Integration of small RNAs, degradome and transcriptome sequencing in hyperaccumulator Sedum alfredii uncovers a complex regulatory network and provides insights into cadmium phytoremediation

A Novel Ah-miR2916-AhERF13-AhSUC3 Module Regulates Al Tolerance via Ethylene-Mediated Signaling in Peanut (Arachnis hypogea L)

Aluminum (Al) toxicity in acidic soils leads to a considerable reduction in crop yields. MicroRNAs play essential roles in abiotic stress responses, but little is known of their role in the response of peanut (Arachnis hypogea L.) to Al stress. In this study, a novel Ah-miR2916 (miR2916)-AhERF13-AhSUC3 module was found to be involved in the Al-stress response via ethylene-mediated signaling in peanut. Overexpression of miR2916 in Arabidopsis resulted in reduced Al tolerance by downregulating ethylene biosynthesis, while knockdown miR2916 in peanut enhanced Al tolerance. Notably, the APETALA2/ethylene-responsive factor (ERF), AhERF13, was identified as a potential target of miR2916. AhERF13 expression was increased in miR2916 knockdown peanut lines and displayed an opposing pattern to that of miR2916 under Al stress. Consistently, knockdown AhERF13 peanut lines indicated that AhERF13 positively regulates Al tolerance by upregulating ethylene biosynthesis. AhERF13 was shown capable of binding to an ERF motif in the promoter region of sucrose transport protein 3 (AhSUC3) and positively regulate its expression. Consequently, AhSUC3 improved Al tolerance by upregulating ethylene biosynthesis. These results provide further insights into the molecular mechanisms operating during peanut response to Al stress, and suggests targets for manipulation in breeding programs for improved Al tolerance.

Single-cell atlases reveal leaf cell-type-specific regulation of metal transporters in the hyperaccumulator Sedum alfredii under cadmium stress

Hyperaccumulation in plants is a complex and dynamic biological process. Sedum alfredii, the most studied Cd hyperaccumulator, can accumulate up to 9000 mg kg-1 Cd in its leaves without suffering toxicity. Although several studies have reported the molecular mechanisms of Cd hyperaccumulation, our understanding of the cell-type-specific transcriptional regulation induced by Cd remains limited. In this study, the first full-length transcriptome of S. alfredii was generated using the PacBio Iso-Seq technology. A total of 18,718,513 subreads (39.90 Gb) were obtained, with an average length of 2133 bp. The single-cell RNA sequencing was employed on leaves of S. alfredii grown under Cd stress. A total of 12,616 high-quality single cells were derived from the control and Cd-treatment samples of S. alfredii leaves. Based on cell heterogeneity and the expression profiles of previously reported marker genes, seven cell types with 12 transcriptionally distinct cell clusters were identified, thereby constructing the first single-cell atlas for S. alfredii leaves. Metal transporters such as CAX5, COPT5, ZIP5, YSL7, and MTP1 were up-regulated in different cell types of S. alfredii leaves under Cd stress. The distinctive gene expression patterns of metal transporters indicate special gene regulatory networks underlying Cd tolerance and hyperaccumulation in S. alfredii. Collectively, our findings are the first observation of the cellular and molecular responses of S. alfredii leaves under Cd stress and lay the cornerstone for future hyperaccumulator scRNA-seq investigations.

Interfamily Grafted Hybrids Vitis vinifera/Schisandra chinensis Resulted in Transcriptomic, Phenotypic, and Metabolic Changes

Long-distance transfer of genetic material and metabolites between rootstock and scions is well documented in homo-grafted hybrids but has rarely been reported in genetically-distant grafts where the rootstock and scion belong to different families. In this study, we grafted Vitis vinifera scions onto Schisandra chinensis stocks and obtained 20 vegetative hybrids, Vitis vinifera/Schisandra chinensis (Vs). After 25 years of growth, we found that the phenotypes of the leaves, internodes, and fruits of the Vs hybrids above the graft union resembled an intermediate phenotype between V. vinifera and S. chinensis, and the new traits were stable when propagated vegetatively. We further analyzed genetic differences between Vv plants and Vs hybrids using high-throughput sequencing, while metabolomes were analyzed by liquid chromatography-mass spectrometry (LC-MS). We found a total of 2113 differentially expressed genes (DEGs). GO annotation and KEGG pathway enrichment analysis showed that these DEGs enriched mainly in oxidation-reduction and metabolic processes. Seventy-nine differentially expressed miRNAs (DEMs) containing 27 known miRNAs and 52 novel miRNAs were identified. A degradation analysis detected 840 target genes corresponding to 252 miRNAs, of which 12 DEMs and their corresponding target gene expression levels were mostly negatively correlated. Furthermore, 1188 differential metabolic compounds were identified. In particular, in Vs hybrids, the abundance of the metabolites schizandrin and gomisin as the main medicinal ingredients in S. chinensis were down-regulated and up-regulated, respectively. Our data demonstrated the effects of interfamily grafts on the phenotype, transcript profile and metabolites of the scion, and also provided new insight into the genetic, phenotypic, and metabolic plasticity associated with genetically distant grafted hybrids.

Non-coding RNAs (ncRNAs) in plant: Master regulators for adapting to extreme temperature conditions

Unusual daily temperature fluctuations caused by climate change and climate variability adversely impact agricultural crop production. Since plants are immobile and constantly receive external environmental signals, such as extreme high (heat) and low (cold) temperatures, they have developed complex molecular regulatory mechanisms to cope with stressful situations to sustain their natural growth and development. Among these mechanisms, non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), small-interfering RNAs (siRNAs), and long-non-coding RNAs (lncRNAs), play a significant role in enhancing heat and cold stress tolerance. This review explores the pivotal findings related to miRNAs, siRNAs, and lncRNAs, elucidating how they functionally regulate plant adaptation to extreme temperatures. In addition, this review addresses the challenges associated with uncovering these non-coding RNAs and understanding their roles in orchestrating heat and cold tolerance in plants.

Cytological observation and RNA-seq analysis reveal novel miRNAs high expression associated with the pollen fertility of neo-tetraploid rice

BACKGROUND

Neo-tetraploid rice lines exhibit high fertility and strong heterosis and harbor novel specific alleles, which are useful germplasm for polyploid rice breeding. However, the mechanism of the fertility associated with miRNAs remains unknown. In this study, a neo-tetraploid rice line, termed Huaduo21 (H21), was used. Cytological observation and RNA-sequencing were employed to identify the fertility-related miRNAs in neo-tetraploid rice.

RESULTS

H21 showed high pollen fertility (88.08%), a lower percentage of the pollen mother cell (PMC) abnormalities, and lower abnormalities during double fertilization and embryogenesis compared with autotetraploid rice. A total of 166 non-additive miRNAs and 3108 non-additive genes were detected between H21 and its parents. GO and KEGG analysis of non-additive genes revealed significant enrichments in the DNA replication, Chromosome and associated proteins, and Replication and repair pathways. Comprehensive multi-omics analysis identified 32 pairs of miRNA/target that were associated with the fertility in H21. Of these, osa-miR408-3p and osa-miR528-5p displayed high expression patterns, targeted the phytocyanin genes, and were associated with high pollen fertility. Suppression of osa-miR528-5p in Huaduo1 resulted in a low seed set and a decrease in the number of grains. Moreover, transgenic analysis implied that osa-MIR397b-p3, osa-miR5492, and osa-MIR5495-p5 might participate in the fertility of H21.

CONCLUSION

Taken together, the regulation network of fertility-related miRNAs-targets pairs might contribute to the high seed setting in neo-tetraploid rice. These findings enhance our understanding of the regulatory mechanisms of pollen fertility associated with miRNAs in neo-tetraploid rice.

Endoplasmic reticulum stress-responsive microRNAs are involved in the regulation of abiotic stresses in wheat

KEY MESSAGE

ER stress-responsive miRNAs, tae-miR164, tae-miR2916, and tae-miR396e-5p, are essential in response to abiotic stress. Investigating ER stress-responsive miRNAs is necessary to improve plant tolerance to environmental stress. MicroRNAs (miRNAs) play vital regulatory roles in plant responses to environmental stress. Recently, the endoplasmic reticulum (ER) stress pathway, an essential signalling pathway in plants in response to adverse conditions, has been widely studied in model plants. However, miRNAs associated with ER stress response remain largely unknown. Using high-throughput sequencing, three ER stress-responsive miRNAs, tae-miR164, tae-miR2916, and tae-miR396e-5p were identified, and their target genes were confirmed. These three miRNAs and their target genes actively responded to dithiothreitol, polyethylene glycol, salt, heat, and cold stresses. Furthermore, in some instances, the expression patterns of the miRNAs and their corresponding target genes were contrasting. Knockdown of tae-miR164, tae-miR2916, or tae-miR396e-5p using a barley stripe mosaic virus-based miRNA silencing system substantially enhanced the tolerance of wheat plants to drought, salt, and heat stress. Under conditions involving these stresses, inhibiting the miR164 function by using the short tandem target mimic approach in Arabidopsis thaliana resulted in phenotypes consistent with those of miR164-silenced wheat plants. Correspondingly, overexpression of tae-miR164 in Arabidopsis resulted in a decreased tolerance to drought stress and, to some extent, a decrease in tolerance to salt and high temperature. These results revealed that tae-miR164 plays a negative regulatory role in wheat/Arabidopsis in response to drought, salt, and heat stress. Taken together, our study provides new insights into the regulatory role of ER stress-responsive miRNAs in abiotic stress responses.

Integration of transcriptome and metabolome analyses reveals sorghum roots responding to cadmium stress through regulation of the flavonoid biosynthesis pathway

Cadmium (Cd) pollution is a serious threat to plant growth and human health. Although the mechanisms controlling the Cd response have been elucidated in other species, they remain unknown in Sorghum (Sorghum bicolor (L.) Moench), an important C₄ cereal crop. Here, one-week-old sorghum seedlings were exposed to different concentrations (0, 10, 20, 50, 100, and 150 μM) of CdCl₂ and the effects of these different concentrations on morphological responses were evaluated. Cd stress significantly decreased the activities of the enzymes peroxidase (POD), superoxide dismutase (SOD), glutathione S-transferase (GST) and catalase (CAT), and increased malondialdehyde (MDA) levels, leading to inhibition of plant height, decreases in lateral root density and plant biomass production. Based on these results, 10 μM Cd concentration was chosen for further transcription and metabolic analyses. A total of 2683 genes and 160 metabolites were found to have significant differential abundances between the control and Cd-treated groups. Multi-omics integrative analysis revealed that the flavonoid biosynthesis pathway plays a critical role in regulating Cd stress responses in sorghum. These results provide new insights into the mechanism underlying the response of sorghum to Cd.

microRNA regulation of skin pigmentation in golden-back mutant of crucian carp from a rice-fish integrated farming system

BACKGROUND

MicroRNAs (miRNAs) are endogenous small non-coding RNAs (21-25 nucleotides) that act as essential components of several biological processes. Golden-back crucian carp (GBCrC, Carassius auratus) is a naturally mutant species of carp that has two distinct body skin color types (golden and greenish-grey), making it an excellent model for research on the genetic basis of pigmentation. Here, we performed small RNA (sRNA) analysis on the two different skin colors via Illumina sequencing.

RESULTS

A total of 679 known miRNAs and 254 novel miRNAs were identified, of which 32 were detected as miRNAs with significant differential expression (DEMs). 23,577 genes were projected to be the targets of 32 DEMs, primarily those involved in melanogenesis, adrenergic signaling in cardiomyocytes, MAPK signaling pathway and wnt signaling pathway by functional enrichment. Furthermore, we built an interaction module of mRNAs, proteins and miRNAs based on 10 up-regulated and 13 down-regulated miRNAs in golden skin. In addition to transcriptional destabilization and translational suppression, we discovered that miRNAs and their target genes were expressed in the same trend at both the transcriptional and translational levels. Finally, we discovered that miR-196d could be indirectly implicated in regulating melanocyte synthesis and motility in the skin by targeting to myh7 (myosin-7) gene through the luciferase reporter assay, antagomir silencing in vivo and qRT-PCR techniques.

CONCLUSIONS

Our study gives a systematic examination of the miRNA profiles expressed in the skin of GBCrC, assisting in the comprehension of the intricate molecular regulation of body color polymorphism and providing insights for C. auratus breeding research.

MicroRNAs balance growth and salt stress responses in sweet sorghum

Salt stress is one of the major causes of reduced crop production, limiting agricultural development globally. Plants have evolved with complex systems to maintain the balance between growth and stress responses, where signaling pathways such as hormone signaling play key roles. Recent studies revealed that hormones are modulated by microRNAs (miRNAs). Previously, two sweet sorghum (Sorghum bicolor) inbred lines with different salt tolerance were identified: the salt-tolerant M-81E and the salt-sensitive Roma. The levels of endogenous hormones in M-81E and Roma varied differently under salt stress, showing a different balance between growth and stress responses. miRNA and degradome sequencing showed that the expression of many upstream transcription factors regulating signal transduction and hormone-responsive genes was directly induced by differentially expressed miRNAs, whose levels were very different between the two sweet sorghum lines. Furthermore, the effects of representative miRNAs on salt tolerance in sorghum were verified through a transformation system mediated by Agrobacterium rhizogenes. Also, miR-6225-5p reduced the level of Ca²⁺ in the miR-6225-5p-overexpressing line by inhibiting the expression of the Ca²⁺ uptake gene SbGLR3.1 in the root epidermis and affected salt tolerance in sorghum. This study provides evidence for miRNA-mediated growth and stress responses in sweet sorghum.

Integrated multi-omics analysis uncovers roles of mdm-miR164b-MdORE1 in strigolactone-mediated inhibition of adventitious root formation in apple

Apple is one of the most important fruit crops in temperate regions and largely relies on cutting propagation. Adventitious root formation is crucial for the success of cutting propagation. Strigolactones have been reported to function in rooting of woody plants. In this study, we determined that strigolactones have inhibitory effects on adventitious root formation in apple. Transcriptome analysis identified 12 051 differentially expressed genes over the course of adventitious root initiation, with functions related to organogenesis, cell wall biogenesis or plant development. Further analysis indicated that strigolactones might inhibit adventitious root formation through repressing two core hub genes, MdLAC3 and MdORE1. Combining small RNA and degradome sequencing, as well as dual-luciferase sensor assays, we identified and validated three negatively correlated miRNA-mRNA pairs, including mdm-miR397-MdLAC3 and mdm-miR164a/b-MdORE1. Overexpression of mdm-miR164b and silencing MdORE1 exhibited enhanced adventitious root formation in tobacco and apple, respectively. Finally, we verified the role of mdm-miR164b-MdORE1 in strigolactone-mediated repression of rooting ability. Overall, the identified comprehensive regulatory network in apple not only provides insight into strigolactone-mediated adventitious root formation in other woody plants, but also points to a potential strategy for genetic improvement of rooting capacity in woody plants.

Parallel analysis of RNA ends reveals global microRNA-mediated target RNA cleavage in maize

MicroRNAs (miRNAs) are endogenous 20-24-nucleotide non-coding RNAs that play important regulatory roles in many biological processes in eukaryotes. miRNAs modulate the expression of target genes at the post-transcriptional level by transcript cleavage or translational inhibition. The identification of miRNA target genes has been extensively investigated in Arabidopsis and rice, but an in-depth global analysis of miRNA-mediated target regulation is still lacking in maize. Here, we report a transcriptome-wide identification of miRNA targets by analyzing parallel analysis of RNA ends (PARE) datasets derived from nine different tissues at five developmental stages of the maize (Zea mays L.) B73 cultivar. In total, 246 targets corresponding to 60 miRNAs from 25 families were identified, including transcription factors and other genes. In addition, PARE analysis revealed that miRNAs guide specific target transcript cleavage in a tissue-preferential manner. Primary transcripts of MIR159c and MIR169e were found to be cleaved by mature miR159 and miR169, respectively, indicating a negative-feedback regulatory mechanism in miRNA biogenesis. Moreover, several miRNA-target gene pairs involved in seed germination were identified and experimentally validated. Our PARE analyses generated a wide and detailed miRNA-target interaction atlas, which provides a valuable resource for investigating the roles of miRNAs and their targets in maize.

Arsenic perception and signaling: The yet unexplored world

Arsenic is one of the most potent carcinogens in the biosphere, jeopardizing the health of millions of people due to its entrance into the human food chain through arsenic-contaminated waters and staple crops, particularly rice. Although the mechanisms of arsenic sensing are widely known in yeast and bacteria, scientific evidence concerning arsenic sensors or components of early arsenic signaling in plants is still in its infancy. However, in recent years, we have gained understanding of the mechanisms involved in arsenic uptake and detoxification in different plant species and started to get insights into arsenic perception and signaling, which allows us to glimpse the possibility to design effective strategies to prevent arsenic accumulation in edible crops or to increase plant arsenic extraction for phytoremediation purposes. In this context, it has been recently described a mechanism according to which arsenite, the reduced form of arsenic, regulates the arsenate/phosphate transporter, consistent with the idea that arsenite functions as a selective signal that coordinates arsenate uptake with detoxification mechanisms. Additionally, several transcriptional and post-translational regulators, miRNAs and phytohormones involved in arsenic signaling and tolerance have been identified. On the other hand, studies concerning the developmental programs triggered to adapt root architecture in order to cope with arsenic toxicity are just starting to be disclosed. In this review, we compile and analyze the latest advances toward understanding how plants perceive arsenic and coordinate its acquisition with detoxification mechanisms and root developmental programs.

Integrated analysis of small RNAs, transcriptome and degradome sequencing reveal the drought stress network in Agropyron mongolicum Keng

Agropyron mongolicum (A. mongolicum) is an excellent gramineous forage with extreme drought tolerance, which lives in arid and semiarid desert areas. However, the mechanism that underlies the response of microRNAs (miRNAs) and their targets in A. mongolicum to drought stress is not well understood. In this study, we analyzed the transcriptome, small RNAome (specifically the miRNAome) and degradome to generate a comprehensive resource that focused on identifying key regulatory miRNA-target circuits under drought stress. The most extended transcript in each collection is known as the UniGene, and a total of 41,792 UniGenes and 1,104 miRNAs were identified, and 99 differentially expressed miRNAs negatively regulated 1,474 differentially expressed target genes. Among them, eight miRNAs were unique to A. mongolicum, and there were 36 target genes. A weighted gene co-expression network analysis identified five hub genes. The miRNAs of five hub genes were screened with an integration analysis of the degradome and sRNAs, such as osa-miR444a-3p.2-MADS47, bdi-miR408-5p_1ss19TA-CCX1, tae-miR9774_L-2R-1_1ss11GT-carC, ata-miR169a-3p-PAO2, and bdi-miR528-p3_2ss15TG20CA-HOX24. The functional annotations revealed that they were involved in mediating the brassinosteroid signal pathway, transporting and exchanging sodium and potassium ions and regulating the oxidation-reduction process, hydrolase activity, plant response to water deprivation, abscisic acid (ABA) and the ABA-activated signaling pathway to regulate drought stress. Five hub genes were discovered, which could play central roles in the regulation of drought-responsive genes. These results show that the combined analysis of miRNA, the transcriptome and degradation group provides a useful platform to investigate the molecular mechanism of drought resistance in A. mongolicum and could provide new insights into the genetic engineering of Poaceae crops in the future.

microRNAs: Key Players in Plant Response to Metal Toxicity

Environmental metal pollution is a common problem threatening sustainable and safe crop production. Heavy metals (HMs) cause toxicity by targeting key molecules and life processes in plant cells. Plants counteract excess metals in the environment by enhancing defense responses, such as metal chelation, isolation to vacuoles, regulating metal intake through transporters, and strengthening antioxidant mechanisms. In recent years, microRNAs (miRNAs), as a small non-coding RNA, have become the central regulator of a variety of abiotic stresses, including HMs. With the introduction of the latest technologies such as next-generation sequencing (NGS), more and more miRNAs have been widely recognized in several plants due to their diverse roles. Metal-regulated miRNAs and their target genes are part of a complex regulatory network. Known miRNAs coordinate plant responses to metal stress through antioxidant functions, root growth, hormone signals, transcription factors (TF), and metal transporters. This article reviews the research progress of miRNAs in the stress response of plants to the accumulation of HMs, such as Cu, Cd, Hg, Cr, and Al, and the toxicity of heavy metal ions.

Transcriptome analysis reveals candidate genes involved in multiple heavy metal tolerance in hyperaccumulator Sedum alfredii

Sedum alfredii Hance is a perennial herb native to China that can particularly be found in regions with abandoned Pb/Zn mines. It is a Cd/Zn hyperaccumulator that is highly tolerant to Pb, Cu, Ni, and Mn, showing potential for phytoremediation of soils contaminated with multiple heavy metals. A better understanding of how this species responds to different heavy metals would advance the phytoremediation efficiency. In this study, transcriptomic regulation of S. alfredii roots after Cd, Zn, Pb, and Cu exposure was analyzed to explore the candidate genes involved in multi-heavy metal tolerance. Although Zn and Cd, Pb and Cu had similar distribution patterns in S. alfredii, distinct expression patterns were exhibited among these four metal treatments, especially about half of the differentially expressed genes were upregulated under Cu treatment, suggesting that it utilizes distinctive and flexible strategies to cope with specific metal stress. Most unigenes regulated by Cu were enriched in catalytic activity, whereas the majority of unigenes regulated by Pb had unknown functions, implying that S. alfredii may have a unique strategy coping with Pb stress different from previous cognition. The unigenes that were co-regulated by multiple heavy metals exhibited functions of antioxidant substances, antioxidant enzymes, transporters, transcription factors, and cell wall components. These metal-induced responses at the transcriptional level in S. alfredii were highly consistent with those at the physiological level. Some of these genes have been confirmed to be related to heavy metal absorption and detoxification, and some were found to be related to heavy metal tolerance for the first time in this study, like Metacaspase-1 and EDR6. These results provide a theoretical basis for the use of genetic engineering technology to modify plants by enhancing multi-metal tolerance to promote phytoremediation efficiency.

Genome-Wide Characterization, Evolutionary Analysis of ARF Gene Family, and the Role of SaARF4 in Cd Accumulation of Sedum alfredii Hance

Auxin response factors (ARFs) play important roles in plant development and environmental adaption. However, the function of ARFs in cadmium (Cd) accumulation are still unknown. Here, 23 SaARFs were detected in the genome of hyperaccumulating ecotype of Sedum alfredii Hance (HE), and they were not evenly distributed on the chromosomes. Their protein domains remained highly conservative. SaARFs in the phylogenetic tree can be divided into three groups. Genes in the group Ⅰ contained three introns at most. However, over ten introns were found in other two groups. Collinearity relationships were exhibited among ten SaARFs. The reasons for generating SaARFs may be segmental duplication and rearrangements. Collinearity analysis among different species revealed that more collinear genes of SaARFs can be found in the species with close relationships of HE. A total of eight elements in SaARFs promoters were related with abiotic stress. The qRT-PCR results indicated that four SaARFs can respond to Cd stress. Moreover, that there may be functional redundancy among six SaARFs. The adaptive selection and functional divergence analysis indicated that SaARF4 may undergo positive selection pressure and an adaptive-evolution process. Overexpressing SaARF4 effectively declined Cd accumulation. Eleven single nucleotide polymorphism (SNP) sites relevant to Cd accumulation can be detected in SaARF4. Among them, only one SNP site can alter the sequence of the SaARF4 protein, but the SaARF4 mutant of this site did not cause a significant difference in cadmium content, compared with wild-type plants. SaARFs may be involved in Cd-stress responses, and SaARF4 may be applied for decreasing Cd accumulation of plants.

Identification and Analysis of bZIP Family Genes in Sedum plumbizincicola and Their Potential Roles in Response to Cadmium Stress

Sedum plumbizincicola (Crassulaceae), a cadmium (Cd)/zinc (Zn)/lead (Pb) hyperaccumulator native to Southeast China, is potentially useful for the phytoremediation of heavy metal-contaminated soil. Basic leucine zipper (bZIP) transcription factors play vital roles in plant growth, development, and abiotic stress responses. However, there has been minimal research on the effects of Cd stress on the bZIP gene family in S. plumbizincicola. In this study, 92 SpbZIP genes were identified in the S. plumbizincicola genome and then classified into 12 subgroups according to their similarity to bZIP genes in Arabidopsis. Gene structure and conserved motif analyses showed that SpbZIP genes within the same subgroup shared similar intron-exon structures and motif compositions. In total, eight pairs of segmentally duplicated SpbZIP genes were identified, but there were no tandemly duplicated SpbZIP genes. Additionally, the duplicated SpbZIP genes were mainly under purifying selection pressure. Hormone-responsive, abiotic and biotic stress-responsive, and plant development-related cis-acting elements were detected in the SpbZIP promoter sequences. Expression profiles derived from RNA-seq and quantitative real-time PCR analyses indicated that the expression levels of most SpbZIP genes were upregulated under Cd stress conditions. Furthermore, a gene co-expression network analysis revealed that most edge genes regulated by hub genes were related to metal transport, responses to stimuli, and transcriptional regulation. Because its expression was significantly upregulated by Cd stress, the hub gene SpbZIP60 was selected for a functional characterization to elucidate its role in the root response to Cd stress. In a transient gene expression analysis involving Nicotiana benthamiana leaves, SpbZIP60 was localized in the nucleus. The overexpression of SpbZIP60 enhanced the Cd tolerance of transgenic Arabidopsis plants by inhibiting ROS accumulation, protecting the photosynthetic apparatus, and decreasing the Cd content. These findings may provide insights into the potential roles of the bZIP family genes during the S. plumbizincicola response to Cd stress.

Transcriptional multiomics reveals the mechanism of seed deterioration in Nicotiana tabacum L. and Oryza sativa L

INTRODUCTION

Mature seeds deteriorate gradually and die eventually during long-term storage. Controlled deterioration is often used to accelerate the seed deterioration rate to assess the seed vigor and physiological quality of seed lots.

OBJECTIVES

Although it is well known that the process of seed deterioration produced by controlled deterioration is distinct from that caused by long-term storage, the differences in transcriptional levels have not been reported. Clarifying the mechanism of seed deterioration is critical for identifying, conserving and utilizing germplasm resources.

METHODS

Tobacco (Nicotiana tabacum L.) seeds were studied thoroughly using transcriptome, small RNA, and degradome sequencing after long-term storage (LS) and controlled deterioration (CD). Co-expression trend analysis identified transcripts involved in tobacco seed deterioration, while phylogenetic analysis helped to uncover comparable targets in rice (Oryza sativa L.) for further verification and utilization.

RESULTS

In LS and CD, a total of 2,112 genes and 164 miRNAs were differentially expressed, including 20 interaction miRNA-mRNA pairs with contrasting expression. Transcriptional multiomics found that the main causes of LS were plant hormone signal transduction and protein processing in the endoplasmic reticulum, whereas the primary cause of CD was nucleotide excision repair dysfunction. The homeostatic balance of RNA degradation and the spliceosome occurred in both modes of seed deterioration. Additionally, co-expression trend analysis identified two coherent pairs, nta-miR160b-NtARF18 and nta-miR396c-NtMBD10, as being significant in LS and CD, respectively. For utilization, rice homologous targets OsARF18 and OsMBD707 were verified to play similar roles in LS and CD, respectively.

CONCLUSION

This study demonstrated the transcriptional mechanism of tobacco and key genes in seed deterioration. And the application of key genes in rice also verified the feasibility of the multiomics method, guiding the identification of candidate genes to precisely delay seed deterioration in other species of seed research.

Temporal analysis of microRNAs associated with wing development in the English grain aphid, Sitobion avenae (F.) (Homoptera: Aphidiae)

Molecular mechanisms underlying wing evolution and development have been a point of scientific inquiry for decades. Phloem-feeding aphids are one of the most devastating global insect pests, where dispersal of winged morphs lead to annual movements, migrations, and range expansions. Aphids show a polyphenic wing dimorphism trait, and offer a model to study the role of environment in determining morphological plasticity of a single genotype. Despite recent progresses in the genetic understanding of wing polyphenism, the influence of environmental cues remains unclear. To investigate the involvement of miRNAs in wing development, we sequenced small RNA libraries of the English grain aphid, Sitobion avenae (F.) across six different developmental stages. As a result, we identified 113 conserved and 193 S. avenae-specific miRNAs. Gene Ontology and KEGG pathway analyses of putative target mRNAs for the six differentially expressed miRNAs are enriched for wing development processes. Dietary uptake of miR-263a, miR-316, and miR-184a agomirs and antagomirs led to significantly higher mortality (>70%) and a lower proportion of winged morphs (<5%). On the other hand, wing malformation was observed in miR-2 and miR-306 agomirs and miR-2 and miR-14 antagomirs, respectively, suggesting their involvement in S. avenae wing morphogenesis. These combined results not only shed light on the regulatory role of miRNAs in wing dimorphism, but also provide potential novel targets for the long-term sustainable management of S. avenae, a devastating global grain pest.

Identification and expression analysis of the PtGATL genes under different nitrogen and carbon dioxide treatments in Populus trichocarpa

Pectin is one of the most important components of the plant cell wall. Galacturonosyltransferase-like (GATL) is an important enzyme involved in forming pectin in Arabidopsis thaliana. In this study, 12 PtGATL genes were identified and characterized based on the Populus trichocarpa genome using bioinformatics methods. The results showed that the PtGATLs contained four typical motifs, including DXD, LPPF, GLG, and HXXGXXKPW. According to phylogenetic analysis, PtGATLs were divided into six groups. Chromosome distribution and genome synteny analysis showed that there were 11 segmental-duplicated gene pairs with repeated fragments on chromosomes 2, 5, 7, 8, 10, and 14. Tissue-specific expression profiles indicated that these PtGATLs had different expression patterns. The transcription level of PtGATLs was regulated by different carbon dioxide and nitrogen concentrations. In conclusion, the identification and analysis of PtGATL genes in poplar provide important information on the gene function.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03129-y.

Integrative analysis of transcriptome and proteome provides insights into adaptation to cadmium stress in Sedum plumbizincicola

Sedum plumbizincicola, a cadmium (Cd) hyperaccumulating herbaceous plant, can accumulate large amounts of Cd in the above-ground tissues without being poisoned. However, the molecular mechanisms regulating the processes are not fully understood. In this study, Transcriptional and proteomic analyses were integrated to investigate the response of S. plumbizincicola plants to Cd stress and to identify key pathways that are potentially responsible for Cd tolerance and accumulation. A total of 630 DAPs (differentially abundant proteins, using fold change >1.5 and adjusted p-value <0.05) were identified from Tandem Mass Tag (TMT)- based quantitative proteomic profiling, which were enriched in processes including phenylpropanoid biosynthesis, protein processing in endoplasmic reticulum, and biosynthesis of secondary metabolites. Combined with the previous transcriptomic study, 209 genes and their corresponding proteins showed the identical expression pattern. The identified genes/proteins revealed the potential roles of several metabolism pathways, including phenylpropanoid biosynthesis, oxidative phosphorylation, phagosome, and glutathione metabolism, in mediating Cd tolerance and accumulation. Lignin staining and Cd accumulation assay of the transgenic lines over-expressing a selected Cd up-regulated gene SpFAOMT (Flavonoid 3',5'-methyltransferase) showed its functions in adapting to Cd stress, and provided insight into its role in lignin biosynthesis and Cd accumulation in S. plumbizincicola during Cd stress.

Genome-Wide Characterization of Sedum plumbizincicola HMA Gene Family Provides Functional Implications in Cadmium Response

Heavy-metal ATPase (HMA), an ancient family of transition metal pumps, plays important roles in the transmembrane transport of transition metals such as Cu, Zn, Cd, and Co. Although characterization of HMAs has been conducted in several plants, scarcely knowledge was revealed in Sedum plumbizincicola, a type of cadmium (Cd) hyperaccumulator found in Zhejiang, China. In this study, we first carried out research on genome-wide analysis of the HMA gene family in S. plumbizincicola and finally identified 8 SpHMA genes and divided them into two subfamilies according to sequence alignment and phylogenetic analysis. In addition, a structural analysis showed that SpHMAs were relatively conserved during evolution. All of the SpHMAs contained the HMA domain and the highly conserved motifs, such as DKTGT, GDGxNDxP, PxxK S/TGE, HP, and CPx/SPC. A promoter analysis showed that the majority of the SpHMA genes had cis-acting elements related to the abiotic stress response. The expression profiles showed that most SpHMAs exhibited tissue expression specificity and their expression can be regulated by different heavy metal stress. The members of Zn/Co/Cd/Pb subgroup (SpHMA1-3) were verified to be upregulated in various tissues when exposed to CdCl₂. Here we also found that the expression of SpHMA7, which belonged to the Cu/Ag subgroup, had an upregulated trend in Cd stress. Overexpression of SpHMA7 in transgenic yeast indicated an improved sensitivity to Cd. These results provide insights into the evolutionary processes and potential functions of the HMA gene family in S. plumbizincicola, laying a theoretical basis for further studies on figuring out their roles in regulating plant responses to biotic/abiotic stresses.

Integration of small RNA, degradome, and transcriptome sequencing data illustrates the mechanism of low phosphorus adaptation in Camellia oleifera

Phosphorus (P) is an indispensable macronutrient for plant growth and development, and it is involved in various cellular biological activities in plants. Camellia oleifera is a unique high-quality woody oil plant that grows in the hills and mountains of southern China. However, the available P content is deficient in southern woodland soil. Until now, few studies focused on the regulatory functions of microRNAs (miRNAs) and their target genes under low inorganic phosphate (Pi) stress. In this study, we integrated small RNA, degradome, and transcriptome sequencing data to investigate the mechanism of low Pi adaptation in C. oleifera. We identified 40,689 unigenes and 386 miRNAs by the deep sequencing technology and divided the miRNAs into four different groups. We found 32 miRNAs which were differentially expressed under low Pi treatment. A total of 414 target genes of 108 miRNAs were verified by degradome sequencing. Gene ontology (GO) functional analysis of target genes found that they were related to the signal response to the stimulus and transporter activity, indicating that they may respond to low Pi stress. The integrated analysis revealed that 31 miRNA-target pairs had negatively correlated expression patterns. A co-expression regulatory network was established based on the profiles of differentially expressed genes. In total, three hub genes (ARF22, WRKY53, and SCL6), which were the targets of differentially expressed miRNAs, were discovered. Our results showed that integrated analyses of the small RNA, degradome, and transcriptome sequencing data provided a valuable basis for investigating low Pi in C. oleifera and offer new perspectives on the mechanism of low Pi tolerance in woody oil plants.

Identification of miRNA-mRNA Regulatory Modules Involved in Lipid Metabolism and Seed Development in a Woody Oil Tree (Camellia oleifera)

Tea oil camellia (Camellia oleifera), an important woody oil tree, is a source of seed oil of high nutritional and medicinal value that is widely planted in southern China. However, there is no report on the identification of the miRNAs involved in lipid metabolism and seed development in the high- and low-oil cultivars of tea oil camellia. Thus, we explored the roles of miRNAs in the key periods of oil formation and accumulation in the seeds of tea oil camellia and identified miRNA–mRNA regulatory modules involved in lipid metabolism and seed development. Sixteen small RNA libraries for four development stages of seed oil biosynthesis in high- and low-oil cultivars were constructed. A total of 196 miRNAs, including 156 known miRNAs from 35 families, and 40 novel miRNAs were identified, and 55 significantly differentially expressed miRNAs were found, which included 34 upregulated miRNAs, and 21 downregulated miRNAs. An integrated analysis of the miRNA and mRNA transcriptome sequence data revealed that 10 miRNA–mRNA regulatory modules were related to lipid metabolism; for example, the regulatory modules of ath-miR858b–MYB82/MYB3/MYB44 repressed seed oil biosynthesis, and a regulation module of csi-miR166e-5p–S-ACP-DES6 was involved in the formation and accumulation of oleic acid. A total of 23 miRNA–mRNA regulatory modules were involved in the regulation of the seed size, such as the regulatory module of hpe-miR162a_L-2–ARF19, involved in early seed development. A total of 12 miRNA–mRNA regulatory modules regulating growth and development were identified, such as the regulatory modules of han-miR156a_L+1–SPL4/SBP2, promoting early seed development. The expression changes of six miRNAs and their target genes were validated using quantitative real-time PCR, and the targeting relationship of the cpa-miR393_R-1–AFB2 regulatory module was verified by luciferase assays. These data provide important theoretical values and a scientific basis for the genetic improvement of new cultivars of tea oil camellia in the future.

Small RNA profiling for identification of microRNAs involved in regulation of seed development and lipid biosynthesis in yellowhorn

BACKGROUND

Yellowhorn (Xanthoceras sorbifolium), an endemic woody oil-bearing tree, has become economically important and is widely cultivated in northern China for bioactive oil production. However, the regulatory mechanisms of seed development and lipid biosynthesis affecting oil production in yellowhorn are still elusive. MicroRNAs (miRNAs) play crucial roles in diverse aspects of biological and metabolic processes in seeds, especially in seed development and lipid metabolism. It is still unknown how the miRNAs regulate the seed development and lipid biosynthesis in yellowhorn.

RESULTS

Here, based on investigations of differences in the seed growth tendency and embryo oil content between high-oil-content and low-oil-content lines, we constructed small RNA libraries from yellowhorn embryos at four seed development stages of the two lines and then profiled small RNA expression using high-throughput sequencing. A total of 249 known miRNAs from 46 families and 88 novel miRNAs were identified. Furthermore, by pairwise comparisons among the four seed development stages in each line, we found that 64 miRNAs (53 known and 11 novel miRNAs) were differentially expressed in the two lines. Across the two lines, 15, 11, 10, and 7 differentially expressed miRNAs were detected at 40, 54, 68, and 81 days after anthesis, respectively. Bioinformatic analysis was used to predict a total of 2654 target genes for 141 differentially expressed miRNAs (120 known and 21 novel miRNAs). Most of these genes were involved in the fatty acid biosynthetic process, regulation of transcription, nucleus, and response to auxin. Using quantitative real-time PCR and an integrated analysis of miRNA and mRNA expression, miRNA-target regulatory modules that may be involved in yellowhorn seed size, weight, and lipid biosynthesis were identified, such as miR172b-ARF2 (auxin response factor 2), miR7760-p3_1-AGL61 (AGAMOUS-LIKE 61), miR319p_1-FAD2-2 (omega-6 fatty acid desaturase 2-2), miR5647-p3_1-DGAT1 (diacylglycerol acyltransferase 1), and miR7760-p5_1-MED15A (Mediator subunit 15a).

CONCLUSIONS

This study provides new insights into the important regulatory roles of miRNAs in the seed development and lipid biosynthesis in yellowhorn. Our results will be valuable for dissecting the post-transcriptional and transcriptional regulation of seed development and lipid biosynthesis, as well as improving yellowhorn in northern China.

Bm-miR172c-5p Regulates Lignin Biosynthesis and Secondary Xylem Thickness by Altering the Ferulate 5 Hydroxylase Gene in Bacopa monnieri

MicroRNAs (miRNAs) are small non-coding, endogenous RNAs containing 20-24 nucleotides that regulate the expression of target genes involved in various plant processes. A total of 1,429 conserved miRNAs belonging to 95 conserved miRNA families and 12 novel miRNAs were identified from Bacopa monnieri using small RNA sequencing. The Bm-miRNA target transcripts related to the secondary metabolism were further selected for validation. The Bm-miRNA expression in shoot and root tissues was negatively correlated with their target transcripts. The Bm-miRNA cleavage sites were mapped within the coding or untranslated region as depicted by the modified RLM-RACE. In the present study, we validate three miRNA targets, including asparagine synthetase, cycloartenol synthase and ferulate 5 hydroxylase (F5H) and elucidate the regulatory role of Bm-miR172c-5p, which cleaves the F5H gene involved in the lignin biosynthesis. Overexpression (OE) of Bm-miR172c-5p precursor in B. monnieri suppresses F5H gene, leading to reduced lignification and secondary xylem thickness under control and drought stress. By contrast, OE of endogenous target mimics (eTMs) showed enhanced lignification and secondary xylem thickness leading to better physiological response under drought stress. Taken together, we suggest that Bm-miRNA172c-5p might be a key player in maintaining the native phenotype of B. monnieri under control and different environmental conditions.

Transcriptome characterization of candidate genes related to chromium uptake, transport and accumulation in Miscanthus sinensis

Miscanthus sinensis is a C4 perennial grass species that is widely used as forage, ornamental grass and bioenergy crop due to its broad adaption and great biological traits. Recent studies indicated that M. sinensis could also grow in marginal lands which were contaminated with heavy metals, and exhibited important ecological restoration potential. In this study, transcriptome characterization of candidate genes related to chromium (Cr) uptake, transport and accumulation in M. sinensis were employed to investigate the molecular mechanism of plant tolerance to heavy metal stress. The result showed that following treatment of 200 mg/L of Cr, plant roots could accumulate most Cr and localize mainly in cell walls and soluble fractions, whereas Cr in stems and leaves was primarily in soluble fractions. A total of 83,645 differentially expressed genes (DEGs) were obtained after the treatment. Many genes involved in heavy metal transport, metal ion chelation and photosynthesis were found to be Cr-induced DEGs. Co-expression and weighted correlation network analysis revealed that Glutathion metabolism and ABC transporters pathways play an important role in Cr tolerance of M. sinensis. A hypothesis schematic diagram for the Cr uptake, transport and accumulation of M. sinensis cells were suggested, which could provide a molecular and genetic basis for future candidate genes validation and breeding of such crops.

Comparative analysis of sRNAs, degradome and transcriptomics in sweet sorghum reveals the regulatory roles of miRNAs in Cd accumulation and tolerance

Key miRNAs including sbi-miR169p/q, sbi-miR171g/j, sbi-miR172a/c/d, sbi-miR172e, sbi-miR319a/b, sbi-miR396a/b, miR408, sbi-miR5384, sbi-miR5565e and nov_23 were identified to function in the regulation of Cd accumulation and tolerance. As an energy plant, sweet sorghum shows great potential in the phytoremediation of Cd-contaminated soils. However, few studies have focused on the regulatory roles of miRNAs and their targets under Cd stress. In this study, comparative analysis of sRNAs, degradome and transcriptomics was conducted in high-Cd accumulation (H18) and low-Cd accumulation (L69) genotypes of sweet sorghum. A total of 38 conserved and 23 novel miRNAs with differential expressions were identified under Cd stress or between H18 and L69, and 114 target genes of 41 miRNAs were validated. Furthermore, 25 miRNA-mRNA pairs exhibited negatively correlated expression profiles and sbi-miR172e together with its target might participate in the distinct Cd tolerance between H18 and L69 as well as sbi-miR172a/c/d. Additionally, two groups of them: miR169p/q-nov_23 and miR408 were focused through the co-expression analysis, which might be involved in Cd uptake and tolerance by regulating their targets associated with transmembrane transportation, cytoskeleton activity, cell wall construction and ROS (reactive oxygen species) homeostasis. Further experiments exhibited that cell wall components of H18 and L69 were different when exposed to cadmium, which might be regulated by miR169p/q, miR171g/j, miR319a/b, miR396a/b, miR5384 and miR5565e through their targets. Through this study, we aim to reveal the potential miRNAs involved in sweet sorghum in response to Cd stress and provide references for developing high-Cd accumulation or high Cd-resistant germplasm of sweet sorghum that can be used in phytoremediation.

Transcriptome and Degradome Profiling Reveals a Role of miR530 in the Circadian Regulation of Gene Expression in Kalanchoë marnieriana

Crassulacean acid metabolism (CAM) is an important photosynthetic pathway for plant adaptation to dry environments. CAM plants feature a coordinated interaction between mesophyll and epidermis functions that involves refined regulations of gene expression. Plant microRNAs (miRNAs) are crucial post-transcription regulators of gene expression, however, their roles underlying the CAM pathway remain poorly investigated. Here, we present a study characterizing the expression of miRNAs in an obligate CAM species Kalanchoë marnieriana. Through sequencing of transcriptome and degradome in mesophyll and epidermal tissues under the drought treatments, we identified differentially expressed miRNAs that were potentially involved in the regulation of CAM. In total, we obtained 84 miRNA genes, and eight of them were determined to be Kalanchoë-specific miRNAs. It is widely accepted that CAM pathway is regulated by circadian clock. We showed that miR530 was substantially downregulated in epidermal peels under drought conditions; miR530 targeted two tandem zinc knuckle/PLU3 domain encoding genes (TZPs) that were potentially involved in light signaling and circadian clock pathways. Our work suggests that the miR530-TZPs module might play a role of regulating CAM-related gene expression in Kalanchoë.

Identification and characterization of long non-coding RNA and their response against citrus bark cracking viroid infection in Humulus lupulus

Long non-coding RNAs (lncRNAs) are a highly heterogeneous class of non-protein-encoding transcripts that play an essential regulatory role in diverse biological processes, including stress responses. The severe stunting disease caused by Citrus bark cracking viroid (CBCVd) poses a major threat to the production of Humulus lupulus (hop) plants. In this study, we systematically investigate the characteristics of the lncRNAs in hop and their role in CBCVd-infection using RNA-sequencing data. Following a stringent filtration criterion, a total of 3598 putative lncRNAs were identified with a high degree of certainty, of which 19% (684) of the lncRNAs were significantly differentially expressed (DE) in CBCVd-infected hop, which were predicted to be mainly involved in plant-pathogen interactions, kinase cascades, secondary metabolism and phytohormone signal transduction. Besides, several lncRNAs and CBCVd-responsive lncRNAs were identified as the precursor of microRNAs and predicted as endogenous target mimics (eTMs) for hop microRNAs involved in CBCVd-infection.

Analysis of miRNA-mediated regulation of flowering induction in Lilium × formolongi

BACKGROUND

MicroRNAs play pivotal roles in plant vegetative phase change and flowering induction via integrating into multiple flowering pathways. Lilium × formolongi is an important ornamental lily cultivar that can flower within one year after sowing. However, it remains unresolved how miRNA-mediated regulation networks contribute to the L. × formolongi characteristics of a short vegetative growth period and rapid flowering.

RESULTS

In this study, the small RNA libraries and one degradome library were constructed for L. × formolongi during vegetative growth and flowering initiation, and 366 conserved miRNAs and 32 novel miRNAs were identified. Additionally, 84 miRNAs were significantly differentially expressed during development. A total of 396 targets of 185 miRNAs were identified and validated through degradome sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that functions of the targets were top enriched in the cold and cadmium ion responses, pentose phosphate pathway and carbon fixation in photosynthetic organisms. Furthermore, among 23 differentially expressed miRNA-target pairs, the miR156s-LfSPL2, miR172a-LfAP2 and miR164a-LfNAC pairs as well as miR159a-LfSPL2 were found to be relevant to flowering based on the correlation analysis of expression profiles in the miRNA libraries, degradome and transcriptome. A coexpression regulatory network focused on differentially expressed pairs was also constructed by WGCNA, and 14 miRNAs were considered putative key miRNAs during vegetative development and flowering induction. miR156a/ d/ e showed particularly strong relationships with other miRNAs in the coexpression network.

CONCLUSIONS

This study provides cues for the further exploration of the regulatory mechanisms of short vegetative development and flowering in L. × formolongi.

Identification of miRNA in Sheep Intramuscular Fat and the Role of miR-193a-5p in Proliferation and Differentiation of 3T3-L1

Intramuscular fat (IMF) is one of the most critical parameters affecting meat quality and mainly affected by genetic factors. MicroRNA as an important regulatory factor, which is still a lack of research in the development of sheep IMF deposition. We used RNA sequencing (RNA-seq) and cell-level validation to explore the role of miRNA in IMF deposition. As for this purpose, longissimus thoracis et lumborum (LTL) samples of 2 month-old (Mth-2) and 12 months-old (Mth-12) Aohan fine-wool sheep (AFWS) were used to identified miRNAs expression. We found 59 differentially expressed miRNAs (DE-miRNA) between these age groups and predicted their 1,796 target genes. KEGG functional enrichment analysis revealed eight pathways involved in lipid metabolism-related processes, including fatty acid elongation and the AMPK signaling pathway. A highly expressed DE-miRNA, miR-193a-5p, was found to serve a function in 3T3-L1 preadipocyte differentiation. Luciferase assay demonstrated that miR-193a-5p directly binds to the 3′-UTR region of ACAA2. By constructing mimics and inhibitor vector transfecting into 3T3-L1 cells to explore the effect of miR-193a-5p on cell proliferation and differentiation, we demonstrated that overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte proliferation, as evidenced by decreased mRNA and protein expression of CDK4 and CyclinB. CCK-8 assay showed that miR-193a-5p significantly inhibited cell proliferation. Similarly, the overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte differentiation and adipocyte-specific molecular markers’ expression, leading to a decrease in PPARγ and C/EBPα and ACAA2. Inhibition of miR-193a-5p had the opposite effects. Our study lists the miRNAs associated with intramuscular lipid deposition in sheep and their potential targets, striving to improve sheep meat quality.

Genome-wide characterization of the hyperaccumulator Sedum alfredii F-box family under cadmium stress

The F-box genes, which form one of the largest gene families in plants, are vital for plant growth, development and stress response. However, F-box gene family in Sedum alfredii remains unknown. Comprehensive studies addressing their function responding to cadmium stress is still limited. In the present study, 193 members of the F-box gene (SaFbox) family were identified, which were classified into nine subfamilies. Most of the SaFboxs had highly conserved domain and motif. Various functionally related cis-elements involved in plant growth regulation, stress and hormone responses were located in the upstream regions of SaFbox genes. RNA-sequencing and co-expression network analysis revealed that the identified SaFbox genes would be involved in Cd stress. Expression analysis of 16 hub genes confirmed their transcription level in different tissues. Four hub genes (SaFbox40, SaFbox51, SaFbox136 and SaFbox170) were heterologously expressed in a Cd-sensitive yeast cell to assess their effects on Cd tolerance. The transgenic yeast cells carrying SaFbox40, SaFbox51, SaFbox136, or SaFbox170 were more sensitive and accumulated more cadmium under Cd stress than empty vector transformed control cells. Our results performed a comprehensive analysis of Fboxs in S. alfredii and identified their potential roles in Cd stress response.

Transcriptome analysis and association mapping reveal the genetic regulatory network response to cadmium stress in Populus tomentosa

Long non-coding RNAs (lncRNAs) play essential roles in plant abiotic stress responses, but the response of lncRNA-mediated genetic networks to cadmium (Cd) treatment remain elusive in trees, the promising candidates for phytoremediation of Cd contamination. We identified 172 Cd-responsive lncRNAs and 295 differentially expressed target genes in the leaves of Cd-treated Populus tomentosa. Functional annotation revealed that these lncRNAs were involved in various processes, including photosynthesis, hormone regulation, and phenylalanine metabolism. Association studies identified 78 significant associations, representing 14 Cd-responsive lncRNAs and 28 target genes for photosynthetic and leaf physiological traits. Epistasis uncovered 83 pairwise interactions among these traits, revealing Cd-responsive lncRNA-mediated genetic networks for photosynthesis and leaf physiology in P. tomentosa. We focused on the roles of two Cd-responsive lncRNA-gene pairs, MSTRG.22608.1-PtoMYB73 and MSTRG.5634.1-PtoMYB27, in Cd tolerance of Populus, and detected insertions/deletions within lncRNAs as polymorphisms driving target gene expression. Genotype analysis of lncRNAs and heterologous overexpression of PtoMYB73 and PtoMYB27 in Arabidopsis indicated their effects on enhancing Cd tolerance, photosynthetic rate, and leaf growth, and the potential interaction mechanisms of PtoMYB73 with abiotic stresses. Our study identifies the genetic basis for the response of Populus to Cd treatment, facilitating genetic improvement of Cd tolerance in trees.

Auxin-Induced SaARF4 Downregulates SaACO4 to Inhibit Lateral Root Formation in Sedum alfredii Hance

Lateral root (LR) formation promotes plant resistance, whereas high-level ethylene induced by abiotic stress will inhibit LR emergence. Considering that local auxin accumulation is a precondition for LR generation, auxin-induced genes inhibiting ethylene synthesis may thus be important for LR development. Here, we found that auxin response factor 4 (SaARF4) in Sedum alfredii Hance could be induced by auxin. The overexpression of SaARF4 decreased the LR number and reduced the vessel diameters. Meanwhile, the auxin distribution mode was altered in the root tips and PIN expression was also decreased in the overexpressed lines compared with the wild-type (WT) plants. The overexpression of SaARF4 could reduce ethylene synthesis, and thus, the repression of ethylene production decreased the LR number of WT and reduced PIN expression in the roots. Furthermore, the quantitative real-time PCR, chromatin immunoprecipitation sequencing, yeast one-hybrid, and dual-luciferase assay results showed that SaARF4 could bind the promoter of 1-aminocyclopropane-1-carboxylate oxidase 4 (SaACO4), associated with ethylene biosynthesis, and could downregulate its expression. Therefore, we concluded that SaARF4 induced by auxin can inhibit ethylene biosynthesis by repressing SaACO4 expression, and this process may affect auxin transport to delay LR development.

Integration of miRNAs, Degradome, and Transcriptome Omics Uncovers a Complex Regulatory Network and Provides Insights Into Lipid and Fatty Acid Synthesis During Sesame Seed Development

Sesame (Sesamum indicum L.) has always been known as a health-promoting oilseed crop because of its nutrient-rich oil. In recent years, studies have focused on lipid and fatty acid (FA) biosynthesis in various plants by high-throughput sequencing. Here, we integrated transcriptomics, small RNAs, and the degradome to establish a comprehensive reserve intensive on key regulatory micro RNA (miRNA)-targeting circuits to better understand the transcriptional and translational regulation of the oil biosynthesis mechanism in sesame seed development. Deep sequencing was performed to differentially express 220 miRNAs, including 65 novel miRNAs, in different developmental periods of seeds. GO and integrated KEGG analysis revealed 32 pairs of miRNA targets with negatively correlated expression profiles, of which 12 miRNA-target pairs were further confirmed by RT-PCR. In addition, a regulatory co-expression network was constructed based on the differentially expressed gene (DEG) profiles. The FAD2, LOC10515945, LOC105161564, and LOC105162196 genes were clustered into groups that regulate the accumulation of unsaturated fatty acid (UFA) biosynthesis. The results provide a unique advanced molecular platform for the study of lipid and FA biosynthesis, and this study may serve as a new theoretical reference to obtain increased levels of UFA from higher-quality sesame seed cultivars and other plants.

Identification and functional characterization of ABCC transporters for Cd tolerance and accumulation in Sedum alfredii Hance

Cd is one of the potential toxic elements (PTEs) exerting great threats on the environment and living organisms and arising extensive attentions worldwide. Sedum alfredii Hance, a Cd hyperaccumulator, is of great importance in studying the mechanisms of Cd hyperaccumulation and has potentials for phytoremediation. ATP-binding cassette sub-family C (ABCC) belongs to the ABC transporter family, which is deemed to closely associate with multiple physiological processes including cellular homeostasis, metal detoxification, and transport of metabolites. In the present work, ten ABCC proteins were identified in S. alfredii Hance, exhibiting uniform domain structure and divergently clustering with those from Arabidopsis. Tissue-specific expression analysis indicated that some SaABCC genes had significantly higher expression in roots (Sa23221 and Sa88F144), stems (Sa13F200 and Sa14F98) and leaves (Sa13F200). Co-expression network analysis using these five SaABCC genes as hub genes produced two clades harboring different edge genes. Transcriptional expression profiles responsive to Cd illustrated a dramatic elevation of Sa14F190 and Sa18F186 genes. Heterologous expression in a Cd-sensitive yeast cell line, we confirmed the functions of Sa14F190 gene encoding ABCC in Cd accumulation. Our study performed a comprehensive analysis of ABCCs in S. alfredii Hance, firstly mapped their tissue-specific expression patterns responsive to Cd stress, and characterized the roles of Sa14F190 genes in Cd accumulation.

Pseudomonas fluorescens accelerates a reverse and long-distance transport of cadmium and sucrose in the hyperaccumulator plant Sedum alfredii

Plant growth-promoting bacteria (PGPB) can promote root uptake and shoot accumulation of cadmium (Cd) in hyperaccumulator plants, but the mechanisms by which PGPB accelerate root-to-shoot transport of Cd is still unknown. A better understanding of these mechanisms is necessary to develop the strategies that can promote the practical phytoextraction of Cd-polluted soils. In this study, we found that Pseudomonas fluorescens accelerates a reversed and a long-distance transport of Cd and sucrose in Sedum alfredii, by examining the xylem and phloem sap and by quantifying the concentrations of Cd and sucrose in shoot and root. The transcriptome sequencing has revealed the up-regulated expressions of starch metabolism and sucrose biosynthesis related genes in the shoots of Cd hyperaccumulator plant S. alfredii that was inoculated with PGPB P. fluorescens. In addition, the genes of sugar, cation and anion transporters were also up-regulated by bacterial treatment, showing a complicated co-expression network with sucrose biosynthesis related genes. The expression levels of Cd transporter genes, such as ZIP1, ZIP2, HMA2, HMA3 and CAX2, were elevated after PGPB inoculation. As a result, the PGPB successfully colonized the root, and promoted the sucrose shoot-to-root transport and Cd root-to-shoot transport in S. alfredii. Since non-photosynthetic root-associated bacteria usually obtain sugars from photosynthetic plants, our results highlight the importance of PGPB-induced changes in hyperaccumlator plants for both the host and the PGPB.

Integrated sRNAome and RNA-Seq analysis reveals miRNA effects on betalain biosynthesis in pitaya

BACKGROUND

MicroRNAs (miRNAs) and their regulatory functions in anthocyanin, carotenoid, and chlorophyll accumulation have been extensively characterized in many plant species. However, the miRNA regulatory mechanism in betalain biosynthesis remains mostly unknown.

RESULTS

In this study, 126 conserved miRNAs and 41 novel miRNAs were first isolated from Hylocereus monacanthus, among which 95 conserved miRNAs belonged to 53 miRNA families. Thirty-four candidate miRNAs related to betalain biosynthesis were differentially expressed. The expression patterns of those differential expressed miRNAs were analyzed in various pitaya tissues by RT-qPCR. A significantly negative correlation was detected between the expression levels of half those miRNAs and corresponding target genes. Target genes of miRNAs i.e. Hmo-miR157b-HmSPL6-like, Hmo-miR160a-Hpcyt P450-like3, Hmo-miR6020-HmCYP71A8-like, Hmo-novel-2-HmCYP83B1-like, Hmo-novel-15-HmTPST-like, Hmo-miR828a-HmTT2-like, Hmo-miR858-HmMYB12-like, Hmo-miR858-HmMYBC1-like and Hmo-miR858-HmMYB2-like were verified by 5'RACE and transient expression system in tobacco.

CONCLUSIONS

Hmo-miR157b, Hmo-miR160a, Hmo-miR6020 Hmo-novel-2, Hmo-novel-15, Hmo-miR828a and Hmo-miR858 play important roles in pitaya fruit coloration and betalain accumulation. Our findings provide new insights into the roles of miRNAs and their target genes of regulatory functions involved in betalain biosynthesis of pitaya.

Dissecting MicroRNA-mRNA Regulatory Networks Underlying Sulfur Assimilation and Cadmium Accumulation in Poplar Leaves

The process of cadmium (Cd) accumulation and detoxification under different sulfur levels remains largely unknown in woody plants. To investigate the physiological and transcriptomic regulation mechanisms of poplars in response to different sulfate (S) supply levels and Cd exposure, we exposed Populus deltoides saplings to one of the low, moderate and high S levels together with either 0 or 50 µM Cd. Cd accumulation was decreased in low S-treated poplar leaves, and it tended to be increased in high S-supplied leaves under the Cd exposure condition. Sulfur nutrition was deficient in low S-supplied poplars, and it was improved in high S-treated leaves. Cd exposure resulted in lower sulfur level in the leaves supplied with moderate S, it exacerbated a Cd-induced sulfur decrease in low S-treated leaves and it caused a higher sulfur concentration in high S-supplied leaves. In line with the physiological changes, a number of mRNAs and microRNAs (miRNAs) involved in Cd accumulation and sulfur assimilation were identified and the miRNA-mRNA networks were dissected. In the networks, miR395 and miR399 members were identified as hub miRNAs and their targets were ATP sulfurylase 3 (ATPS3) and phosphate 2 (PHO2), respectively. These results suggest that Cd accumulation and sulfur assimilation are constrained by low and enhanced by high S supply, and Cd toxicity is aggravated by low and relieved by high S in poplar leaves, and that miRNA-mRNA regulatory networks play pivotal roles in sulfur-mediated Cd accumulation and detoxification in Cd-exposed poplars.

Genome-wide sRNA and mRNA transcriptomic profiling insights into dynamic regulation of taproot thickening in radish (Raphanus sativus L.)

BACKGROUND

Taproot is the main edible organ and ultimately determines radish yield and quality. However, the precise molecular mechanism underlying taproot thickening awaits further investigation in radish. Here, RNA-seq was performed to identify critical genes involved in radish taproot thickening from three advanced inbred lines with different root size.

RESULTS

A total of 2606 differentially expressed genes (DEGs) were shared between 'NAU-DY' (large acicular) and 'NAU-YB' (medium obovate), which were significantly enriched in 'phenylpropanoid biosynthesis', 'glucosinolate biosynthesis', and 'starch and sucrose metabolism' pathway. Meanwhile, a total of 16 differentially expressed miRNAs (DEMs) were shared between 'NAU-DY' and 'NAU-YH' (small circular), whereas 12 miRNAs exhibited specific differential expression in 'NAU-DY'. Association analysis indicated that miR393a-bHLH77, miR167c-ARF8, and miR5658-APL might be key factors to biological phenomenon of taproot type variation, and a putative regulatory model of taproot thickening and development was proposed. Furthermore, several critical genes including SUS1, EXPB3, and CDC5 were characterized and profiled by RT-qPCR analysis.

CONCLUSION

This integrated study on the transcriptional and post-transcriptional profiles could provide new insights into comprehensive understanding of the molecular regulatory mechanism underlying taproot thickening in root vegetable crops.

Degradome, small RNAs and transcriptome sequencing of a high-nicotine cultivated tobacco uncovers miRNA's function in nicotine biosynthesis

Tobacco (Nicotiana tabacum) is considered as the model plant for alkaloid research, of which nicotine accounts for 90%. Many nicotine biosynthetic genes have been identified and were known to be regulated by jasmonate-responsive transcription factors. As an important regulator in plant physiological processes, whether small RNAs are involved in nicotine biosynthesis is largely unknown. Here, we combine transcriptome, small RNAs and degradome analysis of two native tobacco germplasms YJ1 and ZY100 to investigate small RNA's function. YJ1 leaves accumulate twofold higher nicotine than ZY100. Transcriptome analysis revealed 3,865 genes which were differently expressed in leaf and root of two germplasms, including some known nicotine and jasmonate pathway genes. By small RNA sequencing, 193 miRNAs were identified to be differentially expressed between YJ1 and ZY100. Using in silico and degradome sequencing approaches, six nicotine biosynthetic genes and seven jasmonate pathway genes were predicted to be targeted by 77 miRNA loci. Three pairs among them were validated by transient expression in vivo. Combined analysis of degradome and transcriptome datasets revealed 51 novel miRNA-mRNA interactions that may regulate nicotine biosynthesis. The comprehensive analysis of our study may provide new insights into the regulatory network of nicotine biosynthesis.

Integrated small RNA and mRNA expression profiles reveal miRNAs and their target genes in response to Aspergillus flavus growth in peanut seeds

BACKGROUND

MicroRNAs are important gene expression regulators in plants immune system. Aspergillus flavus is the most common causal agents of aflatoxin contamination in peanuts, but information on the function of miRNA in peanut-A. flavus interaction is lacking. In this study, the resistant cultivar (GT-C20) and susceptible cultivar (Tifrunner) were used to investigate regulatory roles of miRNAs in response to A. flavus growth.

RESULTS

A total of 30 miRNAs, 447 genes and 21 potential miRNA/mRNA pairs were differentially expressed significantly when treated with A. flavus. A total of 62 miRNAs, 451 genes and 44 potential miRNA/mRNA pairs exhibited differential expression profiles between two peanut varieties. Gene Ontology (GO) analysis showed that metabolic-process related GO terms were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses further supported the GO results, in which many enriched pathways were related with biosynthesis and metabolism, such as biosynthesis of secondary metabolites and metabolic pathways. Correlation analysis of small RNA, transcriptome and degradome indicated that miR156/SPL pairs might regulate the accumulation of flavonoids in resistant and susceptible genotypes. The miR482/2118 family might regulate NBS-LRR gene which had the higher expression level in resistant genotype. These results provided useful information for further understanding the roles of miR156/157/SPL and miR482/2118/NBS-LRR pairs.

CONCLUSIONS

Integration analysis of the transcriptome, miRNAome and degradome of resistant and susceptible peanut varieties were performed in this study. The knowledge gained will help to understand the roles of miRNAs of peanut in response to A. flavus.

Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land

Heavy metal accumulation in soil has been rapidly increased due to various natural processes and anthropogenic (industrial) activities. As heavy metals are non-biodegradable, they persist in the environment, have potential to enter the food chain through crop plants, and eventually may accumulate in the human body through biomagnification. Owing to their toxic nature, heavy metal contamination has posed a serious threat to human health and the ecosystem. Therefore, remediation of land contamination is of paramount importance. Phytoremediation is an eco-friendly approach that could be a successful mitigation measure to revegetate heavy metal-polluted soil in a cost-effective way. To improve the efficiency of phytoremediation, a better understanding of the mechanisms underlying heavy metal accumulation and tolerance in plant is indispensable. In this review, we describe the mechanisms of how heavy metals are taken up, translocated, and detoxified in plants. We focus on the strategies applied to improve the efficiency of phytostabilization and phytoextraction, including the application of genetic engineering, microbe-assisted and chelate-assisted approaches.

SaHsfA4c From Sedum alfredii Hance Enhances Cadmium Tolerance by Regulating ROS-Scavenger Activities and Heat Shock Proteins Expression

The heat shock transcription factor (Hsf) family, an important member in plant stress response, affects cadmium (Cd) tolerance in plants. In this study, we identified and functionally characterized a transcript of the Hsf A4 subgroup from Sedum alfredii. Designated as SaHsfA4c, the open reading frame was 1,302 bp long and encoded a putative protein of 433 amino acids containing a complete DNA-binding domain (DBD). Heterologous expression of SaHsfA4c in yeast enhanced Cd stress tolerance and accumulation, whereas expression of the alternatively spliced transcript InSaHsfA4c which contained an intron and harbored an incomplete DBD, resulted in relatively poor Cd stress tolerance and low Cd accumulation in transgenic yeast. The function of SaHsfA4c under Cd stress was characterized in transgenic Arabidopsis and non-hyperaccumulation ecotype S. alfredii. SaHsfA4c was able to rescue the Cd sensitivity of the Arabidopsis athsfa4c mutant. SaHsfA4c reduced reactive oxygen species (ROS) accumulation and increased the expression of ROS-scavenging enzyme genes and Hsps in transgenic lines. The present results suggest that SaHsfA4c increases plant resistance to stress by up-regulating the activities of ROS-scavenging enzyme and the expression of Hsps.