Conservation analysis of long non-coding RNAs in plants

Exploring the emerging role of long non-coding RNAs (lncRNAs) in plant biology: Functions, mechanisms of action, and future directions

Long non-coding RNAs (lncRNAs) are a class of RNA transcripts that surpass 200 nucleotides in length and lack discernible coding potential. LncRNAs that have been functionally characterized have pivotal functions in several plant processes, including the regulation of flowering, and development of lateral roots. It also plays a crucial role in the plant's response to abiotic stressors and exhibits vital activities in environmental adaptation. The progress in NGS (next-generation sequencing) and functional genomics technology has facilitated the discovery of lncRNA in plant species. This review is a brief explanation of lncRNA genomics, its molecular role, and the mechanism of action in plants. The review also addresses the challenges encountered in this field and highlights promising molecular and computational methodologies that can aid in the comparative and functional analysis of lncRNAs.

A long noncoding RNA functions in pumpkin fruit development through S-adenosyl-L-methionine synthetase

Long noncoding RNAs (lncRNAs) play important roles in various biological processes. However, the regulatory roles of lncRNAs underlying fruit development have not been extensively studied. The pumpkin (Cucurbita spp.) is a preferred model for understanding the molecular mechanisms regulating fruit development because of its variable shape and size and large inferior ovary. Here, we performed strand-specific transcriptome sequencing on pumpkin (Cucurbita maxima "Rimu") fruits at 6 developmental stages and identified 5,425 reliably expressed lncRNAs. Among the 332 lncRNAs that were differentially expressed during fruit development, the lncRNA MSTRG.44863.1 was identified as a negative regulator of pumpkin fruit development. MSTRG.44863.1 showed a relatively high expression level and an obvious period-specific expression pattern. Transient overexpression and silencing of MSTRG.44863.1 significantly increased and decreased the content of 1-aminocyclopropane carboxylic acid (a precursor of ethylene) and ethylene production, respectively. RNA pull-down and microscale thermophoresis assays further revealed that MSTRG.44863.1 can interact with S-adenosyl-L-methionine synthetase (SAMS), an enzyme in the ethylene synthesis pathway. Considering that ethylene negatively regulates fruit development, these results indicate that MSTRG.44863.1 plays an important role in the regulation of pumpkin fruit development, possibly through interacting with SAMS and affecting ethylene synthesis. Overall, our findings provide a rich resource for further study of fruit-related lncRNAs while offering insights into the regulation of fruit development in plants.

Transcriptomic Profiles of Long Noncoding RNAs and Their Target Protein-Coding Genes Reveals Speciation Adaptation on the Qinghai-Xizang (Tibet) Plateau in Orinus

Long noncoding RNAs (lncRNAs) are RNA molecules longer than 200 nt, which lack the ability to encode proteins and are involved in multifarious growth, development, and regulatory processes in plants and mammals. However, the environmental-regulated expression profiles of lncRNAs in Orinus that may associated with their adaptation on the Qinghai-Xizang (Tibet) Plateau (QTP) have never been characterized. Here, we utilized transcriptomic sequencing data of two Orinus species (O. thoroldii and O. kokonoricus) to identify 1624 lncRNAs, including 1119 intergenic lncRNAs, 200 antisense lncRNAs, five intronic lncRNAs, and 300 sense lncRNAs. In addition, the evolutionary relationships of Orinus lncRNAs showed limited sequence conservation among 39 species, which implied that Orinus-specific lncRNAs contribute to speciation adaptation evolution. Furthermore, considering the cis-regulation mechanism, from 286 differentially expressed lncRNAs (DElncRNAs) and their nearby protein coding genes (PCGs) between O. thoroldii and O. kokonoricus, 128 lncRNA-PCG pairs were obtained in O. thoroldii, whereas 92 lncRNA-PCG pairs were obtained in O. kokonoricus. In addition, a total of 19 lncRNA-PCG pairs in O. thoroldii and 14 lncRNA-PCG pairs in O. kokonoricus were found to participate in different biological processes, indicating that the different expression profiles of DElncRNAs between O. thoroldii and O. kokonoricus were associated with their adaptation at different elevations on the QTP. We also found several pairs of DElncRNA nearby transcription factors (TFs), indicating that these DElncRNAs regulate the expression of TFs to aid O. thoroldii in adapting to the environment. Therefore, this work systematically identified a series of lncRNAs in Orinus, laying the groundwork for further exploration into the biological function of Orinus in environmental adaptation.

From environmental responses to adaptation: the roles of plant lncRNAs

As sessile organisms, plants are continuously exposed to heterogeneous and changing environments and constantly need to adapt their growth strategies. They have evolved complex mechanisms to recognize various stress factors, activate appropriate signaling pathways, and respond accordingly by reprogramming the expression of multiple genes at the transcriptional, post-transcriptional, and even epigenome levels to tolerate stressful conditions such as drought, high temperature, nutrient deficiency, and pathogenic interactions. Apart from protein-coding genes, long non-coding RNAs (lncRNAs) have emerged as key players in plant adaptation to environmental stresses. They are transcripts larger than 200 nucleotides without protein-coding potential. Still, they appear to regulate a wide range of processes, including epigenetic modifications and chromatin reorganization, as well as transcriptional and post-transcriptional modulation of gene expression, allowing plant adaptation to various environmental stresses. LncRNAs can positively or negatively modulate stress responses, affecting processes such as hormone signaling, temperature tolerance, and nutrient deficiency adaptation. Moreover, they also seem to play a role in stress memory, wherein prior exposure to mild stress enhances plant ability to adapt to subsequent stressful conditions. In this review, we summarize the contribution of lncRNAs in plant adaptation to biotic and abiotic stresses, as well as stress memory. The complex evolutionary conservation of lncRNAs is also discussed and provides insights into future research directions in this field.

Retroviral Insertion Polymorphism (RIP) of Porcine Endogenous Retroviruses (PERVs) in Pig Genomes

Endogenous retroviruses (ERVs) are one of the superfamilies of long terminal repeat retrotransposons (LTRs) in mice and humans. Approximately 8% of the pig genome is composed of sequences derived from LTRs. While the majority of ERVs in pigs have decayed, a small number of full-length copies can still mobilize within the genome. This study investigated the unexplored retroviral insertion polymorphisms (RIPs) generated by the mobilization of full-length ERVs (Fl-ERVs), and evaluated their impact on phenotypic variation to gain insights into the biological role of Fl-ERVs in pigs. Overall, 39 RIPs (insertions or deletions relative to the pig reference genome) generated by Fl-ERVs were predicted by comparative genomic analysis, and 18 of them were confirmed by PCR detection. Four RIP sites (D5, D14, D15, and D18) were further evaluated by population analysis, and all of them displayed polymorphisms in multiple breeds. The RIP site of ERV-D14, which is a Fl-ERV inserted in the STAB2-like gene, was further confirmed by sequencing. Population analysis of the polymorphic site of ERV-D14 reveals that it presents moderate polymorphism information in the Large White pig breed, and the association analysis reveals that the RIP of ERV-D14 is associated with age variations at 30 kg body weight (p < 0.05) and 100 kg body weight (p < 0.01) in the population of Large White pigs (N = 480). Furthermore, the ERV-D14 RIP is associated with changes in the expression of the target gene STAB2-like in the liver, backfat, and leaf fat in Sushan pigs. These data suggest that some Fl-ERVs are still mobilizing in the pig's genome, and contribute to genomic and phenotypic variations.

Exploring the Regulatory Dynamics of BrFLC-Associated lncRNA in Modulating the Flowering Response of Chinese Cabbage

Vernalization plays a crucial role in the flowering and yield of Chinese cabbage, a process intricately influenced by long non-coding RNAs (lncRNAs). Our research focused on lncFLC1, lncFLC2a, and lncFLC2b, which emerged as key players in this process. These lncRNAs exhibited an inverse expression pattern to the flowering repressor genes FLOWERING LOCUS C 1 (BrFLC1) and FLOWERING LOCUS C 2 (BrFLC2) during vernalization, suggesting a complex regulatory mechanism. Notably, their expression in the shoot apex and leaves was confirmed through in fluorescent in situ hybridization (FISH). Furthermore, when these lncRNAs were overexpressed in Arabidopsis, a noticeable acceleration in flowering was observed, unveiling functional similarities to Arabidopsis's COLD ASSISTED INTRONIC NONCODING RNA (COOLAIR). This resemblance suggests a potentially conserved regulatory mechanism across species. This study not only enhances our understanding of lncRNAs in flowering regulation, but also opens up new possibilities for their application in agricultural practices.

Long non-coding RNA-mediated epigenetic response for abiotic stress tolerance in plants

Plants perceive environmental fluctuations as stress and confront several stresses throughout their life cycle individually or in combination. Plants have evolved their sensing and signaling mechanisms to perceive and respond to a variety of stresses. Epigenetic regulation plays a critical role in the regulation of genes, spatiotemporal expression of genes under stress conditions and imparts a stress memory to encounter future stress responses. It is quintessential to integrate our understanding of genetics and epigenetics to maintain plant fitness, achieve desired genetic gains with no trade-offs, and durable long-term stress tolerance. The long non-coding RNA >200 nts having no coding potential (or very low) play several roles in epigenetic memory, contributing to the regulation of gene expression and the maintenance of cellular identity which include chromatin remodeling, imprinting (dosage compensation), stable silencing, facilitating nuclear organization, regulation of enhancer-promoter interactions, response to environmental signals and epigenetic switching. The lncRNAs are involved in a myriad of stress responses by activation or repression of target genes and hence are potential candidates for deploying in climate-resilient breeding programs. This review puts forward the significant roles of long non-coding RNA as an epigenetic response during abiotic stresses in plants and the prospects of deploying lncRNAs for designing climate-resilient plants.

The Pivotal Role of Noncoding RNAs in Flowering Time Regulation

Noncoding RNAs constitute a substantial portion of the transcriptome and play pivotal roles in plant growth and development. Among these processes, flowering stands out as a crucial trait, ensuring reproductive success and seed set, and is meticulously controlled by genetic and environmental factors. With remarkable advancements in the identification and characterization of noncoding RNAs in plants, it has become evident that noncoding RNAs are intricately linked to the regulation of flowering time. In this article, we present an overview of the classification of plant noncoding RNAs and delve into their functions in the regulation of flowering time. Furthermore, we review their molecular mechanisms and their involvement in flowering pathways. Our comprehensive review enhances the understanding of how noncoding RNAs contribute to the regulation of flowering time and sheds light on their potential implications in crop breeding.

DNABERT-based explainable lncRNA identification in plant genome assemblies

Long non-coding ribonucleic acids (lncRNAs) have been shown to play an important role in plant gene regulation, involving both epigenetic and transcript regulation. LncRNAs are transcripts longer than 200 nucleotides that are not translated into functional proteins but can be translated into small peptides. Machine learning models have predominantly used transcriptome data with manually defined features to detect lncRNAs, however, they often underrepresent the abundance of lncRNAs and can be biased in their detection. Here we present a study using Natural Language Processing (NLP) models to identify plant lncRNAs from genomic sequences rather than transcriptomic data. The NLP models were trained to predict lncRNAs for seven model and crop species (Zea mays, Arabidopsis thaliana, Brassica napus, Brassica oleracea, Brassica rapa, Glycine max and Oryza sativa) using publicly available genomic references. We demonstrated that lncRNAs can be accurately predicted from genomic sequences with the highest accuracy of 83.4% for Z. mays and the lowest accuracy of 57.9% for B. rapa, revealing that genome assembly quality might affect the accuracy of lncRNA identification. Furthermore, we demonstrated the potential of using NLP models for cross-species prediction with an average of 63.1% accuracy using target species not previously seen by the model. As more species are incorporated into the training datasets, we expect the accuracy to increase, becoming a more reliable tool for uncovering novel lncRNAs. Finally, we show that the models can be interpreted using explainable artificial intelligence to identify motifs important to lncRNA prediction and that these motifs frequently flanked the lncRNA sequence.

Plant long non-coding RNAs: identification and analysis to unveil their physiological functions

Eukaryotic genomes encode thousands of RNA molecules; however, only a minimal fraction is translated into proteins. Among the non-coding elements, long non-coding RNAs (lncRNAs) play important roles in diverse biological processes. LncRNAs are associated mainly with the regulation of the expression of the genome; nonetheless, their study has just scratched the surface. This is somewhat due to the lack of widespread conservation at the sequence level, in addition to their relatively low and highly tissue-specific expression patterns, which makes their exploration challenging, especially in plant genomes where only a few of these molecules have been described completely. Recently published high-quality genomes of crop plants, along with new computational tools, are considered promising resources for studying these molecules in plants. This review briefly summarizes the characteristics of plant lncRNAs, their presence and conservation, the different protocols to find these elements, and the limitations of these protocols. Likewise, it describes their roles in different plant physiological phenomena. We believe that the study of lncRNAs can help to design strategies to reduce the negative effect of biotic and abiotic stresses on the yield of crop plants and, in the future, help create fruits and vegetables with improved nutritional content, higher amounts of compounds with positive effects on human health, better organoleptic characteristics, and fruits with a longer postharvest shelf life.

Shining in the dark: the big world of small peptides in plants

Small peptides represent a subset of dark matter in plant proteomes. Through differential expression patterns and modes of action, small peptides act as important regulators of plant growth and development. Over the past 20 years, many small peptides have been identified due to technical advances in genome sequencing, bioinformatics, and chemical biology. In this article, we summarize the classification of plant small peptides and experimental strategies used to identify them as well as their potential use in agronomic breeding. We review the biological functions and molecular mechanisms of small peptides in plants, discuss current problems in small peptide research and highlight future research directions in this field. Our review provides crucial insight into small peptides in plants and will contribute to a better understanding of their potential roles in biotechnology and agriculture.

Analysis of lncRNAs in Lupinus mutabilis (Tarwi) and Their Potential Role in Drought Response

Lupinus mutabilis is a legume with high agronomic potential and available transcriptomic data for which lncRNAs have not been studied. Therefore, our objective was to identify, characterize, and validate the drought-responsive lncRNAs in L. mutabilis. To achieve this, we used a multilevel approach based on lncRNA prediction, annotation, subcellular location, thermodynamic characterization, structural conservation, and validation. Thus, 590 lncRNAs were identified by at least two algorithms of lncRNA identification. Annotation with the PLncDB database showed 571 lncRNAs unique to tarwi and 19 lncRNAs with homology in 28 botanical families including Solanaceae (19), Fabaceae (17), Brassicaceae (17), Rutaceae (17), Rosaceae (16), and Malvaceae (16), among others. In total, 12 lncRNAs had homology in more than 40 species. A total of 67% of lncRNAs were located in the cytoplasm and 33% in exosomes. Thermodynamic characterization of S03 showed a stable secondary structure with -105.67 kcal/mol. This structure included three regions, with a multibranch loop containing a hairpin with a SECIS-like element. Evaluation of the structural conservation by CROSSalign revealed partial similarities between L. mutabilis (S03) and S. lycopersicum (Solyc04r022210.1). RT-PCR validation demonstrated that S03 was upregulated in a drought-tolerant accession of L. mutabilis. Finally, these results highlighted the importance of lncRNAs in tarwi improvement under drought conditions.

ICAnnoLncRNA: A Snakemake Pipeline for a Long Non-Coding-RNA Search and Annotation in Transcriptomic Sequences

Long non-coding RNAs (lncRNAs) are RNA molecules longer than 200 nucleotides that do not encode proteins. Experimental studies have shown the diversity and importance of lncRNA functions in plants. To expand knowledge about lncRNAs in other species, computational pipelines that allow for standardised data-processing steps in a mode that does not require user control up until the final result were actively developed recently. These advancements enable wider functionality for lncRNA data identification and analysis. In the present work, we propose the ICAnnoLncRNA pipeline for the automatic identification, classification and annotation of plant lncRNAs in assembled transcriptomic sequences. It uses the LncFinder software for the identification of lncRNAs and allows the adjustment of recognition parameters using genomic data for which lncRNA annotation is available. The pipeline allows the prediction of lncRNA candidates, alignment of lncRNA sequences to the reference genome, filtering of erroneous/noise transcripts and probable transposable elements, lncRNA classification by genome location, comparison with sequences from external databases and analysis of lncRNA structural features and expression. We used transcriptomic sequences from 15 maize libraries assembled by Trinity and Hisat2/StringTie to demonstrate the application of the ICAnnoLncRNA pipeline.

Long non-coding RNA and microRNA landscape of two major domesticated cotton species

Allotetraploid cotton plants Gossypium hirsutum and Gossypium barbadense have been widely cultivated for their natural, renewable textile fibres. Even though ncRNAs in domesticated cotton species have been extensively studied, systematic identification and annotation of lncRNAs and miRNAs expressed in various tissues and developmental stages under various biological contexts are limited. This influences the comprehension of their functions and future research on these cotton species. Here, we report high confidence lncRNAs and miRNA collection from G. hirsutum accession and G. barbadense accession using large-scale RNA-seq and small RNA-seq datasets incorporated into a user-friendly database, CoNCRAtlas. This database provides a wide range and depth of lncRNA and miRNA annotation based on the systematic integration of extensive annotations such as expression patterns derived from transcriptome data analysis in thousands of samples, as well as multi-omics annotations. We assume this comprehensive resource will accelerate evolutionary and functional studies in ncRNAs and inform future breeding programs for cotton improvement. CoNCRAtlas is accessible at http://www.nipgr.ac.in/CoNCRAtlas/.

LncRNA expression analysis by comparative transcriptomics among closely related poplars and their regulatory roles in response to salt stress

Long noncoding RNAs (lncRNAs) play crucial roles in regulating key biological processes; however, our knowledge of lncRNAs' roles in plant adaptive evolution is still limited. Here, we determined the divergence of conserved lncRNAs in closely related poplar species that were either tolerant or sensitive to salt stress by comparative transcriptome analysis. Among the 34,363 identified lncRNAs, approximately 3% were shared among poplar species with conserved sequences but diversified in their function, copy number, originating genomic region and expression patterns. Further cluster analysis revealed that the conserved lncRNAs showed more similar expression patterns within salt-tolerant poplars (P. euphratica and P. pruinosa) than between salt-tolerant and salt-sensitive poplars. Among these lncRNAs, the antisense lncRNA lncERF024 was induced by salt and differentiated expression between salt-sensitive and salt-tolerant poplars. Overexpression of lncERF024 in P. alba var. pyramidalis enhanced poplar tolerance to salt stress. Furthermore, RNA pull-down and RNA-seq analysis showed that numerous candidate genes or proteins associated with stress response and photosynthesis might be involved in salt resistance in PeulncERF024-OE poplars. Altogether, our study provided novel insight into how the diversification of lncRNA expression contributes to plant adaptation traits and showed that lncERF024 may be involved in the regulation both of gene expression and protein function conferring salt tolerance in Populus.

Long Non-Coding RNAs of Plants in Response to Abiotic Stresses and Their Regulating Roles in Promoting Environmental Adaption

Abiotic stresses triggered by climate change and human activity cause substantial agricultural and environmental problems which hamper plant growth. Plants have evolved sophisticated mechanisms in response to abiotic stresses, such as stress perception, epigenetic modification, and regulation of transcription and translation. Over the past decade, a large body of literature has revealed the various regulatory roles of long non-coding RNAs (lncRNAs) in the plant response to abiotic stresses and their irreplaceable functions in environmental adaptation. LncRNAs are recognized as a class of ncRNAs that are longer than 200 nucleotides, influencing a variety of biological processes. In this review, we mainly focused on the recent progress of plant lncRNAs, outlining their features, evolution, and functions of plant lncRNAs in response to drought, low or high temperature, salt, and heavy metal stress. The approaches to characterize the function of lncRNAs and the mechanisms of how they regulate plant responses to abiotic stresses were further reviewed. Moreover, we discuss the accumulating discoveries regarding the biological functions of lncRNAs on plant stress memory as well. The present review provides updated information and directions for us to characterize the potential functions of lncRNAs in abiotic stresses in the future.

Comparative transcriptome-wide identification and differential expression of genes and lncRNAs in rice near-isogenic line (KW-Bph36-NIL) in response to BPH feeding

Brown planthopper (BPH) is the most devastating pest of rice in Asia, causing substantial yield losses and has become a challenging task to be controlled under field conditions. Although extensive measures have been taken over the past decades, which resulted in the evolution of new resistant BPH strains. Therefore, besides other possible approaches, equipping host plants with resistant genes is the most effective and environment-friendly technique for BPH control. Here, we systematically analyzed transcriptome changes in the susceptible rice variety Kangwenqingzhan (KW) and the resistant near-isogenic line (NIL) KW-Bph36-NIL, through RNA-seq, depicting the differential expression profiles of mRNAs and long non-coding RNAs (lncRNAs) in rice before and after BPH feeding. We observed a proportion of genes (1.48%) and (2.74%) were altered in KW and NIL, respectively, indicating different responses of rice strains against BPH feeding. Nevertheless, we characterized 384 differentially expressed long non-coding RNAs (DELs) that can be impacted by the two strains by alternatively changing the expression patterns of the respective coding genes, suggesting their certain involvement in response to BPH feeding. In BPH invasion, KW and NIL responded differently by modifying the synthesis, storage, and transformation of intracellular substances, adjusting the nutrient accumulation and utilization inside and outside the cells. In addition, NIL expressed stronger resistance by acutely up-regulating genes and other transcription factors related to stress resistance and plant immunity. Altogether, our study elaborates valuable insights into the genome-wide DEGs and DELs expression profiles of rice under BPH invasion by high throughput sequencing and further suggests that NILs can be utilized in BPH resistance breeding programs in developing high-resistance rice lines.

Long non-coding RNAs reveal new regulatory mechanisms controlling gene expression

A plethora of non-coding RNAs have been found in eukaryotes, notably with the advent of modern sequencing technologies to analyze the transcriptome. Apart from the well-known housekeeping RNA genes (such as the ribosomal RNA or the transfer RNA), many thousands of transcripts detected are not evidently linked to a protein-coding gene. These, so called non-coding RNAs, may code for crucial regulators of gene expression, the small si/miRNAs, for small peptides (translated under specific conditions) or may act as long RNA molecules (antisense, intronic or intergenic long non-coding RNAs or lncRNAs). The lncRNAs interact with members of multiple machineries involved in gene regulation. In this review, we discussed about how plant lncRNAs permitted to discover new regulatory mechanisms acting in epigenetic control, chromatin 3D structure and alternative splicing. These novel regulations diversified the expression patterns and protein variants of target protein-coding genes and are an important element of the response of plants to environmental stresses and their adaptation to changing conditions.

Regulation of seed oil accumulation by lncRNAs in Brassica napus

BACKGROUND

Studies have indicated that long non-coding RNAs (lncRNAs) play important regulatory roles in many biological processes. However, the regulation of seed oil biosynthesis by lncRNAs remains largely unknown.

RESULTS

We comprehensively identified and characterized the lncRNAs from seeds in three developing stages in two accessions of Brassica napus (B. napus), ZS11 (high oil content) and WH5557 (low oil content). Finally, 8094 expressed lncRNAs were identified. LncRNAs MSTRG.22563 and MSTRG.86004 were predicted to be related to seed oil accumulation. Experimental results show that the seed oil content is decreased by 3.1-3.9% in MSTRG.22563 overexpression plants, while increased about 2% in MSTRG.86004, compared to WT. Further study showed that most genes related to lipid metabolism had much lower expression, and the content of some metabolites in the processes of respiration and TCA (tricarboxylic acid) cycle was reduced in MSTRG.22563 transgenic seeds. The expression of genes involved in fatty acid synthesis and seed embryonic development (e.g., LEC1) was increased, but genes related to TAG assembly was decreased in MSTRG.86004 transgenic seeds.

CONCLUSION

Our results suggest that MSTRG.22563 might impact seed oil content by affecting the respiration and TCA cycle, while MSTRG.86004 plays a role in prolonging the seed developmental time to increase seed oil accumulation.

Wheat Long Noncoding RNAs from Organelle and Nuclear Genomes Carry Conserved microRNA Precursors Which May Together Comprise Intricate Networks in Insect Responses

Long noncoding RNAs (lncRNAs) are a diverse class of noncoding RNAs that are typically longer than 200 nucleotides but lack coding potentials. Advances in deep sequencing technologies enabled a better exploration of this type of noncoding transcripts. The poor sequence conservation, however, complicates the identification and annotation of lncRNAs at a large scale. Wheat is among the leading food staples worldwide whose production is threatened by both biotic and abiotic stressors. Here, we identified putative lncRNAs from durum wheat varieties that differ in stem solidness, a major source of defense against wheat stem sawfly, a devastating insect pest. We also analyzed and annotated lncRNAs from two bread wheat varieties, resistant and susceptible to another destructive pest, orange wheat blossom midge, with and without infestation. Several putative lncRNAs contained potential precursor sequences and/or target regions for microRNAs, another type of regulatory noncoding RNAs, which may indicate functional networks. Interestingly, in contrast to lncRNAs themselves, microRNAs with potential precursors within the lncRNA sequences appeared to be highly conserved at the sequence and family levels. We also observed a few putative lncRNAs that have perfect to near-perfect matches to organellar genomes, supporting the recent observations that organellar genomes may contribute to the noncoding transcript pool of the cell.

Integrated analysis of lncRNAs, mRNAs, and TFs to identify network modules underlying diterpenoid biosynthesis in Salvia miltiorrhiza

Long non-coding RNAs (lncRNAs) are transcripts of more than 200 nucleotides (nt) in length, with minimal or no protein-coding capacity. Increasing evidence indicates that lncRNAs play important roles in the regulation of gene expression including in the biosynthesis of secondary metabolites. Salvia miltiorrhiza Bunge is an important medicinal plant in China. Diterpenoid tanshinones are one of the main active components of S. miltiorrhiza. To better understand the role of lncRNAs in regulating diterpenoid biosynthesis in S. miltiorrhiza, we integrated analysis of lncRNAs, mRNAs, and transcription factors (TFs) to identify network modules underlying diterpenoid biosynthesis based on transcriptomic data. In transcriptomic data, we obtained 6,651 candidate lncRNAs, 46 diterpenoid biosynthetic pathway genes, and 11 TFs involved in diterpenoid biosynthesis. Combining the co-expression and genomic location analysis, we obtained 23 candidate lncRNA-mRNA/TF pairs that were both co-expressed and co-located. To further observe the expression patterns of these 23 candidate gene pairs, we analyzed the time-series expression of S. miltiorrhiza induced by methyl jasmonate (MeJA). The results showed that 19 genes were differentially expressed at least a time-point, and four lncRNAs, two mRNAs, and two TFs formed three lncRNA-mRNA and/or TF network modules. This study revealed the relationship among lncRNAs, mRNAs, and TFs and provided new insight into the regulation of the biosynthetic pathway of S. miltiorrhiza diterpenoids.

The dynamics of lncRNAs transcription in interspecific F1 allotriploid hybrids between Brassica species

Interspecific hybridization is the intrinsic forces behind genome evolution. Long non-coding RNAs (lncRNAs) are important for plant biological processes regulation. However, it is unclear that these non-coding fractions are impacted by interspecific hybridization. Here we examined the profiles of lncRNAs by comparing them with coding genes in Brassica napus, three accessions of Brassica rapa, and their F₁ hybrids. 6206 high-confidential lncRNAs were identified in F ₁ hybrids and their parentals, and the lncRNAs transcriptome in the F₁ hybrids was reprogrammed by the genome shock. Notably, genome-wide unbalanced of lncRNAs were observed between A_n and A_r subgenomes, ELD (Expression Level Dominance) was biased toward the A_n -genome in F₁ hybrids, and ELD of non-conserved lncRNAs was more than conserved lncRNAs. Our findings demonstrate that the reprogramed lncRNAs acts as important role in enhancing plant plasticity, leading to the acquisition of desirable traits in polyploid Brassica species.

Roles of non-coding RNAs in the hormonal and nutritional regulation in nodulation and nitrogen fixation

Symbiotic nitrogen fixation is an important component in the nitrogen cycle and is a potential solution for sustainable agriculture. It is the result of the interactions between the plant host, mostly restricted to legume species, and the rhizobial symbiont. From the first encounter between the host and the symbiont to eventual successful nitrogen fixation, there are delicate processes involved, such as nodule organogenesis, rhizobial infection thread progression, differentiation of the bacteroid, deregulation of the host defense systems, and reallocation of resources. All these processes are tightly regulated at different levels. Recent evidence revealed that non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), participate in these processes by controlling the transcription and translation of effector genes. In general, ncRNAs are functional transcripts without translation potential and are important gene regulators. MiRNAs, negative gene regulators, bind to the target mRNAs and repress protein production by causing the cleavage of mRNA and translational silencing. LncRNAs affect the formation of chromosomal loops, DNA methylation, histone modification, and alternative splicing to modulate gene expression. Both lncRNAs and circRNAs could serve as target mimics of miRNA to inhibit miRNA functions. In this review, we summarized and discussed the current understanding of the roles of ncRNAs in legume nodulation and nitrogen fixation in the root nodule, mainly focusing on their regulation of hormone signal transduction, the autoregulation of nodulation (AON) pathway and nutrient homeostasis in nodules. Unraveling the mediation of legume nodulation by ncRNAs will give us new insights into designing higher-performance leguminous crops for sustainable agriculture.

Genome-wide analysis suggests the potential role of lncRNAs during seed development and seed size/weight determination in chickpea

The integrated transcriptome data analyses suggested the plausible roles of lncRNAs during seed development in chickpea. The candidate lncRNAs associated with QTLs and those involved in miRNA-mediated seed size/weight determination in chickpea have been identified. Long non-coding RNAs (lncRNAs) are important regulators of various biological processes. Here, we identified lncRNAs at seven successive stages of seed development in small-seeded and large-seeded chickpea cultivars. In total, 4751 lncRNAs implicated in diverse biological processes were identified. Most of lncRNAs were conserved between the two cultivars, whereas only a few of them were conserved in other plants, suggesting their species-specificity. A large number of lncRNAs differentially expressed between the two chickpea cultivars associated with seed development-related processes were identified. The lncRNAs acting as precursors of miRNAs and those mimicking target protein-coding genes of miRNAs involved in seed size/weight determination, including HAIKU1, BIG SEEDS1, and SHB1, were also revealed. Further, lncRNAs located within seed size/weight associated quantitative trait loci were also detected. Overall, we present a comprehensive resource and identified candidate lncRNAs that may play important roles during seed development and seed size/weight determination in chickpea.

Transcriptome-guided annotation and functional classification of long non-coding RNAs in Arabidopsis thaliana

Long non-coding RNAs (lncRNAs) are a prominent class of eukaryotic regulatory genes. Despite the numerous available transcriptomic datasets, the annotation of plant lncRNAs remains based on dated annotations that have been historically carried over. We present a substantially improved annotation of Arabidopsis thaliana lncRNAs, generated by integrating 224 transcriptomes in multiple tissues, conditions, and developmental stages. We annotate 6764 lncRNA genes, including 3772 that are novel. We characterize their tissue expression patterns and find 1425 lncRNAs are co-expressed with coding genes, with enriched functional categories such as chloroplast organization, photosynthesis, RNA regulation, transcription, and root development. This improved transcription-guided annotation constitutes a valuable resource for studying lncRNAs and the biological processes they may regulate.

Genome-wide identification and characterization of long noncoding RNAs during peach (Prunus persica) fruit development and ripening

LncRNAs represent a class of RNA transcripts of more than 200 nucleotides (nt) in length without discernible protein-coding potential. The expression levels of lncRNAs are significantly affected by stress or developmental cues. Recent studies have shown that lncRNAs participate in fruit development and ripening processes in tomato and strawberry; however, in other fleshy fruits, the association between lncRNAs and fruit ripening remains largely elusive. Here, we constructed 9 ssRNA-Seq libraries from three different peach (Prunus persica) fruit developmental stages comprising the first and second exponential stages and the fruit-ripening stage. In total, 1500 confident lncRNAs from 887 loci were obtained according to the bioinformatics analysis. The lncRNAs identified in peach fruits showed distinct characteristics compared with protein-coding mRNAs, including lower expression levels, lower complexity of alternative splicing, shorter isoforms and smaller numbers of exons. Expression analysis identified 575 differentially expressed lncRNAs (DELs) classified into 6 clusters, among which members of Clusters 1, 2, 4 and 5 were putatively associated with fruit development and ripening processes. Quantitative real-time PCR revealed that the DELs indeed had stage-specific expression patterns in peach fruits. GO and KEGG enrichment analysis revealed that DELs might be associated with fruit-ripening-related physiological and metabolic changes, such as flavonoid biosynthesis, fruit texture softening, chlorophyll breakdown and aroma compound accumulation. Finally, the similarity analysis of lncRNAs within different plant species indicated the low sequence conservation of lncRNAs. Our study reports a large number of fruit-expressed lncRNAs and identifies fruit development phase-specific expressed lncRNA members, which highlights their potential functions in fruit development and ripening processes and lays the foundations for future functional research.

Revealing the novel complexity of plant long non-coding RNA by strand-specific and whole transcriptome sequencing for evolutionarily representative plant species

Background

Previous studies on plant long noncoding RNAs (lncRNAs) lacked consistency and suffered from many factors like heterogeneous data sources and experimental protocols, different plant tissues, inconsistent bioinformatics pipelines, etc. For example, the sequencing of RNAs with poly(A) tails excluded a large portion of lncRNAs without poly(A), and use of regular RNA-sequencing technique did not distinguish transcripts’ direction for lncRNAs. The current study was designed to systematically discover and analyze lncRNAs across eight evolutionarily representative plant species, using strand-specific (directional) and whole transcriptome sequencing (RiboMinus) technique.

Results

A total of 39,945 lncRNAs (25,350 lincRNAs and 14,595 lncNATs) were identified, which showed molecular features of lncRNAs that are consistent across divergent plant species but different from those of mRNA. Further, transposable elements (TEs) were found to play key roles in the origination of lncRNA, as significantly large number of lncRNAs were found to contain TEs in gene body and promoter region, and transcription of many lncRNAs was driven by TE promoters. The lncRNA sequences were divergent even in closely related species, and most plant lncRNAs were genus/species-specific, amid rapid turnover in evolution. Evaluated with PhastCons scores, plant lncRNAs showed similar conservation level to that of intergenic sequences, suggesting that most lincRNAs were young and with short evolutionary age. INDUCED BY PHOSPHATE STARVATION (IPS) was found so far to be the only plant lncRNA group with conserved motifs, which may play important roles in the adaptation of terrestrial life during migration from aquatic to terrestrial. Most highly and specially expressed lncRNAs formed co-expression network with coding genes, and their functions were believed to be closely related to their co-expression genes.

Conclusion

The study revealed novel features and complexity of lncRNAs in plants through systematic analysis, providing important insights into the origination and evolution of plant lncRNAs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08602-9.

Genome-wide identification of lncRNAs, miRNAs, mRNAs and their regulatory networks involved in tapping panel dryness in rubber tree (Hevea brasiliensis)

Noncoding RNAs (ncRNAs) play pivotal roles in various biological processes in plants. However, the role of ncRNAs in tapping panel dryness (TPD) of rubber tree (Hevea brasiliensis Muell. Arg.) is largely unknown. Here, the whole transcriptome analyses of bark tissues from healthy and TPD trees were performed to identify differentially expressed long ncRNAs (DELs), microRNAs/miRNAs (DEMs), genes (DEGs) and their regulatory networks involved in TPD. A total of 263 DELs, 174 DEMs and 1574 DEGs were identified in the bark of TPD tree compared with that of healthy tree. Kyoto Encyclopedia of Genes and Genomes analysis revealed that most of the DEGs and targets of DELs and DEMs were mainly enriched in metabolic pathways, biosynthesis of secondary metabolites and plant hormone signal transduction. Additionally, the majority of DEGs and DELs related to rubber biosynthesis were downregulated in TPD trees. Furthermore, 98 DEGs and 44 DELs were targeted by 54 DEMs, 190 DEGs were identified as putative targets of 56 DELs, and 2 and 44 DELs were predicted as precursors and endogenous target mimics of 2 and 6 DEMs, respectively. Based on these, the DEL-DEM-DEG regulatory network involved in TPD was constructed, and 13 hub DELs, 3 hub DEMs and 2 hub DEGs were identified. The results provide novel insights into the regulatory roles of ncRNAs underlying TPD and lay a foundation for future functional characterization of long ncRNAs, miRNAs and genes involved in TPD in rubber tree.

Cryo-Treatment Enhances the Embryogenicity of Mature Somatic Embryos via the lncRNA-miRNA-mRNA Network in White Spruce

In conifers, somatic embryogenesis is uniquely initiated from immature embryos in a narrow time window, which is considerably hindered by the difficulty to induce embryogenic tissue (ET) from other tissues, including mature somatic embryos. In this study, the embryogenic ability of newly induced ET and DNA methylation levels was detected, and whole-transcriptome sequencing analyses were carried out. The results showed that ultra-low temperature treatment significantly enhanced ET induction from mature somatic embryos, with the induction rate from 0.4% to 15.5%, but the underlying mechanisms remain unclear. The newly induced ET showed higher capability in generating mature embryos than the original ET. DNA methylation levels fluctuated during the ET induction process. Here, WGCNA analysis revealed that OPT4, TIP1-1, Chi I, GASA5, GST, LAX3, WRKY7, MYBS3, LRR-RLK, PBL7, and WIN1 genes are involved in stress response and auxin signal transduction. Through co-expression analysis, lncRNAs MSTRG.505746.1, MSTRG.1070680.1, and MSTRG.33602.1 might bind to pre-novel_miR_339 to promote the expression of WRKY7 genes for stress response; LAX3 could be protected by lncRNAs MSTRG.1070680.1 and MSTRG.33602.1 via serving as sponges for novel_miR_495 to initiate auxin signal transduction; lncRNAs MSTRG.505746.1, MSTRG.1070680.1, and MSTRG.33602.1 might serve as sponges for novel_miR_527 to enhance the expression of Chi I for early somatic embryo development. This study provides new insight into the area of stress-enhanced early somatic embryogenesis in conifers, which is also attributable to practical applications.

The evolutionary landscape and expression pattern of plant lincRNAs

Long intergenic non-coding RNAs (lincRNAs) are important regulators of cellular processes, including development and stress response. Many lincRNAs have been bioinformatically identified in plants, but their evolutionary dynamics and expression characteristics are still elusive. Here, we systematically identified thousands of lincRNAs in 26 plant species, including 6 non-flowering plants, investigated the conservation of the identified lincRNAs in different levels of plant lineages based on sequence and/or synteny homology and explored characteristics of the conserved lincRNAs during plant evolution and their co-expression relationship with protein-coding genes (PCGs). In addition to confirmation of the features well documented in literature for lincRNAs, such as species-specific, fewer exons, tissue-specific expression patterns and less abundantly expressed, we revealed that histone modification signals and/or binding sites of transcription factors were enriched in the conserved lincRNAs, implying their biological functionalities, as demonstrated by identifying conserved lincRNAs related to flower development in both the Brassicaceae and grass families and ancient lincRNAs potentially functioning in meristem development of non-flowering plants. Compared to PCGs, lincRNAs are more likely to be associated with transposable elements (TEs), but with different characteristics in different evolutionary lineages, for instance, the types of TEs and the variable level of association in lincRNAs with different conservativeness. Together, these results provide a comprehensive view on the evolutionary landscape of plant lincRNAs and shed new insights on the conservation and functionality of plant lincRNAs.

A review on microplastic pollution in the mangrove wetlands and microbial strategies for its remediation

Mangroves are one of the most productive ecosystems in the world harboring huge biological diversity. The prime ecological roles of mangroves are prevention of coastal erosion and shoreline protection. Mangroves face varying degrees of threats due to overexploitation, conversion of mangrove habitats for agriculture, settlement and industrial purposes, illegal encroachment, global warming, sea-level rise, El Nino, and pollution. Among them, microplastic (MP) pollution is a major concern threatening not only the mangroves per se but also the rich biodiversity that it shelters. In general, the microbial communities which are paramount to nutrient recycling and ecological dynamics undergo substantial changes upon MP exposure. If the MP pollution in the mangrove habitats continues unabated in the coming decades, there may be serious consequences on the already threatened mangrove ecosystems and the coastal communities. This review article attempts to consolidate MP pollution of mangrove wetlands, its impact on mangroves and associated microbiota, and the microbial solution for its remediation as a sustainable strategy.

Characterization of Long Non-Coding RNAs in the Bollworm, Helicoverpa zea, and Their Possible Role in Cry1Ac-Resistance

Multiple insect pest species have developed field resistance to Bt-transgenic crops. There has been a significant amount of research on protein-coding genes that contribute to resistance, such as the up-regulation of protease activity or altered receptors. However, our understanding of the role of non-protein-coding mechanisms in Bt-resistance is minimal, as is also the case for resistance to chemical pesticides. To address this problem relative to Bt, RNA-seq was used to examine statistically significant, differential gene expression between a Cry1Ac-resistant (~100-fold resistant) and Cry1Ac-susceptible strain of Helicoverpa zea, a prevalent caterpillar pest in the USA. Significant differential expression of putative long non-coding RNAs (lncRNAs) was found in the Cry1Ac-resistant strain (58 up- and 24 down-regulated gene transcripts with an additional 10 found only in resistant and four only in susceptible caterpillars). These lncRNAs were examined as potential pseudogenes and for their genomic proximity to coding genes, both of which can be indicative of regulatory relationships between a lncRNA and coding gene expression. A possible pseudogenic lncRNA was found with similarities to a cadherin. In addition, putative lncRNAs were found significantly proximal to a serine protease, ABC transporter, and CYP coding genes, potentially involved in the mechanism of Bt and/or chemical insecticide resistance. Characterization of non-coding genetic mechanisms in Helicoverpa zea will improve the understanding of the genomic evolution of insect resistance, improve the identification of specific regulators of coding genes in general (some of which could be important in resistance), and is the first step for potentially targeting these regulators for pest control and resistance management (using molecular approaches, such as RNAi and others).

Advances in Non-Coding RNA Sequencing

Non-coding RNAs (ncRNAs) comprise a set of abundant and functionally diverse RNA molecules. Since the discovery of the first ncRNA in the 1960s, ncRNAs have been shown to be involved in nearly all steps of the central dogma of molecular biology. In recent years, the pace of discovery of novel ncRNAs and their cellular roles has been greatly accelerated by high-throughput sequencing. Advances in sequencing technology, library preparation protocols as well as computational biology helped to greatly expand our knowledge of which ncRNAs exist throughout the kingdoms of life. Moreover, RNA sequencing revealed crucial roles of many ncRNAs in human health and disease. In this review, we discuss the most recent methodological advancements in the rapidly evolving field of high-throughput sequencing and how it has greatly expanded our understanding of ncRNA biology across a large number of different organisms.

Data integration and evolutionary analysis of long non-coding RNAs in 25 flowering plants

Background

Long non-coding RNAs (lncRNAs) play vital roles in many important biological processes in plants. Currently, a large fraction of plant lncRNA studies center at lncRNA identification and functional analysis. Only a few plant lncRNA studies focus on understanding their evolutionary history, which is crucial for an in-depth understanding of lncRNAs. Therefore, the integration of large volumes of plant lncRNA data is required to deeply investigate the evolution of lncRNAs.

Results

We present a large-scale evolutionary analysis of lncRNAs in 25 flowering plants. In total, we identified 199,796 high-confidence lncRNAs through data integration analysis, and grouped them into 5497 lncRNA orthologous families. Then, we divided the lncRNAs into groups based on the degree of sequence conservation, and quantified the various characteristics of 756 conserved Arabidopsis thaliana lncRNAs. We found that compared with non-conserved lncRNAs, conserved lncRNAs might have more exons, longer sequence length, higher expression levels, and lower tissue specificities. Functional annotation based on the A. thaliana coding-lncRNA gene co-expression network suggested potential functions of conserved lncRNAs including autophagy, locomotion, and cell cycle. Enrichment analysis revealed that the functions of conserved lncRNAs were closely related to the growth and development of the tissues in which they were specifically expressed.

Conclusions

Comprehensive integration of large-scale lncRNA data and construction of a phylogenetic tree with orthologous lncRNA families from 25 flowering plants was used to provide an oversight of the evolutionary history of plant lncRNAs including origin, conservation, and orthologous relationships. Further analysis revealed a differential characteristic profile for conserved lncRNAs in A. thaliana when compared with non-conserved lncRNAs. We also examined tissue specific expression and the potential functional roles of conserved lncRNAs. The results presented here will further our understanding of plant lncRNA evolution, and provide the basis for further in-depth studies of their functions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08047-6.

Neofunctionalization of a polyploidization-activated cotton long intergenic non-coding RNA DAN1 during drought stress regulation

The genomic shock of whole-genome duplication (WGD) and hybridization introduces great variation into transcriptomes, for both coding and noncoding genes. An altered transcriptome provides a molecular basis for improving adaptation during the evolution of new species. The allotetraploid cotton, together with the putative diploid ancestor species compose a fine model for study the rapid gene neofunctionalization over the genome shock. Here we report on Drought-Associated Non-coding gene 1 (DAN1), a long intergenic noncoding RNA (lincRNA) that arose from the cotton progenitor A-diploid genome after hybridization and WGD events during cotton evolution. DAN1 in allotetraploid upland cotton (Gossypium hirsutum) is a drought-responsive lincRNA predominantly expressed in the nucleoplasm. Chromatin isolation by RNA purification profiling and electrophoretic mobility shift assay analysis demonstrated that GhDAN1 RNA can bind with DNA fragments containing AAAG motifs, similar to DNA binding with one zinc finger transcription factor binding sequences. The suppression of GhDAN1 mainly regulates genes with AAAG motifs in auxin-response pathways, which are associated with drought stress regulation. As a result, GhDAN1-silenced plants exhibit improved tolerance to drought stress. This phenotype resembles the drought-tolerant phenotype of the A-diploid cotton ancestor species, which has an undetectable expression of DAN1. The role of DAN1 in cotton evolution and drought tolerance regulation suggests that the genomic shock of interspecific hybridization and WGD stimulated neofunctionalization of non-coding genes during the natural evolutionary process.

Evolutionary conservation in noncoding genomic regions

Humans may share more genomic commonalities with other species than previously thought. According to current estimates, ~5% of the human genome is functionally constrained, which is a much larger fraction than the ~1.5% occupied by annotated protein-coding genes. Hence, ~3.5% of the human genome comprises likely functional conserved noncoding elements (CNEs) preserved among organisms, whose common ancestors existed throughout hundreds of millions of years of evolution. As whole-genome sequencing emerges as a standard procedure in genetic analyses, interpretation of variations in CNEs, including the elucidation of mechanistic and functional roles, becomes a necessity. Here, we discuss the phenomenon of noncoding conservation via four dimensions (sequence, regulatory conservation, spatiotemporal expression, and structure) and the potential significance of CNEs in phenotype variation and disease.

Transcriptome Profile Analysis of Arabidopsis Reveals the Drought Stress-Induced Long Non-coding RNAs Associated With Photosynthesis, Chlorophyll Synthesis, Fatty Acid Synthesis and Degradation

Long non-coding RNAs (lncRNAs) play an important role in the response of plants to drought stress. The previous studies have reported that overexpression of LEA3 and VOC could enhance drought tolerance and improve the oil content in Brassica napus and Arabidopsis thaliana, and most of the efforts have been invested in the gene function analysis, there is little understanding of how genes that involved in these important pathways are regulated. In the present study, the transcriptomic results of LEA3 and VOC over-expressed (OE) lines were compared with the RNAi lines, mutant lines and control lines under long-term and short-term drought treatment, a series of differentially expressed lncRNAs were identified, and their regulation patterns in mRNA were also investigated in above mentioned materials. The regulation of the target genes of differentially expressed lncRNAs on plant biological functions was studied. It was revealed that the mutant lines had less drought-response related lncRNAs than that of the OE lines. Functional analysis demonstrated that multiple genes were involved in the carbon-fixing and chlorophyll metabolism, such as CDR1, CHLM, and CH1, were regulated by the upregulated lncRNA in OE lines. In LEA-OE, AT4G13180 that promotes the fatty acid synthesis was regulated by five lncRNAs that were upregulated under both long-term and short-term drought treatments. The key genes, including of SHM1, GOX2, and GS2, in the methylglyoxal synthesis pathway were all regulated by a number of down-regulated lncRNAs in OE lines, thereby reducing the content of such harmful compounds produced under stress in plants. This study identified a series of lncRNAs related to the pathways that affect photosynthesis, chlorophyll synthesis, fatty acid synthesis, degradation, and other important effects on drought resistance and oil content. The present study provided a series of lncRNAs for further improvement of crop varieties, especially drought resistant and oil content traits.

Genome-wide analysis of long noncoding RNAs affecting floral bud dormancy in pears in response to cold stress

The versatile role of long noncoding RNAs (lncRNAs) in plant growth and development has been established, but a systematic identification and analysis of lncRNAs in the pear has not been reported. Bud dormancy is a crucial and complicated protective mechanism for plants in winter. The roles of lncRNAs in the dormancy process remain largely unclear. In this study, we induced pear floral buds to enter into different dormant statuses by simulating four different chilling accumulation conditions. Then, a time series of RNA-seq analysis was performed and we identified 7594 lncRNAs in Pyrus pyrifolia (Burm. F.) Nakai that have not been identified. The sequence and expression of the lncRNAs were confirmed by PCR analysis. In total, 6253 lncRNAs were predicted to target protein-coding genes including 692 cis-regulated pairs (596 lncRNAs) and 13,158 trans-regulated pairs (6181 lncRNAs). Gene Ontology analysis revealed that most of lncRNAs' target genes were involved in catalytic activity, metabolic processes and cellular processes. In the trend analysis, 124 long-term cold response lncRNAs and 80 short-term cold response lncRNAs were predicted. Regarding the lncRNA-miRNA regulatory networks, 59 lncRNAs were identified as potential precursors for miRNA members of 20 families, 586 lncRNAs were targets of 261 pear miRNAs and 53 lncRNAs were endogenous target mimics for 26 miRNAs. In addition, three cold response lncRNAs, two miRNAs and their target genes were selected for expression confirmed. The trend of their expression was consistent with the predicted relationships among them and suggested possible roles of lncRNAs in ABA metabolic pathway. Our findings not only suggest the potential roles of lncRNAs in regulating the dormancy of pear floral buds but also provide new insights into the lncRNA-miRNA-mRNA regulatory network in plants.

Genome-Wide Analysis Identified a Set of Conserved lncRNAs Associated with Domestication-Related Traits in Rice

Crop domestication, which gives rise to a number of desirable agronomic traits, represents a typical model system of plant evolution. Numerous genomic evidence has proven that noncoding RNAs such as microRNAs and phasiRNAs, as well as protein-coding genes, are selected during crop domestication. However, limited data shows plant long noncoding RNAs (lncRNAs) are also involved in this biological process. In this study, we performed strand-specific RNA sequencing of cultivated rice Oryza sativa ssp. japonica and O. sativa ssp. indica, and their wild progenitor O. rufipogon. We identified a total of 8528 lncRNAs, including 4072 lncRNAs in O. rufipogon, 2091 lncRNAs in japonica rice, and 2365 lncRNAs in indica rice. The lncRNAs expressed in wild rice were revealed to be shorter in length and had fewer exon numbers when compared with lncRNAs from cultivated rice. We also identified a number of conserved lncRNAs in the wild and cultivated rice. The functional study demonstrated that several of these conserved lncRNAs are associated with domestication-related traits in rice. Our findings revealed the feature and conservation of lncRNAs during rice domestication and will further promote functional studies of lncRNAs in rice.

Comparative analysis of long noncoding RNAs in angiosperms and characterization of long noncoding RNAs in response to heat stress in Chinese cabbage

Long noncoding RNAs (lncRNAs) are widely present in different species and play critical roles in response to abiotic stresses. However, the functions of lncRNAs in Chinese cabbage under heat stress remain unknown. Here, we first conducted a global comparative analysis of 247,242 lncRNAs among 37 species. The results indicated that lncRNAs were poorly conserved among different species, and only 960 lncRNAs were homologous to 524 miRNA precursors. We then carried out lncRNA sequencing for a genome-wide analysis of lncRNAs and their target genes in Chinese cabbage at different stages of heat treatment. In total, 18,253 lncRNAs were identified, of which 1229 differentially expressed (DE) lncRNAs were characterized as being heat-responsive. The ceRNA network revealed that 38 lncRNAs, 16 miRNAs, and 167 mRNAs were involved in the heat response in Chinese cabbage. Combined analysis of the cis- and trans-regulated genes indicated that the targets of DE lncRNAs were significantly enriched in the "protein processing in endoplasmic reticulum" and "plant hormone signal transduction" pathways. Furthermore, the majority of HSP and PYL genes involved in these two pathways exhibited similar expression patterns and responded to heat stress rapidly. Based on the networks of DE lncRNA-mRNAs, 29 and 22 lncRNAs were found to interact with HSP and PYL genes, respectively. Finally, the expression of several critical lncRNAs and their targets was verified by qRT-PCR. Overall, we conducted a comparative analysis of lncRNAs among 37 species and performed a comprehensive analysis of lncRNAs in Chinese cabbage. Our findings expand the knowledge of lncRNAs involved in the heat stress response in Chinese cabbage, and the identified lncRNAs provide an abundance of resources for future comparative and functional studies.

Evolution and diversification of reproductive phased small interfering RNAs in Oryza species

In grasses, two types of phased, small interfering RNAs (phasiRNAs) are expressed largely in young, developing anthers. They are 21 or 24 nucleotides (nt) in length and are triggered by miR2118 or miR2275, respectively. However, most of their functions and activities are not fully understood. We performed comparative genomic analysis of their source loci (PHAS) in five Oryza genomes and combined this with analysis of high-throughput sRNA and degradome datasets. In total, we identified 8216 21-PHAS and 626 24-PHAS loci. Local tandem and segmental duplications mainly contributed to the expansion and supercluster distribution of the 21-PHAS loci. Despite their relatively conserved genomic positions, PHAS sequences diverged rapidly, except for the miR2118/2275 target sites, which were under strong selection for conservation. We found that 21-nt phasiRNAs with a 5'-terminal uridine (U) demonstrated cis-cleavage at PHAS precursors, and these cis-acting sites were also variable among close species. miR2118 could trigger phasiRNA production from its own antisense transcript and the derived phasiRNAs might reversibly regulate miR2118 precursors. We hypothesised that successful initiation of phasiRNA biogenesis is conservatively maintained, while phasiRNA products diverged quickly and are not individually conserved. In particular, phasiRNA production is under the control of multiple reciprocal regulation mechanisms.

Full-length annotation with multistrategy RNA-seq uncovers transcriptional regulation of lncRNAs in cotton

Long noncoding RNAs (lncRNAs) are crucial factors during plant development and environmental responses. To build an accurate atlas of lncRNAs in the diploid cotton Gossypium arboreum, we combined Isoform-sequencing, strand-specific RNA-seq (ssRNA-seq), and cap analysis gene expression (CAGE-seq) with PolyA-seq and compiled a pipeline named plant full-length lncRNA to integrate multi-strategy RNA-seq data. In total, 9,240 lncRNAs from 21 tissue samples were identified. 4,405 and 4,805 lncRNA transcripts were supported by CAGE-seq and PolyA-seq, respectively, among which 6.7% and 7.2% had multiple transcription start sites (TSSs) and transcription termination sites (TTSs). We revealed that alternative usage of TSS and TTS of lncRNAs occurs pervasively during plant growth. Besides, we uncovered that many lncRNAs act in cis to regulate adjacent protein-coding genes (PCGs). It was especially interesting to observe 64 cases wherein the lncRNAs were involved in the TSS alternative usage of PCGs. We identified lncRNAs that are coexpressed with ovule- and fiber development-associated PCGs, or linked to GWAS single-nucleotide polymorphisms. We mapped the genome-wide binding sites of two lncRNAs with chromatin isolation by RNA purification sequencing. We also validated the transcriptional regulatory role of lnc-Ga13g0352 via virus-induced gene suppression assay, indicating that this lncRNA might act as a dual-functional regulator that either activates or inhibits the transcription of target genes.

Insights into long non-coding RNA regulation of anthocyanin carrot root pigmentation

Carrot (Daucus carota L.) is one of the most cultivated vegetable in the world and of great importance in the human diet. Its storage organs can accumulate large quantities of anthocyanins, metabolites that confer the purple pigmentation to carrot tissues and whose biosynthesis is well characterized. Long non-coding RNAs (lncRNAs) play critical roles in regulating gene expression of various biological processes in plants. In this study, we used a high throughput stranded RNA-seq to identify and analyze the expression profiles of lncRNAs in phloem and xylem root samples using two genotypes with a strong difference in anthocyanin production. We discovered and annotated 8484 new genes, including 2095 new protein-coding and 6373 non-coding transcripts. Moreover, we identified 639 differentially expressed lncRNAs between the phenotypically contrasted genotypes, including certain only detected in a particular tissue. We then established correlations between lncRNAs and anthocyanin biosynthesis genes in order to identify a molecular framework for the differential expression of the pathway between genotypes. A specific natural antisense transcript linked to the DcMYB7 key anthocyanin biosynthetic transcription factor suggested how the regulation of this pathway may have evolved between genotypes.

NONCODEV6: an updated database dedicated to long non-coding RNA annotation in both animals and plants

NONCODE (http://www.noncode.org/) is a comprehensive database of collection and annotation of noncoding RNAs, especially long non-coding RNAs (lncRNAs) in animals. NONCODEV6 is dedicated to providing the full scope of lncRNAs across plants and animals. The number of lncRNAs in NONCODEV6 has increased from 548 640 to 644 510 since the last update in 2017. The number of human lncRNAs has increased from 172 216 to 173 112. The number of mouse lncRNAs increased from 131 697 to 131 974. The number of plant lncRNAs is 94 697. The relationship between lncRNAs in human and cancer were updated with transcriptome sequencing profiles. Three important new features were also introduced in NONCODEV6: (i) updated human lncRNA-disease relationships, especially cancer; (ii) lncRNA annotations with tissue expression profiles and predicted function in five common plants; iii) lncRNAs conservation annotation at transcript level for 23 plant species. NONCODEV6 is accessible through http://www.noncode.org/.

From Trash to Luxury: The Potential Role of Plant LncRNA in DNA Methylation During Abiotic Stress

Remarkable progress has been made in elucidating important roles of plant non-coding RNAs. Among these RNAs, long noncoding RNAs (lncRNAs) have gained widespread attention, especially their role in plant environmental stress responses. LncRNAs act at different levels of gene expression regulation, and one of these mechanisms is by recruitment of DNA methyltransferases or demethylases to regulate the target gene transcription. In this mini-review, we highlight the function of lncRNAs, including their potential role in RNA-directed DNA Methylation (RdDM) silencing pathway and their potential function under abiotic stresses conditions. Moreover, we also present and discuss studies of lncRNAs in crops. Finally, we propose a path outlook for future research that may be important for plant breeding.

Identification of lncRNAs in response to infection by Plasmodiophora brassicae in Brassica napus and development of lncRNA-based SSR markers

Clubroot resistance in spring canola has been introgressed from different Brassica sources; however, molecular mechanism underlying this resistance, especially the involvement of long non-coding RNAs (lncRNAs), is yet to be understood. We identified 464 differentially expressed (DE) lncRNAs from the roots of clubroot-resistant canola, carrying resistance on chromosome BnaA03, and susceptible canola lines challenged with Plasmodiophora brassicae pathotype 3. Pathway enrichment analysis showed that most of the target genes regulated by these DE lncRNAs belonged to plant-pathogen interaction and hormone signaling, as well as primary and secondary metabolic pathways. Comparative analysis of these lncRNAs with 530 previously reported DE lncRNAs, identified using resistance located on BnaA08, detected 12 lncRNAs that showed a similar trend of upregulation in both types of resistant lines; these lncRNAs probably play a fundamental role in clubroot resistance. We identified SSR markers within 196 DE lncRNAs. Genotyping of two DH populations carrying resistance on BnaA03 identified a marker capable of detecting the resistance in 98% of the DH lines. To our knowledge, this is the first report of the identification of SSRs within lncRNAs responsive to P. brassicae infection, demonstrating the potential use of lncRNAs in the breeding of Brassica crops.

Long non-coding RNAs: emerging players regulating plant abiotic stress response and adaptation

BACKGROUND

The immobile nature of plants means that they can be frequently confronted by various biotic and abiotic stresses during their lifecycle. Among the various abiotic stresses, water stress, temperature extremities, salinity, and heavy metal toxicity are the major abiotic stresses challenging overall plant growth. Plants have evolved complex molecular mechanisms to adapt under the given abiotic stresses. Long non-coding RNAs (lncRNAs)-a diverse class of RNAs that contain > 200 nucleotides(nt)-play an essential role in plant adaptation to various abiotic stresses.

RESULTS

LncRNAs play a significant role as 'biological regulators' for various developmental processes and biotic and abiotic stress responses in animals and plants at the transcription, post-transcription, and epigenetic level, targeting various stress-responsive mRNAs, regulatory gene(s) encoding transcription factors, and numerous microRNAs (miRNAs) that regulate the expression of different genes. However, the mechanistic role of lncRNAs at the molecular level, and possible target gene(s) contributing to plant abiotic stress response and adaptation, remain largely unknown. Here, we review various types of lncRNAs found in different plant species, with a focus on understanding the complex molecular mechanisms that contribute to abiotic stress tolerance in plants. We start by discussing the biogenesis, type and function, phylogenetic relationships, and sequence conservation of lncRNAs. Next, we review the role of lncRNAs controlling various abiotic stresses, including drought, heat, cold, heavy metal toxicity, and nutrient deficiency, with relevant examples from various plant species. Lastly, we briefly discuss the various lncRNA databases and the role of bioinformatics for predicting the structural and functional annotation of novel lncRNAs.

CONCLUSIONS

Understanding the intricate molecular mechanisms of stress-responsive lncRNAs is in its infancy. The availability of a comprehensive atlas of lncRNAs across whole genomes in crop plants, coupled with a comprehensive understanding of the complex molecular mechanisms that regulate various abiotic stress responses, will enable us to use lncRNAs as potential biomarkers for tailoring abiotic stress-tolerant plants in the future.

Application of deep learning in genomics

In recent years, deep learning has been widely used in diverse fields of research, such as speech recognition, image classification, autonomous driving and natural language processing. Deep learning has showcased dramatically improved performance in complex classification and regression problems, where the intricate structure in the high-dimensional data is difficult to discover using conventional machine learning algorithms. In biology, applications of deep learning are gaining increasing popularity in predicting the structure and function of genomic elements, such as promoters, enhancers, or gene expression levels. In this review paper, we described the basic concepts in machine learning and artificial neural network, followed by elaboration on the workflow of using convolutional neural network in genomics. Then we provided a concise introduction of deep learning applications in genomics and synthetic biology at the levels of DNA, RNA and protein. Finally, we discussed the current challenges and future perspectives of deep learning in genomics.

Decoding the plant genome: From epigenome to 3D organization

The linear genome of eukaryotes is partitioned into diverse chromatin states and packaged into a three-dimensional (3D) structure, which has functional implications in DNA replication, DNA repair, and transcriptional regulation. Over the past decades, research on plant functional genomics and epigenomics has made great progress, with thousands of genes cloned and molecular mechanisms of diverse biological processes elucidated. Recently, 3D genome research has gradually attracted great attention of many plant researchers. Herein, we briefly review the progress in genomic and epigenomic research in plants, with a focus on Arabidopsis and rice, and summarize the currently used technologies and advances in plant 3D genome organization studies. We also discuss the relationships between one-dimensional linear genome sequences, epigenomic states, and the 3D chromatin architecture. This review provides basis for future research on plant 3D genomics.

Transcriptome Analysis of Rice Reveals the lncRNA-mRNA Regulatory Network in Response to Rice Black-Streaked Dwarf Virus Infection

The plant genome can produce long non-coding RNAs (lncRNAs), some of which have been identified as important regulators of gene expression. To better understand the response mechanism of rice plants to Rice black-streaked dwarf virus (RBSDV) infection, we performed a comparative transcriptome analysis between the RBSDV-infected and non-infected rice plants. A total of 1342 mRNAs and 22 lncRNAs were identified to be differentially expressed after RBSDV infection. Most differentially expressed transcripts involved in the plant–pathogen interaction pathway were upregulated after RBSDV infection, indicating the activation of rice defense response by RBSDV. A network of differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs) was then constructed. In this network, there are 56 plant–pathogen interaction-related DEmRNAs co-expressing with 20 DElncRNAs, suggesting these DElncRNAs and DEmRNAs may play essential roles in rice innate immunity against RBSDV. Moreover, some of the lncRNA–mRNA regulatory relationships were experimentally verified in rice calli by a quick and effective method established in this study. Three DElncRNAs were selected to be tested, and the results indicated that five mRNAs were found to be regulated by them. Together, we give a whole landscape of rice mRNAs and lncRNAs in response to RBSDV infection, and a feasible method to rapidly verify the lncRNA–mRNA regulatory relationship in rice.