances. It has been well established that HATs and HDACs interact with various distinct transcription factors and chromatin-remodelling proteins (CRPs) involved in the transcriptional regulation of several developmental processes. This review explores recent research on histone acyltransferases and histone deacetylases, mainly focusing on their involvement in plant biotic stress responses. Moreover, we also emphasized the research gaps that must be filled to fully understand the complete function of histone acetylation dynamics during biotic stress responses in plants. A thorough understanding of histone acetylation will make it possible to enhance tolerance against various kinds of stress and decrease yield losses in many crops.

Genome-Wide Identification and Characterization of the Salvia miltiorrhiza Histone Deacetylase (HDAC) Family in Response to Multiple Abiotic Stresses

Salvia miltiorrhiza is a plant commonly used in traditional Chinese medicine. Its material bases for treating diseases are tanshinones and phenolic acids, including salvianolic acids. Histone deacetylase proteins (HDACs) are a class of specific functional enzymes that interact with acetylation groups on the N-terminal lysine of histone proteins further regulate gene transcription through structural changes at the chromatin level. HDACs involved in the growth and development of various plants, and induced by plant hormones to regulate the internal environment of plants to resist stress, at the same time affect the accumulation of some secondary metabolites. However, the role of SmHDACs on the accumulation of salvianolic acid in S. miltiorrhiza remains unclear. In this study, 16 SmHDACs genes were identified from the high-quality S. miltiorrhiza genome, their physicochemical properties were predicted. In phylogenetic trees co-constructed with HDACs proteins from other plants, SmHDACs was divided into three subfamilies, each with similar motif and conserved domain composition. The distribution of the three subfamilies is similar to that of dicotyledonous plants. Chromosome localization analysis showed that SmHDACs genes were randomly located. Cis-acting element analysis predicted that SmHDACs gene expression may be related to and induced by various phytohormones, such as MeJA and ABA. By combining the expression pattern and co-expression network induced by phytohormones, we speculate that SmHDACs may further influence the synthesis of salvianolic acid, and identified SmHDA5, a potential functional gene, then speculate its downstream target based on the co-expression network. In summary, we analyzed the SmHDACs gene family of S. miltiorrhiza and screened out the potential functional gene SmHDA5. From the perspective of epigenetics, we proposed the molecular mechanism of plant hormone promoting salvianolic acid synthesis, which filled the gap in the subdivision of histone deacetylase in S. miltiorrhiza research, provided a theoretical basis for the culture and transformation of S. miltiorrhiza germplasm resources.

Post-Translational Modifications in Histones and Their Role in Abiotic Stress Tolerance in Plants

Abiotic stresses profoundly alter plant growth and development, resulting in yield losses. Plants have evolved adaptive mechanisms to combat these challenges, triggering intricate molecular responses to maintain tissue hydration and temperature stability during stress. A pivotal player in this defense is histone modification, governing gene expression in response to diverse environmental cues. Post-translational modifications (PTMs) of histone tails, including acetylation, phosphorylation, methylation, ubiquitination, and sumoylation, regulate transcription, DNA processes, and stress-related traits. This review comprehensively explores the world of PTMs of histones in plants and their vital role in imparting various abiotic stress tolerance in plants. Techniques, like chromatin immune precipitation (ChIP), ChIP-qPCR, mass spectrometry, and Cleavage Under Targets and Tag mentation, have unveiled the dynamic histone modification landscape within plant cells. The significance of PTMs in enhancing the plants' ability to cope with abiotic stresses has also been discussed. Recent advances in PTM research shed light on the molecular basis of stress tolerance in plants. Understanding the intricate proteome complexity due to various proteoforms/protein variants is a challenging task, but emerging single-cell resolution techniques may help to address such challenges. The review provides the future prospects aimed at harnessing the full potential of PTMs for improved plant responses under changing climate change.

Multifaceted functions of histone deacetylases in stress response

Histone deacetylases (HDACs) are important chromatin regulators essential for plant tolerance to adverse environments. In addition to histone deacetylation and epigenetic regulation, HDACs deacetylate non-histone proteins and thereby regulate multiple pathways. Like other post-translational modifications (PTMs), acetylation/deacetylation is a reversible switch regulating different cellular processes in plants. Here, by focusing on results obtained in arabidopsis (Arabidopsis thaliana) and rice plants, we analyze the different aspects of HDAC functions and the underlying regulatory mechanisms in modulating plant responses to stress. We hypothesize that, in addition to epigenetic regulation of gene expression, HDACs can also control plant tolerance to stress by regulating transcription, translation, and metabolic activities and possibly assembly-disassembly of stress granules (SGs) through lysine deacetylation of non-histone proteins.

OsSTS, a Novel Allele of Mitogen-Activated Protein Kinase Kinase 4 (OsMKK4), Controls Grain Size and Salt Tolerance in Rice

Soil salinization is one of the most common abiotic stresses of rice, which seriously affects the normal growth of rice. Breeding salt-tolerant varieties have become one of the important ways to ensure food security and sustainable agricultural development. However, the mechanisms underlying salt tolerance control still need to be clarified. In this study, we identified a mutant, termed salt-tolerant and small grains(sts), with salt tolerance and small grains. Gene cloning and physiological and biochemical experiments reveal that sts is a novel mutant allele of Mitogen-activated protein Kinase Kinase 4 (OsMKK4), which controls the grain size, and has recently been found to be related to salt tolerance in rice. Functional analysis showed that OsSTS is constitutively expressed throughout the tissue, and its proteins are localized to the nucleus, cell membrane, and cytoplasm. It was found that the loss of OsSTS function enhanced the salt tolerance of rice seedlings, and further studies showed that the loss of OsSTS function increased the ROS clearance rate of rice seedlings, independent of ionic toxicity. In order to explore the salt tolerance mechanism of sts, we found that the salt tolerance of sts is also regulated by ABA through high-throughput mRNA sequencing. Salt and ABA treatment showed that ABA might alleviate the inhibitory effect of salt stress on root length in sts. These results revealed new functions of grain size gene OsMKK4, expanded new research ideas related to salt tolerance mechanism and hormone regulation network, and provided a theoretical basis for salt-tolerant rice breeding.

OsBTBZ1 Confers Salt Stress Tolerance in Arabidopsis thaliana

Rice (Oryza sativa L.), one of the most important commodities and a primary food source worldwide, can be affected by adverse environmental factors. The chromosome segment substitution line 16 (CSSL16) of rice is considered salt-tolerant. A comparison of the transcriptomic data of the CSSL16 line under normal and salt stress conditions revealed 511 differentially expressed sequence (DEseq) genes at the seedling stage, 520 DEseq genes in the secondary leaves, and 584 DEseq genes in the flag leaves at the booting stage. Four BTB genes, OsBTBZ1, OsBTBZ2, OsBTBN3, and OsBTBN7, were differentially expressed under salt stress. Interestingly, only OsBTBZ1 was differentially expressed at the seedling stage, whereas the other genes were differentially expressed at the booting stage. Based on the STRING database, OsBTBZ1 was more closely associated with other abiotic stress-related proteins than other BTB genes. The highest expression of OsBTBZ1 was observed in the sheaths of young leaves. The OsBTBZ1-GFP fusion protein was localized to the nucleus, supporting the hypothesis of a transcriptionally regulatory role for this protein. The bt3 Arabidopsis mutant line exhibited susceptibility to NaCl and abscisic acid (ABA) but not to mannitol. NaCl and ABA decreased the germination rate and growth of the mutant lines. Moreover, the ectopic expression of OsBTBZ1 rescued the phenotypes of the bt3 mutant line and enhanced the growth of wild-type Arabidopsis under stress conditions. These results suggest that OsBTBZ1 is a salt-tolerant gene functioning in ABA-dependent pathways.

A Transcription Factor SlNAC4 Gene of Suaeda liaotungensis Enhances Salt and Drought Tolerance through Regulating ABA Synthesis

The NAC (NAM, ATAF1/2 and CUC2) transcription factors are ubiquitously distributed in plants and play critical roles in the construction of plant organs and abiotic stress response. In this study, we described the cloning of a Suaeda liaotungensis K. NAC transcription factor gene SlNAC4, which contained 1450 bp, coding a 331 amino acid. We found that SlNAC4 was highly expressed in stems of S. liaotungensis, and the expression of SlNAC4 was considerably up-regulated after salt, drought, and ABA treatments. Transcription analysis and subcellular localization demonstrated that the SlNAC4 protein was located both in the nucleus and cytoplasm, and contained a C-terminal transcriptional activator. The SlNAC4 overexpression Arabidopsis lines significantly enhanced the tolerance to salt and drought treatment and displayed obviously increased activity of antioxidant enzymes under salt and drought stress. Additionally, transgenic plants overexpressing SlNAC4 had a significantly higher level of physiological indices. Interestingly, SlNAC4 promoted the expression of ABA metabolism-related genes including AtABA1, AtABA3, AtNCED3, AtAAO3, but inhibited the expression of AtCYP707A3 in overexpression lines. Using a yeast one-hybrid (Y1H) assay, we identified that the SlNAC4 transcription factor could bind to the promoters of those ABA metabolism-related genes. These results indicate that overexpression of SlNAC4 in plants enhances the tolerance to salt and drought stress by regulating ABA metabolism.

OsFAR1 is involved in primary fatty alcohol biosynthesis and promotes drought tolerance in rice

MAIN CONCLUSION

OsFAR1 encodes a fatty acyl-CoA reductase involved in biosynthesis of primary alcohols and plays an important role in drought stress response in rice. Cuticular waxes cover the outermost surface of terrestrial plants and contribute to inhibiting nonstomatal water loss and improving plant drought resistance. Primary alcohols are the most abundant components in the leaf cuticular waxes of rice (Oryza sativa), but the biosynthesis and regulation of primary alcohol remain largely unknown in rice. Here, we identified and characterized an OsFAR1 gene belonging to the fatty acyl-CoA reductases (FARs) via a homology-based approach in rice. OsFAR1 was activated by abiotic stresses and abscisic acid, resulting in increased production of primary alcohol in rice. Heterologous expression of OsFAR1 enhanced the amounts of C22:0 and C24:0 primary alcohols in yeast (Saccharomyces cerevisiae) and C24:0 to C32:0 primary alcohols in Arabidopsis. Similarly, OsFAR1 overexpression significantly increased the content of C24:0 to C30:0 primary alcohols on rice leaves. Finally, OsFAR1 overexpression lines exhibited reduced cuticle permeability and enhanced drought tolerance in rice and Arabidopsis. Taken together, our results demonstrate that OsFAR1 is involved in rice primary alcohol biosynthesis and plays an important role in responding to drought and other environmental stresses.

Unlocking the Secret to Higher Crop Yield: The Potential for Histone Modifications

Histone modifications are epigenetic mechanisms, termed relative to genetics, and they refer to the induction of heritable changes without altering the DNA sequence. It is widely known that DNA sequences precisely modulate plant phenotypes to adapt them to the changing environment; however, epigenetic mechanisms also greatly contribute to plant growth and development by altering chromatin status. An increasing number of recent studies have elucidated epigenetic regulations on improving plant growth and adaptation, thus making contributions to the final yield. In this review, we summarize the recent advances of epigenetic regulatory mechanisms underlying crop flowering efficiency, fruit quality, and adaptation to environmental stimuli, especially to abiotic stress, to ensure crop improvement. In particular, we highlight the major discoveries in rice and tomato, which are two of the most globally consumed crops. We also describe and discuss the applications of epigenetic approaches in crop breeding programs.

OsJRL40, a Jacalin-Related Lectin Gene, Promotes Salt Stress Tolerance in Rice

High salinity is a major stress factor affecting the quality and productivity of rice (Oryza sativa L.). Although numerous salt tolerance-related genes have been identified in rice, their molecular mechanisms remain unknown. Here, we report that OsJRL40, a jacalin-related lectin gene, confers remarkable salt tolerance in rice. The loss of function of OsJRL40 increased sensitivity to salt stress in rice, whereas its overexpression enhanced salt tolerance at the seedling stage and during reproductive growth. β-glucuronidase (GUS) reporter assays indicated that OsJRL40 is expressed to higher levels in roots and internodes than in other tissues, and subcellular localization analysis revealed that the OsJRL40 protein localizes to the cytoplasm. Further molecular analyses showed that OsJRL40 enhances antioxidant enzyme activities and regulates Na⁺-K⁺ homeostasis under salt stress. RNA-seq analysis revealed that OsJRL40 regulates salt tolerance in rice by controlling the expression of genes encoding Na⁺/K⁺ transporters, salt-responsive transcription factors, and other salt response-related proteins. Overall, this study provides a scientific basis for an in-depth investigation of the salt tolerance mechanism in rice and could guide the breeding of salt-tolerant rice cultivars.

Histone deacetylase 9 regulates disease resistance through fine-tuning histone deacetylation of melatonin biosynthetic genes and melatonin accumulation in cassava

Melatonin participates in plant growth and development and biotic and abiotic stress responses. Histone acetylation regulates many plant biological processes via transcriptional reprogramming. However, the direct relationship between melatonin and histone acetylation in plant disease resistance remains unclear. In this study, we identified cassava bacterial blight (CBB) responsive histone deacetylase 9 (HDA9), which negatively regulated disease resistance to CBB by reducing melatonin content. In addition, exogenous melatonin alleviated disease sensitivity of MeHDA9 overexpressed plants to CBB. Importantly, MeHDA9 inhibited the expression of melatonin biosynthetic genes through decreasing lysine 5 of histone 4 (H4K5) acetylation at the promoter regions of melatonin biosynthetic genes, thereby modulating melatonin accumulation in cassava. Furthermore, protein phosphatase 2C 12 (MePP2C12) interacted with MeHDA9 in vivo and in vitro, and it was involved in MeHDA9-mediated disease resistance via melatonin biosynthetic pathway. In summary, this study highlights the direct interaction between histone deacetylation and melatonin biosynthetic genes in cassava disease resistance via histone deacetylation, providing new insights into the genetic improvement of disease resistance via epigenetic regulation of melatonin level in tropical crops.

Proteome-wide lysine acetylation profiling to investigate the involvement of histone deacetylase HDA5 in the salt stress response of Arabidopsis leaves

Post-translational modifications (PTMs) of proteins play important roles in the acclimation of plants to environmental stress. Lysine acetylation is a dynamic and reversible PTM, which can be removed by histone deacetylases. Here we investigated the role of lysine acetylation in the response of Arabidopsis leaves to 1 week of salt stress. A quantitative mass spectrometry analysis revealed an increase in lysine acetylation of several proteins from cytosol and plastids, which was accompanied by altered histone deacetylase activities in the salt-treated leaves. While activities of HDA14 and HDA15 were decreased upon salt stress, HDA5 showed a mild and HDA19 a strong increase in activity. Since HDA5 is a cytosolic-nuclear enzyme from the class II histone deacetylase family with yet unknown protein substrates, we performed a lysine acetylome analysis on hda5 mutants and characterized its substrate proteins. Next to histone H2B, the salt stress-responsive transcription factor GT2L and the dehydration-related protein ERD7 were identified as HDA5 substrates. In addition, in protein-protein interaction studies, HDA18 was discovered, among other interacting proteins, to work in a complex together with HDA5. Altogether, this study revealed the substrate proteins of HDA5 and identified new lysine acetylation sites which are hyperacetylated upon salt stress. The identification of specific histone deacetylase substrate proteins, apart from histones, will be important to unravel the acclimation response of Arabidopsis to salt stress and their role in plant physiology.

OsWR2 recruits HDA704 to regulate the deacetylation of H4K8ac in the promoter of OsABI5 in response to drought stress

Drought stress is a major environmental factor that limits the growth, development, and yield of rice (Oryza sativa L.). Histone deacetylases (HDACs) are involved in the regulation of drought stress responses. HDA704 is an RPD3/HDA1 class HDAC that mediates the deacetylation of H4K8 (lysine 8 of histone H4) for drought tolerance in rice. In this study, we show that plants overexpressing HDA704 (HDA704-OE) are resistant to drought stress and sensitive to abscisic acid (ABA), whereas HDA704 knockout mutant (hda704) plants displayed decreased drought tolerance and ABA sensitivity. Transcriptome analysis revealed that HDA704 regulates the expression of ABA-related genes in response to drought stress. Moreover, HDA704 was recruited by a drought-resistant transcription factor, WAX SYNTHESIS REGULATORY 2 (OsWR2), and co-regulated the expression of the ABA biosynthesis genes NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), NCED4, and NCED5 under drought stress. HDA704 also repressed the expression of ABA-INSENSITIVE 5 (OsABI5) and DWARF AND SMALL SEED 1 (OsDSS1) by regulating H4K8ac levels in the promoter regions in response to polyethylene glycol 6000 treatment. In agreement, the loss of OsABI5 function increased resistance to dehydration stress in rice. Our results demonstrate that HDA704 is a positive regulator of the drought stress response and offers avenues for improving drought resistance in rice.

Histone deacetylase OsHDA706 increases salt tolerance via H4K5/K8 deacetylation of OsPP2C49 in rice

High salt is a major environmental factor that threatens plant growth and development. Increasing evidence indicates that histone acetylation is involved in plant responses to various abiotic stress; however, the underlying epigenetic regulatory mechanisms remain poorly understood. In this study, we revealed that the histone deacetylase OsHDA706 epigenetically regulates the expression of salt stress response genes in rice (Oryza sativa L.). OsHDA706 localizes to the nucleus and cytoplasm and OsHDA706 expression is significantly induced under salt stress. Moreover, oshda706 mutants showed a higher sensitivity to salt stress than the wild-type. In vivo and in vitro enzymatic activity assays demonstrated that OsHDA706 specifically regulates the deacetylation of lysines 5 and 8 on histone H4 (H4K5 and H4K8). By combining chromatin immunoprecipitation and mRNA sequencing, we identified the clade A protein phosphatase 2 C gene, OsPP2C49, which is involved in the salt response as a direct target of H4K5 and H4K8 acetylation. We found that the expression of OsPP2C49 is induced in the oshda706 mutant under salt stress. Furthermore, the knockout of OsPP2C49 enhances plant tolerance to salt stress, while its overexpression has the opposite effect. Taken together, our results indicate that OsHDA706, a histone H4 deacetylase, participates in the salt stress response by regulating the expression of OsPP2C49 via H4K5 and H4K8 deacetylation.

Histone acetyltransferase HAM1 interacts with molecular chaperone DNAJA2 and confers immune responses through salicylic acid biosynthetic genes in cassava

Cassava bacterial blight (CBB) is one of the most serious diseases in cassava production, so it is essential to explore the underlying mechanism of immune responses. Histone acetylation is an important epigenetic modification, however, its relationship with cassava disease resistance remains unclear. Here, we identified 10 histone acetyltransferases in cassava and found that the transcript of MeHAM1 showed the highest induction to CBB. Functional analysis showed that MeHAM1 positively regulated disease resistance to CBB through modulation of salicylic acid (SA) accumulation. Further investigation revealed that MeHAM1 directly activated SA biosynthetic genes' expression via promoting lysine 9 of histone 3 (H3K9) acetylation and lysine 5 of histone 4 (H4K5) acetylation of these genes. In addition, molecular chaperone MeDNAJA2 physically interacted with MeHAM1, and MeDNAJA2 also regulated plant immune responses and SA biosynthetic genes. In conclusion, this study illustrates that MeHAM1 and MeDNAJA2 confer immune responses through transcriptional programming of SA biosynthetic genes via histone acetylation. The MeHAM1 & MeDNAJA2-SA biosynthesis module not only constructs the direct relationship between histone acetylation and cassava disease resistance, but also provides gene network with potential value for genetic improvement of cassava disease resistance.

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.

Genome-wide H3K9 acetylation level increases with age-dependent senescence of flag leaf in rice

Flag leaf senescence is an important biological process that drives the remobilization of nutrients to the growing organs of rice. Leaf senescence is controlled by genetic information via gene expression and histone modification, but the precise mechanism is as yet unclear. Here, we analysed genome-wide acetylated lysine residue 9 of histone H3 (H3K9ac) enrichment by chromatin immunoprecipitation-sequencing (ChIP-seq), and examined its association with transcriptomes by RNA-seq during flag leaf aging in rice (Oryza sativa). We found that genome-wide H3K9 acetylation levels increased with age-dependent senescence in rice flag leaf, and there was a positive correlation between the density and breadth of H3K9ac with gene expression and transcript elongation. During flag leaf aging, we observed 1249 up-regulated differentially expressed genes (DEGs) and 996 down-regulated DEGs, showing a strong relationship between temporal changes in gene expression and gain/loss of H3K9ac. We produced a landscape of H3K9 acetylation-modified gene expression targets that include known senescence-associated genes, metabolism-related genes, as well as miRNA biosynthesis-related genes. Our findings reveal a complex regulatory network of metabolism- and senescence-related pathways mediated by H3K9ac, and elucidate patterns of H3K9ac-mediated regulation of gene expression during flag leaf aging in rice.

ROS-stimulated Protein Lysine Acetylation Is Required for Crown Root Development in Rice

INTRODUCTION

As signal molecules in aerobic organisms, locally accumulated ROS have been reported to balance cell division and differentiation in the root meristem. Protein posttranslational modifications such as lysine acetylation play critical roles in controlling a variety of cellular processes. However, the mechanism by which ROS regulate root development is unknown. In addition, how protein lysine acetylation is regulated and whether cellular ROS levels affect protein lysine acetylation remain unclear.

OBJECTIVES

We aimed to elucidate the relationship between ROS and protein acetylation by exploring a rice mutant plant that displays a decreased level of ROS in postembryonic crown root (CR) cells and severe defects in CR development.

METHODS

First, proteomic analysis was used to find candidate proteins responsible for the decrease of ROS detected in the wox11 mutant. Then, biochemical, molecular, and genetic analyses were used to study WOX11-regulated genes involved in ROS homeostasis. Finally, acetylproteomic analysis of wild type and wox11 roots treated with or without potassium iodide (KI) and peroxide (H₂O₂) were used to study the effects of ROS on protein acetylation in rice CR cells.

RESULTS

We demonstrated that WOX11 was required to maintain ROS homeostasis by upregulating peroxidase genes in the crown root meristem. Acetylproteomic analysis revealed that WOX11-dependent peroxide (H₂O₂) levels in CR cells promoted lysine acetylation of many non-histone proteins enriched for nitrogen metabolism and peptide/protein synthesis pathways. Further analysis revealed that the redox state affected histone deacetylases (HDACs) activity, which was likely related to the high levels of protein lysine acetylation in CR cells.

CONCLUSION

WOX11-controlled ROS level in CR meristem cells is required for protein lysine acetylation which represents a mechanism of ROS-promoted CR development in rice.

OsPP65 Negatively Regulates Osmotic and Salt Stress Responses Through Regulating Phytohormone and Raffinose Family Oligosaccharide Metabolic Pathways in Rice

Although type 2C protein phosphatases (PP2Cs) have been demonstrated to play important roles in regulating plant development and various stress responses, their specific roles in rice abiotic stress tolerance are still largely unknown. In this study, the functions of OsPP65 in rice osmotic and salt stress tolerance were investigated. Here, we report that OsPP65 is responsive to multiple stresses and is remarkably induced by osmotic and salt stress treatments. OsPP65 was highly expressed in rice seedlings and leaves and localized in the nucleus and cytoplasm. OsPP65 knockout rice plants showed enhanced tolerance to osmotic and salt stresses. Significantly higher induction of genes involved in jasmonic acid (JA) and abscisic acid (ABA) biosynthesis or signaling, as well as higher contents of endogenous JA and ABA, were observed in the OsPP65 knockout plants compared with the wild-type plants after osmotic stress treatment. Further analysis indicated that JA and ABA function independently in osmotic stress tolerance conferred by loss of OsPP65. Moreover, metabolomics analysis revealed higher endogenous levels of galactose and galactinol but a lower content of raffinose in the OsPP65 knockout plants than in the wild-type plants after osmotic stress treatment. These results together suggest that OsPP65 negatively regulates osmotic and salt stress tolerance through regulation of the JA and ABA signaling pathways and modulation of the raffinose family oligosaccharide metabolism pathway in rice. OsPP65 is a promising target for improvement of rice stress tolerance using gene editing.

Uncovering the Epigenetic Marks Involved in Mediating Salt Stress Tolerance in Plants

The toxic effects of salinity on agricultural productivity necessitate development of salt stress tolerance in food crops in order to meet the escalating demands. Plants use sophisticated epigenetic systems to fine-tune their responses to environmental cues. Epigenetics is the study of heritable, covalent modifications of DNA and histone proteins that regulate gene expression without altering the underlying nucleotide sequence and consequently modify the phenotype. Epigenetic processes such as covalent changes in DNA, histone modification, histone variants, and certain non-coding RNAs (ncRNA) influence chromatin architecture to regulate its accessibility to the transcriptional machinery. Under salt stress conditions, there is a high frequency of hypermethylation at promoter located CpG sites. Salt stress results in the accumulation of active histones marks like H3K9K14Ac and H3K4me3 and the downfall of repressive histone marks such as H3K9me2 and H3K27me3 on salt-tolerance genes. Similarly, the H2A.Z variant of H2A histone is reported to be down regulated under salt stress conditions. A thorough understanding of the plasticity provided by epigenetic regulation enables a modern approach to genetic modification of salt-resistant cultivars. In this review, we summarize recent developments in understanding the epigenetic mechanisms, particularly those that may play a governing role in the designing of climate smart crops in response to salt stress.

ABA Mediates Plant Development and Abiotic Stress via Alternative Splicing

Alternative splicing (AS) exists in eukaryotes to increase the complexity and adaptability of systems under biophysiological conditions by increasing transcriptional and protein diversity. As a classic hormone, abscisic acid (ABA) can effectively control plant growth, improve stress resistance, and promote dormancy. At the transcriptional level, ABA helps plants respond to the outside world by regulating transcription factors through signal transduction pathways to regulate gene expression. However, at the post-transcriptional level, the mechanism by which ABA can regulate plant biological processes by mediating alternative splicing is not well understood. Therefore, this paper briefly introduces the mechanism of ABA-induced alternative splicing and the role of ABA mediating AS in plant response to the environment and its own growth.

Screening and Verification of Molecular Markers and Genes Related to Salt-Alkali Tolerance in Portunus trituberculatus

Salt-alkali tolerance is one of the important breeding traits of Portunus trituberculatus. Identification of molecular markers linked to salt-alkali tolerance is prerequisite to develop such molecular marker-assisted breeding. In this study, Bulked Segregant Analysis (BSA) was used to screen molecular markers associated with salt-alkali tolerance trait in P. trituberculatus. Two DNA mixing pools with significant difference in salt-alkali tolerance were prepared and 94.83G of high-quality sequencing data was obtained. 855 SNPs and 1051 Indels were firstly selected as candidate markers by BSA analysis, out of which, 20 markers were further selected via △index value (close to 0 or 1) and eight of those were successfully verified. In addition, based on the located information of the markers in genome, eight candidate genes related to salt-alkali tolerance were anchored including ubiquitin-conjugating enzyme, aspartate-tRNA ligase, vesicle-trafficking protein, and so on. qPCR results showed that the expression patterns of all these genes changed significantly after salt-alkali stress, suggesting that they play certain roles in salt-alkali adaptation. Our results will provide applicable markers for molecular marker-assisted breeding and help to clarify the mechanisms of salt-alkali adaptation of P. trituberculatus.

New approaches to improve crop tolerance to biotic and abiotic stresses

During the last years, a great effort has been dedicated at the development and employment of diverse approaches for achieving more stress-tolerant and climate-flexible crops and sustainable yield increases to meet the food and energy demands of the future. The ongoing climate change is in fact leading to more frequent extreme events with a negative impact on food production, such as increased temperatures, drought, and soil salinization as well as invasive arthropod pests and diseases. In this review, diverse "green strategies" (e.g., chemical priming, root-associated microorganisms), and advanced technologies (e.g., genome editing, high-throughput phenotyping) are described on the basis of the most recent research evidence. Particularly, attention has been focused on the potential use in a context of sustainable and climate-smart agriculture (the so called "next agriculture generation") to improve plant tolerance and resilience to abiotic and biotic stresses. In addition, the gap between the results obtained in controlled experiments and those from application of these technologies in real field conditions (lab to field step) is also discussed.

Histone modifications and chromatin remodelling in plants in response to salt stress

In the face of global food security crises, it is necessary to boost agricultural production. One factor hampering the attempts to increase food production is elevated soil salinity, which can be due to salt that is naturally present in the soil or a consequence of excessive or prolonged irrigation or application of fertiliser. In response to environmental stresses, plants activate multiple molecular mechanisms, including the timely activation of stress-responsive transcriptional networks. However, in the case of salt stress, the combined effects of the initial osmotic shock and the subsequent ion-specific stress increase the complexity in the selective regulation of gene expressions involved in restoring or maintaining osmotic balance, ion homeostasis and reactive oxygen species scavenging. Histone modifications and chromatin remodelling are important epigenetic processes that regulate gene expressions by modifying the chromatin status and recruiting transcription regulators. In this review, we have specifically summarised the currently available knowledge on histone modifications and chromatin remodelling in relation to plant responses to salt stress. Current findings have revealed the functional importance of chromatin modifiers in regulating salt tolerance and identified the effector genes affected by epigenetic modifications, although counteraction between modifiers within the same family may occur. Emerging evidence has also illustrated the crosstalk between epigenetic modifications and hormone signalling pathways which involves formation of protein complexes. With an improved understanding of these processes, plant breeders will be able to develop alternative strategies using genome editing technologies for crop improvement.

Ustilaginoidea virens modulates lysine 2-hydroxyisobutyrylation in rice flowers during infection

The post-translational modification lysine 2-hydroxyisobutyrylation (K_hib ) plays an important role in gene transcription, metabolism, and enzymatic activity. K_hib sites have been identified in rice (Oryza sativa). However, the K_hib status of proteins in rice flowers during pathogen infection remains unclear. Here, we report a comprehensive identification of K_hib -modified proteins in rice flowers, and the changes in these proteins during infection with the fungal pathogen Ustilaginoidea virens. By using a tandem mass tag-based quantitative proteomics approach, we identified 2,891 K_hib sites on 964 proteins in rice flowers. Our data demonstrated that 2-hydroxyisobutyrylated proteins are involved in diverse biological processes. K_hib levels were substantially reduced upon infection with U. virens. Chromatin immunoprecipitation polymerase chain reaction (PCR) and reverse transcription quantitative PCR analyses revealed that histone K_hib is involved in the expression of disease-resistance genes. More importantly, most quantified sites on core histones H3 were downregulated upon U. virens infection. In addition, the histone deacetylases HDA705, HDA716, SRT1, and SRT2 are involved in the removal of K_hib marks in rice. HDA705 was further confirmed to negatively regulate rice disease resistance to pathogens U. virens, Magnaporthe oryzae, and Xanthomonas oryzae pv. oryzae (Xoo). Our data suggest that U. virens could modulate K_hib in rice flowers during infection.

Genome-wide survey of the F-box/Kelch (FBK) members and molecular identification of a novel FBK gene TaAFR in wheat

F-box proteins play critical roles in plant responses to biotic/abiotic stresses. In the present study, a total of 68 wheat F-box/Kelch (TaFBK) genes, unevenly distributed across 21 chromosomes and encoding 74 proteins, were identified in EnsemblPlants. Protein sequences were compared with those of Arabidopsis and three cereal species by phylogenetic and domain analyses, where the wheat sequences were resolved into 6 clades. In silico analysis of a digital PCR dataset revealed that TaFBKs were expressed at multiple developmental stages and tissues, and in response to drought and/or heat stresses. The TaFBK19 gene, a homolog of the Attenuated Far-Red Response (AFR) genes in other plant species, and hence named TaAFR, was selected for further analysis. Reverse-transcription quantitative real-time PCR (RT-qPCR) was carried out to determine tissue-specific, hormone and stress (abiotic/biotic) responsive expression patterns. Of interest, TaAFR was expressed most abundantly in the leaves, and its expression in response to leaf rust variants suggests a potential role in compatible vs incompatible rust responses. The protein was predicted to localize in cytosol, but it was shown experimentally to localize in both the cytosol and the nucleus of tobacco. A series of protein interaction studies, starting with a yeast-2-hybrid (Y2H) library screen (wheat leaf infected with incompatible leaf rust pathogens), led to the identification of three TaAFR interacting proteins. Skp1/ASK1-like protein (Skp1) was found to interact with the F-box domain of TaAFR, while ADP-ribosylation factor 2-like isoform X1 (ARL2) and phenylalanine ammonia-lyase (PAL) were shown to interact with its Kelch domain. The data presented herein provides a solid foundation from which the function and metabolic network of TaAFR and other wheat FBKs can be further explored.

Next-Generation Breeding Strategies for Climate-Ready Crops

Climate change is a threat to global food security due to the reduction of crop productivity around the globe. Food security is a matter of concern for stakeholders and policymakers as the global population is predicted to bypass 10 billion in the coming years. Crop improvement via modern breeding techniques along with efficient agronomic practices innovations in microbiome applications, and exploiting the natural variations in underutilized crops is an excellent way forward to fulfill future food requirements. In this review, we describe the next-generation breeding tools that can be used to increase crop production by developing climate-resilient superior genotypes to cope with the future challenges of global food security. Recent innovations in genomic-assisted breeding (GAB) strategies allow the construction of highly annotated crop pan-genomes to give a snapshot of the full landscape of genetic diversity (GD) and recapture the lost gene repertoire of a species. Pan-genomes provide new platforms to exploit these unique genes or genetic variation for optimizing breeding programs. The advent of next-generation clustered regularly interspaced short palindromic repeat/CRISPR-associated (CRISPR/Cas) systems, such as prime editing, base editing, and de nova domestication, has institutionalized the idea that genome editing is revamped for crop improvement. Also, the availability of versatile Cas orthologs, including Cas9, Cas12, Cas13, and Cas14, improved the editing efficiency. Now, the CRISPR/Cas systems have numerous applications in crop research and successfully edit the major crop to develop resistance against abiotic and biotic stress. By adopting high-throughput phenotyping approaches and big data analytics tools like artificial intelligence (AI) and machine learning (ML), agriculture is heading toward automation or digitalization. The integration of speed breeding with genomic and phenomic tools can allow rapid gene identifications and ultimately accelerate crop improvement programs. In addition, the integration of next-generation multidisciplinary breeding platforms can open exciting avenues to develop climate-ready crops toward global food security.