dsRNA silencing of an R2R3-MYB transcription factor affects flower cell shape in a Dendrobium hybrid

Simultaneous Application of Several Exogenous dsRNAs for the Regulation of Anthocyanin Biosynthesis in Arabidopsis thaliana

Plant surface treatment with double-stranded RNAs (dsRNAs) has gained recognition as a promising method for inducing gene silencing and combating plant pathogens. However, the regulation of endogenous plant genes by external dsRNAs has not been sufficiently investigated. Also, the effect of the simultaneous application of multiple gene-specific dsRNAs has not been analyzed. The aim of this study was to exogenously target five genes in Arabidopsis thaliana, namely, three transcription factor genes (AtCPC, AtMybL2, AtANAC032), a calmodulin-binding protein gene (AtCBP60g), and an anthocyanidin reductase gene (AtBAN), which are known as negative regulators of anthocyanin accumulation. Exogenous dsRNAs encoding these genes were applied to the leaf surface of A. thaliana either individually or in mixtures. The mRNA levels of the five targets were analyzed using qRT-PCR, and anthocyanin content was evaluated through HPLC-MS. The results demonstrated significant downregulation of all five target genes by the exogenous dsRNAs, resulting in enhanced expression of chalcone synthase (AtCHS) gene and increased anthocyanin content. The simultaneous foliar application of the five dsRNAs proved to be more efficient in activating anthocyanin accumulation compared to the application of individual dsRNAs. These findings hold considerable importance in plant biotechnology and gene function studies.

A eudicot MIXTA family ancestor likely functioned in both conical cells and trichomes

The MIXTA family of MYB transcription factors modulate the development of diverse epidermal features in land plants. This study investigates the evolutionary history and function of the MIXTA gene family in the early-diverging eudicot model lineage Thalictrum (Ranunculaceae), with R2R3 SBG9-A MYB transcription factors representative of the pre-core eudicot duplication and thus hereby referred to as "paleoMIXTA" (PMX). Cloning and phylogenetic analysis of Thalictrum paleoMIXTA (ThPMX) orthologs across 23 species reveal a genus-wide duplication coincident with a whole-genome duplication. Expression analysis by qPCR confirmed that the highest expression is found in carpels, while newly revealing high expression in leaves and nuanced differences between paralogs in representative polyploid species. The single-copy ortholog from the diploid species T. thalictroides (TthPMX, previously TtMYBML2), which has petaloid sepals with conical-papillate cells and trichomes on leaves, was functionally characterized by virus-induced gene silencing (VIGS), and its role in leaves was also assessed from heterologous overexpression in tobacco. Another ortholog from a species with conical-papillate cells on stamen filaments, TclPMX, was also targeted for silencing. Overexpression assays in tobacco provide further evidence that the paleoMIXTA lineage has the potential for leaf trichome function in a core eudicot. Transcriptome analysis by RNA-Seq on leaves of VIGS-treated plants suggests that TthPMX modulates leaf trichome development and morphogenesis through microtubule-associated mechanisms and that this may be a conserved pathway for eudicots. These experiments provide evidence for a combined role for paleoMIXTA orthologs in (leaf) trichomes and (floral) conical-papillate cells that, together with data from other systems, makes the functional reconstruction of a eudicot ancestor most likely as also having a combined function.

Transcriptomic and Metabolomic Analyses Reveal Differences in Flavonoid Pathway Gene Expression Profiles between Two Dendrobium Varieties during Vernalization

Dendrobium (Orchidaceae, Epidendoideae) plants have flowers with a wide variety of colors that persist for a long period throughout the year. The yellow coloration of Dendrobium flowers is mainly determined by the flavonol pathway and the flavone pathway, but the relevant biosynthesis mechanisms during vernalization remain unclear. To explore the similarities and differences in flavonoid biosynthesis in different tissues during vernalization, we selected two species of Dendrobium for a flower color study: Dendrobium capillipes Rchb (which has yellow flowers) and Dendrobium nobile Lindl (which has white flowers). We collected a total of 36 samples from six tissue types and both Dendrobium species during vernalization and subjected the samples to metabolic profiling and transcriptome sequencing. A total of 31,504 differentially expressed genes (DEGs) were identified between different tissues of the two Dendrobium species by transcriptomic analysis. However, many differentially accumulated metabolites (DAMs) and DEGs were enriched not only in the general pathway of "flavonoid biosynthesis" but also in multiple subpathways of "flavone and flavonol biosynthesis". According to a combined transcriptome and metabolome analysis, Putrescine hydroxycinnamoyl transferase 1 (LOC110093422) may be the main gene responsible for the differences in flavonoid accumulation during vernalization, which is closely associated with yellow flowers. Taken together, the results of our study preliminarily revealed the metabolites responsible for and the key genes regulating flavonoid biosynthesis during vernalization. These results provide a basis for the further study of the molecular mechanism of flavonoid synthesis during vernalization.

Function and molecular mechanism of a poplar placenta limited MIXTA gene in regulating differentiation of plant epidermal cells

The placenta in fruits of most plants either desiccate and shrink as the fruits mature or develop further to form the fleshy tissues. In poplars, placental epidermal cells protrude collectively to produce catkin fibers. In this study, three carpel limited MIXTA genes, PdeMIXTA02, PdeMIXTA03, PdeMIXTA04, were find to specifically expressed in carpel immediately after pollination. Heterologous expression of the three genes in Arabidopsis demonstrated that PdeMIXTA04 significantly promoted trichomes density and could restore trichomes in the trichomeless mutant. By contrast, such functions were not observed with PdeMIXTA02, PdeMIXTA03. In situ hybridization revealed that PdeMIXTA04 was explicitly expressed in poplar placental epidermal cells. We also confirmed trichome-specific expression of the PdeMIXTA04 promoter. Multiple experimental proofs have confirmed the interaction between PdeMIXTA04, PdeMYC and PdeWD40, indicating PdeMIXTA04 functioned through the MYB-bHLH-WD40 ternary complex. Our work provided distinctive understanding of the molecular mechanism triggering differentiation of poplar catkins.

RNA Interference Past and Future Applications in Plants

Antisense RNA was observed to elicit plant disease resistance and post-translational gene silencing (PTGS). The universal mechanism of RNA interference (RNAi) was shown to be induced by double-stranded RNA (dsRNA), an intermediate produced during virus replication. Plant viruses with a single-stranded positive-sense RNA genome have been instrumental in the discovery and characterization of systemic RNA silencing and suppression. An increasing number of applications for RNA silencing have emerged involving the exogenous application of dsRNA through spray-induced gene silencing (SIGS) that provides specificity and environmentally friendly options for crop protection and improvement.

Exogenously Induced Silencing of Four MYB Transcription Repressor Genes and Activation of Anthocyanin Accumulation in Solanum lycopersicum

RNA interference (RNAi) is a natural post-transcriptional regulatory mechanism that can be artificially induced by exogenous application of double-stranded RNAs (dsRNAs) to the plant surfaces. Recent studies show that it is possible to silence plant genes and change plant properties using plant RNA spraying and other approaches for dsRNA delivery. In this study, we investigated the effect of exogenous gene-specific dsRNAs on the silencing of four tomato genes encoding MYB-family transcription repressors of anthocyanin biosynthesis in the leaves of tomato Solanum lycopersicum L. We found that the exogenous application of dsRNAs encoding for the SlMYBATV1, SlMYB32, SlMYB76, and SlTRY genes downregulated mRNA levels of these endogenous repressors of anthocyanin production, upregulated the expression of anthocyanin biosynthesis-related genes, and enhanced anthocyanin content in the leaves of S. lycopersicum. The data demonstrated that exogenous gene-specific dsRNAs can induce post-transcriptional gene silencing in tomato leaves by direct foliar application of dsRNAs. This approach may be used for plant secondary metabolism induction and as a silencing tool for gene function studies without the need to produce genetically modified plants.

An Optimized/Scale Up-Ready Protocol for Extraction of Bacterially Produced dsRNA at Good Yield and Low Costs

Double-stranded RNA (dsRNA) can trigger RNA interference (RNAi) and lead to directed silencing of specific genes. This natural defense mechanism and RNA-based products have been explored for their potential as a sustainable and ecofriendly alternative for pest control of species of agricultural importance and disease vectors. Yet, further research, development of new products and possible applications require a cost-efficient production of dsRNA. In vivo transcription of dsRNA in bacterial cells has been widely used as a versatile and inducible system for production of dsRNA combined with a purification step required to extract the dsRNA. Here, we optimized an acidic phenol-based protocol for extraction of bacterially produced dsRNA at low cost and good yield. In this protocol, bacterial cells are efficiently lysed, with no viable bacterial cells present in the downstream steps of the purification. Furthermore, we performed a comparative dsRNA quality and yield assessment of our optimized protocol and other protocols available in the literature and confirmed the cost-efficiency of our optimized protocol by comparing the cost of extraction and yields of each extraction method.

Nanovector-mediated exogenous delivery of dsRNA induces silencing of target genes in very young tomato flower buds

RNA interference (RNAi) is a post-translational regulatory mechanism that controls gene expression in plants. This process can be artificially induced by double-stranded RNA (dsRNA) molecules with sequence homology to target mRNAs. Exogenously applied dsRNA on leaves has been shown to silence virulence genes of fungi and viruses, conferring protection to plants. Coupling dsRNA to nanoparticles has been demonstrated to prolong the silencing effect. The ability of exogenous dsRNA to silence endogenous genes in plants is currently under debate, mainly due to the difficulty in delivering dsRNA into plant tissues and organs. Our study aims to develop a method based on the exogenous application of dsRNA on tomato flowers for silencing endogenous genes controlling ovary growth. Two methods of dsRNA delivery into tomato flower buds (i.e., pedicel soaking and injection) were compared to test their efficacy in silencing the tomato Aux/IAA9 (SlIAA9) gene, which encodes for a known repressor of ovary growth. We examined the silencing effect of dsRNA alone and coupled to layered double hydroxide (LDHs) nanoparticles. We found that injection into the pedicel led to the silencing of SlIAA9 and the efficacy of the method was confirmed by choosing a different ovary growth repressor gene (SlAGAMOUS-like 6; SlAGL6). The coupling of dsRNA to LDHs increased the silencing effect in the case of SlIAA9. Silencing of the two repressors caused an increase in ovary size only when flower buds were treated with dsRNA coupled to LDHs. RNA-Seq of small RNAs showed that induction of RNAi was caused by the processing of injected dsRNA. In this work, we demonstrate for the first time that exogenous dsRNA coupled to LDHs can induce post-transcriptional gene silencing in the young tomato ovary by injection into the flower pedicel. This method represents a silencing tool for the study of the molecular changes occurring during the early stages of ovary/fruit growth as a consequence of downregulation of target genes, without the need to produce transgenic plants stably expressing RNAi constructs.

DhMYB22 and DhMYB60 regulate pigment intensity and floral organ shape in Dendrobium hybrid

BACKGROUND

Flower pigment and shape are determined by the coordinated expression of a set of structural genes during flower development. R2R3-MYB transcription factors are known regulators of structural gene expression. The current study focused on two members of this large family of transcription factors that were predicted to have roles in pigment biosynthesis and organ shape development in orchids.

METHODS

Phylogenetic analysis was used to identify candidate Dendrobium catenatum R2R3-MYB (DcaMYB) sequences associated with pigment and cell shape development. Gene silencing of candidate DhMYBs in Dendrobium hybrid by direct application of dsRNA to developing flowers was followed by observation of gene expression level and flower phenotypes. Silencing of the structural gene chalcone synthase was used as a comparative control.

KEY RESULTS

Ten candidate flower-associated DcaMYBs were identified. Flowers treated with dsRNA of DhMYB22 and DhMYB60 sequences were less pigmented and had relatively low expression of anthocyanin biosynthetic genes (F3'H and DFR), lower total anthocyanin concentration and markedly lower levels of cyanidin-3-glucoside and cyanidin-3-rutinoside. Petals of DhMYB22-treated flowers and sepals of DhMYB60-treated flowers showed the greatest colour difference relative to the same organs in untreated flowers. DhMYB22-treated flowers had relatively narrow and constricted lips, while DhMYB60-treated flowers had narrow and constricted sepals. No significant difference in shape was observed for DhCHS-treated or untreated flowers.

CONCLUSIONS

Our results demonstrate that DhMYB22 and DhMYB60 regulate pigment intensity and floral organ shape in Dendrobium. This is a first report of MYB regulation of floral organ shape in orchids.

An R2R3-MYB transcription factor VyMYB24, isolated from wild grape Vitis yanshanesis J. X. Chen., regulates the plant development and confers the tolerance to drought

In grapevines, the MYB transcription factors play an important regulatory role in the phenylpropanoid pathway including proanthocyanidin, anthocyanin, and flavonoid biosynthesis. However, the role of MYB in abiotic stresses is not clear. In this study, an R2R3-MYB transcription factor, VyMYB24, was isolated from a high drought-tolerant Chinese wild Vitis species V. yanshanesis. Our findings demonstrated that it was involved in plant development and drought tolerance. VyMYB24 is a nuclear protein and is significantly induced by drought stress. When over-expressed in tobacco, VyMYB24 caused plant dwarfing including plant height, leaf area, flower size, and seed weight. The GA1+3 content in transgenic plants was reduced significantly, and spraying exogenous gibberellin could recover the dwarf phenotype of VyMYB24 transgenic plants, suggesting that VyMYB24 might inhibit plant development by the regulation of gibberellin (GA) metabolism. Under drought stress, the VyMYB24 transgenic plants improved their tolerance to drought with a lower wilting rate, lower relative electrical conductivity, and stronger roots. Compared to wild-type tobacco plants, VyMYB24 transgenic plants accumulated less reactive oxygen, accompanied by increased antioxidant enzyme activity and upregulated gene expression levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) genes. In addition, transgenic plants accumulated more proline, and their related synthetic genes NtP5CR and NtP5CS genes were significantly upregulated when exposed to drought. Besides, abiotic stress-responsive genes, NtDREB, NtERD10C, NtERD10D, and NtLEA5, were upregulated significantly in VyMYB24 transgenic plants. These results indicate that VyMYB24 plays a positive regulatory role in response to drought stress and also regulates plant development, which provides new evidence to further explore the molecular mechanism of drought stress of the MYB gene family.

RNA Interference for Improving Disease Resistance in Plants and Its Relevance in This Clustered Regularly Interspaced Short Palindromic Repeats-Dominated Era in Terms of dsRNA-Based Biopesticides

RNA interference (RNAi) has been exploited by scientists worldwide to make a significant contribution in the arena of sustainable agriculture and integrated pest management. These strategies are of an imperative need to guarantee food security for the teeming millions globally. The already established deleterious effects of chemical pesticides on human and livestock health have led researchers to exploit RNAi as a potential agri-biotechnology tool to solve the burning issue of agricultural wastage caused by pests and pathogens. On the other hand, CRISPR/Cas9, the latest genome-editing tool, also has a notable potential in this domain of biotic stress resistance, and a constant endeavor by various laboratories is in progress for making pathogen-resistant plants using this technique. Considerable outcry regarding the ill effects of genetically modified (GM) crops on the environment paved the way for the research of RNAi-induced double-stranded RNAs (dsRNA) and their application to biotic stresses. Here, we mainly focus on the application of RNAi technology to improve disease resistance in plants and its relevance in today's CRISPR-dominated world in terms of exogenous application of dsRNAs. We also focused on the ongoing research, public awareness, and subsequent commercialization of dsRNA-based biocontrol products.

Exogenous dsRNA Induces RNA Interference of a Chalcone Synthase Gene in Arabidopsis thaliana

Recent investigations have shown the possibility of artificial induction of RNA interference (RNAi) via plant foliar treatments with naked double-stranded RNA (dsRNA) to silence essential genes in plant fungal pathogens or to target viral RNAs. Furthermore, several studies have documented the downregulation of plant endogenous genes via external application of naked gene-specific dsRNAs and siRNAs to the plant surfaces. However, there are limited studies on the dsRNA processing and gene silencing mechanisms after external dsRNA application. Such studies would assist in the development of innovative tools for crop improvement and plant functional studies. In this study, we used exogenous gene-specific dsRNA to downregulate the gene of chalcone synthase (CHS), the key enzyme in the flavonoid/anthocyanin biosynthesis pathway, in Arabidopsis. The nonspecific NPTII-dsRNA encoding the nonrelated neomycin phosphotransferase II bacterial gene was used to treat plants in order to verify that any observed effects and processing of AtCHS mRNA were sequence specific. Using high-throughput small RNA (sRNA) sequencing, we obtained six sRNA-seq libraries for plants treated with water, AtCHS-dsRNA, or NPTII-dsRNA. After plant foliar treatments, we detected the emergence of a large number of AtCHS- and NPTII-encoding sRNAs, while there were no such sRNAs after control water treatment. Thus, the exogenous AtCHS-dsRNAs were processed into siRNAs and induced RNAi-mediated AtCHS gene silencing. The analysis showed that gene-specific sRNAs mapped to the AtCHS and NPTII genes unevenly with peak read counts at particular positions, involving primarily the sense strand, and documented a gradual decrease in read counts from 17-nt to 30-nt sRNAs. Results of the present study highlight a significant potential of exogenous dsRNAs as a promising strategy to induce RNAi-based downregulation of plant gene targets for plant management and gene functional studies.

RNA Interference: Promising Approach to Combat Plant Viruses

Plant viruses are devastating plant pathogens that severely affect crop yield and quality. Plants have developed multiple lines of defense systems to combat viral infection. Gene silencing/RNA interference is the key defense system in plants that inhibits the virulence and multiplication of pathogens. The general mechanism of RNAi involves (i) the transcription and cleavage of dsRNA into small RNA molecules, such as microRNA (miRNA), or small interfering RNA (siRNA), (ii) the loading of siRNA/miRNA into an RNA Induced Silencing Complex (RISC), (iii) complementary base pairing between siRNA/miRNA with a targeted gene, and (iv) the cleavage or repression of a target gene with an Argonaute (AGO) protein. This natural RNAi pathway could introduce transgenes targeting various viral genes to induce gene silencing. Different RNAi pathways are reported for the artificial silencing of viral genes. These include Host-Induced Gene Silencing (HIGS), Virus-Induced Gene Silencing (VIGS), and Spray-Induced Gene Silencing (SIGS). There are significant limitations in HIGS and VIGS technology, such as lengthy and time-consuming processes, off-target effects, and public concerns regarding genetically modified (GM) transgenic plants. Here, we provide in-depth knowledge regarding SIGS, which efficiently provides RNAi resistance development against targeted genes without the need for GM transgenic plants. We give an overview of the defense system of plants against viral infection, including a detailed mechanism of RNAi, small RNA molecules and their types, and various kinds of RNAi pathways. This review will describe how RNA interference provides the antiviral defense, recent improvements, and their limitations.

The Specificity of Transgene Suppression in Plants by Exogenous dsRNA

The phenomenon of RNA interference (RNAi) is widely used to develop new approaches for crop improvement and plant protection. Recent investigations show that it is possible to downregulate plant transgenes, as more prone sequences to silencing than endogenous genes, by exogenous application of double-stranded RNAs (dsRNAs) and small interfering RNAs (siRNAs). However, there are scarce data on the specificity of exogenous RNAs. In this study, we explored whether plant transgene suppression is sequence-specific to exogenous dsRNAs and whether similar effects can be caused by exogenous DNAs that are known to be perceived by plants and induce certain epigenetic and biochemical changes. We treated transgenic plants of Arabidopsis thaliana bearing the neomycin phosphotransferase II (NPTII) transgene with specific synthetic NPTII-dsRNAs and non-specific dsRNAs, encoding enhanced green fluorescent protein (EGFP), as well as with DNA molecules mimicking the applied RNAs. None of the EGFP-dsRNA doses resulted in a significant decrease in NPTII transgene expression in the NPTII-transgenic plants, while the specific NPTII-dsRNA significantly reduced NPTII expression in a dose-dependent manner. Long DNAs mimicking dsRNAs and short DNA oligonucleotides mimicking siRNAs did not exhibit a significant effect on NPTII transgene expression. Thus, exogenous NPTII-dsRNAs induced a sequence-specific and RNA-specific transgene-suppressing effect, supporting external application of dsRNAs as a promising strategy for plant gene regulation.

Spray-induced gene silencing targeting a glutathione S-transferase gene improves resilience to drought in grapevine

Along with the ongoing climate change, drought events are predicted to become more severe. In this context, the spray-induced gene silencing (SIGS) technique could represent a useful strategy to improve crop stress resilience. A previous study demonstrated that the Arabidopsis mutants for a glutathione S-transferase (GST) gene had increased abscisic acid (ABA) levels and a more activated antioxidant system, both features that improved drought resilience. Here, we used SIGS to target a putative grape GST gene (VvGST40). Then, ecophysiological, biochemical and molecular responses of 'Chardonnay' cuttings were analysed during a drought and recovery time-course. Gas exchange, ABA and t-resveratrol concentration as well as expression of stress-related genes were monitored in not treated controls, dsRNA-VvGST40- and dsRNA-GFP- (negative control of the technique) treated plants, either submitted or not to drought. VvGST40-treated plants revealed increased resilience to severe drought as attested by the ecophysiological data. Analysis of target metabolites and antioxidant- and ABA-related transcripts confirmed that VvGST40-treated plants were in a priming status compared with controls. SIGS targeting an endogenous gene was successfully applied in grapevine, confirming the ability of this technique to be exploited not only for plant protection issues but also for functional genomic studies.

MYB transcription factor family in sweet cherry (Prunus avium L.): genome-wide investigation, evolution, structure, characterization and expression patterns

BACK GROUND

MYB Transcription factors (TFs) are most imperative and largest gene family in plants, which participate in development, metabolism, defense, differentiation and stress response. The MYB TFs has been studied in various plant species. However, comprehensive studies of MYB gene family in the sweet cherry (Prunus avium L.) are still unknown.

RESULTS

In the current study, a total of 69 MYB genes were investigated from sweet cherry genome and classified into 28 subfamilies (C1-C28 based on phylogenetic and structural analysis). Microcollinearity analysis revealed that dispersed duplication (DSD) events might play an important role in the MYB genes family expansion. Chromosomal localization, the synonymous (Ks) and nonsynonymous (Ka) analysis, molecular characteristics (pI, weight and length of amino acids) and subcellular localization were accomplished using several bioinformatics tools. Furthermore, the members of distinct subfamilies have diverse cis-acting regions, conserved motifs, and intron-exon architectures, indicating functional heterogeneity in the MYB family. Moreover, the transcriptomic data exposed that MYB genes might play vital role in bud dormancy. The quantitative real-time qRT-PCR was carried out and the expression pattern indicated that MYB genes significantly expressed in floral bud as compared to flower and fruit.

CONCLUSION

Our comprehensive findings provide supportive insights into the evolutions, expansion complexity and functionality of PavMYB genes. These PavMYB genes should be further investigated as they seem to be brilliant candidates for dormancy manipulation in sweet cherry.

Recent Advanced Metabolic and Genetic Engineering of Phenylpropanoid Biosynthetic Pathways

The MYB transcription factors (TFs) are evolving as critical role in the regulation of the phenylpropanoid and tanshinones biosynthetic pathway. MYB TFs relate to a very important gene family, which are involved in the regulation of primary and secondary metabolisms, terpenoids, bioactive compounds, plant defense against various stresses and cell morphology. R2R3 MYB TFs contained a conserved N-terminal domain, but the domain at C-terminal sorts them different regarding their structures and functions. MYB TFs suppressors generally possess particular repressive motifs, such as pdLNLD/ELxiG/S and TLLLFR, which contribute to their suppression role through a diversity of complex regulatory mechanisms. A novel flower specific "NF/YWSV/MEDF/LW" conserved motif has a great potential to understand the mechanisms of flower development. In the current review, we summarize recent advanced progress of MYB TFs on transcription regulation, posttranscriptional, microRNA, conserved motif and propose directions to future prospective research. We further suggest there should be more focus on the investigation for the role of MYB TFs in microalgae, which has great potential for heterologous protein expression system for future perspectives.

Novel and emerging biotechnological crop protection approaches

Traditional breeding or genetically modified organisms (GMOs) have for a long time been the sole approaches to effectively cope with biotic and abiotic stresses and implement the quality traits of crops. However, emerging diseases as well as unpredictable climate changes affecting agriculture over the entire globe force scientists to find alternative solutions required to quickly overcome seasonal crises. In this review, we first focus on cisgenesis and genome editing as challenging biotechnological approaches for breeding crops more tolerant to biotic and abiotic stresses. In addition, we take into consideration a toolbox of new techniques based on applications of RNA interference and epigenome modifications, which can be adopted for improving plant resilience. Recent advances in these biotechnological applications are mainly reported for non-model plants and woody crops in particular. Indeed, the characterization of RNAi machinery in plants is fundamental to transform available information into biologically or biotechnologically applicable knowledge. Finally, here we discuss how these innovative and environmentally friendly techniques combined with traditional breeding can sustain a modern agriculture and be of potential contribution to climate change mitigation.

Recent Progress in Enhancing Fungal Disease Resistance in Ornamental Plants

Fungal diseases pose a major threat to ornamental plants, with an increasing percentage of pathogen-driven host losses. In ornamental plants, management of the majority of fungal diseases primarily depends upon chemical control methods that are often non-specific. Host basal resistance, which is deficient in many ornamental plants, plays a key role in combating diseases. Despite their economic importance, conventional and molecular breeding approaches in ornamental plants to facilitate disease resistance are lagging, and this is predominantly due to their complex genomes, limited availability of gene pools, and degree of heterozygosity. Although genetic engineering in ornamental plants offers feasible methods to overcome the intrinsic barriers of classical breeding, achievements have mainly been reported only in regard to the modification of floral attributes in ornamentals. The unavailability of transformation protocols and candidate gene resources for several ornamental crops presents an obstacle for tackling the functional studies on disease resistance. Recently, multiomics technologies, in combination with genome editing tools, have provided shortcuts to examine the molecular and genetic regulatory mechanisms underlying fungal disease resistance, ultimately leading to the subsequent advances in the development of novel cultivars with desired fungal disease-resistant traits, in ornamental crops. Although fungal diseases constitute the majority of ornamental plant diseases, a comprehensive overview of this highly important fungal disease resistance seems to be insufficient in the field of ornamental horticulture. Hence, in this review, we highlight the representative mechanisms of the fungal infection-related resistance to pathogens in plants, with a focus on ornamental crops. Recent progress in molecular breeding, genetic engineering strategies, and RNAi technologies, such as HIGS and SIGS for the enhancement of fungal disease resistance in various important ornamental crops, is also described.

External dsRNA Downregulates Anthocyanin Biosynthesis-Related Genes and Affects Anthocyanin Accumulation in Arabidopsis thaliana

Exogenous application of double-stranded RNAs (dsRNAs) and small-interfering RNAs (siRNAs) to plant surfaces has emerged as a promising method for regulation of essential genes in plant pathogens and for plant disease protection. Yet, regulation of plant endogenous genes via external RNA treatments has not been sufficiently investigated. In this study, we targeted the genes of chalcone synthase (CHS), the key enzyme in the flavonoid/anthocyanin biosynthesis pathway, and two transcriptional factors, MYBL2 and ANAC032, negatively regulating anthocyanin biosynthesis in Arabidopsis. Direct foliar application of AtCHS-specific dsRNAs and siRNAs resulted in an efficient downregulation of the AtCHS gene and suppressed anthocyanin accumulation in A. thaliana under anthocyanin biosynthesis-modulating conditions. Targeting the AtMYBL2 and AtANAC032 genes by foliar dsRNA treatments markedly reduced their mRNA levels and led to a pronounced upregulation of the AtCHS gene. The content of anthocyanins was increased after treatment with AtMYBL2-dsRNA. Laser scanning microscopy showed a passage of Cy3-labeled AtCHS-dsRNA into the A. thaliana leaf vessels, leaf parenchyma cells, and stomata, indicating the dsRNA uptake and spreading into leaf tissues and plant individual cells. Together, these data show that exogenous dsRNAs were capable of downregulating Arabidopsis genes and induced relevant biochemical changes, which may have applications in plant biotechnology and gene functional studies.

Physiological Conditions and dsRNA Application Approaches for Exogenously induced RNA Interference in Arabidopsis thaliana

Recent studies have revealed that foliar application of double-stranded RNAs (dsRNAs) or small-interfering RNAs (siRNAs) encoding specific genes of plant pathogens triggered RNA interference (RNAi)-mediated silencing of the gene targets. However, a limited number of reports documented silencing of plant endogenes or transgenes after direct foliar RNA application. This study analyzed the importance of physiological conditions (plant age, time of day, soil moisture, high salinity, heat, and cold stresses) and different dsRNA application means (brush spreading, spraying, infiltration, inoculation, needle injection, and pipetting) for suppression of neomycin phosphotransferase II (NPTII) transgene in Arabidopsis thaliana, as transgenes are more prone to silencing. We observed a higher NPTII suppression when dsRNA was applied at late day period, being most efficient at night, which revealed a diurnal variation in dsRNA treatment efficacy. Exogenous NPTII-dsRNA considerably reduced NPTII expression in 4-week-old plants and only limited it in 2- and 6-week-old plants. In addition, a more discernible NPTII downregulation was detected under low soil moisture conditions. Treatment of adaxial and abaxial leaf surfaces by brushes, spraying, and pipetting showed a higher NPTII suppression, while infiltration and inoculation were less efficient. Thus, appropriate plant age, late time of day, low soil moisture, and optimal dsRNA application modes are important for exogenously induced gene silencing.

Clay nanosheet-mediated delivery of recombinant plasmids expressing artificial miRNAs via leaf spray to prevent infection by plant DNA viruses

Whitefly-transmitted begomoviruses are economically important plant pathogens that cause severe problems in many crop plants, such as tomato, papaya, cotton, and tobacco. Tomato yellow leaf curl virus (TYLCV) is a typical monopartite begomovirus that has been extensively studied, but methods that can efficiently control begomoviruses are still scarce. In this study, we combined artificial microRNA (amiRNA)-mediated silencing technology and clay nanosheet-mediated delivery by spraying and developed a method for efficiently preventing TYLCV infection in tomato plants. We designed three amiRNAs that target different regions of TYLCV to silence virus-produced transcripts. Three plant expression vectors expressing pre-amiRNAs were constructed, and recombinant plasmid DNAs (pDNAs) were loaded onto nontoxic and degradable layered double hydroxide (LDH) clay nanosheets. LDH nanosheets containing multiple pDNAs were sprayed onto plant leaves. We found that the designed amiRNAs were significantly accumulated in leaves 7 days after spraying, while the pDNAs were sustainably detected for 35 days after the spray, suggesting that the LDH nanosheets released pDNAs in a sustained manner, protected pDNAs from degradation and efficiently delivered pDNAs into plant cells. Importantly, when the LDH nanosheets coated with pDNAs were sprayed onto plants infected by TYLCV, both the disease severity and TYLCV viral concentration in sprayed plants were significantly decreased during the 35 days, while the levels of H₂O₂ were significantly increased in those plants. Taken together, these results indicate that LDH nanosheets loaded with pDNAs expressing amiRNAs can be a sustainable and promising tool for begomovirus control.

Characterization of floral morphoanatomy and identification of marker genes preferentially expressed during specific stages of cotton flower development

Characterization of anther and ovule developmental programs and expression analyses of stage-specific floral marker genes in Gossypium hirsutum allowed to build a comprehensive portrait of cotton flower development before fiber initiation. Gossypium hirsutum is the most important cotton species that is cultivated worldwide. Although cotton reproductive development is important for fiber production, since fiber is formed on the epidermis of mature ovules, cotton floral development remains poorly understood. Therefore, this work aims to characterize the cotton floral morphoanatomy by performing a detailed description of anther and ovule developmental programs and identifying stage-specific floral marker genes in G. hirsutum. Using light microscopy and scanning electron microscopy, we analyzed anther and ovule development during 11 stages of flower development. To better characterize the ovule development in cotton, we performed histochemical analyses to evaluate the accumulation of phenolic compounds, pectin, and sugar in ovule tissues. After identification of major hallmarks of floral development, three key stages were established in G. hirsutum floral development: in stage 1 (early-EF), sepal, petal, and stamen primordia were observed; in stage 2 (intermediate-IF), primordial ovules and anthers are present, and the differentiating archesporial cells were observed, marking the beginning of microsporogenesis; and in stage 6 (late-LF), flower buds presented initial anther tapetum degeneration and microspore were released from the tetrad, and nucellus and both inner and outer integuments are developing. We used transcriptome data of cotton EF, IF and LF stages to identify floral marker genes and evaluated their expression by real-time quantitative PCR (qPCR). Twelve marker genes were preferentially expressed in a stage-specific manner, including the putative homologs for AtLEAFY, AtAPETALA 3, AtAGAMOUS-LIKE 19 and AtMALE STERILITY 1, which are crucial for several aspects of reproductive development, such as flower organogenesis and anther and petal development. We also evaluated the expression profile of B-class MADS-box genes in G. hirsutum floral transcriptome (EF, IF, and LF). In addition, we performed a comparative analysis of developmental programs between Arabidopsis thaliana and G. hirsutum that considered major morphoanatomical and molecular processes of flower, anther, and ovule development. Our findings provide the first detailed analysis of cotton flower development.

Genome-wide identification and expression analyses of R2R3-MYB transcription factor genes from two Orchid species

MYB transcription factors play important roles in different plant biological processes during plant growth, development and stress response. In this study, 101 (DoMYB1-101) and 99 (PaMYB1-99) R2R3-MYB genes were identified in the genomes of Dendrobium officinale and Phalaenopsis aphrodite, respectively. To classify the isolated candidate genes, the R2R3-MYB genes from A. thaliana were selected as references. As a result, all identified DoMYB and PaMYB genes were classified into 22 subfamilies. Phylogenetic analysis revealed that S21 had the largest number of members of all the subfamilies. The numbers of introns, exons and conserved sequences in all of the identified genes are different. In addition, 20 DoMYB genes from six subfamilies were selected for further analysis of tissue-specific expression and responses to various abiotic stresses treatments. The results showed that all of the DoMYB genes in S4 and S19 subfamilies exhibited the highest relative expression levels in flowers. And five DoMYB genes including DoMYB31, DoMYB40, DoMYB49, DoMYB52 and DoMYB54, responded to the stress response. These results may provide useful information for further studies of the R2R3-MYB gene family.

Genome-wide identification and expression analysis of the MYB transcription factor in Japanese plum (Prunus salicina)

MYB proteins constitute one of the largest transcription factor families in plants, members of which are involved in various plant physiological and biochemical processes. Japanese plum (Prunus salicina) is one of the important stone fruit crops worldwide. To date, no comprehensive study of the MYB family in Japanese plum has been reported. In this study, we performed genome-wide analysis of MYB genes in Japanese plum including the phylogeny, gene structures, protein motifs, chromosomal locations, collinearity and expression patterns analysis. A total of 96 Japanese plum R2R3-MYB (PsMYB) genes were characterized and distributed on 8 chromosomes at various densities. Collinearity analysis indicated that the segmental duplication events played a crucial role in the expansion of PsMYB genes, and the interspecies synteny analysis revealed the orthologous gene pairs between Japanese plum and other four selected Rosaceae species. The 96 PsMYB genes could be classified into 27 subgroups based on phylogenetic topology, as supported by the conserved gene structures and motif compositions. Further comparative phylogenetic analysis revealed the functional divergence of MYB gene family during evolution, and three subgroups which included only Rasaceae MYB genes were identified. Expression analysis revealed the distinct expression profiles of the PsMYB genes, and further functional predictions found some of them might be associated with the plum fruit quality traits. Our researches provide a global insight into the organization, phylogeny, evolution and expression patterns of the PsMYB genes, and contribute to the greater understanding of their functional roles in Japanese plum.

Application of Exogenous dsRNAs-induced RNAi in Agriculture: Challenges and Triumphs

In recent years, RNA interference (RNAi) machinery has widely been explored by plant biologists for its potential applications in disease management, plant development, and germplasm improvement. RNAi-based technologies have mainly been applied in the form of transgenic plant generation and host-induced-gene-silencing (HIGS). However, the approval of RNAi-based transgenic plants has always been challenging due to the proclaimed concerns surrounding their impacts on human health and the environment. Lately, exogenous applications of double-stranded RNAs (dsRNAs), short interfering RNAs (siRNAs), and hairpin RNAs (hpRNAs) has emerged as another technology that could be regarded as more eco-friendly, sustainable, and publicly acceptable than genetic transformation. Inside the plant cell, dsRNAs can undergo several steps of processing, which not only triggers RNAi machinery but may also involve transitive and systemic silencing, as well as epigenetic modifications. Therefore, along with the considerations of proper exogenous applications of dsRNAs, defining their final destination into plant cells is highly relevant. In this review, we highlighted the significance of several factors that affect dsRNA-induced gene silencing, the fate of exogenous dsRNAs in the plant cell, and the challenges surrounding production technologies, cost-effectiveness, and dsRNAs stability under open-field conditions. This review also provided insights into the potential applications of exogenous dsRNAs in plant protection and crop improvement.

Epigenetic Modifications: An Unexplored Facet of Exogenous RNA Application in Plants

Exogenous RNA interference (exo-RNAi) is a powerful transgene-free tool in modern crop improvement and protection platforms. In exo-RNAi approaches, double-stranded RNAs (dsRNAs) or short-interfering RNAs (siRNAs) are externally applied in plants in order to selectively trigger degradation of target mRNAs. Yet, the applied dsRNAs may also trigger unintended epigenetic alterations and result in epigenetically modified plants, an issue that has not been sufficiently addressed and which merits more careful consideration.

Gene technologies in weed management: a technical feasibility analysis

With the advent of new genetic technologies such as gene silencing and gene drive, efforts to develop additional management tools for weed management is gaining significant momentum. These technologies promise novel ways to develop sustainable weed control options because gene silencing can switch-off genes mediating adaptation (e.g. growth, herbicide resistance), and gene drive can be used to spread modified traits and to engineer wild populations with reduced fitness. However, applying gene silencing and/or gene drive is expected to be inherently complex as their application is constrained by several methodological and technological difficulties. In this review we explore the challenges of these technologies, and discuss strategies and resources accessible to accelerate the development of gene-tech based tools for weed management. We also highlight how gene technologies can be integrated into existing management tactics such as classical biological control, and their possible interactions.

Genome-Wide Identification and Comparative Analysis of MYB Transcription Factor Family in Musa acuminata and Musa balbisiana

MYB transcription factors (TFs) make up one of the most important TF families in plants. These proteins play crucial roles in processes related to development, metabolism, and stimulus-response; however, very few studies have been reported for the characterization of MYB TFs from banana. The current study identified 305 and 251 MYB genes from Musa acuminata and Musa balbisiana, respectively. Comprehensive details of MYBs are reported in terms of gene structure, protein domain, chromosomal localization, phylogeny, and expression patterns. Based on the exon-intron arrangement, these genes were classified into 12 gene models. Phylogenetic analysis of MYBs involving both species of banana, Oryza sativa, and Arabidopsis thaliana distributed these genes into 27 subfamilies. This highlighted not only the conservation, but also the gain/loss of MYBs in banana. Such genes are important candidates for future functional investigations. The MYB genes in both species exhibited a random distribution on chromosomes with variable densities. Estimation of gene duplication events revealed that segmental duplications represented the major factor behind MYB gene family expansion in banana. Expression profiles of MYB genes were also explored for their potential involvement in acetylene response or development. Collectively, the current comprehensive analysis of MYB genes in both species of banana will facilitate future functional studies.

RNA-based biocontrol compounds: current status and perspectives to reach the market

Facing current climate challenges and drastically reduced chemical options for plant protection, the exploitation of RNA interference (RNAi) as an agricultural biotechnology tool has unveiled possible new solutions to the global problems of agricultural losses caused by pests and other biotic and abiotic stresses. While the use of RNAi as a tool in agriculture is still limited to a few transgenic crops, and only adopted in restricted parts of the world, scientists and industry are already seeking innovations in leveraging and exploiting the potential of RNAi in the form of RNA-based biocontrol compounds for external applications. Here, we highlight the expanding research and development pipeline, commercial landscape and regulatory environment surrounding the pursuit of RNA-based biocontrol compounds with improved environmental profiles. The commitments of well-established agrochemical companies to invest in research endeavours and the role of start-up companies are crucial for the successful development of practical applications for these compounds. Additionally, the availability of standardized guidelines to tackle regulatory ambiguities surrounding RNA-based biocontrol compounds will help to facilitate the entire commercialization process. Finally, communication to create awareness and public acceptance will be key to the deployment of these compounds. © 2019 Society of Chemical Industry.

Transgene suppression in plants by foliar application of in vitro-synthesized small interfering RNAs

Recent research has shown that plants can uptake long dsRNAs and dsRNA-derived siRNAs that target important genes of infecting fungi or viruses when applied on the surface of plant leaves. The external RNAs were capable of local and systemic movement inducing plant resistance against the pathogens. Few studies have been made for plant gene regulation by foliar application of RNAs. In this study, several types of ssRNA and siRNA duplexes targeting the neomycin phosphotransferase II (NPTII) transgene were in vitro-synthesized and externally applied to the leaf surface of 4-week-old transgenic Arabidopsis thaliana plants. External application of the synthetic NPTII-encoding siRNAs down-regulated NPTII transcript levels in transgenic A. thaliana 1 and 7 days post-treatment with a higher and more consistent effect being observed for siRNAs methylated at 3' ends. We also analyzed the effects of external NPTII-encoding dsRNA precursors and a dsRNA-derived heterogenous siRNA mix. Digestion of the NPTII-dsRNA to the heterogeneous siRNAs did not improve efficiency of the transgene suppression effect. Key Points• Foliar application of siRNAs down-regulated a commonly used transgene in Arabidopsis. • A more consistent effect was observed for methylated siRNAs. • The findings are important for development of plant gene regulation approaches.

Genetically Modified Organism-Free RNA Interference: Exogenous Application of RNA Molecules in Plants

The latest advances in the field exogenous application of RNA molecules in plants help to protect and modify them through RNA interference (RNAi).

Genetic modification in Malaysia and India: current regulatory framework and the special case of non-transformative RNAi in agriculture

Recent developments in modern biotechnology such as the use of RNA interference (RNAi) have broadened the scope of crop genetic modification. RNAi strategies have led to significant achievements in crop protection against biotic and abiotic stresses, modification of plant traits, and yield improvement. As RNAi-derived varieties of crops become more useful in the field, it is important to examine the capacity of current regulatory systems to deal with such varieties, and to determine if changes are needed to improve the existing frameworks. We review the biosafety frameworks from the perspective of developing countries that are increasingly involved in modern biotechnology research, including RNAi applications, and make some recommendations. Malaysia and India have approved laws regulating living modified organisms and products thereof, highlighting that the use of any genetically modified step requires regulatory scrutiny. In view of production methods for exogenously applied double-stranded RNAs and potential risks from the resulting double-stranded RNA-based products, we argue that a process-based system may be inappropriate for the non-transformative RNAi technology. We here propose that the current legislation needs rewording to take account of the non-transgenic RNAi technology, and discuss the best alternative for regulatory systems in India and Malaysia in comparison with the existing frameworks in other countries.

Bioinformatics-assisted, integrated omics studies on medicinal plants

The immense therapeutic and economic values of medicinal plants have attracted increasing attention from the worldwide researchers. It has been recognized that production of the authentic and high-quality herbal drugs became the prerequisite for maintaining the healthy development of the traditional medicine industry. To this end, intensive research efforts have been devoted to the basic studies, in order to pave a way for standardized authentication of the plant materials, and bioengineering of the metabolic pathways in the medicinal plants. In this paper, the recent advances of omics studies on the medicinal plants were summarized from several aspects, including phenomics and taxonomics, genomics, transcriptomics, proteomics and metabolomics. We proposed a multi-omics data-based workflow for medicinal plant research. It was emphasized that integration of the omics data was important for plant authentication and mechanistic studies on plant metabolism. Additionally, the computational tools for proper storage, efficient processing and high-throughput analyses of the omics data have been introduced into the workflow. According to the workflow, authentication of the medicinal plant materials should not only be performed at the phenomics level but also be implemented by genomic and metabolomic marker-based examination. On the other hand, functional genomics studies, transcriptional regulatory networks and protein-protein interactions will contribute greatly for deciphering the secondary metabolic pathways. Finally, we hope that our work could inspire further efforts on the bioinformatics-assisted, integrated omics studies on the medicinal plants.

High-quality RNA isolation from pigment-rich Dendrobium flowers

Isolation of high-quality RNA from Dendrobium flowers is challenging because of the high levels of pigment, polysaccharides, and polyphenols. In the present study, an efficient CTAB method for RNA extraction from the pigment-rich flowers of Dendrobium was optimised. The optimised method yielded high quantities of RNA (10.1-12.9 µg/g). Spectrophotometric values of A_260/280 in the range of 2.2 to 2.4 and A_260/230 values of 2.0 suggested that the isolated RNA was free of polyphenols, polysaccharides, and protein contaminants. RNA integrity numbers determined by microfluidics were in the range of 7.9-8.9 indicative of intact RNA. In the improved method, the addition of 3 M NaCl and 3% PVP-10 in the extraction buffer, followed by an incubation period of 45 min at 65 °C, eliminated most of the polysaccharides, polyphenolic compounds, and denatured protein. Extraction with phenol:chloroform:isoamyl alcohol (125:24:1) effectively removed pigments from the aqueous phase, while the precipitation of RNA with lithium chloride minimised the co-precipitation of protein, DNA, and polysaccharide and resulted in the extraction of high quality of RNA. The suitability of the RNA for downstream processing was confirmed via RT-PCR amplification of Chalcone synthase gene from cDNA prepared from RNA isolated from different developmental stages of the flower of a Dendrobium hybrid. The present method will be highly useful for the isolation of RNA from pigment, polyphenol, and polysaccharide-rich plant tissues.

Exogenous RNAs for Gene Regulation and Plant Resistance

Recent investigations documented that plants can uptake and process externally applied double-stranded RNAs (dsRNAs), hairpin RNAs (hpRNAs), and small interfering RNAs (siRNAs) designed to silence important genes of plant pathogenic viruses, fungi, or insects. The exogenously applied RNAs spread locally and systemically, move into the pathogens, and induce RNA interference-mediated plant pathogen resistance. Recent findings also provided examples of plant transgene and endogene post-transcriptional down-regulation by complementary dsRNAs or siRNAs applied onto the plant surfaces. Understanding the plant perception and processing of exogenous RNAs could result in the development of novel biotechnological approaches for crop protection. This review summarizes and discusses the emerging studies reporting on exogenous RNA applications for down-regulation of essential fungal and insect genes, targeting of plant viruses, or suppression of plant transgenes and endogenes for increased resistance and changed phenotypes. We also analyze the current understanding of dsRNA uptake mechanisms and dsRNA stability in plant environments.

Genome-wide researches and applications on Dendrobium

This review summarizes current knowledge of chromosome characterization, genetic mapping, genomic sequencing, quality formation, floral transition, propagation, and identification in Dendrobium. The widely distributed Dendrobium has been studied for a long history, due to its important economic values in both medicine and ornamental. In recent years, some species of Dendrobium and other orchids had been reported on genomic sequences, using the next-generation sequencing technology. And the chloroplast genomes of many Dendrobium species were also revealed. The chromosomes of most Dendrobium species belong to mini-chromosomes, and showed 2n = 38. Only a few of genetic studies were reported in Dendrobium. After revealing of genomic sequences, the techniques of transcriptomics, proteomics and metabolomics could be employed on Dendrobium easily. Some other molecular biological techniques, such as gene cloning, gene editing, genetic transformation and molecular marker developing, had also been applied on the basic research of Dendrobium, successively. As medicinal plants, insights into the biosynthesis of some medicinal components were the most important. As ornamental plants, regulation of flower related characteristics was the most important. More, knowledge of growth and development, environmental interaction, evolutionary analysis, breeding of new cultivars, propagation, and identification of species and herbs were also required for commercial usage. All of these studies were improved using genomic sequences and related technologies. To answer some key scientific issues in Dendrobium, quality formation, flowering, self-incompatibility and seed germination would be the focus of future research. And genome related technologies and studies would be helpful.

Coordinated Regulation of Anthocyanin Biosynthesis Genes Confers Varied Phenotypic and Spatial-Temporal Anthocyanin Accumulation in Radish (Raphanus sativus L.)

Anthocyanins are natural pigments that have important functions in plant growth and development. Radish taproots are rich in anthocyanins which confer different taproot colors and are potentially beneficial to human health. The crop differentially accumulates anthocyanin during various stages of growth, yet molecular mechanisms underlying this differential anthocyanin accumulation remains unknown. In the present study, transcriptome analysis was used to concisely identify putative genes involved in anthocyanin biosynthesis in radish. Spatial-temporal transcript expressions were then profiled in four color variant radish cultivars. From the total transcript sequences obtained through illumina sequencing, 102 assembled unigenes, and 20 candidate genes were identified to be involved in anthocyanin biosynthesis. Fifteen genomic sequences were isolated and sequenced from radish taproot. The length of these sequences was between 900 and 1,579 bp, and the unigene coverage to all of the corresponding cloned sequences was more than 93%. Gene structure analysis revealed that RsF3'H is intronless and anthocyanin biosynthesis genes (ABGs) bear asymmetrical exons, except RsSAM. Anthocyanin accumulation showed a gradual increase in the leaf of the red radish and the taproot of colored cultivars during development, with a rapid increase at 30 days after sowing (DAS), and the highest content at maturity. Spatial-temporal transcriptional analysis of 14 genes revealed detectable expressions of 12 ABGs in various tissues at different growth levels. The investigation of anthocyanin accumulation and gene expression in four color variant radish cultivars, at different stages of development, indicated that total anthocyanin correlated with transcript levels of ABGs, particularly RsUFGT, RsF3H, RsANS, RsCHS3 and RsF3'H1. Our results suggest that these candidate genes play key roles in phenotypic and spatial-temporal anthocyanin accumulation in radish through coordinated regulation and the major control point in anthocyanin biosynthesis in radish is RsUFGT. The present findings lend invaluable insights into anthocyanin biosynthesis and may facilitate genetic manipulation for enhanced anthocyanin content in radish.

Genome-wide organization and expression profiling of the R2R3-MYB transcription factor family in pineapple (Ananas comosus)

Background

The MYB proteins comprise one of the largest families of plant transcription factors, which are involved in various plant physiological and biochemical processes. Pineapple (Ananas comosus) is one of three most important tropical fruits worldwide. The completion of pineapple genome sequencing provides a great opportunity to investigate the organization and evolutionary traits of pineapple MYB genes at the genome-wide level.

Results

In the present study, a total of 94 pineapple R2R3-MYB genes were identified and further phylogenetically classified into 26 subfamilies, as supported by the conserved gene structures and motif composition. Collinearity analysis indicated that the segmental duplication events played a crucial role in the expansion of pineapple MYB gene family. Further comparative phylogenetic analysis suggested that there have been functional divergences of MYB gene family during plant evolution. RNA-seq data from different tissues and developmental stages revealed distinct temporal and spatial expression profiles of the AcMYB genes. Further quantitative expression analysis showed the specific expression patterns of the selected putative stress-related AcMYB genes in response to distinct abiotic stress and hormonal treatments. The comprehensive expression analysis of the pineapple MYB genes, especially the tissue-preferential and stress-responsive genes, could provide valuable clues for further function characterization.

Conclusions

In this work, we systematically identified AcMYB genes by analyzing the pineapple genome sequence using a set of bioinformatics approaches. Our findings provide a global insight into the organization, phylogeny and expression patterns of the pineapple R2R3-MYB genes, and hence contribute to the greater understanding of their biological roles in pineapple.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3896-y) contains supplementary material, which is available to authorized users.

Anthocyanin biosynthesis regulation of DhMYB2 and DhbHLH1 in Dendrobium hybrids petals

Dendrobium hybrids orchid are popular throughout the world. They have various floral color and pigmentation patterns that are mainly caused by anthocyanins. It is well established that anthocyanin biosynthesis is regulated by the interplay between MYB and bHLH transcription factors (TF) in most plants. In this study, we identified one R2R3-MYB gene, DhMYB2, and one bHLH gene, DhbHLH1, from a Dendrobium hybrid. Their expression profiles were related to anthocyanin pigmentation in Dendrobium petals. Transient over-expression of these two TF genes showed that both DhMYB2 and DhbHLH1 resulted in anthocyanin production in white petals. The interaction between the two TFs was observed in vitro. In different Dendrobium hybrids petals with various pigmentations, DhMYB2 and DhbHLH1 were co-expressed with DhDFR and DhANS, which are regarded as potential regulatory targets of the two TFs. In flowers with distinct purple lips but white or yellow petals/sepals, the expression of DhbHLH1 was only related to anthocyanin accumulation in the lips. Taken together, DhMYB2 interacted with DhbHLH1 to regulate anthocyanin production in Dendrobium hybrid petals. DhbHLH1 was also responsible for the distinct anthocyanin pigmentation in lip tissues. The functional characterization of DhMYB2 and DhbHLH1 will improve understanding of anthocyanin biosynthesis modulation in Dendrobium orchids.

Clay nanosheets for topical delivery of RNAi for sustained protection against plant viruses

Topical application of pathogen-specific double-stranded RNA (dsRNA) for virus resistance in plants represents an attractive alternative to transgenic RNA interference (RNAi). However, the instability of naked dsRNA sprayed on plants has been a major challenge towards its practical application. We demonstrate that dsRNA can be loaded on designer, non-toxic, degradable, layered double hydroxide (LDH) clay nanosheets. Once loaded on LDH, the dsRNA does not wash off, shows sustained release and can be detected on sprayed leaves even 30 days after application. We provide evidence for the degradation of LDH, dsRNA uptake in plant cells and silencing of homologous RNA on topical application. Significantly, a single spray of dsRNA loaded on LDH (BioClay) afforded virus protection for at least 20 days when challenged on sprayed and newly emerged unsprayed leaves. This innovation translates nanotechnology developed for delivery of RNAi for human therapeutics to use in crop protection as an environmentally sustainable and easy to adopt topical spray.

Methods for genetic transformation in Dendrobium

The genetic transformation of Dendrobium orchids will allow for the introduction of novel colours, altered architecture and valuable traits such as abiotic and biotic stress tolerance. The orchid genus Dendrobium contains species that have both ornamental value and medicinal importance. There is thus interest in producing cultivars that have increased resistance to pests, novel horticultural characteristics such as novel flower colours, improved productivity, longer flower spikes, or longer post-harvest shelf-life. Tissue culture is used to establish clonal plants while in vitro flowering allows for the production of flowers or floral parts within a sterile environment, expanding the selection of explants that can be used for tissue culture or genetic transformation. The latter is potentially the most effective, rapid and practical way to introduce new agronomic traits into Dendrobium. Most (69.4 %) Dendrobium genetic transformation studies have used particle bombardment (biolistics) while 64 % have employed some form of Agrobacterium-mediated transformation. A singe study has explored ovary injection, but no studies exist on floral dip transformation. While most of these studies have involved the use of selector or reporter genes, there are now a handful of studies that have introduced genes for horticulturally important traits.