miR482 regulation of NBS-LRR defense genes during fungal pathogen infection in cotton

The biogenesis, regulation and functions of transitive siRNA in plants

Small RNA (sRNA)-mediated RNA interference (RNAi) is a sequence-specific gene silencing mechanism that modulates gene expression in eukaryotes. As core molecules of RNAi, various sRNAs are encoded in the plant genome or derived from invading RNA molecules, and their biogenesis depends on distinct genetic pathways. Transitive small interfering RNAs (siRNAs), which are sRNAs produced from double-strand RNA (dsRNA) in a process that depends on RNA-dependent RNA polymerases (RDRs), can amplify and spread silencing signals to additional transcripts, thereby enabling a phenomenon termed "transitive RNAi". Members of this class of siRNAs function in various biological processes ranging from development to stress adaptation. In Arabidopsis thaliana, two RDRs participate in the generation of transitive siRNAs, acting cooperatively with various siRNA generation-related factors, such as the RNA-induced silencing complex (RISC) and aberrant RNAs. Transitive siRNAs are produced in diverse subcellular locations and structures under the control of various mechanisms, highlighting the intricacies of their biogenesis and functions. In this review, we discuss recent advances in understanding the molecular events of transitive siRNA biogenesis and its regulation, with a particular focus on factors involved in RDR recruitment. We aim to provide a comprehensive description of the generalized mechanism governing the biogenesis of transitive siRNAs. Additionally, we present an overview of the diverse biological functions of these siRNAs and raise some pressing questions in this area for further investigation.

Are miRNAs applicable for balancing crop growth and defense trade-off?

Securing agricultural supplies for the increasing population without negative impacts on environment demands new crop varieties with higher yields, better quality, and stronger stress resilience. But breeding such super crop varieties is restrained by growth-defense (G-D) trade-off. MicroRNAs (miRNAs) are versatile regulators of plant growth and immune responses, with several being demonstrated to simultaneously regulate crop growth and defense against biotic stresses and to balance G-D trade-off. Increasing evidence also links miRNAs to the metabolism and signaling of phytohormones, another type of master regulator of plant growth and defense. Here, we synthesize the reported functions of miRNAs in crop growth, development, and responses to bio-stressors, summarize the regulatory scenarios of miRNAs based on their relationship with target(s), and discuss how miRNAs, particularly those involved in crosstalk with phytohormones, can be applied in balancing G-D trade-off in crops. We also propose several open questions to be addressed for adopting miRNAs in balancing crop G-D trade-off.

MiRNAs profiles among three poplar varieties provide insights into different molecular responses in resistance to newly emerging bacterial pathogen

Canker caused by Lonsdalea populi has seriously reduced the economic and ecological benefits of poplar. MicroRNAs play vital roles in the response of plants to biotic stress. However, there is little research about the regulatory mechanism of miRNAs among different tree varieties upon pathogen infection. To dissect miRNAs involved in L. populi resistance, three poplar varieties, 2025 (susceptible), 107 (moderately resistant) and Populus. tomentosa cv 'henan' (resistant) were selected to elucidate the expression profiles of miRNAs using small RNA-seq. A total of 227 miRNAs were identified from all varieties. Intriguingly, miR160, miR169, miR171 and miR482b-5p were only identified in the resistant variety P. tomentosa upon pathogen infection, and these miRNAs might be important candidates for future investigation to improve the tolerance of poplar to L. populi. Among all identified miRNAs, 174 were differentially expressed in all varieties. Functional annotation analysis indicated that an array of miRNAs, including miR482, miR472, miR169, miR481, and miR172, should be involved in disease resistance and phytohormone signal transduction. Furthermore, correlation analysis of small RNA-seq and RNA-seq identified a handful of L. populi-responsive miRNAs and target genes, which exhibited that miR159 and miR172 played key roles in resistant variety P. tomentosa by targeting MYB and ERF, while miR6462c-5p and miR828 were related to the susceptibility of 2025 by targeting MYB. The comprehensive integration analysis in this research provides new insights into the regulatory pathways involved in the defence response of poplar to L. populi and offers crucial candidate miRNAs-target genes modules for poplar resistance improvement.

Plant microRNAs regulate the defense response against pathogens

MicroRNAs (miRNAs) are a class of small non-coding RNAs, typically 20-25 nucleotides in length, that play a crucial role in regulating gene expression post-transcriptionally. They are involved in various biological processes such as plant growth, development, stress response, and hormone signaling pathways. Plants interact with microbes through multiple mechanisms, including mutually beneficial symbiotic relationships and complex defense strategies against pathogen invasions. These defense strategies encompass physical barriers, biochemical defenses, signal recognition and transduction, as well as systemic acquired resistance. MiRNAs play a central role in regulating the plant's innate immune response, activating or suppressing the transcription of specific genes that are directly involved in the plant's defense mechanisms against pathogens. Notably, miRNAs respond to pathogen attacks by modulating the balance of plant hormones such as salicylic acid, jasmonic acid, and ethylene, which are key in activating plant defense mechanisms. Moreover, miRNAs can cross boundaries into fungal and bacterial cells, performing cross-kingdom RNA silencing that enhances the plant's disease resistance. Despite the complex and diverse roles of miRNAs in plant defense, further research into their function in plant-pathogen interactions is essential. This review summarizes the critical role of miRNAs in plant defense against pathogens, which is crucial for elucidating how miRNAs control plant defense mechanisms.

The floral development of the allotetraploid Coffea arabica L. correlates with a small RNA dynamic reprogramming

Noncoding and coding RNAs are key regulators of plant growth, development, and stress responses. To investigate the types of transcripts accumulated during the vegetative to reproductive transition and floral development in the Coffea arabica L., we sequenced small RNA libraries from eight developmental stages, up to anthesis. We combined these data with messenger RNA and PARE sequencing of two important development stages that marks the transition of an apparent latent to a rapid growth stage. In addition, we took advantage of multiple in silico tools to characterize genomic loci producing small RNAs such as phasiRNAs, miRNAs, and tRFs. Our differential and co-expression analysis showed that some types of small RNAs such as tRNAs, snoRNAs, snRNAs, and phasiRNAs preferentially accumulate in a stage-specific manner. Members of the miR482/miR2118 superfamily and their 21-nucleotide phasiRNAs originating from resistance genes show a robust co-expression pattern that is maintained across all the evaluated developmental stages. Finally, the majority of miRNAs accumulate in a family stage-specific manner, related to modulated hormonal responses and transcription factor expression.

Identification of microRNAs and their target genes associated with chasmogamous and cleistogamous flower development in Viola prionantha

MAIN CONCLUSION

Differentially expressed microRNAs were found associated with the development of chasmogamous and cleistogamous flowers in Viola prionantha, revealing potential roles of microRNAs in the developmental evolution of dimorphic flowers. In Viola prionantha, chasmogamous (CH) flowers are induced by short daylight, while cleistogamous (CL) flowers are triggered by long daylight. How environmental factors and microRNAs (miRNAs) affect dimorphic flower formation remains unknown. In this study, small RNA sequencing was performed on CH and CL floral buds at different developmental stages in V. prionantha, differentially expressed miRNAs (DEmiRNAs) were identified, and their target genes were predicted. In CL flowers, Viola prionantha miR393 (vpr-miR393a/b) and vpr-miRN3366 were highly expressed, while in CH flowers, vpr-miRN2005, vpr-miR172e-2, vpr-miR166m-3, vpr-miR396f-2, and vpr-miR482d-2 were highly expressed. In the auxin-activated signaling pathway, vpr-miR393a/b and vpr-miRN2005 could target Vpr-TIR1/AFB and Vpr-ARF2, respectively, and other DEmiRNAs could target genes involved in the regulation of transcription, e.g., Vpr-AP2-7. Moreover, Vpr-UFO and Vpr-YAB5, the main regulators in petal and stamen development, were co-expressed with Vpr-TIR1/AFB and Vpr-ARF2 and showed lower expression in CL flowers than in CH flowers. Some V. prionantha genes relating to the stress/defense responses were co-expressed with Vpr-TIR1/AFB, Vpr-ARF2, and Vpr-AP2-7 and highly expressed in CL flowers. Therefore, in V. prionantha, CH-CL flower development may be regulated by the identified DEmiRNAs and their target genes, thus providing the first insight into the formation of dimorphic flowers in Viola.

Genome-wide identification and in silico characterization of major RNAi gene families in date palm (Phoenix dactylifera)

BACKGROUND

Dates contain various minerals that are essential for good health. The major RNA interference (RNAi) gene families play a vital role in plant growth and development by controlling the expression of protein-coding genes against different biotic and abiotic stresses. However, these gene families for date palm are not yet studied. Therefore, this study has explored major RNAi genes and their characteristics in date palm.

RESULTS

We have identified 4 PdDCLs, 7 PdAGOs, and 3 PdRDRs as RNAi proteins from the date palm genome by using AtRNAi genes as query sequences in BLASTp search. Domain analysis of predicted RNAi genes has revealed the Helicase_C, Dicer_dimer, PAZ, RNase III, and Piwi domains that are associated with the gene silencing mechanisms. Most PdRNAi proteins have been found in the nucleus and cytosol associated with the gene silencing actions. The gene ontology (GO) enrichment analysis has revealed some important GO terms including RNA interference, dsRNA fragmentation, and ribonuclease_III activity that are related to the protein-coding gene silencing mechanisms. Gene regulatory network (GRN) analysis has identified PAZ and SNF2 as the transcriptional regulators of PdRNAi genes. Top-ranked 10 microRNAs including Pda-miR156b, Pda-miR396a, Pda-miR166a, Pda-miR167d, and Pda-miR529a have been identified as the key post-transcriptional regulators of PdRNAi genes that are associated with different biotic/abiotic stresses. The cis-acting regulatory element analysis of PdRNAi genes has detected some vital cis-acting elements including ABRE, MBS, MYB, MYC, Box-4, G-box, I-box, and STRE that are linked with different abiotic stresses.

CONCLUSION

The results of this study might be valuable resources for the improvement of different characteristics in date palm by further studies in wet-lab.

Epigenetic weapons of plants against fungal pathogens

In the natural environment, plants face constant exposure to biotic stress caused by fungal attacks. The plant's response to various biotic stresses relies heavily on its ability to rapidly adjust the transcriptome. External signals are transmitted to the nucleus, leading to activation of transcription factors that subsequently enhance the expression of specific defense-related genes. Epigenetic mechanisms, including histone modifications and DNA methylation, which are closely linked to chromatin states, regulate gene expression associated with defense against biotic stress. Additionally, chromatin remodelers and non-coding RNA play a significant role in plant defense against stressors. These molecular modifications enable plants to exhibit enhanced resistance and productivity under diverse environmental conditions. Epigenetic mechanisms also contribute to stress-induced environmental epigenetic memory and priming in plants, enabling them to recall past molecular experiences and utilize this stored information for adaptation to new conditions. In the arms race between fungi and plants, a significant aspect is the cross-kingdom RNAi mechanism, whereby sRNAs can traverse organismal boundaries. Fungi utilize sRNA as an effector molecule to silence plant resistance genes, while plants transport sRNA, primarily through extracellular vesicles, to pathogens in order to suppress virulence-related genes. In this review, we summarize contemporary knowledge on epigenetic mechanisms of plant defense against attack by pathogenic fungi. The role of epigenetic mechanisms during plant-fungus symbiotic interactions is also considered.

Phased secondary small interfering RNAs in Camellia sinensis var. assamica

Phased secondary small interfering RNAs (phasiRNAs) in plants play important roles in regulating genome stability, plant development and stress adaption. Camellia sinensis var. assamica has immense economic, medicinal and cultural significance. However, there are still no studies of phasiRNAs and their putative functions in this valuable plant. We identified 476 and 43 PHAS loci which generated 4290 twenty one nucleotide (nt) and 264 twenty four nt phasiRNAs, respectively. Moreover, the analysis of degradome revealed more than 35000 potential targets for these phasiRNAs. We identified several conserved 21 nt phasiRNA generation pathways in tea plant, including miR390 → TAS3, miR482/miR2118 → NB-LRR, miR393 → F-box, miR828 → MYB/TAS4, and miR7122 → PPR in this study. Furthermore, we found that some transposase and plant mobile domain genes could generate phasiRNAs. Our results show that phasiRNAs target genes in the same family in cis- or trans-manners, and different members of the same gene family may generate the same phasiRNAs. The phasiRNAs, generated by transposase and plant mobile domain genes, and their targets, suggest that phasiRNAs may be involved in the inhibition of transposable elements in tea plant. To summarize, these results provide a comprehensive view of phasiRNAs in Camellia sinensis var. assamica.

miR2118 Negatively Regulates Bacterial Blight Resistance through Targeting Several Disease Resistance Genes in Rice

Plant miRNAs are a class of noncoding RNA with a length of 21-24 nt that play an important role in plant responses to biotic and abiotic stresses. Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious bacterial diseases in rice. Our previous work showed that osa-miR2118b/n was induced by Xoo infection. However, the biological function of miR2118 has not yet been characterized in experiments. Herein, we constructed MIR2118b OE, as well as single and double mutants of MIR2118b/n using CRISPR/Cas9. Further results showed that osa-MIR2118b OE plants exhibited longer lesion lengths than the wild type after Xoo inoculation, while MIR2118 CRISPR plants exhibited shorter lesion lengths than the wild type after Xoo inoculation. Co-transformation experiments in rice protoplasts indicated that osa-miR2118 negatively regulated the transcripts of three nucleotide-binding sites and leucine-rich repeat (NLR) genes (LOC_Os08g42700.1, LOC_Os01g05600.1, and LOC_Os12g37290.1) which are predicted target genes of miR2118, but not the mutated NLR genes with a 3 bp insertion at the center of the binding sites. The transcriptional level of the three NLR genes was reversed relative to osa-miR2118 in the MIR2118b OE and MIR2118b CRISPR plants. The above results demonstrate that osa-miR2118b/n negatively regulates the resistance to bacterial blight through negatively regulating several NLR genes.

Osa-miR11117 Targets OsPAO4 to Regulate Rice Immunity against the Blast Fungus Magnaporthe oryzae

The intricate regulatory process governing rice immunity against the blast fungus Magnaporthe oryzae remains a central focus in plant-pathogen interactions. In this study, we investigated the important role of Osa-miR11117, an intergenic microRNA, in regulating rice defense mechanisms. Stem-loop qRT-PCR analysis showed that Osa-miR11117 is responsive to M. oryzae infection, and overexpression of Osa-miR11117 compromises blast resistance. Green fluorescent protein (GFP)-based reporter assay indicated OsPAO4 is one direct target of Osa-miR11117. Furthermore, qRT-PCR analysis showed that OsPAO4 reacts to M. oryzae infection and polyamine (PA) treatment. In addition, OsPAO4 regulates rice resistance to M. oryzae through the regulation of PA accumulation and the expression of the ethylene (ETH) signaling genes. Taken together, these results suggest that Osa-miR11117 is targeting OsPAO4 to regulate blast resistance by adjusting PA metabolism and ETH signaling pathways.

In silico and computational analysis of zinc finger motif-associated homeodomain (ZF-HD) family genes in chilli (Capsicum annuum L)

Zinc finger-homeodomain (ZHD) proteins are mostly expressed in plants and are involved in proper growth and development and minimizing biotic and abiotic stress. A recent study identified and characterized the ZHD gene family in chilli (Capsicum annuum L.) to determine their probable molecular function. ZHD genes with various physicochemical characteristics were discovered on twelve chromosomes in chilli. We separated ZHD proteins into two major groups using sequence alignment and phylogenetic analysis. These groups differ in gene structure, motif distribution, and a conserved ZHD and micro-zinc finger ZF domain. The majority of the CaZHDs genes are preserved, early duplication occurred recently, and significant pure selection took place throughout evolution, according to evolutionary study. According to expression profiling, the genes were found to be equally expressed in tissues above the ground, contribute to plant growth and development and provide tolerance to biotic and abiotic stress. This in silico analysis, taken as a whole, hypothesized that these genes perform distinct roles in molecular and phytohormone signaling processes, which may serve as a foundation for subsequent research into the roles of these genes in other crops.

Functional role of microRNA in the regulation of biotic and abiotic stress in agronomic plants

The increasing demand for food is the result of an increasing population. It is crucial to enhance crop yield for sustainable production. Recently, microRNAs (miRNAs) have gained importance because of their involvement in crop productivity by regulating gene transcription in numerous biological processes, such as growth, development and abiotic and biotic stresses. miRNAs are small, non-coding RNA involved in numerous other biological functions in a plant that range from genomic integrity, metabolism, growth, and development to environmental stress response, which collectively influence the agronomic traits of the crop species. Additionally, miRNA families associated with various agronomic properties are conserved across diverse plant species. The miRNA adaptive responses enhance the plants to survive environmental stresses, such as drought, salinity, cold, and heat conditions, as well as biotic stresses, such as pathogens and insect pests. Thus, understanding the detailed mechanism of the potential response of miRNAs during stress response is necessary to promote the agronomic traits of crops. In this review, we updated the details of the functional aspects of miRNAs as potential regulators of various stress-related responses in agronomic plants.

Tae-miR397 Negatively Regulates Wheat Resistance to Blumeria graminis

MicroRNA (miRNA) plays a crucial role in the interactions between plants and pathogens, and identifying disease-related miRNAs could help us understand the mechanisms underlying plant disease pathogenesis and breed resistant varieties. However, the role of miRNA in wheat defense responses remains largely unexplored. The miR397 family is highly conserved in plants and involved in plant development and defense response. Therefore, the purpose of this study was to investigate the function of tae-miR397 in wheat resistance to powdery mildew. The expression pattern analysis revealed that tae-miR397 expression was higher in young leaves than in other tissues and was significantly decreased in wheat Bainong207 leaves after Blumeria graminis (Bgt) infection and chitin treatment. Additionally, the expression of tae-miR397 was significantly down-regulated by salicylic acid and induced under jasmonate treatment. The overexpression of tae-miR397 in common wheat Bainong207 enhanced the wheat's susceptibility to powdery mildew in the seedling and adult stages. The rate of Bgt spore germination and mycelial growth in transgenic wheat plants overexpressing tae-miR397 was faster than in the untransformed wild-type plants. The target gene of tae-miR397 was predicted to be a wound-induced protein (Tae-WIP), and the function was investigated. We demonstrated that silencing of Tae-WIP via barley-stripe-mosaic-virus-induced gene silencing enhanced wheat's susceptibility to powdery mildew. qRT-PCR indicated that tae-miR397 regulated wheat immunity by controlling pathogenesis-related gene expressions. Moreover, the transgenic plants overexpressing tae-miR397 exhibited more tillers than the wild-type plants. This work suggests that tae-miR397 is a negative regulator of resistance against powdery mildew and has great potential for breeding disease-resistant cultivars.

Cotton RSG2 Mediates Plant Resistance against Verticillium dahliae by miR482b Regulation

Cotton Verticillium wilt, mainly caused by Verticillium dahliae, has a serious impact on the yield and quality of cotton fiber. Many microRNAs (miRNAs) have been identified to participate in plant resistance to V. dahliae infection, but the exploration of miRNA's function mechanism in plant defense is needed. Here, we demonstrate that the ghr-miR482b-GhRSG2 module mediates cotton plant resistance to V. dahliae infection. Based on the mRNA degradation data and GUS fusion experiments, ghr-miR482b directedly bonds to GhRSG2 mRNA to lead to its degradation. The knockdown and overexpression of ghr-miR482b through virus-induced gene silencing strategies enhanced (decreased by 0.39-fold in disease index compared with the control) and weakened (increased by 0.46-fold) the plant resistance to V. dahliae, respectively. In addition, silencing GhRSG2 significantly increased (increased by 0.93-fold in disease index) the plant sensitivity to V. dahliae compared with the control plants treated with empty vector. The expression levels of two SA-related disease genes, GhPR1 and GhPR2, significantly decreased in GhRSG2-silenced plants by 0.71 and 0.67 times, respectively, and in ghr-miR482b-overexpressed (OX) plants by 0.59 and 0.75 times, respectively, compared with the control, whereas the expression levels of GhPR1 and GhPR2 were significantly increased by 1.21 and 2.59 times, respectively, in ghr-miR482b knockdown (KD) plants. In sum, the ghr-miR482b-GhRSG2 module participates in the regulation of plant defense against V. dahliae by inducing the expression of PR1 and PR2 genes.

Insights to Gossypium defense response against Verticillium dahliae: the Cotton Cancer

The soil-borne pathogen Verticillium dahliae, also referred as "The Cotton Cancer," is responsible for causing Verticillium wilt in cotton crops, a destructive disease with a global impact. To infect cotton plants, the pathogen employs multiple virulence mechanisms such as releasing enzymes that degrade cell walls, activating genes that contribute to virulence, and using protein effectors. Conversely, cotton plants have developed numerous defense mechanisms to combat the impact of V. dahliae. These include strengthening the cell wall by producing lignin and depositing callose, discharging reactive oxygen species, and amassing hormones related to defense. Despite the efforts to develop resistant cultivars, there is still no permanent solution to Verticillium wilt due to a limited understanding of the underlying molecular mechanisms that drive both resistance and pathogenesis is currently prevalent. To address this challenge, cutting-edge technologies such as clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), host-induced gene silencing (HIGS), and gene delivery via nano-carriers could be employed as effective alternatives to control the disease. This article intends to present an overview of V. dahliae virulence mechanisms and discuss the different cotton defense mechanisms against Verticillium wilt, including morphophysiological and biochemical responses and signaling pathways including jasmonic acid (JA), salicylic acid (SA), ethylene (ET), and strigolactones (SLs). Additionally, the article highlights the significance of microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs) in gene expression regulation, as well as the different methods employed to identify and functionally validate genes to achieve resistance against this disease. Gaining a more profound understanding of these mechanisms could potentially result in the creation of more efficient strategies for combating Verticillium wilt in cotton crops.

Characterization of microRNAs and Target Genes in Musa acuminata subsp. burmannicoides, var. Calcutta 4 during Interaction with Pseudocercospora musae

Endogenous microRNAs (miRNAs) are small non-coding RNAs that perform post-transcriptional regulatory roles across diverse cellular processes, including defence responses to biotic stresses. Pseudocercospora musae, the causal agent of Sigatoka leaf spot disease in banana (Musa spp.), is an important fungal pathogen of the plant. Illumina HiSeq 2500 sequencing of small RNA libraries derived from leaf material in Musa acuminata subsp. burmannicoides, var. Calcutta 4 (resistant) after inoculation with fungal conidiospores and equivalent non-inoculated controls revealed 202 conserved miRNAs from 30 miR-families together with 24 predicted novel miRNAs. Conserved members included those from families miRNA156, miRNA166, miRNA171, miRNA396, miRNA167, miRNA172, miRNA160, miRNA164, miRNA168, miRNA159, miRNA169, miRNA393, miRNA535, miRNA482, miRNA2118, and miRNA397, all known to be involved in plant immune responses. Gene ontology (GO) analysis of gene targets indicated molecular activity terms related to defence responses that included nucleotide binding, oxidoreductase activity, and protein kinase activity. Biological process terms associated with defence included response to hormone and response to oxidative stress. DNA binding and transcription factor activity also indicated the involvement of miRNA target genes in the regulation of gene expression during defence responses. sRNA-seq expression data for miRNAs and RNAseq data for target genes were validated using stem-loop quantitative real-time PCR (qRT-PCR). For the 11 conserved miRNAs selected based on family abundance and known involvement in plant defence responses, the data revealed a frequent negative correlation of expression between miRNAs and target host genes. This examination provides novel information on miRNA-mediated host defence responses, applicable in genetic engineering for the control of Sigatoka leaf spot disease.

MicroRNA Expression Profiles in Response to Phytophthora infestans and Oidium neolycopersici and Functional Identification of sly-miR397 in Tomato

Late blight and powdery mildew are two widespread tomato diseases caused by Phytophthora infestans and Oidium neolycopersici, respectively, which reduce the quantity and quality of tomato. MicroRNAs (miRNAs) play critical roles in tomato resistance to various pathogens. Investigating the function of miRNAs is of great significance in controlling tomato diseases. To identify potential miRNAs involved in the interaction of tomato with P. infestans or O. neolycopersici, we analyzed the expression profiles of small RNAs in tomato leaves infected with these two pathogens using RNA-seq technology. A total of 330 and 288 miRNAs exhibited differences in expression levels after exposure to P. infestans and O. neolycopersici, respectively. One hundred and forty-six commonly differentially expressed (DE) miRNAs responsive to P. infestans and O. neolycopersici infestation were detected, including 10 commonly known conserved DE miRNAs and 136 novel miRNAs. Among these known DE miRNAs, sly-miR397 was strongly downregulated in response to P. infestans or O. neolycopersici infection. Silencing of sly-miR397 resulted in enhanced tolerance to the pathogens, whereas overexpression of sly-miR397 showed increased susceptibility. Furthermore, changes in sly-miR397 expression could also affect expression levels of pathogenesis-related genes and reactive oxygen species-scavenging genes, leading to altered necrotic cells and H₂O₂ levels. In addition, the number of lateral branches significantly changed in transgenic plants. Taken together, our results provide potential miRNA resources for further research of miRNA-disease associations and indicates that sly-miR397 acts as a negative regulator of disease resistance and influences lateral branch development in tomato.

Role of long non-coding RNA in regulatory network response to Candidatus Liberibacter asiaticus in citrus

Long non-coding RNAs (lncRNAs) serve as crucial regulators in plant response to various diseases, while none have been systematically identified and characterized in response to citrus Huanglongbing (HLB) caused by Candidatus Liberibacter asiaticus (CLas) bacteria. Here, we comprehensively investigated the transcriptional and regulatory dynamics of the lncRNAs in response to CLas. Samples were collected from leaf midribs of CLas- and mock-inoculated HLB-tolerant rough lemon (Citrus jambhiri) and HLB-sensitive sweet orange (C. sinensis) at week 0, 7, 17, and 34 following inoculation using CLas+ budwood of three biological replicates in the greenhouse. A total of 8,742 lncRNAs, including 2,529 novel lncRNAs, were identified from RNA-seq data with rRNA-removed from strand-specific libraries. Genomic variation analyses of conserved lncRNAs from 38 citrus accessions showed that 26 single nucleotide polymorphisms (SNPs) were significantly correlated with HLB. In addition, lncRNA-mRNA weighted gene co-expression network analysis (WGCNA) showed a significant module correlated with CLas-inoculation in rough lemon. Notably, the most significant LNC_28805 and multiple co-expressed genes related to plant defense in the module were targeted by miRNA5021, suggesting that LNC28805 might compete with endogenous miR5021 to maintain the homeostasis of immune gene expression levels. Candidate WRKY33 and SYP121 genes targeted by miRNA5021 were identified as two key hub genes interacting with bacteria pathogen response genes based on the prediction of protein-protein interaction (PPI) network. These two genes were also found within HLB-associated QTL in linkage group 6. Overall, our findings provide a reference for a better understanding of the role of lncRNAs involved in citrus HLB regulation.

Identification of miRNAs Involved in Maize-Induced Systemic Resistance Primed by Trichoderma harzianum T28 against Cochliobolus heterostrophus

microRNAs (miRNAs) are known to play important roles in the immune response to pathogen infection in different plants. Further, Trichoderma strains are able to activate plant defense responses against pathogen attacks. However, little is known about the involvement of miRNAs in the defense response primed by Trichoderma strains. To explore the miRNAs sensitive to priming by Trichoderma, we studied the small RNAs and transcriptome changes in maize leaves that were systemically induced by seed treatment with Trichoderma harzianum (strain T28) against Cochliobolus heterostrophus (C. heterostrophus) infection in leaves. Through analysis of the sequencing data, 38 differentially expressed miRNAs (DEMs) and 824 differentially expressed genes (DEGs) were identified. GO and KEGG analyses of DEGs demonstrated that genes involved in the plant hormone signal transduction pathway and oxidation-reduction process were significantly enriched. In addition, 15 miRNA-mRNA interaction pairs were identified through the combined analysis of DEMs and DEGs. These pairs were supposed to play roles in the maize resistance primed by T. harzianum T28 to C. heterostrophus, in which miR390, miR169j, miR408b, miR395a/p, and novel miRNA (miRn5231) were more involved in the induction of maize resistance. This study provided valuable information for understanding the regulatory role of miRNA in the T. harzianum primed defense response.

Genome-wide identification, characterization, and evolutionary analysis of NBS genes and their association with disease resistance in Musa spp

Banana is an important food crop that is susceptible to a wide range of pests and diseases that can reduce yield and quality. The primary objective of banana breeding programs is to increase disease resistance, which requires the identification of resistance (R) genes. Despite the fact that resistant sources have been identified in bananas, the genes, particularly the nucleotide-binding site (NBS) family, which play an important role in protecting plants against pathogens, have received little attention. As a result, this study included a thorough examination of the NBS disease resistance gene family's classification, phylogenetic analysis, genome organization, evolution, cis-elements, differential expression, regulation by microRNAs, and protein-protein interaction. A total of 116 and 43 putative NBS genes from M. acuminata and M. balbisiana, respectively, were identified and characterized, and were classified into seven sub-families. Structural analysis of NBS genes revealed the presence of signal peptides, their sub-cellular localization, molecular weight and pI. Eight commonly conserved motifs were found, and NBS genes were unevenly distributed across multiple chromosomes, with the majority of NBS genes being located in chr3 and chr1 of the A and B genomes, respectively. Tandem duplication occurrences have helped bananas' NBS genes spread throughout evolution. Transcriptome analysis of NBS genes revealed significant differences in expression between resistant and susceptible cultivars of fusarium wilt, eumusae leaf spot, root lesion nematode, and drought, implying that they can be used as candidate resistant genes. Ninety miRNAs were discovered to have targets in 104 NBS genes from the A genome, providing important insights into NBS gene expression regulation. Overall, this study offers a valuable genomic resource and understanding of the function and evolution of NBS genes in relation to rapidly evolving pathogens, as well as providing breeders with selection targets for fast-tracking breeding of banana varieties with more durable resistance to pathogens.

An atlas of small RNAs from potato

Small RNAs, including microRNAs (miRNAs), phased secondary small interfering RNAs (phasiRNA), and heterochromatic small interfering RNAs (hc-siRNA) are an essential component of gene regulation. To establish a broad potato small RNA atlas, we constructed an expression atlas of leaves, flowers, roots, and tubers of Desiree and Eva, which are commercially important potato (Solanum tuberosum) cultivars. All small RNAs identified were observed to be conserved between both cultivars, supporting the hypothesis that small RNAs have a low evolutionary rate and are mostly conserved between lineages. However, we also found that a few miRNAs showed differential accumulation between the two potato cultivars, and that hc-siRNAs have a tissue specific expression. We further identified dozens of reproductive and non-reproductive phasiRNAs originating from coding and noncoding regions that appeared to exhibit tissue-specific expression. Together, this study provides an extensive small RNA profiling of different potato tissues that might be used as a resource for future investigations.

Integrated High-Throughput Sequencing, Microarray Hybridization and Degradome Analysis Uncovers MicroRNA-Mediated Resistance Responses of Maize to Pathogen Curvularia lunata

Curvularia lunata (Wakker) Boed, the causal agent of leaf spot in maize, is prone to mutation, making it difficult to control. RNAi technology has proven to be an important tool of genetic engineering and functional genomics aimed for crop improvement. MicroRNAs (miRNAs), which act as post-transcriptional regulators, often cause translational repression and gene silencing. In this article, four small RNA (sRNA) libraries were generated from two maize genotypes inoculated by C. lunata; among these, ltR1 and ltR2 were from the susceptible variety Huangzao 4 (HZ), ltR3 and ltR4, from the resistant variety Luyuan (LY), and 2286, 2145, 1556 and 2504 reads were annotated as miRNA in these four sRNA libraries, respectively. Through the combined analysis of high-throughput sequencing, microarray hybridization and degradome, 48 miRNAs were identified as being related to maize resistance to C. lunata. Among these, PC-732 and PC-169, two new maize miRNAs discovered, were predicted to cleave mRNAs of metacaspase 1 (AMC1) and thioredoxin family protein (Trx), respectively, possibly playing crucial roles in the resistance of maize to C. lunata. To further confirm the role of PC-732 in the interaction of maize and C. lunata, the miRNA was silenced through STTM (short tandem target mimic) technology, and we found that knocking down PC-732 decreased the susceptibility of maize to C. lunata. Precisely speaking, the target gene of PC-732 might inhibit the expression of disease resistance-related genes during the interaction between maize and C. lunata. Overall, the findings of this study indicated the existence of miRNAs involved in the resistance of maize to C. lunata and will contribute to rapidly clarify the resistant mechanism of maize to C. lunata.

Multiple Functions of MiRNAs in Brassica napus L

The worldwide climate changes every year due to global warming, waterlogging, drought, salinity, pests, and pathogens, impeding crop productivity. Brassica napus is one of the most important oil crops in the world, and rapeseed oil is considered one of the most health-beneficial edible vegetable oils. Recently, miRNAs have been found and confirmed to control the expression of targets under disruptive environmental conditions. The mechanism is through the formation of the silencing complex that mediates post-transcriptional gene silencing, which pairs the target mRNA and target cleavage and/or translation inhibition. However, the functional role of miRNAs and targets in B. napus is still not clarified. This review focuses on the current knowledge of miRNAs concerning development regulation and biotic and abiotic stress responses in B. napus. Moreover, more strategies for miRNA manipulation in plants are discussed, along with future perspectives, and the enormous amount of transcriptome data available provides cues for miRNA functions in B. napus. Finally, the construction of the miRNA regulatory network can lead to the significant development of climate change-tolerant B. napus through miRNA manipulation.

The Conservation of Long Intergenic Non-Coding RNAs and Their Response to Verticillium dahliae Infection in Cotton

Long intergenic non-coding RNAs (lincRNAs) have been demonstrated to be vital regulators of diverse biological processes in both animals and plants. While many lincRNAs have been identified in cotton, we still know little about the repositories and conservativeness of lincRNAs in different cotton species or about their role in responding to biotic stresses. Here, by using publicly available RNA-seq datasets from diverse sources, including experiments of Verticillium dahliae (Vd) infection, we identified 24,425 and 17,713 lincRNAs, respectively, in Gossypium hirsutum (Ghr) and G. barbadense (Gba), the two cultivated allotetraploid cotton species, and 6933 and 5911 lincRNAs, respectively, in G. arboreum (Gar) and G. raimondii (Gra), the two extant diploid progenitors of the allotetraploid cotton. While closely related subgenomes, such as Ghr_At and Gba_At, tend to have more conserved lincRNAs, most lincRNAs are species-specific. The majority of the synthetic and transcribed lincRNAs (78.2%) have a one-to-one orthologous relationship between different (sub)genomes, although a few of them (0.7%) are retained in all (sub)genomes of the four species. The Vd responsiveness of lincRNAs seems to be positively associated with their conservation level. The major functionalities of the Vd-responsive lincRNAs seem to be largely conserved amongst Gra, Ghr, and Gba. Many Vd-responsive Ghr-lincRNAs overlap with Vd-responsive QTL, and several lincRNAs were predicted to be endogenous target mimicries of miR482/2118, with a pair being highly conserved between Ghr and Gba. On top of the confirmation of the feature characteristics of the lincRNAs previously reported in cotton and other species, our study provided new insights into the conservativeness and divergence of lincRNAs during cotton evolution and into the relationship between the conservativeness and Vd responsiveness of lincRNAs. The study also identified candidate lincRNAs with a potential role in disease response for functional characterization.

Heightened miR6024-NLR interactions facilitate necrotrophic pathogenesis in tomato

miR6024 acts as a negative regulator of R genes, hence of Tomato plant immunity, and facilitates disease by the necrotrophic pathogen A. solani. Plant resistance genes or Nucleotide-binding leucine-rich repeat (NLR) genes, integral components of plant disease stress-signaling are targeted by variable groups of miRNAs. However, the significance of miRNA-mediated regulation of NLRs during a pathogen stress response, specifically for necrotrophic fungus, is poorly understood. A thorough examination of Tomato NLRs and miRNAs could map substantial interactions of which half the annotated NLRs were targets of Solanaceae-specific and conserved miRNAs, at the NB subdomain. The Solanaceae-specific miR6024 and its NLR targets analysed in different phytopathogenic stresses revealed differential and mutually antagonistic regulation. Interestingly, miR6024-targeted cleavage of a target NLR also triggered the generation of secondary phased siRNAs which could potentially amplify the defense signal. RNA-seq analysis of leaf tissues from miR6024 overexpressing Tomato plants evidenced a perturbation in the defense transcriptome with the transgenics showing unwarranted immune response-related genes' expression with or without infection with necrotrophic Alternaria solani, though no adverse effect could be observed in the growth and development of the transgenic plants. Transgenic plants exhibited constitutive downregulation of the target NLRs, aggravated disease phenotype with an enhanced lesion, greater ROS generation and hypersusceptibility to A. solani infection, thus establishing that miR6024 negatively impacts plant immune response during necrotrophic pathogenesis. Limited knowledge about the outcome of NLR-miRNA interaction during necrotrophic pathogenesis is a hindrance to the deployment of miRNAs in crop improvement programs. With the elucidation of the necrotrophic disease-synergistic role played by miR6024, it becomes a potent candidate for biotechnological manipulation for the rapid development of pathogen-tolerant solanaceous plants.

Effects of acute and chronic oxidative stress on the blood-brain barrier in 2D and 3D in vitro models

Oxidative stress is a shared pathology of neurodegenerative disease and brain injuries, and is derived from perturbations to normal cell processes by aging or environmental factors such as UV exposure and air pollution. As oxidative cues are often present in systemic circulation, the blood-brain barrier (BBB) plays a key role in mediating the effect of these cues on brain dysfunction. Therefore, oxidative damage and disruption of the BBB is an emergent focus of neurodegenerative disease etiology and progression. We assessed barrier dysfunction in response to chronic and acute oxidative stress in 2D and 3D in vitro models of the BBB with human iPSC-derived brain microvascular endothelial-like cells (iBMECs). We first established doses of hydrogen peroxide to induce chronic damage (modeling aging and neurodegenerative disease) and acute damage (modeling the response to traumatic brain injury) by assessing barrier function via transendothelial electrical resistance in 2D iBMEC monolayers and permeability and monolayer integrity in 3D tissue-engineered iBMEC microvessels. Following application of these chronic and acute doses in our in vitro models, we found local, discrete structural changes were the most prevalent responses (rather than global barrier loss). Additionally, we validated unique functional changes in response to oxidative stress, including dysfunctional cell turnover dynamics and immune cell adhesion that were consistent with changes in gene expression.

lncRNA7 and lncRNA2 modulate cell wall defense genes to regulate cotton resistance to Verticillium wilt

In plants, long noncoding RNAs (lncRNAs) regulate disease resistance against fungi and other pathogens. However, the specific mechanism behind this regulation remains unclear. In this study, we identified disease resistance-related lncRNAs as well as their regulating genes and assessed their functions by infection of cotton (Gossypium) chromosome segment substitution lines with Verticillium dahliae. Our results demonstrated that lncRNA7 and its regulating gene Pectin methylesterase inhibitor 13 (GbPMEI13) positively regulated disease resistance via the silencing approach, while ectopic overexpression of GbPMEI13 in Arabidopsis (Arabidopsis thaliana) promoted growth and enhanced resistance to V. dahliae. In contrast, lncRNA2 and its regulating gene Polygalacturonase 12 (GbPG12) negatively regulated resistance to V. dahliae. We further found that fungal disease-related agents, including the pectin-derived oligogalacturonide (OG), could downregulate the expression of lncRNA2 and GbPG12, leading to pectin accumulation. Conversely, OG upregulated the expression of lncRNA7, which encodes a plant peptide phytosulfokine (PSK-α), which was confirmed by lncRNA7 overexpression and Ultra Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS) experiments. We showed that PSK-α promoted 3-Indoleacetic acid (IAA) accumulation and activated GbPMEI13 expression through Auxin Response Factor 5. Since it is an inhibitor of pectin methylesterase (PME), GbPMEI13 promotes pectin methylation and therefore increases the resistance to V. dahliae. Consistently, we also demonstrated that GbPMEI13 inhibits the mycelial growth and spore germination of V. dahliae in vitro. In this study, we demonstrated that lncRNA7, lncRNA2, and their regulating genes modulate cell wall defense against V. dahliae via auxin-mediated signaling, providing a strategy for cotton breeding.

Genome-Wide Identification and Characterization of the CC-NBS-LRR Gene Family in Cucumber (Cucumis sativus L.)

The NBS-LRR (NLR) gene family plays a pivotal role in regulating disease defense response in plants. Cucumber is one of the most important vegetable crops in the world, and various plant diseases, including powdery mildew (PM), cause severe losses in both cucumber productivity and quality annually. To characterize and understand the role of the CC-NBS-LRR(CNL) family of genes in disease defense response in cucumber plants, we performed bioinformatical analysis to characterize these genes systematically. We identified 33 members of the CNL gene family in cucumber plants, and they are distributed on each chromosome with chromosome 4 harboring the largest cluster of five different genes. The corresponding CNL family member varies in the number of amino acids and exons, molecular weight, theoretical isoelectric point (pI) and subcellular localization. Cis-acting element analysis of the CNL genes reveals the presence of multiple phytohormone, abiotic and biotic responsive elements in their promoters, suggesting that these genes might be responsive to plant hormones and stress. Phylogenetic and synteny analysis indicated that the CNL proteins are conserved evolutionarily in different plant species, and they can be divided into four subfamilies based on their conserved domains. MEME analysis and multiple sequence alignment showed that conserved motifs exist in the sequence of CNLs. Further DNA sequence analysis suggests that CsCNL genes might be subject to the regulation of different miRNAs upon PM infection. By mining available RNA-seq data followed by real-time quantitative PCR (qRT-PCR) analysis, we characterized expression patterns of the CNL genes, and found that those genes exhibit a temporospatial expression pattern, and their expression is also responsive to PM infection, ethylene, salicylic acid, and methyl jasmonate treatment in cucumber plants. Finally, the CNL genes targeted by miRNAs were predicted in cucumber plants. Our results in this study provided some basic information for further study of the functions of the CNL gene family in cucumber plants.

Role of phasiRNAs in plant-pathogen interactions: molecular perspectives and bioinformatics tools

The genome of an organism is regulated in concert with the organized action of various genetic regulators at different hierarchical levels. Small non-coding RNAs are one of these regulators, among which microRNAs (miRNAs), a distinguished sRNA group with decisive functions in the development, growth and stress-responsive activities of both plants as well as animals, are keenly explored over a good number of years. Recent studies in plants revealed that apart from the silencing activity exhibited by miRNAs on their targets, miRNAs of specific size and structural features can direct the phasing pattern of their target loci to form phased secondary small interfering RNAs (phasiRNAs). These trigger-miRNAs were identified to target both coding and long non-coding RNAs that act as potent phasiRNA precursors or PHAS loci. The phasiRNAs produced thereby exhibit a role in enhancing further downstream regulation either on their own precursors or on those transcripts that are distinct from their genetic source of origin. Hence, these tiny regulators can stimulate an elaborative cascade of interacting RNA networks via cis and trans-regulatory mechanisms. Our review focuses on the comprehensive understanding of phasiRNAs and their trigger miRNAs, by giving much emphasis on their role in the regulation of plant defense responses, together with a summary of the computational tools available for the prediction of the same.

Comparative analysis of herbivory responsive miRNAs to delineate pod borer (Helicoverpa armigera) resistance mechanisms in Cajanus cajan and its wild relative Cajanus scarabaeoides

Comparative analysis of herbivory responsive miRNAs between pod borer susceptible C. cajan and its resistant Crop Wild Relative (CWR) C. scarabaeoides revealed miRNA-based regulation of defense genes and plant-insect interactions. Gram pod borer (Helicoverpa armigera) is one of most devastating pests of pigeon pea (Cajanus cajan) worldwide, responsible for huge losses in crop productivity. The lack of genes conferring resistance to pod borer in pigeon pea has proven to be a bottleneck for its improvement. One of its CWR, C. scarabaeoides has demonstrated resistance to this pest and can be exploited for developing pest resistant crop varieties. Differences in expression patterns of herbivory responsive microRNAs in the susceptible C. cajan and resistant C. scarabaeoides after different time duration of pod borer infestation (2 h, 8 h and 18 h) were identified, characterized and functionally validated to understand their role in insect defense response. A total of 462 conserved and 449 novel miRNAs and 273 conserved and 185 novel miRNAs, were identified in C. cajan and C. scarabaeoides, respectively. Among the identified miRNAs, 65, 68 and 65 miRNAs were found to be differentially expressing between the C. scarabaeoides and C. cajan libraries 2 h, 8 h and 18 h post infestation, respectively. These miRNAs were found to target genes involved in a number of pathways contributing to defense and acquired resistance in C. scarabaeoides against pod borer, indicating miRNA-based regulation of defense pathways. Expression patterns of eight of these miRNAs were validated by qRT-PCR. This study provides novel insights into the miRNA-mediated plant-insect interactions and the mechanisms of regulatory pathways involved in insect defense. These findings can be utilized for further exploring the mechanism of herbivore defense in plant systems.

Transcriptome Responses of Wild Arachis to UV-C Exposure Reveal Genes Involved in General Plant Defense and Priming

Stress priming is an important strategy for enhancing plant defense capacity to deal with environmental challenges and involves reprogrammed transcriptional responses. Although ultraviolet (UV) light exposure is a widely adopted approach to elicit stress memory and tolerance in plants, the molecular mechanisms underlying UV-mediated plant priming tolerance are not fully understood. Here, we investigated the changes in the global transcriptome profile of wild Arachis stenosperma leaves in response to UV-C exposure. A total of 5751 differentially expressed genes (DEGs) were identified, with the majority associated with cell signaling, protein dynamics, hormonal and transcriptional regulation, and secondary metabolic pathways. The expression profiles of DEGs known as indicators of priming state, such as transcription factors, transcriptional regulators and protein kinases, were further characterized. A meta-analysis, followed by qRT-PCR validation, identified 18 metaDEGs as being commonly regulated in response to UV and other primary stresses. These genes are involved in secondary metabolism, basal immunity, cell wall structure and integrity, and may constitute important players in the general defense processes and establishment of a priming state in A. stenosperma. Our findings contribute to a better understanding of transcriptional dynamics involved in wild Arachis adaptation to stressful conditions of their natural habitats.

Novel insights into water-deficit-responsive mRNAs and lncRNAs during fiber development in Gossypium hirsutum

BACKGROUND

The fiber yield and quality of cotton are greatly and periodically affected by water deficit. However, the molecular mechanism of the water deficit response in cotton fiber cells has not been fully elucidated.

RESULTS

In this study, water deficit caused a significant reduction in fiber length, strength, and elongation rate but a dramatic increase in micronaire value. To explore genome-wide transcriptional changes, fibers from cotton plants subjected to water deficit (WD) and normal irrigation (NI) during fiber development were analyzed by transcriptome sequencing. Analysis showed that 3427 mRNAs and 1021 long noncoding RNAs (lncRNAs) from fibers were differentially expressed between WD and NI plants. The maximum number of differentially expressed genes (DEGs) and lncRNAs (DERs) was identified in fibers at the secondary cell wall biosynthesis stage, suggesting that this is a critical period in response to water deficit. Twelve genes in cotton fiber were differentially and persistently expressed at ≥ five time points, suggesting that these genes are involved in both fiber development and the water-deficit response and could potentially be used in breeding to improve cotton resistance to drought stress. A total of 540 DEGs were predicted to be potentially regulated by DERs by analysis of coexpression and genomic colocation, accounting for approximately 15.76% of all DEGs. Four DERs, potentially acting as target mimics for microRNAs (miRNAs), indirectly regulated their corresponding DEGs in response to water deficit.

CONCLUSIONS

This work provides a comprehensive transcriptome analysis of fiber cells and a set of protein-coding genes and lncRNAs implicated in the cotton response to water deficit, significantly affecting fiber quality during the fiber development stage.

Integration of Small RNA and Degradome Sequencing Reveals the Regulatory Network of Al-Induced Programmed Cell Death in Peanut

Peanut is one of the most important oil crops in the world. In China, the peanut is highly produced in its southern part, in which the arable land is dominated by acid soil. At present, miRNAs have been identified in stress response, but their roles and mechanisms are not clear, and no miRNA studies have been found related to aluminum (Al)-induced programmed cell death (PCD). In the present study, transcriptomics, sRNAs, and degradome analysis in the root tips of two peanut cultivars ZH2 (Al-sensitive, S) and 99-1507 (Al-tolerant, T) were carried out. Here, we generated a comprehensive resource focused on identifying key regulatory miRNA-target circuits that regulate PCD under Al stress. Through deep sequencing, 2284 miRNAs were identified and 147 miRNAs were differentially expressed under Al stress. Furthermore, 19237 target genes of 749 miRNAs were validated by degradome sequencing. GO and KEGG analyses of differential miRNA targets showed that the pathways of synthesis and degradation of ketone bodies, citrate cycle (TCA cycle), and peroxisome were responded to Al stress. The combined analysis of the degradome data sets revealed 89 miRNA-mRNA interactions that may regulate PCD under Al stress. Ubiquitination may be involved in Al-induced PCD in peanut. The regulatory networks were constructed based on the differentially expressed miRNAs and their targets related to PCD. Our results will provide a useful platform to research on PCD induced by Al and new insights into the genetic engineering for plant stress response.

Influence of virus-host interactions on plant response to abiotic stress

Environmental factors play a significant role in controlling growth, development and defense responses of plants. Changes in the abiotic environment not only significantly alter the physiological and molecular pathways in plants, but also result in attracting the insect pests that carry a payload of viruses. Invasion of plants by viruses triggers the RNA silencing based defense mechanism in plants. In counter defense the viruses have gained the ability to suppress the host RNA silencing activities. A new paradigm has emerged, with the recognition that plant viruses also have the intrinsic capacity to modulate host plant response to environmental cues, in an attempt to favour their own survival. Thus, plant-virus interactions provide an excellent system to understand the signals in crosstalk between biotic (virus) and abiotic stresses. In this review, we have summarized the basal plant defense responses to pathogen invasion while emphasizing on the role of RNA silencing as a front line of defense response to virus infection. The emerging knowledge indicates overlap between RNA silencing with the innate immune responses during antiviral defense. The suppressors of RNA silencing serve as Avr proteins, which can be recognized by the host R proteins. The defense signals also function in concert with the phytohormones to influence plant responses to abiotic stresses. The current evidence on the role of virus induced host tolerance to abiotic stresses is also discussed.

Molecular mechanism of modulating miR482b level in tomato with botrytis cinerea infection

BACKGROUND

Plant miRNAs are involved in the response to biotic and abiotic stresses by altering their expression levels, and they play an important role in the regulation of plant resistance to stress. However, the molecular mechanism that regulates the expression levels of miRNAs in plants with biotic and abiotic stress still needs to be explored. Previously, we found that the expression of the miR482 family was changed in tomato infected by Botrytis cinerea. In this study, we investigated and uncovered the mechanism underlying the response of miR482 to B. cinerea infection in tomato.

RESULTS

First, RT-qPCR was employed to detect the expression patterns of miR482b in tomato infected by B. cinerea, and results showed that miR482b primary transcripts (pri-miR482b) were up-regulated in B. cinerea-infected leaves, but the mature miR482b was down-regulated. Subsequently, we used rapid amplification cDNA end method to amplify the full-length of pri-miR482b. Result showed that the pri-miR482b had two isoforms, with the longer one (consisting 300 bp) having an extra fragment of 53 bp in the 3'-end compared with the shorter one. In vitro Dicer assay indicated that the longer isoform pri-miR482b-x1 had higher efficiency in the post-transcriptional splicing of miRNA than the shorter isoform pri-miR482b-x2. In addition, the transcription level of mature miR482b was much higher in transgenic Arabidopsis overexpressing pri-miR482b-x1 than that in OE pri-miR482b-x2 Arabidopsis. These results confirmed that this extra 53 bp in pri-miR482b-x1 might play a key role in the miR482b biogenesis of post-transcription processing.

CONCLUSIONS

Extra 53 bp in pri-miR482b-x1 enhanced miR482b biogenesis, which elevated the transcription level of miR482b. This study clarified the response of miR482 to B. cinerea infection in tomato, thereby helping us further understand the molecular mechanisms that regulate the expression levels of other miRNAs.

A New MiRNA MiRm0002 in Eggplant Participates in the Regulation of Defense Responses to Verticillium Wilt

Verticillium wilt is a major disease that severely affects eggplant production, and a new eggplant miRNA named miRm0002 identified through high-throughput sequencing was highly induced by Verticillium wilt infection. However, the miRm0002 function was still elusive. In this study, the sequence of the miRm0002 precursor was cloned and transgenic eggplants were constructed. In vivo inoculation test and in vitro fungistatic test showed that overexpressing miRm0002 lines were more resistant to Verticillium dahliae and inhibiting miRm0002 lines were more sensitive, compared to the wild-type (WT) control. Some physiological indicators were selected and the results showed that SOD, POD, and CAT activities were significantly increased in Verticillium wilt-infected overexpressing miRm0002 lines, indicating that the expression of miRm0002 activates the antioxidant system. QRT-PCR assay showed that the transcript expression of miRm0002 candidate target ARF8, a gene encoding auxin response factor was negatively related to miRm0002 in WT as well as transgenic eggplants. However, RLM-RACE mapping and degradome sequencing showed miRm0002 could not cleave the sequence of ARF8. Taken together, these data suggest that miRm0002 plays a positive role in the defense response of eggplant against Verticillium wilt.

Evolutionary and Characteristic Analysis of RING-DUF1117 E3 Ubiquitin Ligase Genes in Gossypium Discerning the Role of GhRDUF4D in Verticillium dahliae Resistance

Verticillium wilt, primarily induced by the soil-borne fungus Verticillium dahliae, is a serious threat to cotton fiber production. There are a large number of really interesting new gene (RING) domain-containing E3 ubiquitin ligases in Arabidopsis, of which three (At2g39720 (AtRHC2A), At3g46620 (AtRDUF1), and At5g59550 (AtRDUF2)) have a domain of unknown function (DUF) 1117 domain in their C-terminal regions. This study aimed to detect and characterize the RDUF members in cotton, to gain an insight into their roles in cotton’s adaptation to environmental stressors. In this study, a total of 6, 7, 14, and 14 RDUF (RING-DUF1117) genes were detected in Gossypium arboretum, G. raimondii, G. hirsutum, and G. barbadense, respectively. These RDUF genes were classified into three groups. The genes in each group were highly conserved based on gene structure and domain analysis. Gene duplication analysis revealed that segmental duplication occurred during cotton evolution. Expression analysis revealed that the GhRDUF genes were widely expressed during cotton growth and under abiotic stresses. Many cis-elements related to hormone response and environment stressors were identified in GhRDUF promoters. The predicted target miRNAs and transcription factors implied that GhRDUFs might be regulated by gra-miR482c, as well as by transcription factors, including MYB, C2H2, and Dof. The GhRDUF genes responded to cold, drought, and salt stress and were sensitive to jasmonic acid, salicylic acid, and ethylene signals. Meanwhile, GhRDUF4D expression levels were enhanced after V. dahliae infection. Subsequently, GhRDUF4D was verified by overexpression in Arabidopsis and virus-induced gene silencing treatment in upland cotton. We observed that V. dahliae resistance was significantly enhanced in transgenic Arabidopsis, and weakened in GhRDUF4D silenced plants. This study conducted a comprehensive analysis of the RDUF genes in Gossypium, hereby providing basic information for further functional studies.

Biotic stress-associated microRNA families in plants

Plants and animals utilize various regulatory mechanisms for control of gene expression during development in different tissues and cell types. About 30 years ago, a new mechanism of gene regulation, termed RNA interference (RNAi), was discovered and proved revolutionary for the mechanistic understanding of gene regulation. Noncoding RNAs, including short, 21-24 nucleotide (nt) long microRNAs (miRNAs), endogenously-generated from MIR genes, are key components of RNAi processes, by post-transcriptionally controlling transcripts with antisense complementarity through either translational repression or mRNA degradation. Since their discovery, important roles in regulation of ontogenetic development, cell differentiation, proliferation, and apoptosis in eukaryotes have been elucidated. In plants, miRNAs are known regulatory elements of basic endogenous functions and responses to the environmental stimuli. While the role of miRNAs in regulation of nutrient uptake, circadian clock and general response to abiotic stress is already well understood, a comprehensive understanding of their immune-regulatory roles in response to various biotic stress factors has not yet been achieved. This review summarizes the current understanding of the function of miRNAs and their targets in plants during interaction with microbial pathogens and symbionts. Additionally, we provide a consensus conclusion regarding the typical induction or repression response of conserved miRNA families to pathogenic and beneficial fungi, bacteria, and oomycetes, as well as an outlook of agronomic application of miRNAs in plants. Further investigation of plant miRNAs responsive to microbes, aided with novel sequencing and bioinformatics approaches for discovery and prediction in non-model organisms holds great potential for development of new forms of plant protection.

Transcriptomic analysis to reveal the differentially expressed miRNA targets and their miRNAs in response to Ralstonia solanacearum in ginger species

BACKGROUND

Bacterial wilt is the most devastating disease in ginger caused by Ralstonia solanacearum. Even though ginger (Zingiber officinale) and mango ginger (Curcuma amada) are from the same family Zingiberaceae, the latter is resistant to R. solanacearum infection. MicroRNAs have been identified in many crops which regulates plant-pathogen interaction, either through silencing genes or by blocking mRNA translation. However, miRNA's vital role and its targets in mango ginger in protecting bacterial wilt is not yet studied extensively. In the present study, using the "psRNATarget" server, we analyzed available ginger (susceptible) and mango ginger (resistant) transcriptome to delineate and compare the microRNAs (miRNA) and their target genes (miRTGs).

RESULTS

A total of 4736 and 4485 differential expressed miRTGs (DEmiRTGs) were identified in ginger and mango ginger, respectively, in response to R. solanacearum. Functional annotation results showed that mango ginger had higher enrichment than ginger in top enriched GO terms. Among the DEmiRTGs, 2105 were common in ginger and mango ginger. However, 2337 miRTGs were expressed only in mango ginger which includes 62 defence related and upregulated miRTGs. We also identified 213 miRTGs upregulated in mango ginger but downregulated in ginger, out of which 23 DEmiRTGS were defence response related. We selected nine miRNA/miRTGs pairs from the data set of common miRTGs of ginger and mango ginger and validated using qPCR.

CONCLUSIONS

Our data covered the expression information of 9221 miRTGs. We identified nine miRNA/miRTGs key candidate pairs in response to R. solanacearum infection in ginger. This is the first report of the integrated analysis of miRTGs and miRNAs in response to R. solanacearum infection among ginger species. This study is expected to deliver several insights in understanding the miRNA regulatory network in ginger and mango ginger response to bacterial wilt.

Investigation of long non-coding RNAs as regulatory players of grapevine response to powdery and downy mildew infection

BACKGROUND

Long non-coding RNAs (lncRNAs) are regulatory transcripts of length > 200 nt. Owing to the rapidly progressing RNA-sequencing technologies, lncRNAs are emerging as considerable nodes in the plant antifungal defense networks. Therefore, we investigated their role in Vitis vinifera (grapevine) in response to obligate biotrophic fungal phytopathogens, Erysiphe necator (powdery mildew, PM) and Plasmopara viticola (downy mildew, DM), which impose huge agro-economic burden on grape-growers worldwide.

RESULTS

Using computational approach based on RNA-seq data, 71 PM- and 83 DM-responsive V. vinifera lncRNAs were identified and comprehensively examined for their putative functional roles in plant defense response. V. vinifera protein coding sequences (CDS) were also profiled based on expression levels, and 1037 PM-responsive and 670 DM-responsive CDS were identified. Next, co-expression analysis-based functional annotation revealed their association with gene ontology (GO) terms for 'response to stress', 'response to biotic stimulus', 'immune system process', etc. Further investigation based on analysis of domains, enzyme classification, pathways enrichment, transcription factors (TFs), interactions with microRNAs (miRNAs), and real-time quantitative PCR of lncRNAs and co-expressing CDS pairs suggested their involvement in modulation of basal and specific defense responses such as: Ca²⁺-dependent signaling, cell wall reinforcement, reactive oxygen species metabolism, pathogenesis related proteins accumulation, phytohormonal signal transduction, and secondary metabolism.

CONCLUSIONS

Overall, the identified lncRNAs provide insights into the underlying intricacy of grapevine transcriptional reprogramming/post-transcriptional regulation to delay or seize the living cell-dependent pathogen growth. Therefore, in addition to defense-responsive genes such as TFs, the identified lncRNAs can be further examined and leveraged to candidates for biotechnological improvement/breeding to enhance fungal stress resistance in this susceptible fruit crop of economic and nutritional importance.

Role of miRNAs in the host-pathogen interaction between sugarcane and Colletotrichum falcatum, the red rot pathogen

KEY MESSAGE

Sugarcane microRNAs specifically involved during compatible and incompatible interactions with red rot pathogen Colletotrichum falcatum were identified. We have identified how the miRNAs regulate their gene targets and elaborated evidently on the underlying molecular mechanism of sugarcane defense response to C. falcatum for the first time. Resistance against the fungal pathogen Colletotrichum falcatum causing red rot is one of the most desirable traits for sustainable crop cultivation in sugarcane. To gain new insight into the host defense mechanism against C. falcatum, we studied the role of sugarcane microRNAs during compatible and incompatible interactions by adopting the NGS platform. We have sequenced a total of 80 miRNA families that comprised 980 miRNAs, and the putative targets of the miRNAs include transcription factors, membrane-bound proteins, glutamate receptor proteins, lignin biosynthesis proteins, signaling cascade proteins, transporter proteins, mitochondrial proteins, ER proteins, defense-related, stress response proteins, translational regulation proteins, cell proliferation, and ubiquitination proteins. Further, qRT-PCR analyses of 8 differentially regulated miRNAs and 26 gene transcript targets expression indicated that these miRNAs have a regulatory effect on the expression of respective target genes in most of the cases. Also, the results suggest that certain miRNA regulates many target genes that are involved in inciting early responses to the pathogen infection, signaling pathways, endoplasmic reticulum stress, and resistance gene activation through feedback response from various cellular processes during the compatible and incompatible interaction with the red rot pathogen C. falcatum. The present study revealed the role of sugarcane miRNAs and their target genes during sugarcane-C. falcatum interaction and provided new insight into the miRNA-mediated defense mechanism in sugarcane for the first time.

Differential miRNA profiles in South African cassava mosaic virus-infected cassava landraces reveal clues to susceptibility and tolerance to cassava mosaic disease

Specific miRNA families are involved in susceptibility or antiviral immunity in plants. Manihot esculenta Crantz (cassava) is a perennial plant that is an important food security crop in sub-Saharan Africa. Cassava is susceptible to several begomoviruses that cause cassava mosaic disease (CMD). In this study, we investigated the leaf miRNAome response in a tolerant (TME3) and susceptible (T200) cassava landrace challenged with South African cassava mosaic virus. RNAseq was performed on leaf samples at 12, 32 and 67 days post infection (dpi), representing early, symptomatic and late persistent stages of CMD infection. Significantly, distinct profiles of conserved miRNA family expression between the T200 and TME3 landraces at the three infection stages were observed. Notably at 12 days post SACMV infection, TME3 exhibited significant downregulation (log2fold<2.0) of 42 %, compared to 9% in T200, of the conserved miRNA families. This demonstrates an overall early response to SACMV in TME3 prior to symptom appearance not observed in T200, and expression of a large cohort of miRNA-regulated genes. Notably, at early infection, downregulation of mes-miR162 and 168 that target antiviral posttransriptional gene silencing (PTGS) regulators DCL1 and AGO1, respectively, was observed in TME3, and AGO1 and DCL1 expression was higher compared to T200 post infection. Early rapid responses prior to symptom development, including RNA silencing, may be key to establishing the tolerance/recovery phenotype exhibited by TME3 landrace later on at 67 dpi. At recovery, TME3 was hallmarked by a highly significant down-regulation of mes-miR167. MiR167 targets an auxin responsive factor which plays a role in auxin signaling and adaptive responses to stress, suggesting the importance of the auxin signaling in recovery of SACMV-induced symptoms. The gene targets of these miRNAs and their associated networks may provide clues to the molecular basis of CMD tolerance in perennial hosts such as cassava.

miRNA Mediated Regulation and Interaction between Plants and Pathogens

Plants have evolved diverse molecular mechanisms that enable them to respond to a wide range of pathogens. It has become clear that microRNAs, a class of short single-stranded RNA molecules that regulate gene expression at the transcriptional or post-translational level, play a crucial role in coordinating plant-pathogen interactions. Specifically, miRNAs have been shown to be involved in the regulation of phytohormone signals, reactive oxygen species, and NBS-LRR gene expression, thereby modulating the arms race between hosts and pathogens. Adding another level of complexity, it has recently been shown that specific lncRNAs (ceRNAs) can act as decoys that interact with and modulate the activity of miRNAs. Here we review recent findings regarding the roles of miRNA in plant defense, with a focus on the regulatory modes of miRNAs and their possible applications in breeding pathogen-resistance plants including crops and trees. Special emphasis is placed on discussing the role of miRNA in the arms race between hosts and pathogens, and the interaction between disease-related miRNAs and lncRNAs.

Characterization and Genetic Mapping of Black Root Rot Resistance in Gossypium arboreum L

Black root rot (BRR) is an economically important disease of cotton and other crops, especially in cooler regions with short growing seasons. Symptoms include black discoloration of the roots, reduced number of lateral roots and stunted or slow plant growth. The cultivated tetraploid Gossypium species are susceptible to BRR. Resistance to BRR was identified in G. arboreum accession BM13H and is associated with reduced and restricted hyphal growth and less sporulation. Transcriptome analysis indicates that BM13H responds to infection at early time points 2- and 3-days post-inoculation, but by day 5, few differentially expressed genes are observed between infected and uninfected roots. Inheritance of BM13H resistance to BRR was evaluated in an F₆ recombinant inbred population and shows a single semi-dominant locus conferring resistance that was fine mapped to a region on chromosome 1, containing ten genes including five putative resistance-like genes.

A Rice NBS-ARC Gene Conferring Quantitative Resistance to Bacterial Blight Is Regulated by a Pathogen Effector-Inducible miRNA

The bacterium Xanthomonas oryzae pv. Oryzae (Xoo) causes blight in rice worldwide, resulting in significant crop loss. However, no gene underlying a quantitative trait locus (QTL) for resistance against Xoo has been cloned yet. Here, we report the map-based cloning of a QTL, in which the NBS8R gene confers quantitative resistance to Xoo. NBS8R encodes an NB-ARC protein, which is involved in pathogen/microbe-associated molecular pattern-triggered immunity and whose expression is regulated by non-TAL effector XopQ-inducible Osa-miR1876 through DNA methylation. Sequence analysis of NBS8R in wild rice species and rice cultivars suggests that the Osa-miR1876 binding sites in the 5' UTR of NBS8R are inserted by chance and have undergone variations with Osa-miR1876 throughout evolution. The interaction between NBS8R and XopQ-inducible Osa-miR1876 is partially in keeping with the zigzag model, revealing that quantitative genes may also follow this model to control the innate immune response or basal disease resistance, and may prove valuable in utilizing the existing landraces that harbor the NBS8R gene but with no Osa-miR1876 binding site in rice breeding for bacterial blight resistance.