Genome-wide profiling of circular RNAs, alternative splicing, and R-loops in stem-differentiating xylem of Populus trichocarpa

Multilayer regulatory landscape and new regulators identification for bud dormancy release and bud break in Populus

For trees originating from boreal and temperate regions, the dormancy-to-active transition, also known as bud dormancy release and bud break, are crucial processes that allow trees to reactive growth in the spring. The molecular mechanisms underlying these two processes remain poorly understood. Here, through integrative multiomics analysis of the transcriptome, DNA methylome, and proteome, we gained insights into the reprogrammed cellular processes associated with bud dormancy release and bud break. Our findings revealed multilayer regulatory landscapes governing bud dormancy release and bud break regulation, providing a valuable reference framework for future functional studies. Based on the multiomics analysis, we have determined a novel long intergenic noncoding RNA named Phenology Responsive Intergenic lncRNA 1 (PRIR1) plays a role in the activation of bud break. that the molecular mechanism of PRIR1 has been preliminary explored, and it may partially promote bud break by activating its neighbouring gene, EXORDIUM LIKE 5 (PtEXL5), which has also been genetically confirmed as an activator for bud break. This study has revealed a lncRNA-mediated regulatory mechanism for the control of bud break in Populus, operating independently of known regulatory pathways.

Advances in CircRNAs in the Past Decade: Review of CircRNAs Biogenesis, Regulatory Mechanisms, and Functions in Plants

Circular RNA (circRNA) is a type of non-coding RNA with multiple biological functions. Whole circRNA genomes in plants have been identified, and circRNAs have been demonstrated to be widely present and highly expressed in various plant tissues and organs. CircRNAs are highly stable and conserved in plants, and exhibit tissue specificity and developmental stage specificity. CircRNAs often interact with other biomolecules, such as miRNAs and proteins, thereby regulating gene expression, interfering with gene function, and affecting plant growth and development or response to environmental stress. CircRNAs are less studied in plants than in animals, and their regulatory mechanisms of biogenesis and molecular functions are not fully understood. A variety of circRNAs in plants are involved in regulating growth and development and responding to environmental stress. This review focuses on the biogenesis and regulatory mechanisms of circRNAs, as well as their biological functions during growth, development, and stress responses in plants, including a discussion of plant circRNA research prospects. Understanding the generation and regulatory mechanisms of circRNAs is a challenging but important topic in the field of circRNAs in plants, as it can provide insights into plant life activities and their response mechanisms to biotic or abiotic stresses as well as new strategies for plant molecular breeding and pest control.

LncRNAs: the art of being influential without protein

The plant long noncoding (lnc)RNA field is on the brink of transitioning from large-scale identification of lncRNAs to their functional characterization. Due to the cross-kingdom conservation of interaction types and molecular functions, there is much to be learned from mammalian lncRNA research. Here, we discuss the different molecular processes involving lncRNAs from the regulation of chromatin to splicing. Furthermore, we discuss the lncRNA interactome, which includes proteins, other RNAs, and DNA. We explore and discuss how mammalian lncRNA functionalities could be reflected in similar pathways in plants and hypothesize that several breakthroughs in mammalian research could lead to the discovery of novel plant lncRNA molecular functions. Expanding our knowledge of the biological role of lncRNAs and their multiple applications paves the way for future agricultural applications.

CircR-loop: a novel RNA:DNA interaction on genome instability

CircR-loop, a recently unearthed regulatory mechanism situated at the crossroads of circular RNA and DNA interactions, constitute a subset of R-loop. This circR-loop have emerged as a crucial player in pivotal regulatory functions within both animal and plant systems. The journey into the realm of circR-loop commenced with their discovery within the human mitochondrial genome, where they serve as critical directors of mitochondrial DNA replication. In the plant kingdom, circR-loop wield influence over processes such as alternative splicing and centromere organization, impacting the intricacies of floral development and genome stability, respectively. Their significance extends to the animal domain, where circR-loop has captured attention for their roles in cancer-related phenomena, exerting control over transcription, chromatin architecture, and orchestrating responses to DNA damage. Moreover, their involvement in nuclear export anomalies further underscores their prominence in cellular regulation. This article summarizes the important regulatory mechanisms and physiological roles of circR-loop in plants and animals, and offers a comprehensive exploration of the methodologies employed for the identification, characterization, and functional analysis of circR-loop, underscoring the pressing need for innovative approaches that can effectively distinguish them from their linear RNA counterparts while elucidating their precise functions. Lastly, the article sheds light on the challenges and opportunities that lie ahead in the field of circR-loop research, emphasizing the vital importance of continued investigations to uncover their regulatory roles and potential applications in the realm of biology. In summary, circR-loop represents a captivating and novel regulatory mechanism with broad-reaching implications spanning the realms of genetics, epigenetics, and disease biology. Their exploration opens new avenues for comprehending gene regulation and holds significant promise for future therapeutic interventions.

CircRNA: An emerging star in plant research: A review

CircRNAs are a class of covalently closed non-coding RNA formed by linking the 5' terminus and the 3' terminus after reverse splicing. CircRNAs are widely found in eukaryotes, and they are highly conserved, with spatio-temporal expression specificity and stability. CircRNAs can act as miRNA sponges to regulate the expression of downstream target genes, regulating the transcription of parental genes and some can even be translated into peptides or proteins. Research on circRNAs in plants is still in its infancy compared to that in animals. With the deepening of research, the results of a variety of plant circRNAs suggest that they play an important role in growth and development, and tolerance towards abiotic stresses such as salt, drought, low temperature, high temperature and other adverse environments. In this review paper, we elaborated the molecular characteristics, mechanism of action, function and bioinformatics databases of plant circRNAs, combined with the progress of circRNA research in animals, discussed the potential mechanism of action of plant circRNAs, and proposed the unsolved problems and prospects for future application of plant circRNAs.

R-loops act as regulatory switches modulating transcription of COLD-responsive genes in rice

COLD is a major naturally occurring stress that usually causes complex symptoms and severe yield loss in crops. R-loops function in various cellular processes, including development and stress responses, in plants. However, how R-loops function in COLD responses is largely unknown in COLD susceptible crops like rice (Oryza sativa L.). We conducted DRIP-Seq along with other omics data (RNA-Seq, DNase-Seq and ChIP-Seq) in rice with or without COLD treatment. COLD treatment caused R-loop reprogramming across the genome. COLD-biased R-loops had higher GC content and novel motifs for the binding of distinct transcription factors (TFs). Moreover, R-loops can directly/indirectly modulate the transcription of a subset of COLD-responsive genes, which can be mediated by R-loop overlapping TF-centered or cis-regulatory element-related regulatory networks and lncRNAs, accounting for c. 60% of COLD-induced expression of differential genes in rice, which is different from the findings in Arabidopsis. We validated two R-loop loci with contrasting (negative/positive) roles in the regulation of two individual COLD-responsive gene expression, as potential targets for enhanced COLD resistance. Our study provides detailed evidence showing functions of R-loop reprogramming during COLD responses and provides some potential R-loop loci for genetic and epigenetic manipulation toward breeding of rice varieties with enhanced COLD tolerance.

Multi-omics of Circular RNAs and Their Responses to Hormones in Moso Bamboo (Phyllostachys edulis)

Circular RNAs (circRNAs) are endogenous non-coding RNAs with covalently closed structures, which have important functions in plants. However, their biogenesis, degradation, and function upon treatment with gibberellins (GAs) and auxins (1-naphthaleneacetic acid, NAA) remain unknown. Here, we systematically identified and characterized the expression patterns, evolutionary conservation, genomic features, and internal structures of circRNAs using RNase R-treated libraries from moso bamboo (Phyllostachys edulis) seedlings. Moreover, we investigated the biogenesis of circRNAs dependent on both cis- and trans-regulation. We explored the function of circRNAs, including their roles in regulating microRNA (miRNA)-related genes and modulating the alternative splicing of their linear counterparts. Importantly, we developed a customized degradome sequencing approach to detect miRNA-mediated cleavage of circRNAs. Finally, we presented a comprehensive view of the participation of circRNAs in the regulation of hormone metabolism upon treatment of bamboo seedlings with GA and NAA. Collectively, our study provides insights into the biogenesis, function, and miRNA-mediated degradation of circRNAs in moso bamboo.

Understanding the roles and regulation patterns of circRNA on its host gene in tumorigenesis and tumor progression

Circular RNAs (circRNAs) are a novel type of endogenous non-coding RNAs, which are covalently closed loop structures formed by precursor mRNAs (pre-mRNAs) through back-splicing. CircRNAs are abnormally expressed in many tumors, and play critical roles in a variety of tumors as oncogenes or tumor suppressor genes by sponging miRNAs, regulating alternative splicing and transcription, cis-regulating host genes, interacting with RNA binding proteins (RBPs) or encoding polypeptides. Among them, the regulation of circRNAs on their corresponding host genes is a critical way for circRNAs to exit their functions. Accumulating evidence suggests that circRNAs are able to regulate the expression of host genes at the transcriptional level, post-transcriptional level, translational level, post-translational level, or by encoding polypeptides. Therefore, this paper mainly summarized the roles and association of circRNAs and their corresponding host genes in tumorigenesis and tumor progression, generalized the circRNAs that function synergistically or antagonistically with their host genes, and elaborated the mechanisms of mutual regulation between circRNAs and their host genes. More importantly, this review provides specific references for revealing the potential application of circRNAs combined with their host genes in tumor diagnosis, treatment and prognosis.

Identification, biogenesis, function, and mechanism of action of circular RNAs in plants

Circular RNAs (circRNAs) are a class of single-stranded, closed RNA molecules with unique functions that are ubiquitously expressed in all eukaryotes. The biogenesis of circRNAs is regulated by specific cis-acting elements and trans-acting factors in humans and animals. circRNAs mainly exert their biological functions by acting as microRNA sponges, forming R-loops, interacting with RNA-binding proteins, or being translated into polypeptides or proteins in human and animal cells. Genome-wide identification of circRNAs has been performed in multiple plant species, and the results suggest that circRNAs are abundant and ubiquitously expressed in plants. There is emerging compelling evidence to suggest that circRNAs play essential roles during plant growth and development as well as in the responses to biotic and abiotic stress. However, compared with recent advances in human and animal systems, the roles of most circRNAs in plants are unclear at present. Here we review the identification, biogenesis, function, and mechanism of action of plant circRNAs, which will provide a fundamental understanding of the characteristics and complexity of circRNAs in plants.

Beyond the Primary Structure of Nucleic Acids: Potential Roles of Epigenetics and Noncanonical Structures in the Regulations of Plant Growth and Stress Responses

Epigenetics deals with changes in gene expression that are not caused by modifications in the primary sequence of nucleic acids. These changes beyond primary structures of nucleic acids not only include DNA/RNA methylation, but also other reversible conversions, together with histone modifications or RNA interference. In addition, under particular conditions (such as specific ion concentrations or protein-induced stabilization), the right-handed double-stranded DNA helix (B-DNA) can form noncanonical structures commonly described as "non-B DNA" structures. These structures comprise, for example, cruciforms, i-motifs, triplexes, and G-quadruplexes. Their formation often leads to significant differences in replication and transcription rates. Noncanonical RNA structures have also been documented to play important roles in translation regulation and the biology of noncoding RNAs. In human and animal studies, the frequency and dynamics of noncanonical DNA and RNA structures are intensively investigated, especially in the field of cancer research and neurodegenerative diseases. In contrast, noncanonical DNA and RNA structures in plants have been on the fringes of interest for a long time and only a few studies deal with their formation, regulation, and physiological importance for plant stress responses. Herein, we present a review focused on the main fields of epigenetics in plants and their possible roles in stress responses and signaling, with special attention dedicated to noncanonical DNA and RNA structures.

R-loop: The new genome regulatory element in plants

An R-loop is a three-stranded chromatin structure that consists of a displaced single strand of DNA and an RNA:DNA hybrid duplex, which was thought to be a rare by-product of transcription. However, recent genome-wide data have shown that R-loops are widespread and pervasive in a variety of genomes, and a growing body of experimental evidence indicates that R-loops have both beneficial and harmful effects on an organism. To maximize benefit and avoid harm, organisms have evolved several means by which they tightly regulate R-loop levels. Here, we summarize our current understanding of the biogenesis and effects of R-loops, the mechanisms that regulate them, and methods of R-loop profiling, reviewing recent research advances on R-loops in plants. Furthermore, we provide perspectives on future research directions for R-loop biology in plants, which might lead to a more comprehensive understanding of R-loop functions in plant genome regulation and contribute to future agricultural improvements.

CircRNA: a rising star in plant biology

Circular RNAs (circRNAs) are covalently closed single-stranded RNA molecules, which are widespread in eukaryotic cells. As regulatory molecules, circRNAs have various functions, such as regulating gene expression, binding miRNAs or proteins, and being translated into proteins, which are important for cell proliferation and cell differentiation, individual growth and development, as well as many other biological processes. However, compared with that in animal models, studies of circRNAs in plants lags behind and, particularly, the regulatory mechanisms of biogenesis and molecular functions of plant circRNAs remain elusive. Recent studies have shown that circRNAs are wide spread in plants with tissue- or development-specific expression patterns and are responsive to a variety of environmental stresses. In this review, we summarize these advances, focusing on the regulatory mechanisms of biogenesis, molecular and biological functions of circRNAs, and the methods for investigating circRNAs. We also discuss the challenges and the prospects of plant circRNA studies.

Drought induces epitranscriptome and proteome changes in stem-differentiating xylem of Populus trichocarpa

Understanding gene expression and regulation requires insights into RNA transcription, processing, modification, and translation. However, the relationship between the epitranscriptome and the proteome under drought stress remains undetermined in poplar (Populus trichocarpa). In this study, we used Nanopore direct RNA sequencing and tandem mass tag-based proteomic analysis to examine epitranscriptomic and proteomic regulation induced by drought treatment in stem-differentiating xylem (SDX). Our results revealed a decreased full-length read ratio under drought treatment and, especially, a decreased association between transcriptome and proteome changes in response to drought. Epitranscriptome analysis of cellulose- and lignin-related genes revealed an increased N6-Methyladenosine (m6A) ratio, which was accompanied by decreased RNA abundance and translation, under drought stress. Interestingly, usage of the distal poly(A) site increased during drought stress. Finally, we found that transcripts of highly expressed genes tend to have shorter poly(A) tail length (PAL), and drought stress increased the percentage of transcripts with long PAL. These findings provide insights into the interplay among m6A, polyadenylation, PAL, and translation under drought stress in P. trichocarpa SDX.