Alternative splicing at the intersection of biological timing, development, and stress responses

Phenotypic Plasticity and Stability in Plants: Genetic Mechanisms, Environmental Adaptation, Evolutionary Implications, and Future Directions

The phenotypic display, survival, and reproduction of organisms depend on genotype-environment interactions that drive development, evolution, and diversity. Biological systems exhibit two basic but paradoxical features that contribute to developmental robustness: plasticity and stability. However, the understanding of these concepts remains ambiguous. The morphology and structure of plant reproductive organs-flowers and fruits-exhibit substantial stability but display a certain level of plasticity under environmental changes, thus representing promising systems for the study of how stability and plasticity jointly govern plant development and evolution. Beyond the genes underlying organ formation, certain genes may maintain stability and induce plasticity. Variations in relevant genes can induce developmental repatterning, thereby altering stability or plasticity under light and temperature fluctuations, which often affects fitness. The regulation of developmental robustness in plant vegetative organs involves transcriptional and post-transcriptional regulation, epigenetics, and phase separation; however, these mechanisms in the reproductive organs of flowering plants remain poorly investigated. Moreover, genes that specifically determine phenotypic plasticity have rarely been cloned. This review clarifies the concepts and attributes of phenotypic plasticity and stability and further proposes potential avenues and a paradigm to investigate the underlying genes and elucidate how plants adapt and thrive in diverse environments, which is crucial for the design of genetically modified crops.

ABA-induced alternative splicing drives transcriptomic reprogramming for drought tolerance in barley

BACKGROUND

Abscisic acid (ABA) is a phytohormone that mediates plant responses to drought stress by regulating stomatal conductance, gene expression, and photosynthetic efficiency. Although ABA-induced stress priming has shown the potential to improve drought tolerance, the molecular mechanisms underlying ABA pretreatment effects remain poorly understood. This study aimed to determine how ABA pre-treatment at the booting stage influences physiological and molecular responses to drought at the heading stage in barley.

RESULTS

The ABA-treated plants exhibited earlier stomatal closure, increased expression of ABA-responsive genes (HvNCED1, HvBG8, and HvA22), and maintained higher chlorophyll levels under drought conditions. Photosynthetic parameters, including photosystem II activity, electron transport rate, and the number of active reaction centers, were preserved in ABA-pretreated plants compared with drought-only plants. Transcriptomic analysis revealed that ABA pre-treatment primed plants for faster activation of stress-responsive pathways, with enhanced expression of genes related to chromatin modifications, RNA metabolism, and ABA signaling during drought. Importantly, Alternative splicing (AS) and isoform switching were significantly amplified in ABA-pretreated plants, underscoring a unique molecular mechanism of ABA priming that enhances drought resilience. Post-stress recovery analysis revealed a greater number of differentially expressed genes (DEGs) and alternatively spliced transcripts (DAS) in ABA-pretreated plants, particularly those involved in chromatin organization and photosynthesis. Physiological analyses demonstrated that time- and dose-optimized ABA applications improved yield parameters, including grain weight and seed area, while mitigating spike sterility under drought conditions.

CONCLUSIONS

This study demonstrates that ABA pretreatment enhances drought resilience in barley by triggering early stomatal closure, preserving chlorophyll content, and maintaining photosynthetic performance under water stress. At the molecular level, ABA priming accelerates stress-response pathways, promoting alternative splicing, isoform switching, and chromatin modifications that enable transcriptome plasticity. These processes facilitate faster recovery and sustain critical yield components, such as spike number and grain weight, when ABA is applied at optimized timing and concentrations. While large-scale ABA application poses challenges, this study provides a framework for breeding and agronomic strategies to mimic ABA effects, offering a practical path to enhance drought tolerance and yield stability in barley.

MCTASmRNA: A deep learning framework for alternative splicing events classification

Alternative splicing (AS) plays crucial post-transcriptional gene function regulation roles in eukaryotic. Despite progress in studying AS at the RNA level, existing methods for AS event identification face challenges such as inefficiency, lengthy processing times, and limitations in capturing the complexity of RNA sequences. To overcome these challenges, we evaluated 10 AS detection tools and selected rMATS for dataset construction. We then developed a multi-scale convolutional and Transformer-based model (MCTASmRNA) to classify AS events in mRNA sequences without relying on a reference genome. To handle the problem of large intra-class and small inter-class difference in AS event sequences, we incorporated an efficient channel attention mechanism and designed a new joint loss function to optimize MCTASmRNA training. MCTASmRNA outperformed baseline models, with an accuracy improvement and exhibited enhanced cross-species generalizability. This model provides valuable support for AS research across different organisms. Future work will focus on optimizing and expanding the model to further explore the complex mechanisms underlying AS.

Deciphering the Vulnerability of Pollen to Heat Stress for Securing Crop Yields in a Warming Climate

Climate change is leading to more frequent and severe extreme temperature events, negatively impacting agricultural productivity and threatening global food security. Plant reproduction, the process fundamental to crop yield, is highly susceptible to heatwaves, which disrupt pollen development and ultimately affect seed-set and crop yields. Recent research has increasingly focused on understanding how pollen grains from various crops react to heat stress at the molecular and cellular levels. This surge in interest over the last decade has been driven by advances in genomic technologies, such as single-cell RNA sequencing, which holds significant potential for revealing the underlying regulatory reprogramming triggered by heat stress throughout the various stages of pollen development. This review focuses on how heat stress affects gene regulatory networks, including the heat stress response, the unfolded protein response, and autophagy, and discusses the impact of these changes on various stages of pollen development. It highlights the potential of pollen selection as a key strategy for improving heat tolerance in crops by leveraging the genetic variability among pollen grains. Additionally, genome-wide association studies and population screenings have shed light on the genetic underpinnings of traits in major crops that respond to high temperatures during male reproductive stages. Gene-editing tools like CRISPR/Cas systems could facilitate precise genetic modifications to boost pollen heat resilience. The information covered in this review is valuable for selecting traits and employing molecular genetic approaches to develop heat-tolerant genotypes.

The Arabidopsis thaliana core splicing factor PORCUPINE/SmE1 requires intron-mediated expression

Plants are prone to genome duplications and tend to preserve multiple gene copies. This is also the case for the genes encoding the Sm proteins of Arabidopsis thaliana (L). The Sm proteins are best known for their roles in RNA processing such as pre-mRNA splicing and nonsense-mediated mRNA decay. In this study, we have taken a closer look at the phylogeny and differential regulation of the SmE-coding genes found in A. thaliana, PCP/SmE1, best known for its cold-sensitive phenotype, and its paralog, PCPL/SmE2. The phylogeny of the PCP homologs in the green lineage shows that SmE duplications happened multiple times independently in different plant clades and that the duplication that gave rise to PCP and PCPL occurred only in the Brassicaceae family. Our analysis revealed that A. thaliana PCP and PCPL proteins, which only differ in two amino acids, exhibit a very high level of functional conservation and can perform the same function in the cell. However, our results indicate that PCP is the prevailing copy of the two SmE genes in A. thaliana as it is more highly expressed and that the main difference between PCP and PCPL resides in their transcriptional regulation, which is strongly linked to intronic sequences. Our results provide insight into the complex mechanisms that underlie the differentiation of the paralogous gene expression as an adaptation to stress.

Identification of pine SF3B1 protein and cross-species comparison highlight its conservation and biological significance in pre-mRNA splicing regulation

As a key component of the largest subunit of the splicing machinery, SF3B1 plays essential roles in eukaryotic growth and development. However, only a few studies have focused on the evolutionary features and functions of this protein in plants. In this study, with the assistance of a bioinformatic analysis, we determined the complete coding sequence of the gene encoding the pine SF3B1 protein using RT-PCR and DNA sequencing. The evolutionary features of SF3B1 proteins were further examined based on a phylogenetic tree of SF3B1 homologous proteins from different eukaryotes, along with comprehensive comparisons of their functional domains, conserved motifs, and cis-regulatory elements and the structures of the corresponding genes. Furthermore, the effects of the splicing modulator GEX1a on several plant species were analysed, confirming that the re-identified SF3B1, with a full-length HEAT repeat domain, is expressed and functions in pre-mRNA splicing regulation in pines. In summary, we conducted a systematic cross-species comparison of SF3B1 homologous proteins, with an emphasis on complete sequence determination and the functional confirmation of pine SF3B1, illustrating the conservation of homologous proteins in plants. This study provides a valuable reference for understanding functional and regulatory mechanisms, as well as the potential applications of SF3B1.

Regulation of alternative splicing by CBF-mediated protein condensation in plant response to cold stress

Cold acclimation is critical for the survival of plants in temperate regions under low temperatures, and C-REPEAT BINDING FACTORs (CBFs) are well established as key transcriptional factors that regulate this adaptive process by controlling the expression of cold-responsive genes. Here we demonstrate that CBFs are involved in modulating alternative splicing during cold acclimation through their interaction with subunits of the spliceosome complex. Under cold stress, CBF proteins accumulate and directly interact with SKI-INTERACTING PROTEIN (SKIP), a key component of the spliceosome, which positively regulates acquired freezing tolerance. This interaction facilitates the formation of SKIP nuclear condensates, which enhances the association between SKIP and specific cold-responsive transcripts, thereby increasing their splicing efficiency. Our findings uncover a regulatory role of CBFs in alternative splicing and highlight their pivotal involvement in the full development of cold acclimation, bridging transcriptional and post-transcriptional regulatory mechanisms.

A gene expression atlas of Nicotiana tabacum across various tissues at transcript resolution

Alternative splicing (AS) expands the transcriptome diversity by selectively splicing exons and introns from pre-mRNAs to generate different protein isoforms. This mechanism is widespread in eukaryotes and plays a crucial role in development, environmental adaptation, and stress resistance. In this study, we collected 599 tobacco RNA-seq datasets from 35 projects. 207,689 transcripts were identified in this study, of which 35,519 were annotated in the reference genome, while 172,170 transcripts were newly annotated. Additionally, tissue-specific analysis revealed 4,585 transcripts that were uniquely expressed in different tissues, highlighting the complexity and specialization of tobacco gene expression. The analysis of AS events (ASEs) across different tissues showed significant variability in the expression levels of ASE-derived transcripts, with some of these transcripts being associated with stress resistance, such as the geranyl diphosphate synthase (GGPPS). Moreover, we identified 21,763 splicing quantitative trait locus (sQTLs), which were enriched in genes involved in biological processes such as histone acetylation. Furthermore, sQTLs involved genes related to plant hormone signal transduction, terpenoid backbone biosynthesis, and other resistance pathways. These findings not only reveal the diversity of gene expression in tobacco but also provide new insights and strategies for improving tobacco quality and resistance.

Identification and characterization of the auxin-response factor family in moso bamboo reveals that PeARF41 negatively regulates second cell wall formation

Auxin response factors (ARFs) are key transcriptional factors mediating the transcriptional of auxin-related genes that play crucial roles in a range of plant metabolic activities. The characteristics of 47 PeARFs, identified in moso bamboo and divided into three classes, were evaluated. Structural feature analysis showed that intron numbers ranged from 3 to 14, while Motif 1, 2, 7 and 10 were highly conserved, altogether forming DNA-binding and ARF domains. Analysis of RNA-seq from different tissues revealed that PeARFs showed tissue-specificity. Additionally, abundant hormone-response and stress-related elements were enriched in promoters of PeARFs, supporting the hypothesis that the expression of PeARFs was significantly activated or inhibited by ABA and cold treatments. Further, PeARF41 overexpression inhibited SCW formation by reducing hemicellulose, cellulose and lignin contents. Moreover, a co-expression network, containing 28 genes with PeARF41 at its core was predicted, and the results of yeast one hybridization (Y1H), electrophoretic mobility shift assay (EMSA) and dual-luciferase (Dul-LUC) assays showed that PeARF41 bound the PeSME1 promoter to inhibit its expression. We conclude that a 'PeARF41-PeSME1' regulatory cascade mediates SCW formation. Our findings provided a solid theoretical foundation for further research on the role of PeARFs.

Cooperative condensation of RNA-DIRECTED DNA METHYLATION 16 splicing isoforms enhances heat tolerance in Arabidopsis

Dissecting the mechanisms underlying heat tolerance is important for understanding how plants acclimate to heat stress. Here, we identify a heat-responsive gene in Arabidopsis thaliana, RNA-DIRECTED DNA METHYLATION 16 (RDM16), which encodes a pre-mRNA splicing factor. Knockout mutants of RDM16 are hypersensitive to heat stress, which is associated with impaired splicing of the mRNAs of 18 out of 20 HEAT SHOCK TRANSCRIPTION FACTOR (HSF) genes. RDM16 forms condensates upon exposure to heat. The arginine residues in intrinsically disordered region 1 (IDR1) of RDM16 are responsible for RDM16 condensation and its function in heat stress tolerance. Notably, RDM16 produces two alternatively spliced transcripts designated RDM16-LONG (RDL) and RDM16-SHORT (RDS). RDS also forms condensates and can promote RDL condensation to improve heat tolerance. Our findings provide insight into the cooperative condensation of the two RDM16 isoforms encoded by RDM16 splice variants in enhancing heat tolerance in Arabidopsis.

ZmHSFA2B self-regulatory loop is critical for heat tolerance in maize

The growth and development of maize (Zea mays L.) are significantly impeded by prolonged exposure to high temperatures. Heat stress transcription factors (HSFs) play crucial roles in enabling plants to detect and respond to elevated temperatures. However, the genetic mechanisms underlying the responses of HSFs to heat stress in maize remain unclear. Thus, we aimed to investigate the role of ZmHSFA2B in regulating heat tolerance in maize. Here, we report that ZmHSFA2B has two splicing variants, ZmHSFA2B-I and ZmHSFA2B-II. ZmHSFA2B-I encodes full-length ZmHSFA2B (ZmHSFA2B-I), whereas ZmHSFA2B-II encodes a truncated ZmHSFA2B (ZmHSFA2B-II). Overexpression of ZmHSFA2B-I improved heat tolerance in maize and Arabidopsis thaliana, but it also resulted in growth retardation as a side effect. RNA-sequencing and CUT&Tag analyses identified ZmMBR1 as a putative target of ZmHSFA2B-I. Overexpression of ZmMBR1 also enhanced heat tolerance in Arabidopsis. ZmHSFA2B-II was primarily synthesized in response to heat stress and competitively interacted with ZmHSFA2B-I. This interaction consequently reduced the DNA-binding activities of ZmHSFA2B-I homodimers to the promoter of ZmMBR1. Subsequent investigations indicate that ZmHSFA2B-II limits the transactivation and tempers the function of ZmHSFA2B-I, thereby reducing the adverse effects of excessive ZmHSFA2B-I accumulation. Based on these observations, we propose that the alternative splicing of ZmHSFA2B generates a self-regulatory loop that fine-tunes heat stress response in maize.

Transcriptomic profiling reveals distinct responses to beet curly top virus (BCTV) infection in resistant and susceptible sugar beet genotypes

BACKGROUND

Sugar beets (Beta vulgaris L.) are grown worldwide and suffer economic loss annually due to curly top disease caused by the beet curly top virus (BCTV). The virus is spread by the beet leafhopper (BLH), Circulifer tenellus Baker. Current management strategies rely on chemical control and planting BCTV-resistant sugar beet genotypes. However, the genetic mechanism underlying BCTV resistance in sugar beet is unknown. This study aimed to determine these mechanisms by comparing a resistant (EL10) and susceptible (FC709-2) sugar beet genotype using host plant suitability (no-choice), host preference (choice) assays, and transcriptomic analysis.

RESULTS

Host plant suitability assays revealed no significant differences in adult survival or nymph production between viruliferous and non-viruliferous BLH on either genotype, suggesting that BCTV resistance is not directly associated with reduced beet leafhopper fitness. However, host preference assays showed that viruliferous BLH preferred settling on the susceptible genotype, FC709-2, compared to the resistant genotype, EL10 whereas the non-viruliferous BLH showed no preference. RNA-sequencing analysis of BCTV-inoculated (viruliferous BLH-fed) and mock-inoculated (non-viruliferous BLH-fed) plants at day 1, 7, or 14 post-inoculations highlighted dynamic and contrasting responses between the two genotypes. The resistant genotype had differentially expressed transcripts (DETs) associated with jasmonic acid and abscisic acid biosynthesis and signaling. DETs associated with stress mitigation mechanisms and reduction in plant primary metabolic processes were also observed. In contrast, the susceptible genotype had DETs associated with opposing phytohormones like salicylic acid and auxin. Moreover, this genotype exhibited an upregulation in DETs involved in volatile organic compounds (VOCs) production and increased primary plant metabolic processes.

CONCLUSIONS

These results provide novel insight into the opposing transcriptional responses underlying BCTV resistance and susceptibility in sugar beet. Understanding and classifying the mechanisms of resistance or susceptibility to BCTV infection in sugar beet is beneficial to researchers and plant breeders as it provides a basis for further exploration of the host plant-virus-vector interactions.

Pathogen-responsive alternative splicing in plant immunity

Plant immunity involves a complex and finely tuned response to a wide variety of pathogens. Alternative splicing, a post-transcriptional mechanism that generates multiple transcripts from a single gene, enhances both the versatility and effectiveness of the plant immune system. Pathogen infection induces alternative splicing in numerous plant genes involved in the two primary layers of pathogen recognition: pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). However, the mechanisms underlying pathogen-responsive alternative splicing are just beginning to be understood. In this article, we review recent findings demonstrating that the interaction between pathogen elicitors and plant receptors modulates the phosphorylation status of splicing factors, altering their function, and that pathogen effectors target components of the host spliceosome, controlling the splicing of plant immunity-related genes.

The Arabidopsis splicing factor PORCUPINE/SmE1 orchestrates temperature-dependent root development via auxin homeostasis maintenance

Appropriate abiotic stress response is pivotal for plant survival and makes use of multiple signaling molecules and phytohormones to achieve specific and fast molecular adjustments. A multitude of studies has highlighted the role of alternative splicing in response to abiotic stress, including temperature, emphasizing the role of transcriptional regulation for stress response. Here we investigated the role of the core-splicing factor PORCUPINE (PCP) on temperature-dependent root development. We used marker lines and transcriptomic analyses to study the expression profiles of meristematic regulators and mitotic markers, and chemical treatments, as well as root hormone profiling to assess the effect of auxin signaling. The loss of PCP significantly alters RAM architecture in a temperature-dependent manner. Our results indicate that PCP modulates the expression of central meristematic regulators and is required to maintain appropriate levels of auxin in the RAM. We conclude that alternative pre-mRNA splicing is sensitive to moderate temperature fluctuations and contributes to root meristem maintenance, possibly through the regulation of phytohormone homeostasis and meristematic activity.

SCI1, a flower regulator of cell proliferation, and its partners NtCDKG2 and NtRH35 interact with the splicing machinery

Successful plant reproduction depends on the adequate development of floral organs controlled by cell proliferation and other processes. The Stigma/style cell-cycle inhibitor 1 (SCI1) gene regulates cell proliferation and affects the final size of the female reproductive organ. To unravel the molecular mechanism exerted by Nicotiana tabacum SCI1 in cell proliferation control, we searched for its interaction partners through semi-in vivo pull-down experiments, uncovering a cyclin-dependent kinase, NtCDKG;2. Bimolecular fluorescence complementation and co-localization experiments showed that SCI1 interacts with NtCDKG;2 and its cognate NtCyclin L in nucleoli and splicing speckles. The screening of a yeast two-hybrid cDNA library using SCI1 as bait revealed a novel DEAD-box RNA helicase (NtRH35). Interaction between the NtCDKG;2-NtCyclin L complex and NtRH35 is also shown. Subcellular localization experiments showed that SCI1, NtRH35, and the NtCDKG;2-NtCyclin L complex associate with each other within splicing speckles. The yeast two-hybrid screening of NtCDKG;2 and NtRH35 identified the conserved spliceosome components U2a', NF-κB activating protein (NKAP), and CACTIN. This work presents SCI1 and its interactors, the NtCDKG;2-NtCyclin L complex and NtRH35, as new spliceosome-associated proteins. Our findings reveal a network of interactions and indicate that SCI1 may regulate cell proliferation through the splicing process, providing new insights into the intricate molecular pathways governing plant development.

Comparative transcriptomic analyses of diploid and tetraploid citrus reveal how ploidy level influences salt stress tolerance

Introduction

Citrus is an important fruit crop for human health. The sensitivity of citrus trees to a wide range of abiotic stresses is a major challenge for their overall growth and productivity. Among these abiotic stresses, salinity results in a significant loss of global citrus yield. In order to find straightforward and sustainable solutions for the future and to ensure citrus productivity, it is of paramount importance to decipher the mechanisms responsible for salinity stress tolerance. Thisstudy aimed to investigate how ploidy levels influence salt stress tolerance in citrus by comparing the transcriptomic responses of diploid and tetraploid genotypes. In a previous article we investigated the physiological and biochemical response of four genotypes with different ploidy levels: diploid trifoliate orange (Poncirus trifoliata [L.] Raf.) (PO2x) and Cleopatra mandarin (Citrus reshni Hort. Ex Tan.) (CL2x) and their respective tetraploids (PO4x, CL4x).

Methods

In this study, we useda multifactorial gene selection and gene clustering approach to finely dissect the influence of ploidy level on the salt stress response of each genotype. Following transcriptome sequencing, differentially expressed genes (DEGs) were identified in response to salt stress in leaves and roots of the different citrus genotypes.

Result and discussion

Gene expression profiles and functional characterization of genes involved in the response to salt stress, as a function of ploidy level and the interaction between stress response and ploidy level, have enabled us to highlight the mechanisms involved in the varieties tested. Saltstress induced overexpression of carbohydrate biosynthesis and cell wall remodelling- related genes specifically in CL4x Ploidy level enhanced oxidative stress response in PO and ion management capacity in both genotypes. Results further highlighted that under stress conditions, only the CL4x genotype up- regulated genes involved in sugar biosynthesis, transport management, cell wall remodelling, hormone signalling, enzyme regulation and antioxidant metabolism. These findings provide crucial insights that could inform breeding strategies for developing salt-tolerant citrus varieties.

Full-Length Transcriptome Profile of Apis cerana Revealed by Nanopore Sequencing

The Asian honey bee (Apis cerana) plays a crucial role in providing abundant bee products and in maintaining ecological balance. Despite the availability of the genomic sequence of the Asian honey bee, its transcriptomic information remains largely incomplete. To address this issue, here we constructed three pooled RNA samples from the queen, drone, and worker bees of A. cerana and performed full-length RNA sequencing using Nanopore single-molecule sequencing technology. Ultimately, we obtained 160,811 full-length transcript sequences from 19,859 genes, with 141,189 being novel transcripts, of which 130,367 were functionally annotated. We detected 520, 324, and 1823 specifically expressed transcripts in the queen, worker, and drone bees, respectively. Furthermore, we identified 38,799 alternative splicing (AS) events from 5710 genes, 44,243 alternative polyadenylation (APA) sites from 1649 gene loci, 88,187 simple sequence repeats (SSRs), and 17,387 long noncoding RNAs (lncRNAs). Leveraging these transcripts as references, we identified 6672, 7795, and 6804 differentially expressed transcripts (DETs) in comparisons of queen ovaries vs drone testes, worker ovaries vs drone testes, and worker ovaries vs queen ovaries, respectively. Our research results provide a comprehensive set of reference transcript datasets for Apis cerana, offering important sequence information for further exploration of its gene functions.

Population-level exploration of alternative splicing and its unique role in controlling agronomic traits of rice

Alternative splicing (AS) plays crucial roles in regulating various biological processes in plants. However, the genetic mechanisms underlying AS and its role in controlling important agronomic traits in rice (Oryza sativa) remain poorly understood. In this study, we explored AS in rice leaves and panicles using the rice minicore collection. Our analysis revealed a high level of transcript isoform diversity, with approximately one-fifth of the potential isoforms acting as major transcripts in both tissues. Regarding the genetic mechanism of AS, we found that the splicing of 833 genes in the leaf and 1,230 genes in the panicle was affected by cis-genetic variation. Twenty-one percent of these AS events could only be explained by large structural variations. Approximately 77.5% of genes with significant splicing quantitative trait loci (sGenes) exhibited tissue-specific regulation, and AS can cause 26.9% (leaf) and 23.6% (panicle) of sGenes to have altered, lost, or gained functional domains. Additionally, through splicing-phenotype association analysis, we identified phosphate-starvation-induced RING-type E3 ligase (OsPIE1; LOC_Os01g72480), whose splicing ratio was significantly associated with plant height. In summary, this study provides an understanding of AS in rice and its contribution to the regulation of important agronomic traits.

Genome-wide identification and gene expression networks of LBD transcription factors in Populus trichocarpa

The Lateral Organ Boundaries Domain (LBD) proteins, an exclusive family of transcription factors (TFs) found solely in plants, play pivotal roles in lateral organogenesis, stress adaptation, secondary growth, and hormonal signaling responses. In this study, a total of 55 PtLBD TFs from Populus trichocarpa were identified and systematically classified into two subfamilies, designated as subfamily-I and subfamily-II with seven distinct groups based on phylogenetic analysis. Gene structure detection indicated that the difference of phase numbers linking adjacent exons contribute to the variations in splicing patterns among different PtLBD groups. Numerous transcription factor binding sites and cis-elements pertinent to hormone signaling pathways and stress response mechanisms were identified within the upstream promoter regions of the PtLBD genes. Thirty-five PtLBDs were found to be engaged in either tandem or segmental duplications, and genomic collinearity analysis revealed a stronger alignment between PtLBD genes and eudicots plants compared to their relationship with monocots. GO enrichment and temporal-spatio expression patterns showed that PtLBD7 from subfamily-I and PtLBD20 from subfamily-II, along with other 13 PtLBDs, were involved in plant growth and development biological processes. The multilayered hierarchical gene networks (ML-hGRN) mediated by PtLBD7 and PtLBD20 indicated that PtLBDs were mainly function in poplar growth and stress tolerance through a multifaceted and intricate regulatory machinery. This study lays a solid groundwork for delving deeper into the roles and underlying mechanisms of LBD transcription factors in poplar, specifically those related to plant hormones and stress tolerance.

The U1 small nuclear RNA enhances drought tolerance in Arabidopsis

Alternative splicing (AS) is an important posttranscriptional regulatory mechanism that improves plant tolerance to drought stress by modulating gene expression and generating proteome diversity. The interaction between the 5' end of U1 small nuclear RNA (U1 snRNA) and the conserved 5' splice site of precursor messenger RNA (pre-mRNA) is pivotal for U1 snRNP involvement in AS. However, the roles of U1 snRNA in drought stress responses remain unclear. This study provides a comprehensive analysis of AtU1 snRNA in Arabidopsis (Arabidopsis thaliana), revealing its high conservation at the 5' end and a distinctive four-leaf clover structure. AtU1 snRNA is localized in the nucleus and expressed in various tissues, with prominent expression in young floral buds, flowers, and siliques. The overexpression of AtU1 snRNA confers enhanced abiotic stress tolerance, as evidenced in seedlings by longer seedling primary root length, increased fresh weight, and a higher greening rate compared with the wild-type. Mature AtU1 snRNA overexpressor plants exhibit higher survival rates and lower water loss rates under drought stress, accompanied by a significant decrease in H2O2 and an increase in proline. This study also provides evidence of altered expression levels of drought-related genes in AtU1 snRNA overexpressor or genome-edited lines, reinforcing the crucial role of AtU1 snRNA in drought stress responses. Furthermore, the overexpression of AtU1 snRNA influences the splicing of downstream target genes, with a notable impact on SPEECHLESS (SPCH), a gene associated with stomatal development, potentially explaining the observed decrease in stomatal aperture and density. These findings elucidate the critical role of U1 snRNA as an AS regulator in enhancing drought stress tolerance in plants, contributing to a deeper understanding of the AS pathway in drought tolerance and increasing awareness of the molecular network governing drought tolerance in plants.

Rare occurrence of cryptic 5' splice sites by downstream 3' splice site/exon boundary mutations in a heavy-ion-induced egy1-4 allele of Arabidopsis thaliana

Pre-mRNA splicing is a fundamental process in eukaryotic gene expression, and the mechanism of intron definition, involving the recognition of the canonical GU (5'-splice site) and AG (3'-splice site) dinucleotides by splicing factors, has been postulated for most cases of splicing initiation in plants. Splice site mutations have played crucial roles in unraveling the mechanism of pre-mRNA splicing in planta. Typically, splice site mutations abolish splicing events or activate one or more cryptic splice sites surrounding the mutated region. In this report, we investigated the splicing pattern of the EGY1 gene in an Ar-ion-induced egy1-4 allele of Arabidopsis thaliana. egy1-4 has an AG-to-AC mutation in the 3'-end of intron 3, along with 4-bp substitutions and a 5-bp deletion in adjacent exon 4. RT-PCR, cDNA cloning, and amplicon sequencing analyses of EGY1 revealed that while most wild-type EGY1 mRNAs had a single splicing pattern, egy1-4 mRNAs had multiple splicing defects. Almost half of EGY1 transcripts showed 'intron retention' at intron 3, while the other half exhibited activation of 3' cryptic splice sites either upstream or downstream of the original 3'-splice site. Unexpectedly, around 8% of EGY1 transcripts in egy1-4 exhibited activation of cryptic 5'-splice sites positioned upstream of the authentic 5'-splice site of intron 3. Whole genome resequencing of egy1-4 indicated that it has no other known impactful mutations. These results may provide a rare, but real case of activation of cryptic 5'-splice sites by downstream 3'-splice site/exon mutations in planta.

Integrative analyses of long and short-read RNA sequencing reveal the spliced isoform regulatory network of seedling growth dynamics in upland cotton

The polyploid genome of cotton has significantly increased the transcript complexity. Recent advances in full-length transcript sequencing are now widely used to characterize the complete landscape of transcriptional events. Such studies in cotton can help us to explore the genetic mechanisms of the cotton seedling growth. Through long-read single-molecule RNA sequencing, this study compared the transcriptomes of three yield contrasting genotypes of upland cotton. Our analysis identified different numbers of spliced isoforms from 31,166, 28,716, and 28,713 genes in SJ48, Z98, and DT8 cotton genotypes, respectively, most of which were novel compared to previous cotton reference transcriptomes, and showed significant differences in the number of exon structures and coding sequence length due to intron retention. Quantification of isoform expression revealed significant differences in expression in the root and leaf of each genotype. An array of key isoform target genes showed protein kinase or phosphorylation functions, and their protein interaction network contained most of the circadian oscillator proteins. Spliced isoforms from the GIGANTEA (GI) protien were differentially regulated in each genotype and might be expected to regulate translational activities, including the sequence and function of target proteins. In addition, these spliced isoforms generate diurnal expression profiles in cotton leaves, which may alter the transcriptional regulatory network of seedling growth. Silencing of the novel spliced GI isoform Gh_A02G0645_N17 significantly affected biomass traits, contributed to variable growth, and increased transcription of the early flowering pathway gene ELF in cotton. Our high-throughput hybrid sequencing results will be useful to dissect functional differences among spliced isoforms in the polyploid cotton genome.

RNA splicing modulates the postharvest physiological deterioration of cassava storage root

Rapid postharvest physiological deterioration (PPD) of cassava (Manihot esculenta Crantz) storage roots is a major constraint that limits the potential of this plant as a food and industrial crop. Extensive studies have been performed to explore the regulatory mechanisms underlying the PPD processes in cassava to understand their molecular and physiological responses. However, the exceptional functional versatility of alternative splicing (AS) remains to be explored during the PPD process in cassava. Here, we identified several aberrantly spliced genes during the early PPD stage. An in-depth analysis of AS revealed that the abscisic acid (ABA) biosynthesis pathway might serve as an additional molecular layer in attenuating the onset of PPD. Exogenous ABA application alleviated PPD symptoms through maintaining ROS generation and scavenging. Interestingly, the intron retention transcript of MeABA1 (ABA DEFICIENT 1) was highly correlated with PPD symptoms in cassava storage roots. RNA yeast 3-hybrid and RNA immunoprecipitation (RIP) assays showed that the serine/arginine-rich protein MeSCL33 (SC35-like splicing factor 33) binds to the precursor mRNA of MeABA1. Importantly, overexpressing MeSCL33 in cassava conferred improved PPD resistance by manipulating the AS and expression levels of MeABA1 and then modulating the endogenous ABA levels in cassava storage roots. Our results uncovered the pivotal role of the ABA biosynthesis pathway and RNA splicing in regulating cassava PPD resistance and proposed the essential roles of MeSCL33 for conferring PPD resistance, broadening our understanding of SR proteins in cassava development and stress responses.

Alternative splicing regulation in plants by SP7-like effectors from symbiotic arbuscular mycorrhizal fungi

Most plants in natural ecosystems associate with arbuscular mycorrhizal (AM) fungi to survive soil nutrient limitations. To engage in symbiosis, AM fungi secrete effector molecules that, similar to pathogenic effectors, reprogram plant cells. Here we show that the Glomeromycotina-specific SP7 effector family impacts on the alternative splicing program of their hosts. SP7-like effectors localize at nuclear condensates and interact with the plant mRNA processing machinery, most prominently with the splicing factor SR45 and the core splicing proteins U1-70K and U2AF35. Ectopic expression of these effectors in the crop plant potato and in Arabidopsis induced developmental changes that paralleled to the alternative splicing modulation of a specific subset of genes. We propose that SP7-like proteins act as negative regulators of SR45 to modulate the fate of specific mRNAs in arbuscule-containing cells. Unraveling the communication mechanisms between symbiotic fungi and their host plants will help to identify targets to improve plant nutrition.

The overlooked manipulation of nucleolar functions by plant pathogen effectors

Pathogens need to manipulate plant functions to facilitate the invasion of their hosts. They do this by secreting a cocktail of molecules called effectors. Studies of these molecules have mostly focused on the mechanisms underlying their recognition and the subsequent transcriptional reprogramming of cells, particularly in the case of R gene-dependent resistance. However, the roles of these effectors are complex, as they target all cell compartments and their plant targets remain largely uncharacterized. An understanding of the mechanisms involved would be a considerable asset for plant breeding. The nucleolus is the site of many key cellular functions, such as ribosome biogenesis, cellular stress regulation and many other functions that could be targets for pathogenicity. However, little attention has been paid to effectors targeting nucleolar functions. In this review, we aim to fill this gap by providing recent findings on pathogen effectors that target and manipulate nucleolar functions and dynamics to promote infection. In particular, we look at how some effectors hijack ribosome biogenesis, the modulation of transcription or alternative splicing, all key functions occurring at least partially in the nucleolus. By shedding light on the role of the plant nucleolus in pathogen interactions, this review highlights the importance of understanding nucleolar biology in the context of plant immunity and the mechanisms manipulated by plant pathogens.

Relevance and regulation of alternative splicing in plant secondary metabolism: current understanding and future directions

The secondary metabolism of plants is an essential life process enabling organisms to navigate various stages of plant development and cope with ever-changing environmental stresses. Secondary metabolites, abundantly found in nature, possess significant medicinal value. Among the regulatory mechanisms governing these metabolic processes, alternative splicing stands out as a widely observed post-transcriptional mechanism present in multicellular organisms. It facilitates the generation of multiple mRNA transcripts from a single gene by selecting different splicing sites. Selective splicing events in plants are widely induced by various signals, including external environmental stress and hormone signals. These events ultimately regulate the secondary metabolic processes and the accumulation of essential secondary metabolites in plants by influencing the synthesis of primary metabolites, hormone metabolism, biomass accumulation, and capillary density. Simultaneously, alternative splicing plays a crucial role in enhancing protein diversity and the abundance of the transcriptome. This paper provides a summary of the factors inducing alternative splicing events in plants and systematically describes the progress in regulating alternative splicing with respect to different secondary metabolites, including terpenoid, phenolic compounds, and nitrogen-containing compounds. Such elucidation offers critical foundational insights for understanding the role of alternative splicing in regulating plant metabolism and presents novel avenues and perspectives for bioengineering.

Genome-Wide Identification and Characterization of U-Box Gene Family Members and Analysis of Their Expression Patterns in Phaseolus vulgaris L. under Cold Stress

The common bean (Phaseolus vulgaris L.) is an economically important food crop grown worldwide; however, its production is affected by various environmental stresses, including cold, heat, and drought stress. The plant U-box (PUB) protein family participates in various biological processes and stress responses, but the gene function and expression patterns of its members in the common bean remain unclear. Here, we systematically identified 63 U-box genes, including 8 tandem genes and 55 non-tandem genes, in the common bean. These PvPUB genes were unevenly distributed across 11 chromosomes, with chromosome 2 holding the most members of the PUB family, containing 10 PUB genes. The analysis of the phylogenetic tree classified the 63 PUB genes into three groups. Moreover, transcriptome analysis based on cold-tolerant and cold-sensitive varieties identified 4 differentially expressed PvPUB genes, suggesting their roles in cold tolerance. Taken together, this study serves as a valuable resource for exploring the functional aspects of the common bean U-box gene family and offers crucial theoretical support for the development of new cold-tolerant common bean varieties.

AtSNU13 modulates pre-mRNA splicing of RBOHD and ALD1 to regulate plant immunity

Pre-mRNA splicing is a significant step for post-transcriptional modifications and functions in a wide range of physiological processes in plants. Human NHP2L binds to U4 snRNA during spliceosome assembly; it is involved in RNA splicing and mediates the development of human tumors. However, no ortholog has yet been identified in plants. Therefore, we report At4g12600 encoding the ortholog NHP2L protein, and AtSNU13 associates with the component of the spliceosome complex; the atsnu13 mutant showed compromised resistance in disease resistance, indicating that AtSNU13 is a positive regulator of plant immunity. Compared to wild-type plants, the atsnu13 mutation resulted in altered splicing patterns for defense-related genes and decreased expression of defense-related genes, such as RBOHD and ALD1. Further investigation shows that AtSNU13 promotes the interaction between U4/U6.U5 tri-snRNP-specific 27 K and the motif in target mRNAs to regulate the RNA splicing. Our study highlights the role of AtSNU13 in regulating plant immunity by affecting the pre-mRNA splicing of defense-related genes.

A foundational large language model for edible plant genomes

Significant progress has been made in the field of plant genomics, as demonstrated by the increased use of high-throughput methodologies that enable the characterization of multiple genome-wide molecular phenotypes. These findings have provided valuable insights into plant traits and their underlying genetic mechanisms, particularly in model plant species. Nonetheless, effectively leveraging them to make accurate predictions represents a critical step in crop genomic improvement. We present AgroNT, a foundational large language model trained on genomes from 48 plant species with a predominant focus on crop species. We show that AgroNT can obtain state-of-the-art predictions for regulatory annotations, promoter/terminator strength, tissue-specific gene expression, and prioritize functional variants. We conduct a large-scale in silico saturation mutagenesis analysis on cassava to evaluate the regulatory impact of over 10 million mutations and provide their predicted effects as a resource for variant characterization. Finally, we propose the use of the diverse datasets compiled here as the Plants Genomic Benchmark (PGB), providing a comprehensive benchmark for deep learning-based methods in plant genomic research. The pre-trained AgroNT model is publicly available on HuggingFace at https://huggingface.co/InstaDeepAI/agro-nucleotide-transformer-1b  for future research purposes.

An alternative 3' splice site of PeuHKT1;3 improves the response to salt stress through enhancing affinity to K+ in Populus

Alternative splicing (AS) serves as a crucial post-transcriptional regulator in plants that contributes to the resistance to salt stress. However, the underlying mechanism is largely unknown. In this research, we identified an important AS transcript in Populus euphratica, PeuHKT1:3a, generated by alternative 3' splice site splicing mode that resulted in the removal of 252 bases at the 5' end of the first exon in PeuHKT1:3. Protein sequence comparison showed that the site of AS occurred in PeuHKT1:3 is located at a crucial Ser residue within the first pore-loop domain, which leads to inefficient K+ transport in HKT I-type transporters. Expressing PeuHKT1;3a in an axt3 mutant yeast strain can effectively compensate for the lack of intracellular K+, whereas the expression of PeuHKT1;3 cannot yield the effect. Furthermore, in transgenic Arabidopsis and poplar plants, it was observed that lines expressing PeuHKT1;3a exhibited greater salt tolerance compared to those expressing the PeuHKT1;3 strain. Analysis of ion content and flux demonstrated that the transgenic PeuHKT1;3a line exhibited significantly higher K+ content compared to the PeuHKT1;3 line, while there was no significant difference in Na+ content. In conclusion, our findings revealed that AS can give rise to novel variants of HKT I-type proteins in P. euphratica with modified K+ selectivity to keep a higher K+/Na+ ratio to enhanced salt tolerance.

Positioning of pyrimidine motifs around cassette exons defines their PTB-dependent splicing in Arabidopsis

Alternative splicing (AS) is a complex process that generates transcript variants from a single pre-mRNA and is involved in numerous biological functions. Many RNA-binding proteins are known to regulate AS; however, little is known about the underlying mechanisms, especially outside the mammalian clade. Here, we show that polypyrimidine tract binding proteins (PTBs) from Arabidopsis thaliana regulate AS of cassette exons via pyrimidine (Py)-rich motifs close to the alternative splice sites. Mutational studies on three PTB-dependent cassette exon events revealed that only some of the Py motifs in this region are critical for AS. Moreover, in vitro binding of PTBs did not reflect a motif's impact on AS in vivo. Our mutational studies and bioinformatic investigation of all known PTB-regulated cassette exons from A. thaliana and human suggested that the binding position of PTBs relative to a cassette exon defines whether its inclusion or skipping is induced. Accordingly, exon skipping is associated with a higher frequency of Py stretches within the cassette exon, and in human also upstream of it, whereas exon inclusion is characterized by increased Py motif occurrence downstream of said exon. Enrichment of Py motifs downstream of PTB-activated 5' splice sites is also seen for PTB-dependent intron removal and alternative 5' splice site events from A. thaliana, suggesting this is a common step of exon definition. In conclusion, the position-dependent AS regulatory mechanism by PTB homologs has been conserved during the separate evolution of plants and mammals, while other critical features, in particular intron length, have considerably changed.

Alternative Splicing Underpins the ALMT9 Transporter Function for Vacuolar Malic Acid Accumulation in Apple

Vacuolar malic acid accumulation largely determines fruit acidity, a key trait for the taste and flavor of apple and other fleshy fruits. Aluminum-activated malate transporter 9 (ALMT9/Ma1) underlies a major genetic locus, Ma, for fruit acidity in apple, but how the protein transports malate across the tonoplast is unclear. Here, it is shown that overexpression of the coding sequence of Ma1 (Ma1α) drastically decreases fruit acidity in "Royal Gala" apple, leading to uncovering alternative splicing underpins Ma1's function. Alternative splicing generates two isoforms: Ma1β is 68 amino acids shorter with much lower expression than the full-length protein Ma1α. Ma1β does not transport malate itself but interacts with the functional Ma1α to form heterodimers, creating synergy with Ma1α for malate transport in a threshold manner (When Ma1β/Ma1α ≥ 1/8). Overexpression of Ma1α triggers feedback inhibition on the native Ma1 expression via transcription factor MYB73, decreasing the Ma1β level well below the threshold that leads to significant reductions in Ma1 function and malic acid accumulation in fruit. Overexpression of Ma1α and Ma1β or genomic Ma1 increases both isoforms proportionally and enhances fruit malic acid accumulation. These findings reveal an essential role of alternative splicing in ALMT9-mediated malate transport underlying apple fruit acidity.

Arginine methylation of SM-LIKE PROTEIN 4 antagonistically affects alternative splicing during Arabidopsis stress responses

Arabidopsis (Arabidopsis thaliana) PROTEIN ARGININE METHYLTRANSFERASE5 (PRMT5) post-translationally modifies RNA-binding proteins by arginine (R) methylation. However, the impact of this modification on the regulation of RNA processing is largely unknown. We used the spliceosome component, SM-LIKE PROTEIN 4 (LSM4), as a paradigm to study the role of R-methylation in RNA processing. We found that LSM4 regulates alternative splicing (AS) of a suite of its in vivo targets identified here. The lsm4 and prmt5 mutants show a considerable overlap of genes with altered AS raising the possibility that splicing of those genes could be regulated by PRMT5-dependent LSM4 methylation. Indeed, LSM4 methylation impacts AS, particularly of genes linked with stress response. Wild-type LSM4 and an unmethylable version complement the lsm4-1 mutant, suggesting that methylation is not critical for growth in normal environments. However, LSM4 methylation increases with abscisic acid and is necessary for plants to grow under abiotic stress. Conversely, bacterial infection reduces LSM4 methylation, and plants that express unmethylable-LSM4 are more resistant to Pseudomonas than those expressing wild-type LSM4. This tolerance correlates with decreased intron retention of immune-response genes upon infection. Taken together, this provides direct evidence that R-methylation adjusts LSM4 function on pre-mRNA splicing in an antagonistic manner in response to biotic and abiotic stress.

High Overexpression of SiAAP9 Leads to Growth Inhibition and Protein Ectopic Localization in Transgenic Arabidopsis

Amino acid permeases (AAPs) transporters are crucial for the long-distance transport of amino acids in plants, from source to sink. While Arabidopsis and rice have been extensively studied, research on foxtail millet is limited. This study identified two transcripts of SiAAP9, both of which were induced by NO3- and showed similar expression patterns. The overexpression of SiAAP9L and SiAAP9S in Arabidopsis inhibited plant growth and seed size, although SiAAP9 was found to transport more amino acids into seeds. Furthermore, SiAAP9-OX transgenic Arabidopsis showed increased tolerance to high concentrations of glutamate (Glu) and histidine (His). The high overexpression level of SiAAP9 suggested its protein was not only located on the plasma membrane but potentially on other organelles, as well. Interestingly, sequence deletion reduced SiAAP9's sensitivity to Brefeldin A (BFA), and SiAAP9 had ectopic localization on the endoplasmic reticulum (ER). Protoplast amino acid uptake experiments indicated that SiAAP9 enhanced Glu transport into foxtail millet cells. Overall, the two transcripts of SiAAP9 have similar functions, but SiAAP9L shows a higher colocalization with BFA compartments compared to SiAAP9S. Our research identifies a potential candidate gene for enhancing the nutritional quality of foxtail millet through breeding.

Molecular Mechanism of Resistance to Alternaria alternata Apple Pathotype in Apple by Alternative Splicing of Transcription Factor MdMYB6-like

As a fruit tree with great economic value, apple is widely cultivated in China. However, apple leaf spot disease causes significant damage to apple quality and economic value. In our study, we found that MdMYB6-like is a transcription factor without auto-activation activity and with three alternative spliced variants. Among them, MdMYB6-like-β responded positively to the pathogen infection. Overexpression of MdMYB6-like-β increased the lignin content of leaves and improved the pathogenic resistance of apple flesh callus. In addition, all three alternative spliced variants of MdMYB6-like could bind to the promoter of MdBGLU H. Therefore, we believe that MdMYB6-like plays an important role in the infection process of the pathogen and lays a solid foundation for breeding disease-resistant cultivars of apple in the future.

The landscape of abiotic and biotic stress-responsive splice variants with deep RNA-seq datasets in hot pepper

Alternative splicing (AS) is a widely observed phenomenon in eukaryotes that plays a critical role in development and stress responses. In plants, the large number of RNA-seq datasets in response to different environmental stressors can provide clues for identification of condition-specific and/or common AS variants for preferred agronomic traits. We report RNA-seq datasets (350.7 Gb) from Capsicum annuum inoculated with one of three bacteria, one virus, or one oomycete and obtained additional existing transcriptome datasets. In this study, we investigated the landscape of AS in response to environmental stressors, signaling molecules, and tissues from 425 total samples comprising 841.49 Gb. In addition, we identified genes that undergo AS under specific and shared stress conditions to obtain potential genes that may be involved in enhancing tolerance to stressors. We uncovered 1,642,007 AS events and identified 4,354 differential alternative splicing genes related to environmental stressors, tissues, and signaling molecules. This information and approach provide useful data for basic-research focused on enhancing tolerance to environmental stressors in hot pepper or establishing breeding programs.

Alternative splicing patterns of hnrnp genes in gill tissues of rainbow trout (Oncorhynchus mykiss) during salinity changes

Alternative splicing (AS) plays an important role in various physiological processes in eukaryotes, such as the stress response. However, patterns of AS events remain largely unexplored during salinity acclimation in fishes. In this study, we conducted AS analysis using RNA-seq datasets to explore splicing patterns in the gill tissues of rainbow trout exposed to altered salinity environments, ranging from 0 ‰ (T0) to 30 ‰ (T30). The results revealed 1441, 351, 483, 1051 and 1049 differentially alternatively spliced (DAS) events in 5 pairwise comparisons, including T6 vs. T0, T12 vs. T0, T18 vs. T0, T24 vs. T0, and T30 vs. T0, respectively. These DAS events were derived from 1290, 328, 444, 963 and 948 genes. Enrichment analysis indicated that these DAS genes were related to RNA splicing and processing. Among these, 14 DAS genes were identified as members of the large heterogeneous nuclear RNP (hnRNP) gene family. Alternative 3' splice site (A3SS), exon skipping (SE) and intron retention (RI) events resulted in the fragmentation or even loss of the functional RNA recognition motif (RRM) domains in hnrnpa0, hnrnp1a, hnrnp1b and hnrnpc genes. The incomplete RRM domains would hinder the interactions between hnRNP genes and pre-mRNAs. It would in turn influence the splicing patterns and mRNA stability of downstream target genes in response to salinity changes. The study provides insights into salinity acclimation in gill tissues of rainbow trout and serves as a significant reference on the osmoregulation mechanisms at post-transcription regulation levels in fish.

Integrated analysis of transcriptome and small RNAome reveals regulatory network of rapid and long-term response to heat stress in Rhododendron moulmainense

MAIN CONCLUSION

The post-transcriptional gene regulatory pathway and small RNA pathway play important roles in regulating the rapid and long-term response of Rhododendron moulmainense to high-temperature stress. The Rhododendron plays an important role in maintaining ecological balance. However, it is difficult to domesticate for use in urban ecosystems due to their strict optimum growth temperature condition, and its evolution and adaptation are little known. Here, we combined transcriptome and small RNAome to reveal the rapid response and long-term adaptability regulation strategies in Rhododendron moulmainense under high-temperature stress. The post-transcriptional gene regulatory pathway plays important roles in stress response, in which the protein folding pathway is rapidly induced at 4 h after heat stress, and alternative splicing plays an important role in regulating gene expression at 7 days after heat stress. The chloroplasts oxidative damage is the main factor inhibiting photosynthesis efficiency. Through WGCNA analysis, we identified gene association patterns and potential key regulatory genes responsible for maintaining the ROS steady-state under heat stress. Finally, we found that the sRNA synthesis pathway is induced under heat stress. Combined with small RNAome, we found that more miRNAs are significantly changed under long-term heat stress. Furthermore, MYBs might play a central role in target gene interaction network of differentially expressed miRNAs in R. moulmainense under heat stress. MYBs are closely related to ABA, consistently, ABA synthesis and signaling pathways are significantly inhibited, and the change in stomatal aperture is not obvious under heat stress. Taken together, we gained valuable insights into the transplantation and long-term conservation domestication of Rhododendron, and provide genetic resources for genetic modification and molecular breeding to improve heat resistance in Rhododendron.

A transient in planta editing assay identifies specific binding of the splicing regulator PTB as a prerequisite for cassette exon inclusion

The dynamic interaction of RNA-binding proteins (RBPs) with their target RNAs contributes to the diversity of ribonucleoprotein (RNP) complexes that are involved in a myriad of biological processes. Identifying the RNP components at high resolution and defining their interactions are key to understanding their regulation and function. Expressing fusions between an RBP of interest and an RNA editing enzyme can result in nucleobase changes in target RNAs, representing a recent addition to experimental approaches for profiling RBP/RNA interactions. Here, we have used the MS2 protein/RNA interaction to test four RNA editing proteins for their suitability to detect target RNAs of RBPs in planta. We have established a transient test system for fast and simple quantification of editing events and identified the hyperactive version of the catalytic domain of an adenosine deaminase (hADARcd) as the most suitable editing enzyme. Examining fusions between homologs of polypyrimidine tract binding proteins (PTBs) from Arabidopsis thaliana and hADARcd allowed determining target RNAs with high sensitivity and specificity. Moreover, almost complete editing of a splicing intermediate provided insight into the order of splicing reactions and PTB dependency of this particular splicing event. Addition of sequences for nuclear localisation of the fusion protein increased the editing efficiency, highlighting this approach's potential to identify RBP targets in a compartment-specific manner. Our studies have established the editing-based analysis of interactions between RBPs and their RNA targets in a fast and straightforward assay, offering a new system to study the intricate composition and functions of plant RNPs in vivo.

Identification of the lateral organ boundary domain gene family and its preservation by exogenous salicylic acid in Cerasus humilis

The gene family known as the Lateral Organ Boundary Domain (LBD) is responsible for producing transcription factors unique to plants, which play a crucial role in controlling diverse biological activities, including their growth and development. This research focused on examining Cerasus humilis'ChLBD gene, owing to its significant ecological, economic, and nutritional benefits. Examining the ChLBD gene family's member count, physicochemical characteristics, phylogenetic evolution, gene configuration, and motif revealed 41 ChLBD gene family members spread across 8 chromosomes, with ChLBD gene's full-length coding sequences (CDSs) ranging from 327 to 1737 base pairs, and the protein sequence's length spanning 109 (ChLBD30)-579 (ChLBD35) amino acids. The molecular weights vary from 12.068 (ChLBD30) to 62.748 (ChLBD35) kDa, and the isoelectric points span from 4.74 (ChLBD20) to 9.19 (ChLBD3). Categorizing them into two evolutionary subfamilies: class I with 5 branches, class II with 2, the majority of genes with a single intron, and most members of the same subclade sharing comparable motif structures. The results of collinearity analysis showed that there were 3 pairs of tandem repeat genes and 12 pairs of fragment repeat genes in the Cerasus humilis genome, and in the interspecific collinearity analysis, the number of collinear gene pairs with apples belonging to the same family of Rosaceae was the highest. Examination of cis-acting elements revealed that methyl jasmonate response elements stood out as the most abundant, extensively dispersed in the promoter areas of class 1 and class 2 ChLBD. Genetic transcript analysis revealed that during Cerasus humilis' growth and maturation, ChLBD developed varied control mechanisms, with ChLBD27 and ChLBD40 potentially playing a role in managing color alterations in fruit ripening. In addition, the quality of calcium fruit will be affected by the environment during transportation and storage, and it is particularly important to use appropriate means to preserve the fruit. The research used salicylic acid-treated Cerasus humilis as the research object and employed qRT-PCR to examine the expression of six ChLBD genes throughout storage. Variations in the expression of the ChLBD gene were observed when exposed to salicylic acid, indicating that salicylic acid could influence ChLBD gene expression during the storage of fruits. This study's findings lay the groundwork for additional research into the biological role of the LBD gene in Cerasus humilis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01438-5.

Exploiting DNA methylation in cassava under water deficit for crop improvement

DNA methylation plays a key role in the development and plant responses to biotic and abiotic stresses. This work aimed to evaluate the DNA methylation in contrasting cassava genotypes for water deficit tolerance. The varieties BRS Formosa (bitter) and BRS Dourada (sweet) were grown under greenhouse conditions for 50 days, and afterwards, irrigation was suspended. The stressed (water deficit) and non-stressed plants (negative control) consisted the treatments with five plants per variety. The DNA samples of each variety and treatment provided 12 MethylRAD-Seq libraries (two cassava varieties, two treatments, and three replicates). The sequenced data revealed methylated sites covering 18 to 21% of the Manihot esculenta Crantz genome, depending on the variety and the treatment. The CCGG methylated sites mapped mostly in intergenic regions, exons, and introns, while the CCNGG sites mapped mostly intergenic, upstream, introns, and exons regions. In both cases, methylated sites in UTRs were less detected. The differentially methylated sites analysis indicated distinct methylation profiles since only 12% of the sites (CCGG and CCNGG) were methylated in both varieties. Enriched gene ontology terms highlighted the immediate response of the bitter variety to stress, while the sweet variety appears to suffer more potential stress-damages. The predicted protein-protein interaction networks reinforced such profiles. Additionally, the genomes of the BRS varieties uncovered SNPs/INDELs events covering genes stood out by the interactomes. Our data can be useful in deciphering the roles of DNA methylation in cassava drought-tolerance responses and adaptation to abiotic stresses.

SCR106 splicing factor modulates abiotic stress responses by maintaining RNA splicing in rice

Plants employ sophisticated molecular machinery to fine-tune their responses to growth, developmental, and stress cues. Gene expression influences plant cellular responses through regulatory processes such as transcription and splicing. Pre-mRNA is alternatively spliced to increase the genome coding potential and further regulate expression. Serine/arginine-rich (SR) proteins, a family of pre-mRNA splicing factors, recognize splicing cis-elements and regulate both constitutive and alternative splicing. Several studies have reported SR protein genes in the rice genome, subdivided into six subfamilies based on their domain structures. Here, we identified a new splicing factor in rice with an RNA recognition motif (RRM) and SR-dipeptides, which is related to the SR proteins, subfamily SC. OsSCR106 regulates pre-mRNA splicing under abiotic stress conditions. It localizes to the nuclear speckles, a major site for pre-mRNA splicing in the cell. The loss-of-function scr106 mutant is hypersensitive to salt, abscisic acid, and low-temperature stress, and harbors a developmental abnormality indicated by the shorter length of the shoot and root. The hypersensitivity to stress phenotype was rescued by complementation using OsSCR106 fused behind its endogenous promoter. Global gene expression and genome-wide splicing analysis in wild-type and scr106 seedlings revealed that OsSCR106 regulates its targets, presumably through regulating the alternative 3'-splice site. Under salt stress conditions, we identified multiple splice isoforms regulated by OsSCR106. Collectively, our results suggest that OsSCR106 is an important splicing factor that plays a crucial role in accurate pre-mRNA splicing and regulates abiotic stress responses in plants.

Exitrons: offering new roles to retained introns-the novel regulators of protein diversity and utility

Exitrons are exonic introns. This subclass of intron retention alternative splicing does not contain a Pre-Terminating stop Codon. Therefore, when retained, they are always a part of a protein. Intron retention is a frequent phenomenon predominantly found in plants, which results in either the degradation of the transcripts or can serve as a stable intermediate to be processed upon induction by specific signals or the cell status. Interestingly, exitrons have coding ability and may confer additional attributes to the proteins that retain them. Therefore, exitron-containing and exitron-spliced isoforms will be a driving force for creating protein diversity in the proteome of an organism. This review establishes a basic understanding of exitron, discussing its genesis, key features, identification methods and functions. We also try to depict its other potential roles. The present review also aims to provide a fundamental background to those who found such exitronic sequences in their gene(s) and to speculate the future course of studies.

Alternative Splicing Reveals Acute Stress Response of Litopenaeus vannamei at High Alkalinity

Alkalinity is regarded as one of the primary stressors for aquatic animals in saline-alkaline water. Alternative splicing (AS) can significantly increase the diversity of transcripts and play key roles in stress response; however, the studies on AS under alkalinity stress of crustaceans are still limited. In the present study, we devoted ourselves to the study of AS under acute alkalinity stress at control (50 mg/L) and treatment groups (350 mg/L) by RNA-seq in pacific white shrimp (Litopenaeus vannamei). We identified a total of 10,556 AS events from 4865 genes and 619 differential AS (DAS) events from 519 DAS genes in pacific white shrimp. Functional annotation showed that the DAS genes primarily involved in spliceosome. Five splicing factors (SFs), U2AF1, PUF60, CHERP, SR140 and SRSF2 were significantly up-regulated and promoted AS. Furthermore, alkalinity activated the Leukocyte transendothelial migration, mTOR signaling pathway and AMPK signaling pathway, which regulated MAPK1, EIF3B and IGFP-RP1 associated with these pathways. We also studied three SFs (HSFP1, SRSF2 and NHE-RF1), which underwent AS to form different transcript isoforms. The above results demonstrated that AS was a regulatory mechanism in pacific white shrimp in response to acute alkalinity stress. SFs played vital roles in AS of pacific white shrimp, such as HSFP1, SRSF2 and NHE-RF1. DAS genes were significantly modified in immunity of pacific white shrimp to cope with alkalinity stress. This is the first study on the response of AS to acute alkalinity stress, which provided scientific basis for AS mechanism of crustaceans response to alkalinity stress.

Nonsense-mediated mRNA decay pathway in plants under stress: general gene regulatory mechanism and advances

MAIN CONCLUSION

Nonsense-mediated mRNA decay in eukaryotes is vital to cellular homeostasis. Further knowledge of its putative role in plant RNA metabolism under stress is pivotal to developing fitness-optimizing strategies. Nonsense-mediated mRNA decay (NMD), part of the mRNA surveillance pathway, is an evolutionarily conserved form of gene regulation in all living organisms. Degradation of mRNA-bearing premature termination codons and regulation of physiological RNA levels highlight NMD's role in shaping the cellular transcriptome. Initially regarded as purely a tool for cellular RNA quality control, NMD is now considered to mediate various aspects of plant developmental processes and responses to environmental changes. Here we offer a basic understanding of NMD in eukaryotes by explaining the concept of premature termination codon recognition and NMD complex formation. We also provide a detailed overview of the NMD mechanism and its role in gene regulation. The potential role of effectors, including ABCE1, in ribosome recycling during the translation process is also explained. Recent reports of alternatively spliced variants of corresponding genes targeted by NMD in Arabidopsis thaliana are provided in tabular format. Detailed figures are also provided to clarify the NMD concept in plants. In particular, accumulating evidence shows that NMD can serve as a novel alternative strategy for genetic manipulation and can help design RNA-based therapies to combat stress in plants. A key point of emphasis is its function as a gene regulatory mechanism as well as its dynamic regulation by environmental and developmental factors. Overall, a detailed molecular understanding of the NMD mechanism can lead to further diverse applications, such as improving cellular homeostasis in living organisms.

Diurnal regulation of alternative splicing associated with thermotolerance in rice by two glycine-rich RNA-binding proteins

Rice (Oryza sativa L.) production is threatened by global warming associated with extreme high temperatures, and rice heat sensitivity is differed when stress occurs between daytime and nighttime. However, the underlying molecular mechanism are largely unknown. We show here that two glycine-rich RNA binding proteins, OsGRP3 and OsGRP162, are required for thermotolerance in rice, especially at nighttime. The rhythmic expression of OsGRP3/OsGRP162 peaks at midnight, and at these coincident times, is increased by heat stress. This is largely dependent on the evening complex component OsELF3-2. We next found that the double mutant of OsGRP3/OsGRP162 is strikingly more sensitive to heat stress in terms of survival rate and seed setting rate when comparing to the wild-type plants. Interestingly, the defect in thermotolerance is more evident when heat stress occurred in nighttime than that in daytime. Upon heat stress, the double mutant of OsGRP3/OsGRP162 displays globally reduced expression of heat-stress responsive genes, and increases of mRNA alternative splicing dominated by exon-skipping. This study thus reveals the important role of OsGRP3/OsGRP162 in thermotolerance in rice, and unravels the mechanism on how OsGRP3/OsGRP162 regulate thermotolerance in a diurnal manner.

The first high-altitude autotetraploid haplotype-resolved genome assembled (Rhododendron nivale subsp. boreale) provides new insights into mountaintop adaptation

BACKGROUND

Rhododendron nivale subsp. boreale Philipson et M. N. Philipson is an alpine woody species with ornamental qualities that serve as the predominant species in mountainous scrub habitats found at an altitude of ∼4,200 m. As a high-altitude woody polyploid, this species may serve as a model to understand how plants adapt to alpine environments. Despite its ecological significance, the lack of genomic resources has hindered a comprehensive understanding of its evolutionary and adaptive characteristics in high-altitude mountainous environments.

FINDINGS

We sequenced and assembled the genome of R. nivale subsp. boreale, an assembly of the first subgenus Rhododendron and the first high-altitude woody flowering tetraploid, contributing an important genomic resource for alpine woody flora. The assembly included 52 pseudochromosomes (scaffold N50 = 42.93 Mb; BUSCO = 98.8%; QV = 45.51; S-AQI = 98.69), which belonged to 4 haplotypes, harboring 127,810 predicted protein-coding genes. Conjoint k-mer analysis, collinearity assessment, and phylogenetic investigation corroborated autotetraploid identity. Comparative genomic analysis revealed that R. nivale subsp. boreale originated as a neopolyploid of R. nivale and underwent 2 rounds of ancient polyploidy events. Transcriptional expression analysis showed that differences in expression between alleles were common and randomly distributed in the genome. We identified extended gene families and signatures of positive selection that are involved not only in adaptation to the mountaintop ecosystem (response to stress and developmental regulation) but also in autotetraploid reproduction (meiotic stabilization). Additionally, the expression levels of the (group VII ethylene response factor transcription factors) ERF VIIs were significantly higher than the mean global gene expression. We suspect that these changes have enabled the success of this species at high altitudes.

CONCLUSIONS

We assembled the first high-altitude autopolyploid genome and achieved chromosome-level assembly within the subgenus Rhododendron. In addition, a high-altitude adaptation strategy of R. nivale subsp. boreale was reasonably speculated. This study provides valuable data for the exploration of alpine mountaintop adaptations and the correlation between extreme environments and species polyploidization.

A Method to Quantitatively Examine Heat Stress-Induced Alternative Splicing in Plants by RNA-Seq and RT-PCR

Alternative splicing (AS) of pre-mRNAs is a type of post-transcriptional regulation in eukaryotes that expands the number of mRNA isoforms. Intron retention is the primary form of AS in plants and occurs more frequently when plants are exposed to environmental stresses. Several wet-lab and bioinformatics techniques are used to detect AS events, but these techniques are technically challenging or unsuitable for studying AS in plants. Here, we report a method that combines RNA-sequencing and reverse transcription PCR for visualizing and validating heat stress-induced AS events in plants, using Arabidopsis thaliana and HEAT SHOCK PROTEIN21 (HSP21) as examples.

Effects of miR-722 on gene expression and alternative splicing in the liver of half-smooth tongue sole after infection with Vibrio anguillarum

MicroRNAs play crucial roles in various biological processes, including but not limited to differentiation, development, disease, and immunity. However, their immunoregulatory roles in half-smooth tongue sole are lacking. Our previous studies indicated that miR-722 could target C5aR1 to modulate the complement pathway to alleviate inflammatory response and even affect the mortality after the bacterial infection with Vibrio anguillarum. Driven by the purpose of revealing the underlying mechanisms, in this study, we investigated the effects of miR-722 on the gene expression and alternative splicing (AS) in the liver of half-smooth tongue sole after Vibrio anguillarum infection, with the approach of miR-722 overexpression/silencing and subsequent RNA-seq. Among the different comparisons, the I group (miR-722 inhibitor and V. anguillarum) versus blank control (PBS) exhibited the highest number of differentially expressed genes (DEGs), suggesting that the immune response was overactivated after inhibiting the miR-722. In addition, enrichment analyses were performed to reveal the functions of DEGs and differential AS (DAS) genes, reflecting the enrichment of RNA splicing and immune-related pathways including NF-κB and T cell receptor signaling pathway. Comparing the M group (miR-722 mimic and V. anguillarum) with the negative control (random sequence and V. anguillarum), two immune-related genes, cd48 and mapk8, were differentially expressed, of which mapk8 was also differentially spliced, indicating their importance in the immune response. Furthermore, representative gene analysis was performed, suggesting their corresponding functional changes due to AS. To verify the RNA-seq data, quantitative real-time PCR was employed with twenty pairs of primers for DEGs and DAS events. Overall, our results demonstrated that miR-722 could mediate the transcriptome-wide changes of gene expression and AS in half-smooth tongue sole, and provided insights into the regulatory role of miR-722 in immune responses, laying the foundation for further functional analyses and practical applications in aquaculture.

Genome-wide identification and expression analysis of the JMJ-C gene family in melon (Cucumis melo L.) reveals their potential role in fruit development

BACKGROUND

Proteins with the jumonji (JMJ)-C domain belong to the histone demethylase family and contribute to reverse histone methylation. Although JMJ-C family genes have an essential role in regulating plant growth and development, the characterization of the JMJ-C family genes in melon has not been uncovered.

RESULTS

In this study, a total of 17 JMJ-C proteins were identified in melon (Cucumis melo L.). CmJMJs were categorized into five subfamilies based on the specific conserved domain: KDM4/JHDM3, KDM5/JARID1, JMJD6, KDM3/JHDM2, and JMJ-C domain-only. The chromosome localization analyses showed that 17 CmJMJs were distributed on nine chromosomes. Cis-acting element analyses of the 17 CmJMJ genes showed numerous hormone, light, and stress response elements distributed in the promoter region. Covariance analysis revealed one pair of replicated fragments (CmJMJ3a and CmJMJ3b) in 17 CmJMJ genes. We investigated the expression profile of 17 CmJMJ genes in different lateral organs and four developmental stages of fruit by RNA-seq transcriptome analysis and RT-qPCR. The results revealed that most CmJMJ genes were prominently expressed in female flowers, ovaries, and developing fruits, suggesting their active role in melon fruit development. Subcellular localization showed that the fruit-related CmJMJ5a protein is specifically localized in the cell nucleus.

CONCLUSIONS

This study provides a comprehensive understanding of the gene structure, classification, and evolution of JMJ-C in melon and supports the clarification of the JMJ-C functions in further research.