Systematic identification of long non-coding RNAs during pollen development and fertilization in Brassica rapa

Identification and fine mapping of Brmmd1 gene controlling recessive genic male sterility in Brassica rapa L

Recessive genic male sterility (RGMS) provides an effective approach for the commercial exploitation of heterosis, especially in Brassica crops. Although some artificial RGMS mutants have been reported in B. rapa, no causal genes derived from these natural mutants have been identified so far. In this study, a spontaneous RGMS mutant Bcajh97-01A derived from the 'Aijiaohuang' line traced back to the 1980 s was identified. Genetic analysis revealed that the RGMS trait was controlled by a single locus in the Bcajh97-01A/B system. Bulk segregant analysis (BSA) in combination with linkage analysis was employed to delimit the causal gene to an approximate 129 kb interval on chromosome A02. The integrated information of transcriptional levels and the predicted genes in the target region indicated that the Brmmd1 (BraA02g017420) encoding a PHD-containing nuclear protein was the most likely candidate gene. A 374 bp miniature inverted-repeat transposable element (MITE) was inserted into the first exon to prematurely stop the Brmmd1 gene translation, thus blocking the normal expression of this gene at the tetrad stage in the Bcajh97-01A. Additionally, a co-segregating structure variation (SV) marker was developed to rapidly screen the RGMS progenies from Bcajh97-01A/B system. Our findings reveal that BraA02g017420 is the causal gene responsible for the RGMS trait. This study lays a foundation for marker-assisted selection and further molecular mechanism exploration of pollen development in B. rapa.

Tetrad stage transient cold stress skews auxin-mediated energy metabolism balance in Chinese cabbage pollen

Changing ambient temperature often impairs plant development and sexual reproduction, particularly pollen ontogenesis. However, mechanisms underlying cold stress-induced male sterility are not well understood. Here, we exposed Chinese cabbage (Brassica campestris) to different cold conditions during flowering and demonstrated that the tetrad stage was the most sensitive. After completion of pollen development at optimal conditions, transient cold stress at the tetrad stage still impacted auxin levels, starch and lipid accumulation, and pollen germination, ultimately resulting in partial male sterility. Transcriptome and metabolome analyses and histochemical staining indicated that the reduced pollen germination rate was due to the imbalance of energy metabolism during pollen maturation. The investigation of β-glucuronidase (GUS)-overexpressing transgenic plants driven by the promoter of DR5 (DR5::GUS report system) combined with cell tissue staining and metabolome analysis further validated that cold stress during the tetrad stage reduced auxin levels in mature pollen grains. Low-concentration auxin treatment on floral buds at the tetrad stage before cold exposure improved the cold tolerance of mature pollen grains. Artificially changing the content of endogenous auxin during pollen maturation by spraying chemical reagents and loss-of-function investigation of the auxin biosynthesis gene YUCCA6 by artificial microRNA technology showed that starch overaccumulation severely reduced the pollen germination rate. In summary, we revealed that transient cold stress at the tetrad stage of pollen development in Chinese cabbage causes auxin-mediated starch-related energy metabolism imbalance that contributes to the decline in pollen germination rate and ultimately seed set.

Identification and Analysis of lncRNA and circRNA Related to Wheat Grain Development

The role of lncRNA and circRNA in wheat grain development is still unclear. The objectives of this study were to characterize the lncRNA and circRNA in the wheat grain development and to construct the interaction network among lncRNA, circRNA, and their target miRNA to propose a lncRNA-circRNA-miRNA module related to wheat grain development. Full transcriptome sequencing on two wheat varieties (Annong 0942 and Anke 2005) with significant differences in 1000-grain weight at 10 d (days after pollination), 20 d, and 30 d of grain development were conducted. We detected 650, 736, and 609 differentially expressed lncRNA genes, and 769, 1054, and 1062 differentially expressed circRNA genes in the grains of 10 days, 20 days and 30 days after pollination between Annong 0942 and Anke 2005, respectively. An analysis of the lncRNA-miRNA and circRNA-miRNA targeting networks reveals that circRNAs exhibit a more complex and extensive interaction network in the development of cereal grains and the formation of grain shape. Central to these interactions are tae-miR1177, tae-miR1128, and tae-miR1130b-3p. In contrast, lncRNA genes only form a singular network centered around tae-miR1133 and tae-miR5175-5p when comparing between varieties. Further analysis is conducted on the underlying genes of all target miRNAs, we identified TaNF-YB1 targeted by tae-miR1122a and TaTGW-7B targeted by miR1130a as two pivotal regulatory genes in the development of wheat grains. The quantitative real-time PCR (qRT-PCR) and dual-luciferase reporter assays confirmed the target regulatory relationships between miR1130a-TaTGW-7B and miR1122a-TaNF-YB1. We propose a network of circRNA and miRNA-mediated gene regulation in the development of wheat grains.

Transcriptome analysis reveals the potential lncRNA-mRNA modules involved in genetic male sterility and fertility of Chinese cabbage (brassica rapa L. ssp. pekinensis)

BACKGROUND

Long non-coding RNAs (lncRNAs) play a crucial role in regulating gene expression vital for the growth and development of plants. Despite this, the role of lncRNAs in Chinese cabbage (Brassica rapa L. ssp. pekinensis) pollen development and male fertility remains poorly understood.

RESULTS

In this study, we characterized a recessive genic male sterile mutant (366-2 S), where the delayed degradation of tapetum and the failure of tetrad separation primarily led to the inability to form single microspores, resulting in male sterility. To analyze the role of lncRNAs in pollen development, we conducted a comparative lncRNA sequencing using anthers from the male sterile mutant line (366-2 S) and the wild-type male fertile line (366-2 F). We identified 385 differentially expressed lncRNAs between the 366-2 F and 366-2 S lines, with 172 of them potentially associated with target genes. To further understand the alterations in mRNA expression and explore potential lncRNA-target genes (mRNAs), we performed comparative mRNA transcriptome analysis in the anthers of 366-2 S and 366-2 F at two stages. We identified 1,176 differentially expressed mRNAs. Remarkably, GO analysis revealed significant enrichment in five GO terms, most notably involving mRNAs annotated as pectinesterase and polygalacturonase, which play roles in cell wall degradation. The considerable downregulation of these genes might contribute to the delayed degradation of tapetum in 366-2 S. Furthermore, we identified 15 lncRNA-mRNA modules through Venn diagram analysis. Among them, MSTRG.9997-BraA04g004630.3 C (β-1,3-glucanase) is associated with callose degradation and tetrad separation. Additionally, MSTRG.5212-BraA02g040020.3 C (pectinesterase) and MSTRG.13,532-BraA05g030320.3 C (pectinesterase) are associated with cell wall degradation of the tapetum, indicating that these three candidate lncRNA-mRNA modules potentially regulate pollen development.

CONCLUSION

This study lays the foundation for understanding the roles of lncRNAs in pollen development and for elucidating their molecular mechanisms in regulating male sterility in Chinese cabbage.

Emerging roles and mechanisms of lncRNAs in fruit and vegetables

With the development of genome sequencing technologies, many long non-coding RNAs (lncRNAs) have been identified in fruit and vegetables. lncRNAs are primarily transcribed and spliced by RNA polymerase II (Pol II) or plant-specific Pol IV/V, and exhibit limited evolutionary conservation. lncRNAs intricately regulate various aspects of fruit and vegetables, including pigment accumulation, reproductive tissue development, fruit ripening, and responses to biotic and abiotic stresses, through diverse mechanisms such as gene expression modulation, interaction with hormones and transcription factors, microRNA regulation, and involvement in alternative splicing. This review presents a comprehensive overview of lncRNA classification, basic characteristics, and, most importantly, recent advances in understanding their functions and regulatory mechanisms.

The roles of non-coding RNAs in male reproductive development and abiotic stress responses during this unique process in flowering plants

Successful male reproductive development is the guarantee for sexual reproduction of flowering plants. Male reproductive development is a complicated and multi-stage process that integrates physiological processes and adaptation and tolerance to a myriad of environmental stresses. This well-coordinated process is governed by genetic and epigenetic machineries. Non-coding RNAs (ncRNAs) play pleiotropic roles in the plant growth and development. The identification, characterization and functional analysis of ncRNAs and their target genes have opened a new avenue for comprehensively revealing the regulatory network of male reproductive development and its response to environmental stresses in plants. This review briefly addresses the types, origin, biogenesis and mechanisms of ncRNAs in plants, highlights important updates on the roles of ncRNAs in regulating male reproductive development and emphasizes the contribution of ncRNAs, especially miRNAs and lncRNAs, in responses to abiotic stresses during this unique process in flowering plants.

Identifying long non-coding RNAs involved in heat stress response during wheat pollen development

Introduction

Wheat is a staple food crop for over one-third of the global population. However, the stability of wheat productivity is threatened by heat waves associated with climate change. Heat stress at the reproductive stage can result in pollen sterility and failure of grain development.

Methods

This study used transcriptome data analysis to explore the specific expression of long non-coding RNAs (lncRNAs) in response to heat stress during pollen development in four wheat cultivars.

Results and discussion

We identified 11,054 lncRNA-producing loci, of which 5,482 lncRNAs showed differential expression in response to heat stress. Heat-responsive lncRNAs could target protein-coding genes in cis and trans and in lncRNA-miRNA-mRNA regulatory networks. Gene ontology analysis predicted that target protein-coding genes of lncRNAs regulate various biological processes such as hormonal responses, protein modification and folding, response to stress, and biosynthetic and metabolic processes. We also noted some paired lncRNA/protein-coding gene modules and some lncRNA-miRNA-mRNA regulatory modules shared in two or more wheat cultivars. These modules were related to regulating plant responses to heat stress, such as heat-shock proteins and transcription factors, and protein domains, such as MADS-box, Myc-type, and Alpha crystallin/Hsp20 domain.

Conclusion

Our results provide the basic knowledge and molecular resources for future functional studies investigating wheat reproductive development under heat stress.

From TgO/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma

Toxoplasma gondii causes morbidity, mortality, and disseminates widely via cat sexual stages. Here, we find T. gondii ornithine aminotransferase (OAT) is conserved across phyla. We solve TgO/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for TgO/GABA-AT over human OAT and GABA-AT. However, abrogating TgO/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat's oocyst shedding. Increased sporozoite/merozoite TgO/GABA-AT expression led to our study of a mutagenized clone with oocyst formation blocked, arresting after forming male and female gametes, with "Rosetta stone"-like mutations in genes expressed in merozoites. Mutations are similar to those in organisms from plants to mammals, causing defects in conception and zygote formation, affecting merozoite capacitation, pH/ionicity/sodium-GABA concentrations, drawing attention to cyclic AMP/PKA, and genes enhancing energy or substrate formation in TgO/GABA-AT-related-pathways. These candidates potentially influence merozoite's capacity to make gametes that fuse to become zygotes, thereby contaminating environments and causing disease.

Current perspectives of lncRNAs in abiotic and biotic stress tolerance in plants

Abiotic/biotic stresses pose a major threat to agriculture and food security by impacting plant growth, productivity and quality. The discovery of extensive transcription of large RNA transcripts that do not code for proteins, termed long non-coding RNAs (lncRNAs) with sizes larger than 200 nucleotides in length, provides an important new perspective on the centrality of RNA in gene regulation. In plants, lncRNAs are widespread and fulfill multiple biological functions in stress response. In this paper, the research advances on the biological function of lncRNA in plant stress response were summarized, like as Natural Antisense Transcripts (NATs), Competing Endogenous RNAs (ceRNAs) and Chromatin Modification etc. And in plants, lncRNAs act as a key regulatory hub of several phytohormone pathways, integrating abscisic acid (ABA), jasmonate (JA), salicylic acid (SA) and redox signaling in response to many abiotic/biotic stresses. Moreover, conserved sequence motifs and structural motifs enriched within stress-responsive lncRNAs may also be responsible for the stress-responsive functions of lncRNAs, it will provide a new focus and strategy for lncRNA research. Taken together, we highlight the unique role of lncRNAs in integrating plant response to adverse environmental conditions with different aspects of plant growth and development. We envisage that an improved understanding of the mechanisms by which lncRNAs regulate plant stress response may further promote the development of unconventional approaches for breeding stress-resistant crops.

Transcription Factors and Their Regulatory Roles in the Male Gametophyte Development of Flowering Plants

Male gametophyte development in plants relies on the functions of numerous genes, whose expression is regulated by transcription factors (TFs), non-coding RNAs, hormones, and diverse environmental stresses. Several excellent reviews are available that address the genes and enzymes associated with male gametophyte development, especially pollen wall formation. Growing evidence from genetic studies, transcriptome analysis, and gene-by-gene studies suggests that TFs coordinate with epigenetic machinery to regulate the expression of these genes and enzymes for the sequential male gametophyte development. However, very little summarization has been performed to comprehensively review their intricate regulatory roles and discuss their downstream targets and upstream regulators in this unique process. In the present review, we highlight the research progress on the regulatory roles of TF families in the male gametophyte development of flowering plants. The transcriptional regulation, epigenetic control, and other regulators of TFs involved in male gametophyte development are also addressed.

A lncRNA bra-miR156HG regulates flowering time and leaf morphology as a precursor of miR156 in Brassica campestris and Arabidopsis thaliana

Long non-coding RNAs (lncRNAs) are important regulators in plant growth and development. Here the function of a lncRNA fragment was studied, which was predicted as an endogenous target mimic (eTM) of miR156 in Brassica campesrtis. Unexpectedly, the transformation of this lncRNA into Arabidopsis thaliana neither inhibited the expression of miR156a nor resulted in any phenotypes that differed from the control plants (CK). The full-length sequence of the lncRNA (named bra-miR156HG) was then obtained using RACE and transferred into A. thaliana. The transgenic plants displayed a delay in flowering time, an increasing number of rosette leaves, and a changed morphology of cauline leaves, which was similar to the plants that expressed bra-miR156a. In contrast, the overexpression of bra-miR156HG in B. campestris resulted in an increased tip angle of leaves and changed the length-width ratio of leaves at different nodes, suggesting that bra-miR156HG may be involved in regulating the leaf morphology. Collectively, our study showed that bra-miR156HG functions as a precursor of bra-miR156a involved in regulating plant flowering time and leaf development under different biological backgrounds. The secondary structure of lncRNA is essential not only for the normal roles that it plays but also for expanding the functional diversities.

Deciphering shared attributes of plant long non-coding RNAs through a comparative computational approach

Over the past decade, long non-coding RNA (lncRNA), which lacks protein-coding potential, has emerged as an essential regulator of the genome. The present study examined 13,599 lncRNAs in Arabidopsis thaliana, 11,565 in Oryza sativa, and 32,397 in Zea mays for their characteristic features and explored the associated genomic and epigenomic features. We found lncRNAs were distributed throughout the chromosomes and the Helitron family of transposable elements (TEs) enriched, while the terminal inverted repeat depleted in lncRNA transcribing regions. Our analyses determined that lncRNA transcribing regions show rare or weak signals for most epigenetic marks except for H3K9me2 and cytosine methylation in all three plant species. LncRNAs showed preferential localization in the nucleus and cytoplasm; however, the distribution ratio in the cytoplasm and nucleus varies among the studied plant species. We identified several conserved endogenous target mimic sites in the lncRNAs among the studied plants. We found 233, 301, and 273 unique miRNAs, potentially targeting the lncRNAs of A. thaliana, O. sativa, and Z. mays, respectively. Our study has revealed that miRNAs, which interact with lncRNAs, target genes that are involved in a diverse array of biological and molecular processes. The miRNA-targeted lncRNAs displayed a strong affinity for several transcription factors, including ERF and BBR-BPC, mutually present in all three plants, advocating their conserved functions. Overall, the present study showed that plant lncRNAs exhibit conserved genomic and epigenomic characteristics and potentially govern the growth and development of plants.

An insight into the roles of regulatory ncRNAs in plants: An abiotic stress and developmental perspective

Different environmental cues lead to changes in physiology, biochemistry and molecular status of plant's growth. Till date, various genes have been accounted for their role in regulating plant development and response to abiotic stress. Excluding genes that code for a functional protein in a cell, a large chunk of the eukaryotic transcriptome consists of non-coding RNAs (ncRNAs) which lack protein coding capacity but are still functional. Recent advancements in Next Generation Sequencing (NGS) technology have led to the unearthing of different types of small and large non-coding RNAs in plants. Non-coding RNAs are broadly categorised into housekeeping ncRNAs and regulatory ncRNAs which work at transcriptional, post-transcriptional and epigenetic levels. Diverse ncRNAs play different regulatory roles in nearly all biological processes including growth, development and response to changing environments. This response can be perceived and counteracted by plants using diverse evolutionarily conserved ncRNAs like miRNAs, siRNAs and lncRNAs to participate in complex molecular regimes by activating gene-ncRNA-mRNA regulatory modules to perform the downstream function. Here, we review the current understanding with a focus on recent advancements in the functional studies of the regulatory ncRNAs at the nexus of abiotic stresses and development. Also, the potential roles of ncRNAs in imparting abiotic stress tolerance and yield improvement in crop plants are also discussed with their future prospects.

Plant long noncoding RNAs: Recent progress in understanding their roles in growth, development, and stress responses

Long noncoding RNA (lncRNA) transcripts are longer than 200 nt and are not translated into proteins. LncRNAs function in a wide variety of processes in plants and animals, but, perhaps because of their lower expression and conservation levels, plant lncRNAs had attracted less attention than protein-coding mRNAs. Now, recent studies have made remarkable progress in identifying lncRNAs and understanding their functions. In this review, we discuss a number of lncRNAs that have important functions in growth, development, reproduction, responses to abiotic stresses, and regulation of disease and insect resistance in plants. Additionally, we describe the known mechanisms of action of plant lncRNAs according to their origins within the genome. This review thus provides a guide for identifying and functionally characterizing new lncRNAs in plants.

The cotton pectin methyl esterase gene GhPME21 functions in microspore development and fertility in Gossypium hirsutum L

Pectin widely exists in higher plants' cell walls and intercellular space of higher plants and plays an indispensable role in plant growth and development. We identified 55 differentially expressed genes related to pectin degradation by transcriptomic analysis in the male sterile mutant, ms1. A gene encoding pectin methylesterase (GhPME21) was found to be predominantly expressed in the developing stamens of cotton but was significantly down-regulated in ms1 stamens. The tapetal layer of GhPME21 interfered lines (GhPME21i) was significantly thickened compared to that of WT at the early stage; anther compartment morphology of GhPME21i lines was abnormal, and the microspore wall was broken at the middle stage; Alexander staining showed that the pollen grains of GhPME21i lines differed greatly in volume at the late stage. The mature pollen surfaces of GhPME21i lines were deposited with discontinuous and broken sheets and prickles viewed under SEM. Fewer pollen tubes were observed to germinate in vitro in GhPME21i lines, while tiny of those in vivo were found to elongate to the ovary. The seeds harvested from GhPME21i lines as pollination donors were dry and hollow. The changes of phenotypes in GhPME21i lines at various stages illustrated that the GhPME21 gene played a vital role in the development of cotton stamens and controlled plant fertility by affecting stamen development, pollen germination, and pollen tube elongation. The findings of this study laid the groundwork for further research into the molecular mechanisms of PMEs involved in microspore formation and the creation of cotton male sterility materials.

The proposed role of MSL-lncRNAs in causing sex lability of female poplars

Labile sex expression is frequently observed in dioecious plants, but the underlying genetic mechanism remains largely unknown. Sex plasticity is also observed in many Populus species. Here we carried out a systematic study on a maleness-promoting gene, MSL, detected in the Populus deltoides genome. Our results showed that both strands of MSL contained multiple cis-activating elements, which generated long non-coding RNAs (lncRNAs) promoting maleness. Although female P. deltoides did not have the male-specific MSL gene, a large number of partial sequences with high sequence similarity to this gene were detected in the female poplar genome. Based on sequence alignment, the MSL sequence could be divided into three partial sequences, and heterologous expression of these partial sequences in Arabidopsis confirmed that they could promote maleness. Since activation of the MSL sequences can only result in female sex lability, we propose that MSL-lncRNAs might play a role in causing sex lability of female poplars.

Genomic survey of high-throughput RNA-Seq data implicates involvement of long intergenic non-coding RNAs (lincRNAs) in cytoplasmic male-sterility and fertility restoration in pigeon pea

BACKGROUND

Long-intergenic non-coding RNAs (lincRNAs) originate from intergenic regions and have no coding potential. LincRNAs have emerged as key players in the regulation of various biological processes in plant development. Cytoplasmic male-sterility (CMS) in association with restorer-of-fertility (Rf) systems makes it a highly reliable tool for exploring heterosis for producing commercial hybrid seeds. To date, there have been no reports of lincRNAs during pollen development in CMS and fertility restorer lines in pigeon pea.

OBJECTIVE

Identification of lincRNAs in the floral buds of cytoplasmic male-sterile (AKCMS11) and fertility restorer (AKPR303) pigeon pea lines.

METHODS

We employed a computational approach to identify lincRNAs in the floral buds of cytoplasmic male-sterile (AKCMS11) and fertility restorer (AKPR303) pigeon pea lines using RNA-Seq data.

RESULTS

We predicted a total of 2145 potential lincRNAs of which 966 were observed to be differentially expressed between the sterile and fertile pollen. We identified, 927 cis-regulated and 383 trans-regulated target genes of the lincRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the target genes revealed that these genes were specifically enriched in pathways like pollen and pollen tube development, oxidative phosphorylation, etc. We detected 23 lincRNAs that were co-expressed with 17 pollen-related genes with known functions. Fifty-nine lincRNAs were predicted to be endogenous target mimics (eTMs) for 25 miRNAs, and found to be associated with pollen development. The, lincRNA regulatory networks revealed that different lincRNA-miRNA-mRNA networks might be associated with CMS and fertility restoration.

CONCLUSION

Thus, this study provides valuable information by highlighting the functions of lincRNAs as regulators during pollen development in pigeon pea and utilization in hybrid seed production.

Promoter Variation of the Key Apple Fruit Texture Related Gene MdPG1 and the Upstream Regulation Analysis

MdPG1 encoding polygalacturonase in apple (Malus × domestica) is a key gene associated with fruit firmness and texture variations among apple cultivars. However, the causative variants of MdPG1 are still not known. In this study, we identified a SNP^A/C variant within an ERF-binding element located in the promoter region of MdPG1. The promoter containing the ERF-binding element with SNP^A, rather than the SNP^C, could be strongly bound and activated by MdCBF2, a member of the AP2/ERF transcription factor family, as determined by yeast-one-hybrid and dual-luciferase reporter assays. We also demonstrated that the presence of a novel long non-coding RNA, lncRNA_PG1, in the promoter of MdPG1 was a causative variant. lncRNA_PG1 was specifically expressed in fruit tissues postharvest. lncRNA_PG1 could reduce promoter activity when it was fused to the promoter of MdPG1 and a tobacco gene encoding Mg-chelatase H subunit (NtCHLH) in transgenic tobacco cells but could not reduce promoter activity when it was supplied in a separate gene construct, indicating a cis-regulatory effect. Our results provide new insights into genetic regulation of MdPG1 allele expression and are also useful for the development of elite apple cultivars.

Construction of ceRNA Networks at Different Stages of Somatic Embryogenesis in Garlic

LncRNA (long non-coding RNA) and mRNA form a competitive endogenous RNA (ceRNA) network by competitively binding to common miRNAs. This network regulates various processes of plant growth and development at the post-transcriptional level. Somatic embryogenesis is an effective means of plant virus-free rapid propagation, germplasm conservation, and genetic improvement, which is also a typical process to study the ceRNA regulatory network during cell development. Garlic is a typical asexual reproductive vegetable. Somatic cell culture is an effective means of virus-free rapid propagation in garlic. However, the ceRNA regulatory network of somatic embryogenesis remains unclear in garlic. In order to clarify the regulatory role of the ceRNA network in garlic somatic embryogenesis, we constructed lncRNA and miRNA libraries of four important stages (explant stage: EX; callus stage: AC; embryogenic callus stage: EC; globular embryo stage: GE) in the somatic embryogenesis of garlic. It was found that 44 lncRNAs could be used as precursors of 34 miRNAs, 1511 lncRNAs were predicted to be potential targets of 144 miRNAs, and 45 lncRNAs could be used as eTMs of 29 miRNAs. By constructing a ceRNA network with miRNA as the core, 144 miRNAs may bind to 1511 lncRNAs and 12,208 mRNAs. In the DE lncRNA-DE miRNA-DE mRNA network of adjacent stages of somatic embryo development (EX-VS-CA, CA-VS-EC, EC-VS-GE), by KEGG enrichment of adjacent stage DE mRNA, plant hormone signal transduction, butyric acid metabolism, and C5-branched dibasic acid metabolism were significantly enriched during somatic embryogenesis. Since plant hormones play an important role in somatic embryogenesis, further analysis of plant hormone signal transduction pathways revealed that the auxin pathway-related ceRNA network (lncRNAs-miR393s-TIR) may play a role in the whole stage of somatic embryogenesis. Further verification by RT-qPCR revealed that the lncRNA125175-miR393h-TIR2 network plays a major role in the network and may affect the occurrence of somatic embryos by regulating the auxin signaling pathway and changing the sensitivity of cells to auxin. Our results lay the foundation for studying the role of the ceRNA network in the somatic embryogenesis of garlic.

Research progress on the roles of lncRNAs in plant development and stress responses

Long non-coding RNAs (lncRNAs) are RNAs of more than 200 nucleotides in length that are not (or very rarely) translated into proteins. In eukaryotes, lncRNAs regulate gene expression at the transcriptional, post-transcriptional, and epigenetic levels. lncRNAs are categorized according to their genomic position and molecular mechanism. This review summarized the characteristics and mechanisms of plant lncRNAs involved in vegetative growth, reproduction, and stress responses. Our discussion and model provide a theoretical basis for further studies of lncRNAs in plant breeding.

Plant non-coding RNAs function in pollen development and male sterility

Male sterility is classified as either cytoplasmic male sterility (CMS) or genic male sterility (GMS). Generally, CMS involves mitochondrial genomes interacting with the nuclear genome, while GMS is caused by nuclear genes alone. Male sterility is regulated by multilevel mechanisms in which non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and phased small interfering RNAs (phasiRNAs), which have been proven to be critical elements. The development of high-throughput sequencing technology offers new opportunities to evaluate the genetic mechanism of ncRNAs in plant male sterility. In this review, we summarize the critical ncRNAs that regulate gene expression in ways dependent on or independent of hormones, which involve the differentiation of the stamen primordia, degradation of the tapetum, formation of microspores, and the release of pollen. In addition, the key mechanisms of the miRNA-lncRNA-mRNA interaction networks mediating male sterility in plants are elaborated. We present a different perspective on exploring the ncRNA-mediated regulatory pathways that control CMS in plants and create male-sterile lines through hormones or genome editing. A refined understanding of the ncRNA regulatory mechanisms in plant male sterility for the development of new sterile lines would be conducive to improve hybridization breeding.

Genome-wide analysis reveals the crucial role of lncRNAs in regulating the expression of genes controlling pollen development

The genomic location and stage-specific expression pattern of many long non-coding RNAs reveal their critical role in regulating protein-coding genes crucial in pollen developmental progression and male germ line specification. Long non-coding RNAs (lncRNAs) are transcripts longer than 200 bp with no apparent protein-coding potential. Multiple investigations have revealed high expression of lncRNAs in plant reproductive organs in a cell and tissue-specific manner. However, their potential role as essential regulators of molecular processes involved in sexual reproduction remains largely unexplored. We have used developing field mustard (Brassica rapa) pollen as a model system for investigating the potential role of lncRNAs in reproductive development. Reference-based transcriptome assembly performed to update the existing genome annotation identified novel expressed protein-coding genes and long non-coding RNAs (lncRNAs), including 4347 long intergenic non-coding RNAs (lincRNAs, 1058 expressed) and 2,045 lncRNAs overlapping protein-coding genes on the opposite strand (lncNATs, 780 expressed). The analysis of expression profiles reveals that lncRNAs are significant and stage-specific contributors to the gene expression profile of developing pollen. Gene co-expression networks accompanied by genome location analysis identified 38 cis-acting lincRNA, 31 cis-acting lncNAT, 7 trans-acting lincRNA and 14 trans-acting lncNAT to be substantially co-expressed with target protein-coding genes involved in biological processes regulating pollen development and male lineage specification. These findings provide a foundation for future research aiming at developing strategies to employ lncRNAs as regulatory tools for gene expression control during reproductive development.

Investigating nicotine pathway-related long non-coding RNAs in tobacco

Long non-coding RNAs (lncRNAs) are transcripts longer than 200 bp with low or no protein-coding ability, which play essential roles in various biological processes in plants. Tobacco is an ideal model plant for studying nicotine biosynthesis and metabolism, and there is little research on lncRNAs in this field. Therefore, how to take advantage of the mature tobacco system to profoundly investigate the lncRNAs involved in the nicotine pathway is intriguing. By exploiting 549 public RNA-Seq datasets of tobacco, 30,212 lncRNA candidates were identified, including 24,084 large intervening non-coding RNAs (lincRNAs), 5,778 natural antisense transcripts (NATs) and 350 intronic non-coding RNAs (incRNAs). Compared with protein-coding genes, lncRNAs have distinct properties in terms of exon number, sequence length, A/U content, and tissue-specific expression pattern. lincRNAs showed an asymmetric evolutionary pattern, with a higher proportion (68.71%) expressed from the Nicotiana sylvestris (S) subgenome. We predicted the potential cis/trans-regulatory effects on protein-coding genes. One hundred four lncRNAs were detected as precursors of 30 known microRNA (miRNA) family members, and 110 lncRNAs were expected to be the potential endogenous target mimics for 39 miRNAs. By combining the results of weighted gene co-expression network analysis with the differentially expressed gene analysis of topping RNA-seq data, we constructed a sub-network containing eight lncRNAs and 25 nicotine-related coding genes. We confirmed that the expression of seven lncRNAs could be affected by MeJA treatment and may be controlled by the transcription factor NtMYC2 using a quantitative PCR assay and gene editing. The results suggested that lncRNAs are involved in the nicotine pathway. Our findings further deepened the understanding of the features and functions of lncRNAs and provided new candidates for regulating nicotine biosynthesis in tobacco.

Identification of NPF Family Genes in Brassica rapa Reveal Their Potential Functions in Pollen Development and Response to Low Nitrate Stress

Nitrate Transporter 1/Peptide Transporter Family (NPF) genes encode membrane transporters involved in the transport of diverse substrates. However, little is known about the diversity and functions of NPFs in Brassica rapa. In this study, 85 NPFs were identified in B. rapa (BrNPFs) which comprised eight subfamilies. Gene structure and conserved motif analysis suggested that BrNFPs were conserved throughout the genus. Stress and hormone-responsive cis-acting elements and transcription factor binding sites were identified in BrNPF promoters. Syntenic analysis suggested that tandem duplication contributed to the expansion of BrNPFs in B. rapa. Transcriptomic profiling analysis indicated that BrNPF2.6, BrNPF2.15, BrNPF7.6, and BrNPF8.9 were expressed in fertile floral buds, suggesting important roles in pollen development. Thirty-nine BrNPFs were responsive to low nitrate availability in shoots or roots. BrNPF2.10, BrNPF2.19, BrNPF2.3, BrNPF5.12, BrNPF5.16, BrNPF5.8, and BrNPF6.3 were only up-regulated in roots under low nitrate conditions, indicating that they play positive roles in nitrate absorption. Furthermore, many genes were identified in contrasting genotypes that responded to vernalization and clubroot disease. Our results increase understanding of BrNPFs as candidate genes for genetic improvement studies of B. rapa to promote low nitrate availability tolerance and for generating sterile male lines based on gene editing methods.

Comparative study on abortion characteristics of Nsa CMS and Pol CMS and analysis of long non-coding RNAs related to pollen abortion in Brassica napus

Cytoplasmic male sterile system (CMS) is one of the important methods for the utilization of heterosisin Brassica napus. The involvement of long non-coding RNAs (lncRNAs) in anther and pollen development in B.napus has been recognized, but there is little data on the involvement of lncRNAs in pollen abortion in different types of rapeseed CMS. The present study compared the cytological, physiological and biochemical characteristics of Nsa CMS (1258A) and Pol CMS (P5A) during pollen abortion, and high-throughput sequencing of flower buds of different sizes before and after pollen abortion. The results showed that insufficient energy supply was an important physiological basis for 1258A and P5A pollen abortion, and 1258A had excessive ROS (reactive oxygen species) accumulation in the stage of pollen abortion. Functional analysis showed that Starch and sucrose metabolism and Sulfur metabolism were significantly enriched before and after pollen abortion in 1258A and P5A, and a large number of genes were down-regulated. In 1258A, 227 lncRNAs had cis-targeting regulation, and 240 cis-target genes of the lncRNAs were identified. In P5A, 116 lncRNAs had cis-targeting regulation, and 101 cis-target genes of the lncRNAs were identified. There were five lncRNAs cis-target genes in 1258A and P5A during pollen abortion, and LOC106445716 encodes β-D-glucopyranosyl abscisate β-glucosidase and could regulate pollen abortion. Taken together, this study, provides a new perspective for lncRNAs to participate in the regulation of Nsa CMS and Pol CMS pollen abortion.

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.

Role of long non-coding RNAs in rice reproductive development

Rice is a staple crop, feeding over half of the global population. The future demand of population growth and climate change requires substantial rice improvement. Recent advances in rice genomics have highlighted the vital role of the non-coding part of the genome. The protein-coding regions account for only a tiny portion of the eukaryotic genome, and most of the genomic regions transcribe copious amounts of non-coding RNAs. Of these, the long non-coding RNAs, including linear non-coding RNAs (lncRNAs) and circular non-coding RNAs (circRNAs), have been shown to play critical roles in various developmental processes by regulating the expression of genes and functions of proteins at transcriptional, post-transcriptional and post-translational levels. With the advances in next-generation sequencing technologies, a substantial number of long non-coding RNAs have been found to be expressed in plant reproductive organs in a cell- and tissue-specific manner suggesting their reproductive development-related functions. Accumulating evidence points towards the critical role of these non-coding RNAs in flowering, anther, and pollen development, ovule and seed development and photoperiod and temperature regulation of male fertility. In this mini review, we provide a brief overview of the role of the linear and circular long non-coding RNAs in rice reproductive development and control of fertility and crop yield.

Regulatory mechanisms of fatty acids biosynthesis in Armeniaca sibirica seed kernel oil at different developmental stages

Background

Armeniaca sibirica seed kernel oil is rich in oleic acid and linoleic acid, thus holding potential value as a source of high-quality edible oils. However, some regulatory factors involved in fatty acids accumulation in A. sibirica seed kernels remain largely elusive. Thus, the aim of this study was to elucidate the regulatory mechanisms underlying fatty acids biosynthesis in A. sibirica developing seed kernels.

Methods

Seed kernels from six plants from a single A. sibirica clone were taken at five different developmental stages (days 30, 41, 52, 63, and 73 after anthesis). Fatty acid composition in seed kernel oil was determined by gas chromatography-mass spectrometry (GC-MS). In addition, transcriptome analysis was conducted using second-generation sequencing (SGS) and single-molecule real-time sequencing (SMRT).

Results

Rapid accumulation of fatty acids occurred throughout the different stages of seed kernels development, with oleic acid and linoleic acid as the main fatty acids. A total of 10,024, 9,803, 6,004, 6,719 and 9,688 unigenes were matched in the Nt, Nr, KOG, GO and KEGG databases, respectively. In the category lipid metabolism, 228 differentially expressed genes (DEGs) were annotated into 13 KEGG pathways. Specific unigenes encoding 12 key enzymes related to fatty acids biosynthesis were determined. Co-expression network analysis identified 11 transcription factors (TFs) and 13 long non-coding RNAs (lncRNAs) which putatively participate in the regulation of fatty acid biosynthesis. This study provides insights into the molecular regulatory mechanisms of fatty acids biosynthesis in A. sibirica developing seed kernels, and enabled the identification of novel candidate factors for future improvement of the production and quality of seed kernel oil by breeding.

Long Non-Coding RNAs: New Players in Plants

During the process of growth and development, plants are prone to various biotic and abiotic stresses. They have evolved a variety of strategies to resist the adverse effects of these stresses. lncRNAs (long non-coding RNAs) are a type of less conserved RNA molecules of more than 200 nt (nucleotides) in length. lncRNAs do not code for any protein, but interact with DNA, RNA, and protein to affect transcriptional, posttranscriptional, and epigenetic modulation events. As a new regulatory element, lncRNAs play a critical role in coping with environmental pressure during plant growth and development. This article presents a comprehensive review on the types of plant lncRNAs, the role and mechanism of lncRNAs at different molecular levels, the coordination between lncRNA and miRNA (microRNA) in plant immune responses, the latest research progress of lncRNAs in plant growth and development, and their response to biotic and abiotic stresses. We conclude with a discussion on future direction for the elaboration of the function and mechanism of lncRNAs.

Identification of long non-coding RNAs and microRNAs involved in anther development in the tropical Camellia oleifera

BACKGROUND

Explored the molecular science of anther development is important for improving productivity and overall yield of crops. Although the role of regulatory RNAs, including long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), in regulating anther development has been established, their identities and functions in Camellia oleifera, an important industrial crop, have yet not been clearly explored. Here, we report the identification and characterization of genes, lncRNAs and miRNAs during three stages of the tropical C. oleifera anther development by single-molecule real-time sequencing, RNA sequencing and small RNA sequencing, respectively.

RESULTS

These stages, viz. the pollen mother cells stage, tetrad stage and uninucleate pollen stage, were identified by analyzing paraffin sections of floral buds during rapid expansion periods. A total of 18,393 transcripts, 414 putative lncRNAs and 372 miRNAs were identified, of which 5,324 genes, 115 lncRNAs, and 44 miRNAs were differentially accumulated across three developmental stages. Of these, 44 and 92 genes were predicted be regulated by 37 and 30 differentially accumulated lncRNAs and miRNAs, respectively. Additionally, 42 differentially accumulated lncRNAs were predicted as targets of 27 miRNAs. Gene ontology enrichment indicated that potential target genes of lncRNAs were enriched in photosystem II, regulation of autophagy and carbohydrate phosphatase activity, which are essential for anther development. Functional annotation of genes targeted by miRNAs indicated that they are relevant to transcription and metabolic processes that play important roles in microspore development. An interaction network was built with 2 lncRNAs, 6 miRNAs and 10 mRNAs. Among these, miR396 and miR156 family were up-regulated, while their targets, genes (GROWTH REGULATING FACTORS and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE genes) and lncRNAs, were down-regulated. Further, the trans-regulated targets of these lncRNAs, like wall-associated kinase2 and phosphomannose isomerase1, are involved in pollen wall formation during anther development.

CONCLUSIONS

This study unravels lncRNAs, miRNAs and miRNA-lncRNA-mRNA networks involved in development of anthers of the tropical C. oleifera lays a theoretical foundation for further elucidation of regulatory roles of lncRNAs and miRNAs in anther development.

Comparative full-length transcriptome analysis by Oxford Nanopore Technologies reveals genes involved in anthocyanin accumulation in storage roots of sweet potatoes (Ipomoea batatas L.)

Background

Storage roots of sweet potatoes (Ipomoea batatas L.) with different colors vary in anthocyanin content, indicating different economically agronomic trait. As the newest DNA/RNA sequencing technology, Oxford Nanopore Technologies (ONT) have been applied in rapid transcriptome sequencing for investigation of genes related to nutrient metabolism. At present, few reports concern full-length transcriptome analysis based on ONT for study on the molecular mechanism of anthocyanin accumulation leading to color change of tuberous roots of sweet potato cultivars.

Results

The storage roots of purple-fleshed sweet potato (PFSP) and white-fleshed sweet potato (WFSP) at different developmental stages were subjected to anthocyanin content comparison by UV-visible spectroscopy as well as transcriptome analysis at ONT MinION platform. UV-visible spectrophotometric measurements demonstrated the anthocyanin content of PFSP was much higher than that of WFSP. ONT RNA-Seq results showed each sample generated average 2.75 GB clean data with Full-Length Percentage (FL%) over 70% and the length of N50 ranged from 1,192 to 1,395 bp, indicating reliable data for transcriptome analysis. Subsequent analysis illustrated intron retention was the most prominent splicing event present in the resulting transcripts. As compared PFSP with WFSP at the relative developmental stages with the highest (PH vs. WH) and the lowest (PL vs. WL) anthocyanin content, 282 and 216 genes were up-regulated and two and 11 genes were down-regulated respectively. The differential expression genes involved in flavonoid biosynthesis pathway include CCoAOMT, PpLDOX, DFR, Cytochrome P450, CHI, and CHS. The genes encoding oxygenase superfamily were significantly up-regulated when compared PFSP with WFSP at the relative developmental stages.

Conclusions

Comparative full-length transcriptome analysis based on ONT serves as an effective approach to detect the differences in anthocyanin accumulation in the storage roots of different sweet potato cultivars at transcript level, with noting that some key genes can now be closely related to flavonoids biosynthesis. This study helps to improve understanding of molecular mechanism for anthocyanin accumulation in sweet potatoes and also provides a theoretical basis for high-quality sweet potato breeding.

Transcript Complexity and New Insights of Restorer Line in CMS-D8 Cotton Through Full-Length Transcriptomic Analysis

Hybrid utilization has proficiently increased crop production worldwide. The cytoplasmic male sterility (CMS) system has emerged as an efficient tool for commercial hybrid cotton seed production. The restorer line with dominant Rf₂ gene can restore the fertility of the CMS-D8 sterile line. However, the molecular mechanism of fertility restoration remains unclear in CMS-D8 cotton that limits wider utilization of three-line hybrid breeding. In our study, the Pacific Biosciences (PacBio) Iso-Seq technology was applied to understand fertility restoration mechanism of CMS-D8 cotton. In total, 228,106 full-length non-chimeric transcriptome sequences were obtained from anthers of developing flowering buds. The analysis results identified 3,174 novel isoforms, 2,597 novel gene loci, 652 long non-coding RNAs predicted from novel isoforms, 7,234 alternative splicing events, 114 fusion transcripts, and 1,667 genes with alternative polyadenylation. Specially, two novel genes associated with restoration function, Ghir_D05.742.1 and m64033_190821_201011/21103726/ccs were identified and showed significant higher levels of expression in restorer line than sterile and maintainer lines. Our comparative full-length transcriptome analysis provides new insights into the molecular function of Rf₂ fertility restorer gene. The results of this study offer a platform for fertility restoration candidate gene discovery in CMS-D8 cotton.

Gypsy retrotransposon-derived maize lncRNA GARR2 modulates gibberellin response

Long non-coding RNAs (lncRNAs) mediate diverse biological events mainly through the modulation of transcriptional hierarchy. The phytohormone gibberellin (GA) is essential for various aspects of plant growth and development. However, the roles of lncRNAs in the regulation of the GA response remain largely unknown. Through sequencing multiple strand-specific and ribosomal-depleted RNA libraries, we delineated the landscape of lncRNAs in maize (Zea mays). Out of identified lncRNAs, 445 GIBBERELLIN-RESPONSIVE lncRNAs (GARRs) were differentially expressed upon GA application. By the intersection of GARRs from normal-height and dwarf plants from an advanced backcross population, four shared GARRs (GARR1 to GARR4) were identified. Out of these four shared GARRs, GARR2 was derived from a Gypsy LTR retrotransposon. GA-responsive element P-boxes were identified upstream of GARR2. GARR2-edited lines exhibited a GA-induced phenotype. Editing of GARR2 resulted in changes in the transcriptional abundance of GA pathway components and endogenous GA contents. Besides GA, GARR2 affected the primary auxin response. An RNA pull-down assay revealed the HECT ubiquitin-protein ligase family member ZmUPL1 as a potential interaction target of GARR2. GARR2 influenced the abundance of ZmUPL1 in the GA response. Our study uncovers lncRNA players involved in the modulation of the GA response and guides the development of plant height ideotype driven by knowledge of the phytohormone GA.

Long non-coding RNA transcriptome landscape of anthers at different developmental stages in response to drought stress in tomato

Pollen development is particularly susceptible to drought stress. Long non-coding RNAs (lncRNAs) are known to play a role in plant development and responses to drought stress. However, the expression profile and putative function of lncRNAs in drought-induced male sterility remain largely unknown. In this study, we investigated the lncRNA transcriptome landscape of tomato anthers at early and late stages-tetrad-vacuolated microspore (TED-VUM) and binucleate-mature pollen (BIN-MP) anthers, respectively-in response to drought stress using RNA-sequencing. In total, we identified 67,770 lncRNAs, of which 3053 lncRNAs were drought responsive. Interestingly, there were more differentially expressed (DE) lncRNAs in TED-VUM (2879) than in BIN-MP (174) anthers, which was consistent with the TED-VUM anthers being more drought sensitive. Functional enrichment analysis revealed that the target genes of DE lncRNAs were significantly enriched in diverse metabolic processes, including in carbohydrate metabolism and hormone synthesis. Co-expression analysis also identified 1407 lncRNAs that strongly co-expressed with 8 target genes that are involved in hormone (abscisic acid and jasmonic acid) and carbohydrate (sucrose and starch) metabolisms and tapetum development, highlighting the potential of lncRNA-target-gene modulation of anther development under drought stress. Our results serve as a baseline for future investigations of the potential function of lncRNAs in plant reproductive development under drought stress.

The Characters of Non-Coding RNAs and Their Biological Roles in Plant Development and Abiotic Stress Response

Plant growth and development are greatly affected by the environment. Many genes have been identified to be involved in regulating plant development and adaption of abiotic stress. Apart from protein-coding genes, more and more evidence indicates that non-coding RNAs (ncRNAs), including small RNAs and long ncRNAs (lncRNAs), can target plant developmental and stress-responsive mRNAs, regulatory genes, DNA regulatory regions, and proteins to regulate the transcription of various genes at the transcriptional, posttranscriptional, and epigenetic level. Currently, the molecular regulatory mechanisms of sRNAs and lncRNAs controlling plant development and abiotic response are being deeply explored. In this review, we summarize the recent research progress of small RNAs and lncRNAs in plants, focusing on the signal factors, expression characters, targets functions, and interplay network of ncRNAs and their targets in plant development and abiotic stress responses. The complex molecular regulatory pathways among small RNAs, lncRNAs, and targets in plants are also discussed. Understanding molecular mechanisms and functional implications of ncRNAs in various abiotic stress responses and development will benefit us in regard to the use of ncRNAs as potential character-determining factors in molecular plant breeding.

Transcript Profiling Analysis and ncRNAs' Identification of Male-Sterile Systems of Brassica campestris Reveal New Insights Into the Mechanism Underlying Anther and Pollen Development

Male-sterile mutants are useful materials to study the anther and pollen development. Here, whole transcriptome sequencing was performed for inflorescences in three sterile lines of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis), the genic male-sterile line (A line), the Polima cytoplasmic male-sterile (CMS) line (P line), and the Ogura CMS line (O line) along with their maintainer line (B line). In total, 7,136 differentially expressed genes (DEGs), 361 differentially expressed long non-coding RNAs (lncRNAs) (DELs), 56 differentially expressed microRNAs (miRNAs) (DEMs) were selected out. Specific regulatory networks related to anther cell differentiation, meiosis cytokinesis, pollen wall formation, and tapetum development were constructed based on the abortion characteristics of male-sterile lines. Candidate genes and lncRNAs related to cell differentiation were identified in sporocyteless P line, sixteen of which were common to the DEGs in Arabidopsis spl/nzz mutant. Genes and lncRNAs concerning cell plate formation were selected in A line that is defected in meiosis cytokinesis. Also, the orthologs of pollen wall formation and tapetum development genes in Arabidopsis showed distinct expression patterns in the three different sterile lines. Among 361 DELs, 35 were predicted to interact with miRNAs, including 28 targets, 47 endogenous target mimics, and five precursors for miRNAs. Two lncRNAs were further proved to be functional precursors for bra-miR156 and bra-miR5718, respectively. Overexpression of bra-miR5718HG in B. campestris slowed down the growth of pollen tubes, caused shorter pollen tubes, and ultimately affected the seed set. Our study provides new insights into molecular regulation especially the ncRNA interaction during pollen development in Brassica crops.

Genetic and Physiological Responses to Heat Stress in Brassica napus

Given the current rise in global temperatures, heat stress has become a major abiotic challenge affecting the growth and development of various crops and reducing their productivity. Brassica napus, the second largest source of vegetable oil worldwide, experiences a drastic reduction in seed yield and quality in response to heat. This review outlines the latest research that explores the genetic and physiological impact of heat stress on different developmental stages of B. napus with a special attention to the reproductive stages of floral progression, organogenesis, and post flowering. Several studies have shown that extreme temperature fluctuations during these crucial periods have detrimental effects on the plant and often leading to impaired growth and reduced seed production. The underlying mechanisms of heat stress adaptations and associated key regulatory genes are discussed. Furthermore, an overview and the implications of the polyploidy nature of B. napus and the regulatory role of alternative splicing in forming a priming-induced heat-stress memory are presented. New insights into the dynamics of epigenetic modifications during heat stress are discussed. Interestingly, while such studies are scarce in B. napus, opposite trends in expression of key genetic and epigenetic components have been identified in different species and in cultivars within the same species under various abiotic stresses, suggesting a complex role of these genes and their regulation in heat stress tolerance mechanisms. Additionally, omics-based studies are discussed with emphasis on the transcriptome, proteome and metabolome of B. napus, to gain a systems level understanding of how heat stress alters its yield and quality traits. The combination of omics approaches has revealed crucial interactions and regulatory networks taking part in the complex machinery of heat stress tolerance. We identify key knowledge gaps regarding the impact of heat stress on B. napus during its yield determining reproductive stages, where in-depth analysis of this subject is still needed. A deeper knowledge of heat stress response components and mechanisms in tissue specific models would serve as a stepping-stone to gaining insights into the regulation of thermotolerance that takes place in this important crop species and support future breeding of heat tolerant crops.

Transcriptional Association between mRNAs and Their Paired Natural Antisense Transcripts Following Fusarium oxysporum Inoculation in Brassica rapa L

Long noncoding RNAs (lncRNAs) play important roles in abiotic and biotic stress responses; however, studies on the mechanism of regulation of lncRNA expression are limited in plants. The present study examined the relationship between lncRNA expression level and two active histone modifications (H3K4me3 and H3K36me3) in Brassica rapa. Both histone marks were enriched in the chromatin regions encoding lncRNAs, especially around the transcription start site. The transcription level of long intergenic noncoding RNAs was positively associated with the level of H3K4me3 and H3K36me3, while this association was not observed in natural antisense RNAs (NATs) and intronic noncoding RNAs. As coordinate expression of mRNAs and paired NATs under biotic stress treatment has been identified, the transcriptional relationship between mRNAs and their paired NATs following Fusarium oxysporum f. sp. conglutinans (Foc) inoculation was examined. A positive association of expression levels between mRNAs and their paired NATs following Foc inoculation was observed. This association held for several defense-response-related genes and their NAT pairs. These results suggest that coordinate expression of mRNAs and paired NATs plays a role in the defense response against Foc.

Comprehensive Analysis of Arabinogalactan Protein-Encoding Genes Reveals the Involvement of Three BrFLA Genes in Pollen Germination in Brassica rapa

Arabinogalactan proteins (AGPs) are a superfamily of hydroxyproline-rich glycoproteins that are massively glycosylated, widely implicated in plant growth and development. No comprehensive analysis of the AGP gene family has been performed in Chinese cabbage (Brassica rapa ssp. chinensis). Here, we identified a total of 293 putative AGP-encoding genes in B. rapa, including 25 classical AGPs, three lysine-rich AGPs, 30 AG-peptides, 36 fasciclin-like AGPs (FLAs), 59 phytocyanin-like AGPs, 33 xylogen-like AGPs, 102 other chimeric AGPs, two non-classical AGPs and three AGP/extensin hybrids. Their protein structures, phylogenetic relationships, chromosomal location and gene duplication status were comprehensively analyzed. Based on RNA sequencing data, we found that 73 AGP genes were differentially expressed in the floral buds of the sterile and fertile plants at least at one developmental stage in B. rapa, suggesting a potential role of AGPs in male reproductive development. We further characterized BrFLA2, BrFLA28 and BrFLA32, three FLA members especially expressed in anthers, pollen grains and pollen tubes. BrFLA2, BrFLA28 and BrFLA32 are indispensable for the proper timing of pollen germination under high relative humidity. Our study greatly extends the repertoire of AGPs in B. rapa and reveals a role for three members of the FLA subfamily in pollen germination.

Long noncoding RNA lncRNA354 functions as a competing endogenous RNA of miR160b to regulate ARF genes in response to salt stress in upland cotton

Long non-coding RNAs (lncRNAs) play important roles in response to biotic and abiotic stress through acting as competing endogenous RNAs (ceRNAs) to decoy mature miRNAs. However, whether this mechanism is involved in cotton salt stress response remains unknown. We report the characterization of an endogenous lncRNA, lncRNA354, whose expression was reduced in salt-treated cotton and was localized at the nucleus and cytoplasm. Using endogenous target mimic (eTM) analysis, we predicted that lncRNA354 had a potential binding site for miR160b. Transient expression in tobacco demonstrated that lncRNA354 was a miR160b eTM and attenuated miR160b suppression of its target genes, including auxin response factors (ARFs). Silencing or overexpressing lncRNA354 affected the expression of miR160b and target ARFs. Silencing lncRNA354 and targets GhARF17/18 resulted in taller cotton plants and enhanced the resistant to salt stress. Overexpression of lncRNA354 and targets GhARF17/18 in Arabidopsis led to dwarf plants, decreased root dry weight and reduced salt tolerance. Our results show that the lncRNA354-miR160b effect on GhARF17/18 expression may modulate auxin signalling and thus affect growth. These results also shed new light on a mechanism of lncRNA-associated responses to salt stress.

Circular RNAs Repertoire and Expression Profile during Brassica rapa Pollen Development

Circular RNAs (circRNAs) are covalently closed RNA molecules generated by the back-splicing of exons from linear precursor mRNAs. Though various linear RNAs have been shown to play important regulatory roles in many biological and developmental processes, little is known about the role of their circular counterparts. In this study, we performed high-throughput RNA sequencing to delineate the expression profile and potential function of circRNAs during the five stages of pollen development in Brassica rapa. A total of 1180 circRNAs were detected in pollen development, of which 367 showed stage-specific expression patterns. Functional enrichment and metabolic pathway analysis showed that the parent genes of circRNAs were mainly involved in pollen-related molecular and biological processes such as mitotic and meiotic cell division, DNA processes, protein synthesis, protein modification, and polysaccharide biosynthesis. Moreover, by predicting the circRNA–miRNA network from our differentially expressed circRNAs, we found 88 circRNAs with potential miRNA binding sites, suggesting their role in post-transcriptional regulation of the genes. Finally, we confirmed the back-splicing sites of nine selected circRNAs using divergent primers and Sanger sequencing. Our study presents the systematic analysis of circular RNAs during pollen development and forms the basis of future studies for unlocking complex gene regulatory networks underpinning reproduction in flowering plants.

Characterization of lncRNAs and mRNAs Involved in Powdery Mildew Resistance in Cucumber

Powdery mildew (PM) is a severe fungal disease of cucumber worldwide. Identification of genetic factors resistant to PM is of great importance for marker-assisted breeding to ensure cucumber production. Long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) have been shown to play important roles in plant development and immunity; however, whether they have a role in PM response in cucurbit crops remains unknown. We performed strand-specific RNA sequencing and miRNA sequencing using RNA from cucumber leaves of two near-isogenic lines (NILs), S1003 and NIL (Pm5.1) infected with PM, and systematically characterized the profiles of cucumber lncRNAs and messenger RNA (mRNAs) responsive to PM. In total, we identified 12,903 lncRNAs and 25,598 mRNAs responsive to PM. Differential expression (DE) analysis showed that 119 lncRNAs and 136 mRNAs correlated with PM resistance. Functional analysis of these DE lncRNAs and DE mRNAs revealed that they are significantly associated with phenylpropanoid biosynthesis, phenylalanine metabolism, ubiquinone and other terpenoid-quinone biosynthesis, and endocytosis. Particularly, two lncRNAs, LNC_006805 and LNC_012667, might play important roles in PM resistance. In addition, we also predicted mature miRNAs and competing endogenous RNA (ceRNA) networks of lncRNA-miRNA-mRNA involved in PM resistance. A total of 49 DE lncRNAs could potentially act as target mimics for 106 miRNAs. Taken together, our results provide an abundant resource for further exploration of cucumber lncRNAs, mRNAs, miRNAs, and ceRNAs in PM resistance, and will facilitate the molecular breeding for PM-resistant varieties to control this severe disease in cucumber.

A combination of genome-wide and transcriptome-wide association studies reveals genetic elements leading to male sterility during high temperature stress in cotton

Global warming has reduced the productivity of many field-grown crops, as the effects of high temperatures can lead to male sterility in such plants. Genetic regulation of the high temperature (HT) response in the major crop cotton is poorly understood. We determined the functionality and transcriptomes of the anthers of 218 cotton accessions grown under HT stress. By analyzing transcriptome divergence and implementing a genome-wide association study (GWAS), we identified three thermal tolerance associated loci which contained 75 protein coding genes and 27 long noncoding RNAs, and provided expression quantitative trait loci (eQTLs) for 13 132 transcripts. A transcriptome-wide association study (TWAS) confirmed six causal elements for the HT response (three genes overlapped with the GWAS results) which are involved in protein kinase activity. The most susceptible gene, GhHRK1, was confirmed to be a previously uncharacterized negative regulator of the HT response in both cotton and Arabidopsis. These functional variants provide a new understanding of the genetic basis for HT tolerance in male reproductive organs.

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.

Identification of the specific long-noncoding RNAs involved in night-break mediated flowering retardation in Chenopodium quinoa

Background

Night-break (NB) has been proven to repress flowering of short-day plants (SDPs). Long-noncoding RNAs (lncRNAs) play key roles in plant flowering. However, investigation of the relationship between lncRNAs and NB responses is still limited, especially in Chenopodium quinoa, an important short-day coarse cereal.

Results

In this study, we performed strand-specific RNA-seq of leaf samples collected from quinoa seedlings treated by SD and NB. A total of 4914 high-confidence lncRNAs were identified, out of which 91 lncRNAs showed specific responses to SD and NB. Based on the expression profiles, we identified 17 positive- and 7 negative-flowering lncRNAs. Co-expression network analysis indicated that 1653 mRNAs were the common targets of both types of flowering lncRNAs. By mapping these targets to the known flowering pathways in model plants, we found some pivotal flowering homologs, including 2 florigen encoding genes (FT (FLOWERING LOCUS T) and TSF (TWIN SISTER of FT) homologs), 3 circadian clock related genes (EARLY FLOWERING 3 (ELF3), LATE ELONGATED HYPOCOTYL (LHY) and ELONGATED HYPOCOTYL 5 (HY5) homologs), 2 photoreceptor genes (PHYTOCHROME A (PHYA) and CRYPTOCHROME1 (CRY1) homologs), 1 B-BOX type CONSTANS (CO) homolog and 1 RELATED TO ABI3/VP1 (RAV1) homolog, were specifically affected by NB and competed by the positive and negative-flowering lncRNAs. We speculated that these potential flowering lncRNAs may mediate quinoa NB responses by modifying the expression of the floral homologous genes.

Conclusions

Together, the findings in this study will deepen our understanding of the roles of lncRNAs in NB responses, and provide valuable information for functional characterization in future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07605-2.

Mutation of a major CG methylase alters genome-wide lncRNA expression in rice

Plant long non-coding RNAs (lncRNAs) function in diverse biological processes, and lncRNA expression is under epigenetic regulation, including by cytosine DNA methylation. However, it remains unclear whether 5-methylcytosine (5mC) plays a similar role in different sequence contexts (CG, CHG, and CHH). In this study, we characterized and compared the profiles of genome-wide lncRNA profiles (including long intergenic non-coding RNAs [lincRNAs] and long noncoding natural antisense transcripts [lncNATs]) of a null mutant of the rice DNA methyltransferase 1, OsMET1-2 (designated OsMET1-2-/-) and its isogenic wild type (OsMET1-2+/+). The En/Spm transposable element (TE) family, which was heavily methylated in OsMET1-2+/+, was transcriptionally de-repressed in OsMET1-2-/- due to genome-wide erasure of CG methylation, and this led to abundant production of specific lncRNAs. In addition, RdDM-mediated CHH hypermethylation was increased in the 5'-upstream genomic regions of lncRNAs in OsMET1-2-/-. The positive correlation between the expression of lincRNAs and that of their proximal protein-coding genes was also analyzed. Our study shows that CG methylation negatively regulates the TE-related expression of lncRNA and demonstrates that CHH methylation is also involved in the regulation of lncRNA expression.

Genome-wide analysis of long noncoding RNAs, 24-nt siRNAs, DNA methylation and H3K27me3 marks in Brassica rapa

Long noncoding RNAs (lncRNAs) are RNA fragments that generally do not code for a protein but are involved in epigenetic gene regulation. In this study, lncRNAs of Brassica rapa were classified into long intergenic noncoding RNAs, natural antisense RNAs, and intronic noncoding RNAs and their expression analyzed in relation to genome-wide 24-nt small interfering RNAs (siRNAs), DNA methylation, and histone H3 lysine 27 trimethylation marks (H3K27me3). More than 65% of the lncRNAs analyzed consisted of one exon, and more than 55% overlapped with inverted repeat regions (IRRs). Overlap of lncRNAs with IRRs or genomic regions encoding for 24-nt siRNAs resulted in increased DNA methylation levels when both were present. LncRNA did not overlap greatly with H3K27me3 marks, but the expression level of intronic noncoding RNAs that did coincide with H3K27me3 marks was higher than without H3K27me3 marks. The Brassica genus comprises important vegetables and oil seed crops grown across the world. B. rapa is a diploid (AA genome) thought to be one of the ancestral species of both B. juncea (AABB genome) and B. napus (AACC) through genome merging (allotetrapolyploidization). Complex genome restructuring and epigenetic alterations are thought to be involved in these allotetrapolyploidization events. Comparison of lncRNAs between B. rapa and B. nigra, B. oleracea, B. juncea, and B. napus showed the highest conservation with B. oleracea. This study presents a comprehensive analysis of the epigenome structure of B. rapa at multi-epigenetic levels (siRNAs, DNA methylation, H3K27me3, and lncRNAs) and identified a suite of candidate lncRNAs that may be epigenetically regulated in the Brassica genus.

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.

Identification of long noncoding RNAs involved in resistance to downy mildew in Chinese cabbage

Brassica downy mildew, a severe disease caused by Hyaloperonospora brassicae, can cause enormous economic losses in Chinese cabbage (Brassica rapa L. ssp. pekinensis) production. Although some research has been reported recently concerning the underlying resistance to this disease, no studies have identified or characterized long noncoding RNAs involved in this defense response. In this study, using high-throughput RNA sequencing, we analyzed the disease-responding mRNAs and long noncoding RNAs in two resistant lines (T12-19 and 12-85) and one susceptible line (91-112). Clustering and Gene Ontology analysis of differentially expressed genes (DEGs) showed that more DEGs were involved in the defense response in the two resistant lines than in the susceptible line. Different expression patterns and proposed functions of differentially expressed long noncoding RNAs among T12-19, 12-85, and 91-112 indicated that each has a distinct disease response mechanism. There were significantly more cis- and trans-functional long noncoding RNAs in the resistant lines than in the susceptible line, and the genes regulated by these RNAs mostly participated in the disease defense response. Furthermore, we identified a candidate resistance-related long noncoding RNA, MSTRG.19915, which is a long noncoding natural antisense transcript of a MAPK gene, BrMAPK15. Via an agroinfiltration-mediated transient overexpression system and virus-induced gene silencing technology, BrMAPK15 was indicated to have a greater ability to defend against pathogens. MSTRG.19915-silenced seedlings showed enhanced resistance to downy mildew, probably because of the upregulated expression of BrMAPK15. This research identified and characterized long noncoding RNAs involved in resistance to downy mildew, laying a foundation for future in-depth studies of disease resistance mechanisms in Chinese cabbage.