A Cotton Lignin Biosynthesis Gene, GhLAC4, Fine-Tuned by ghr-miR397 Modulates Plant Resistance Against Verticillium dahliae

The Analysis, Description, and Examination of the Maize LAC Gene Family's Reaction to Abiotic and Biotic Stress

Laccase (LAC) is a diverse group of genes found throughout the plant genome essential for plant growth and the response to stress by converting monolignin into intricate lignin formations. However, a comprehensive investigation of maize laccase has not yet been documented. A bioinformatics approach was utilized in this research to conduct a thorough examination of maize (Zea mays L.), resulting in the identification and categorization of 22 laccase genes (ZmLAC) into six subfamilies. The gene structure and motifs of each subgroup were largely consistent. The distribution of the 22 LAC genes was uneven among the maize chromosomes, with the exception of chromosome 9. The differentiation of the genes was based on fragment replication, and the differentiation time was about 33.37 million years ago. ZmLAC proteins are primarily acidic proteins. There are 18 cis-acting elements in the promoter sequences of the maize LAC gene family associated with growth and development, stress, hormones, light response, and stress response. The analysis of tissue-specific expression revealed a high expression of the maize LAC gene family prior to the V9 stage, with minimal expression at post-V9. Upon reviewing the RNA-seq information from the publicly available transcriptome, it was discovered that ZmLAC5, ZmLAC10, and ZmLAC17 exhibited significant expression levels when exposed to various biotic and abiotic stress factors, suggesting their crucial involvement in stress responses and potential value for further research. This study offers an understanding of the functions of the LAC genes in maize's response to biotic and abiotic stress, along with a theoretical basis for comprehending the molecular processes at play.

Modifying lignin: A promising strategy for plant disease control

Lignin is a complex polymer found in the cell walls of plants, providing structural support and protection against pathogens. By modifying lignin composition and structure, scientists aim to optimize plant defense responses and increase resistance to pathogens. This can be achieved through various genetic engineering techniques which involve manipulating the genes responsible for lignin synthesis. By either up regulating or down regulating specific genes, researchers can alter the lignin content, composition, or distribution in plant tissues. Reducing lignin content in specific tissues like leaves can improve the effectiveness of defense mechanisms by allowing for better penetration of antimicrobial compounds. Overall, Lignin modification through techniques has shown promising results in enhancing various plants resistance against pathogens. Furthermore, lignin modification can have additional benefits beyond pathogen resistance. It can improve biomass processing for biofuel production by reducing lignin recalcitrance, making the extraction of sugars from cellulose more efficient. The complexity of lignin biosynthesis and its interactions with other plant components make it a challenging target for modification. Additionally, the potential environmental impact and regulatory considerations associated with genetically modified organisms (GMOs) require careful evaluation. Ongoing research aims to further optimize this approach and develop sustainable solutions for crop protection.

The CsmiR397a-CsLAC17 module regulates lignin biosynthesis to balance the tenderness and gray blight resistance in young tea shoots

Lignin accumulation can enhance the disease resistance of young tea shoots (Camellia sinensis). It also greatly reduces their tenderness, which indirectly affects the quality and yield of tea. Therefore, the regulation of lignin biosynthesis appears to be an effective way to balance tenderness and disease resistance in young tea shoots. In this study, we identified a laccase gene, CsLAC17, that is induced during tenderness reduction and gray blight infection in young tea shoots. Overexpression of CsLAC17 significantly increased the lignin content in transgenic Arabidopsis, enhancing their resistance to gray blight and decreasing stem tenderness. In addition, we found that CsLAC17 was negatively regulated by the upstream CsmiR397a by 5'-RLM-RACE, dual-luciferase assay, and transient expression in young tea shoots. Interestingly, the expression of CsmiR397a was inhibited during tenderness reduction and gray blight infection of young tea shoots. Overexpression of CsmiR397a reduced lignin accumulation, resulting in decreased resistance to gray blight and increased stem tenderness in transgenic Arabidopsis. Furthermore, the transient overexpression of CsmiR397a and CsLAC17 in tea leaves directly confirms the function of the CsmiR397a-CsLAC17 module in lignin biosynthesis and its effect on disease resistance. These results suggest that the CsmiR397a-CsLAC17 module is involved in balancing tenderness and gray blight resistance in young tea shoots by regulating lignin biosynthesis.

A dual-subcellular localized β-glucosidase confers pathogen and insect resistance without a yield penalty in maize

Maize is one of the most important crops for food, cattle feed and energy production. However, maize is frequently attacked by various pathogens and pests, which pose a significant threat to maize yield and quality. Identification of quantitative trait loci and genes for resistance to pests will provide the basis for resistance breeding in maize. Here, a β-glucosidase ZmBGLU17 was identified as a resistance gene against Pythium aphanidermatum, one of the causal agents of corn stalk rot, by genome-wide association analysis. Genetic analysis showed that both structural variations at the promoter and a single nucleotide polymorphism at the fifth intron distinguish the two ZmBGLU17 alleles. The causative polymorphism near the GT-AG splice site activates cryptic alternative splicing and intron retention of ZmBGLU17 mRNA, leading to the downregulation of functional ZmBGLU17 transcripts. ZmBGLU17 localizes in both the extracellular matrix and vacuole and contribute to the accumulation of two defence metabolites lignin and DIMBOA. Silencing of ZmBGLU17 reduces maize resistance against P. aphanidermatum, while overexpression significantly enhances resistance of maize against both the oomycete pathogen P. aphanidermatum and the Asian corn borer Ostrinia furnacalis. Notably, ZmBGLU17 overexpression lines exhibited normal growth and yield phenotype in the field. Taken together, our findings reveal that the apoplastic and vacuolar localized ZmBGLU17 confers resistance to both pathogens and insect pests in maize without a yield penalty, by fine-tuning the accumulation of lignin and DIMBOA.

Genetic Mapping and Characterization of Verticillium Wilt Resistance in a Recombinant Inbred Population of Upland Cotton

Verticillium wilt (VW) is an important and widespread disease of cotton and once established is long-lived and difficult to manage. In Australia, the non-defoliating pathotype of Verticillium dahliae is the most common, and extremely virulent. Breeding cotton varieties with increased VW resistance is the most economical and effective method of controlling this disease and is greatly aided by understanding the genetics of resistance. This study aimed to investigate VW resistance in 240 F7 recombinant inbred lines (RIL) derived from a cross between MCU-5, which has good resistance, and Siokra 1-4, which is susceptible. Using a controlled environment bioassay, we found that resistance based on plant survival or shoot biomass was complex but with major contributions from chromosomes D03 and D09, with genomic prediction analysis estimating a prediction accuracy of 0.73 based on survival scores compared to 0.36 for shoot biomass. Transcriptome analysis of MCU-5 and Siokra 1-4 roots uninfected or infected with V. dahliae revealed that the two cultivars displayed very different root transcriptomes and responded differently to V. dahliae infection. Ninety-nine differentially expressed genes were located in the two mapped resistance regions and so are potential candidates for further identifying the genes responsible for VW resistance.

Harnessing the potential of non-coding RNA: An insight into its mechanism and interaction in plant biotic stress

Plants have developed diverse physical and chemical defence mechanisms to ensure their continued growth and well-being in challenging environments. Plants also have evolved intricate molecular mechanisms to regulate their responses to biotic stress. Non-coding RNA (ncRNA) plays a crucial role in this process that affects the expression or suppression of target transcripts. While there have been numerous reviews on the role of molecules in plant biotic stress, few of them specifically focus on how plant ncRNAs enhance resistance through various mechanisms against different pathogens. In this context, we explored the role of ncRNA in exhibiting responses to biotic stress endogenously as well as cross-kingdom regulation of transcript expression. Furthermore, we address the interplay between ncRNAs, which can act as suppressors, precursors, or regulators of other ncRNAs. We also delve into the regulation of ncRNAs in response to attacks from different organisms, such as bacteria, viruses, fungi, nematodes, oomycetes, and insects. Interestingly, we observed that diverse microorganisms interact with distinct ncRNAs. This intricacy leads us to conclude that each ncRNA serves a specific function in response to individual biotic stimuli. This deeper understanding of the molecular mechanisms involving ncRNAs in response to biotic stresses enhances our knowledge and provides valuable insights for future research in the field of ncRNA, ultimately leading to improvements in plant traits.

Emerging roles of plant microRNAs during Colletotrichum spp. infection

MAIN CONCLUSION

This review provides valuable insights into plant molecular regulatory mechanisms during fungus attacks, highlighting potential miRNA candidates for future disease management. Plant defense responses to biotic stress involve intricate regulatory mechanisms, including post-transcriptional regulation of genes mediated by microRNAs (miRNAs). These small RNAs play a vital role in the plant's innate immune system, defending against viral, bacterial, and fungal attacks. Among the plant pathogenic fungi, Colletotrichum spp. are notorious for causing anthracnose, a devastating disease affecting economically important crops worldwide. Understanding the molecular machinery underlying the plant immune response to Colletotrichum spp. is crucial for developing tools to reduce production losses. In this comprehensive review, we examine the current understanding of miRNAs associated with plant defense against Colletotrichum spp. We summarize the modulation patterns of miRNAs and their respective target genes. Depending on the function of their targets, miRNAs can either contribute to host resistance or susceptibility. We explore the multifaceted roles of miRNAs during Colletotrichum infection, including their involvement in R-gene-dependent immune system responses, hormone-dependent defense mechanisms, secondary metabolic pathways, methylation regulation, and biosynthesis of other classes of small RNAs. Furthermore, we employ an integrative approach to correlate the identified miRNAs with various strategies and distinct phases of fungal infection. This study provides valuable insights into the current understanding of plant miRNAs and their regulatory mechanisms during fungus attacks.

Genome-wide identification and expression patterns of the laccase gene family in response to kiwifruit bacterial canker infection

BACKGROUND

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease worldwide. Resistance genes that respond to Psa infection urgently need to be identified for controlling this disease. Laccase is mainly involved in the synthesis of lignin in the plant cell wall and plays a prominent role in plant growth and resistance to pathogen infection. However, the role of laccase in kiwifruit has not been reported, and whether laccase is pivotal in the response to Psa infection remains unclear.

RESULTS

We conducted a bioinformatics analysis to identify 55 laccase genes (AcLAC1-AcLAC55) in the kiwifruit genome. These genes were classified into five cluster groups (I-V) based on phylogenetic analysis, with cluster groups I and II having the highest number of members. Analysis of the exon-intron structure revealed that the number of exons varied from 1 to 8, with an average of 5 introns. Our evolutionary analysis indicated that fragment duplication played a key role in the expansion of kiwifruit laccase genes. Furthermore, evolutionary pressure analysis suggested that AcLAC genes were under purifying selection. We also performed a cis-acting element analysis and found that AcLAC genes contained multiple hormone (337) and stress signal (36) elements in their promoter regions. Additionally, we investigated the expression pattern of laccase genes in kiwifruit stems and leaves infected with Psa. Our findings revealed that laccase gene expression levels in the stems were higher than those in the leaves 5 days after inoculation with Psa. Notably, AcLAC2, AcLAC4, AcLAC17, AcLAC18, AcLAC26, and AcLAC42 showed significantly higher expression levels (p < 0.001) compared to the non-inoculated control (0 d), suggesting their potential role in resisting Psa infection. Moreover, our prediction indicated that 21 kiwifruit laccase genes are regulated by miRNA397, they could potentially act as negative regulators of lignin biosynthesis.

CONCLUSIONS

These results are valuable for further analysis of the resistance function and molecular mechanism of laccases in kiwifruit.

The PcMYB44-mediated miR397-PcLACs module regulates defence-induced lignification in pear resistance to fungal disease

Diseases caused by Alternaria alternata and Botryosphaeria dothidea diminish pear yield and quality, and restrict the pear agricultural industry. Lignification is a conserved mechanism for plant resistance against pathogen invasion. The regulatory mechanisms underlying defence-induced lignification in pear in response to fungal pathogen infection remain unknown. In this study, analysis of lignification level and lignin content in pear revealed that A. alternata and B. dothidea induced lignification, and transcriptomics showed that lignin biosynthesis was affected. To explore whether laccases (LACs) mediated by miR397 regulate lignification in pear, we investigated the role of PcmiR397 in repressing the expression of PcLACs using 5'-RNA ligase-mediated-RACE and co-transformation in tobacco. Opposite expression patterns for PcmiR397 and PcLAC target genes were observed in pear in response to pathogens. Transient transformation in pear demonstrated that silencing PcmiR397 and overexpressing a single PcLAC enhanced resistance to pathogens via lignin synthesis. To further reveal the mechanism underpinning the PcMIR397 response of pear to pathogens, the PcMIR397 promoter was analysed, and pMIR397-1039 was found to be inhibited by pathogen infection. The transcription factor PcMYB44 was up-regulated, and it bound to the PcMIR397 promoter and inhibited transcription following pathogen infection. The results demonstrate the role of PcmiR397-PcLACs in broad-spectrum resistance to fungal disease, and the potential role of PcMYB44 involved in the miR397-PcLAC module in regulating defence-induced lignification. The findings provide valuable candidate gene resources and guidance for molecular breeding to improve resistance to fungal disease in pear.

The cotton miR171a-SCL6 module mediates plant resistance through regulating GhPR1 expression

Plants have developed intricate defense mechanisms in response to fluctuating environmental cues, including the use of microRNA (miRNA) as post-transcriptional regulators. However, the specific mechanisms through which miRNA contributes to disease resistance remain largely elusive. While the miR171-SCLs have been investigated in an eclectic array of plants, there has been a notable scarcity of research specifically focused on cotton (Gossypium hirsutum). In our previous miRNA-sequencing analysis, we found that ghr-miR171a displayed a differential response to infections by Verticillium dahliae. In this study, we further investigated the function of the miR171a-SCL6 module in cotton during V. dahliae infection. The ghr-miR171a was confirmed to direct the cleavage of GhSCL6 mRNA in the post-transcriptional process, as evidenced by 5' RLM-RACE, β-glucuronidase (GUS) histochemical staining and enzyme activity assay. Interestingly, we found that overexpressing ghr-miR171a reduced cotton plants' resistance to V. dahliae, while suppressing ghr-miR171a increased the plants' defense capacity. The GhSCL6 protein, when fused with green fluorescent protein (GFP), localizes in the cell nucleus, indicating its potential role in gene regulation. This was further corroborated by yeast two-hybrid assays, which verified GhSCL6's transcriptional activation ability. Through quantitative reverse transcriptase PCR (qRT-PCR), luciferase (LUC) fluorescence, and yeast one-hybrid assays, we found that GhSCL6 binds to the GT-box element of the GhPR1 promoter, activating its expression and thereby enhancing plant disease resistance. Taken together, our findings demonstrate that the cotton miR171a-SCL6 module regulates Verticillium wilt resistance in plants through the post-transcriptional process. This insight may offer new perspectives for disease resistance strategies in cotton.

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.

The cotton miR530-SAP6 module activated by systemic acquired resistance mediates plant defense against Verticillium dahliae

Many cotton miRNAs in root responding to Verticillium dahliae infection have been identified. Conversely, the miRNAs in leaf distantly responding to this fungal infection from roots via systemic acquired resistance (SAR) remain to be explored. Here, we constructed two groups of leaf sRNA libraries in cotton treated with V. dahliae via root-dipped method at 7- and 10-day post inoculation. Analysis of high-throughput sRNA sequencing identified 75 known and 379 novel miRNAs, of which 41 miRNAs significantly differentially expressed in fungal treatment plant leaves compared to the mock treatment at two time points. Then we characterized the cotton miR530-SAP6 module as a representative in the distant response to V. dahliae infection in roots. Based on degradome data and a luciferase (LUC) fusion reporter analysis, ghr-miR530 directedly cleaved GhSAP6 mRNA during the post-transcriptional process. Silencing of ghr-miR530 increased plant defense to this fungus, while its overexpression attenuated plant resistance. In link with ghr-miR530 function, the knockdown of GhSAP6 also decreased the plant resistance, resulting from down-regulation of SA-relative gene expression including GhNPR1 and GhPR1. In all, these results demonstrated that there are numerous miRNAs in leaf distantly responding to V. dahliae infection in roots mediate plant immunity.

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.

Characterization of plant laccase genes and their functions

Laccase is a copper-containing polyphenol oxidase found in different organisms. The multigene family that encodes laccases is widely distributed in plant genomes. Plant laccases oxidize monolignols to produce lignin which is important for plant growth and stress responses. Industrial applications of fungal and bacterial laccases are extensively explored and addressed. Recently many studies have focused on the significance of plant laccase, particularly in crop yield, and its functions in different environmental conditions. This review summarizes the transcriptional and posttranscriptional regulation of plant laccase genes and their functions in plant growth and development. It especially describes the responses of laccase genes to various stresses and their contributions to plant biotic and abiotic stress resistance. In-depth explanations and scientific advances will serve as foundations for research into plant laccase genes' function, mechanism, and possible applications.

Recent progression and future perspectives in cotton genomic breeding

Upland cotton is an important global cash crop for its long seed fibers and high edible oil and protein content. Progress in cotton genomics promotes the advancement of cotton genetics, evolutionary studies, functional genetics, and breeding, and has ushered cotton research and breeding into a new era. Here, we summarize high-impact genomics studies for cotton from the last 10 years. The diploid Gossypium arboreum and allotetraploid Gossypium hirsutum are the main focus of most genetic and genomic studies. We next review recent progress in cotton molecular biology and genetics, which builds on cotton genome sequencing efforts, population studies, and functional genomics, to provide insights into the mechanisms shaping abiotic and biotic stress tolerance, plant architecture, seed oil content, and fiber development. We also suggest the application of novel technologies and strategies to facilitate genome-based crop breeding. Explosive growth in the amount of novel genomic data, identified genes, gene modules, and pathways is now enabling researchers to utilize multidisciplinary genomics-enabled breeding strategies to cultivate "super cotton", synergistically improving multiple traits. These strategies must rise to meet urgent demands for a sustainable cotton industry.

Induced defense strategies of plants against Ralstonia solanacearum

Plants respond to Ralstonia solanacearum infestation through two layers of immune system (PTI and ETI). This process involves the production of plant-induced resistance. Strategies for inducing resistance in plants include the formation of tyloses, gels, and callose and changes in the content of cell wall components such as cellulose, hemicellulose, pectin, lignin, and suberin in response to pathogen infestation. When R. solanacearum secrete cell wall degrading enzymes, plants also sense the status of cell wall fragments through the cell wall integrity (CWI) system, which activates deep-seated defense responses. In addition, plants also fight against R. solanacearum infestation by regulating the distribution of metabolic networks to increase the production of resistant metabolites and reduce the production of metabolites that are easily exploited by R. solanacearum. We review the strategies used by plants to induce resistance in response to R. solanacearum infestation. In particular, we highlight the importance of plant-induced physical and chemical defenses as well as cell wall defenses in the fight against R. solanacearum.

Multicopper oxidases GbAO and GbSKS are involved in the Verticillium dahliae resistance in Gossypium barbadense

Ascorbate oxidase (AO) and skewed5 (SKU5)-similar (SKS) proteins belong to the multicopper oxidase (MCO) family and play important roles in plants in response to environmental stress via modulation of oxidoreduction homeostasis. Currently, reports on the response of Gossypium barbadense MCO to Verticillium wilt (VW) caused by Verticillium dahliae are still limited. Herein, RNA sequencing of two G. barbadense cultivars of VW-resistant XH21 and VW-susceptible XH7 under V. dahliae treatment, combined with physiological and genetic analysis, was performed to analyze the function and mechanism of multicopper oxidases GbAO and GbSKS involved in V. dahliae resistance. The identified differentially expressed genes are mainly involved in the regulation of oxidoreduction reaction, and extracellular components and signaling. Interestingly, ascorbate oxidase family members were discovered as the most significantly upregulated genes after V. dahliae treatment, including GbAO3A/D, GbSKS3A/D, and GbSKS16A/D. H₂O₂ and Asc contents, especially reductive Asc in both XH21 and XH7, were shown to be increased. Silenced expression of respective GbAO3A/D, GbSKS3A/D, and GbSKS16A/D in virus-induced gene silencing (VIGS) cotton plants significantly decreased the resistance to V. dahliae, coupled with the reduced contents of pectin and lignin. Our results indicate that AO might be involved in cotton VW resistance via the regulation of cell wall components.

Modulation of lignin biosynthesis for drought tolerance in plants

Lignin is a complex polymer that is embedded in plant cell walls to provide physical support and water protection. For these reasons, the production of lignin is closely linked with plant adaptation to terrestrial regions. In response to developmental cues and external environmental conditions, plants use an elaborate regulatory network to determine the timing and location of lignin biosynthesis. In this review, we summarize the canonical lignin biosynthetic pathway and transcriptional regulatory network of lignin biosynthesis, consisting of NAC and MYB transcription factors, to explain how plants regulate lignin deposition under drought stress. Moreover, we discuss how the transcriptional network can be applied to the development of drought tolerant plants.

Identification of Competing Endogenous RNAs (ceRNAs) Network Associated with Drought Tolerance in Medicago truncatula with Rhizobium Symbiosis

Drought, bringing the risks of agricultural production losses, is becoming a globally environmental stress. Previous results suggested that legumes with nodules exhibited superior drought tolerance compared with the non-nodule group. To investigate the molecular mechanism of rhizobium symbiosis impacting drought tolerance, transcriptome and sRNAome sequencing were performed to identify the potential mRNA-miRNA-ncRNA dynamic network. Our results revealed that seedlings with active nodules exhibited enhanced drought tolerance by reserving energy, synthesizing N-glycans, and medicating systemic acquired resistance due to the early effects of symbiotic nitrogen fixation (SNF) triggered in contrast to the drought susceptible with inactive nodules. The improved drought tolerance might be involved in the decreased expression levels of miRNA such as mtr_miR169l-5p, mtr_miR398b, and mtr_miR398c and its target genes in seedlings with active nodules. Based on the negative expression pattern between miRNA and its target genes, we constructed an mRNA-miR169l-ncRNA ceRNA network. During severe drought stress, the lncRNA alternative splicings TCONS_00049507 and TCONS_00049510 competitively interacted with mtr_miR169l-5p, which upregulated the expression of NUCLEAR FACTOR-Y (NF-Y) transcription factor subfamily NF-YA genes MtNF-YA2 and MtNF-YA3 to regulate their downstream drought-response genes. Our results emphasized the importance of SNF plants affecting drought tolerance. In conclusion, our work provides insight into ceRNA involvement in rhizobium symbiosis contributing to drought tolerance and provides molecular evidence for future study.

Proteomic and metabolic disturbances in lignin-modified Brachypodium distachyon

Lignin biosynthesis begins with the deamination of phenylalanine and tyrosine (Tyr) as a key branch point between primary and secondary metabolism in land plants. Here, we used a systems biology approach to investigate the global metabolic responses to lignin pathway perturbations in the model grass Brachypodium distachyon. We identified the lignin biosynthetic protein families and found that ammonia-lyases (ALs) are among the most abundant proteins in lignifying tissues in grasses. Integrated metabolomic and proteomic data support a link between lignin biosynthesis and primary metabolism mediated by the ammonia released from ALs that is recycled for the synthesis of amino acids via glutamine. RNA interference knockdown of lignin genes confirmed that the route of the canonical pathway using shikimate ester intermediates is not essential for lignin formation in Brachypodium, and there is an alternative pathway from Tyr via sinapic acid for the synthesis of syringyl lignin involving yet uncharacterized enzymatic steps. Our findings support a model in which plant ALs play a central role in coordinating the allocation of carbon for lignin synthesis and the nitrogen available for plant growth. Collectively, these data also emphasize the value of integrative multiomic analyses to advance our understanding of plant metabolism.

Integrative Analysis of Expression Profiles of mRNA and MicroRNA Provides Insights of Cotton Response to Verticillium dahliae

Cotton Verticillium wilt, caused by the notorious fungal phytopathogen Verticillium dahliae (V. dahliae), is a destructive soil-borne vascular disease and severely decreases cotton yield and quality worldwide. Transcriptional and post-transcriptional regulation of genes responsive to V. dahliae are crucial for V. dahliae tolerance in plants. However, the specific microRNAs (miRNAs) and the miRNA/target gene crosstalk involved in cotton resistance to Verticillium wilt remain largely limited. To investigate the roles of regulatory RNAs under V. dahliae induction in upland cotton, mRNA and small RNA libraries were constructed from mocked and infected roots of two upland cotton cultivars with the V. dahliae-sensitive cultivar Jimian 11 (J11) and the V. dahliae-tolerant cultivar Zhongzhimian 2 (Z2). A comparative transcriptome analysis revealed 8330 transcripts were differentially expressed under V. dahliae stress and associated with several specific biological processes. Moreover, small RNA sequencing identified a total of 383 miRNAs, including 330 unique conserved miRNAs and 53 novel miRNAs. Analysis of the regulatory network involved in the response to V. dahliae stress revealed 31 differentially expressed miRNA−mRNA pairs, and the up-regulation of GhmiR395 and down-regulation of GhmiR165 were possibly involved in the response to V. dahliae by regulating sulfur assimilation through the GhmiR395-APS1/3 module and the establishment of the vascular pattern and secondary cell wall formation through GhmiR165-REV module, respectively. The integrative analysis of mRNA and miRNA expression profiles from upland cotton lays the foundation for further investigation of regulatory mechanisms of resistance to Verticillium wilt in cotton and other crops.