TaADF4, an actin-depolymerizing factor from wheat, is required for resistance to the stripe rust pathogen Puccinia striiformis f. sp. tritici

ZmADF5, a Maize Actin-Depolymerizing Factor Conferring Enhanced Drought Tolerance in Maize

Drought stress is seriously affecting the growth and production of crops, especially when agricultural irrigation still remains quantitatively restricted in some arid and semi-arid areas. The identification of drought-tolerant genes is important for improving the adaptability of maize under stress. Here, we found that a new member of the actin-depolymerizing factor (ADF) family; the ZmADF5 gene was tightly linked with a consensus drought-tolerant quantitative trait locus, and the significantly associated signals were detected through genome wide association analysis. ZmADF5 expression could be induced by osmotic stress and the application of exogenous abscisic acid. Its overexpression in Arabidopsis and maize helped plants to keep a higher survival rate after water-deficit stress, which reduced the stomatal aperture and the water-loss rate, as well as improved clearance of reactive oxygen species. Moreover, seventeen differentially expressed genes were identified as regulated by both drought stress and ZmADF5, four of which were involved in the ABA-dependent drought stress response. ZmADF5-overexpressing plants were also identified as sensitive to ABA during the seed germination and seedling stages. These results suggested that ZmADF5 played an important role in the response to drought stress.

The Wheat Annexin TaAnn12 Plays Positive Roles in Plant Disease Resistance by Regulating the Accumulation of Reactive Oxygen Species and Callose

(1) Annexins are proteins that bind phospholipids and calcium ions in cell membranes and mediate signal transduction between Ca2+ and cell membranes. They play key roles in plant immunity. (2) In this study, virus mediated gene silencing and the heterologous overexpression of TaAnn12 in Arabidopsis thaliana Col-0 trials were used to determine whether the wheat annexin TaAnn12 plays a positive role in plant disease resistance. (3) During the incompatible interaction between wheat cv. Suwon 11 and the Puccinia striiformis f. sp. tritici (Pst) race CYR23, the expression of TaAnn12 was significantly upregulated at 24 h post inoculation (hpi). Silencing TaAnn12 in wheat enhanced the susceptibility to Pst. The salicylic acid hormone contents in the TaAnn12-silenced plants were significantly reduced. The overexpression of TaAnn12 in A. thaliana significantly increased resistance to Pseudomonas syringae pv. tomato DC3000, and the symptoms of the wild-type plants were more serious than those of the transgenic plants; the amounts of bacteria were significantly lower than those in the control group, the accumulation of Reactive Oxygen Species (ROS)and callose deposition increased, and the expression of resistance-related genes (AtPR1, AtPR2, and AtPR5) significantly increased. (4) Our results suggest that wheat TaAnn12 resisted the invasion of pathogens by inducing the production and accumulation of ROS and callose.

Research progress on the roles of actin-depolymerizing factor in plant stress responses

Actin-depolymerizing factors (ADFs) are highly conserved small-molecule actin-binding proteins found throughout eukaryotic cells. In land plants, ADFs form a small gene family that displays functional redundancy despite variations among its individual members. ADF can bind to actin monomers or polymerized microfilaments and regulate dynamic changes in the cytoskeletal framework through specialized biochemical activities, such as severing, depolymerizing, and bundling. The involvement of ADFs in modulating the microfilaments' dynamic changes has significant implications for various physiological processes, including plant growth, development, and stress response. The current body of research has greatly advanced our comprehension of the involvement of ADFs in the regulation of plant responses to both biotic and abiotic stresses, particularly with respect to the molecular regulatory mechanisms that govern ADF activity during the transmission of stress signals. Stress has the capacity to directly modify the transcription levels of ADF genes, as well as indirectly regulate their expression through transcription factors such as MYB, C-repeat binding factors, ABF, and 14-3-3 proteins. Furthermore, apart from their role in regulating actin dynamics, ADFs possess the ability to modulate the stress response by influencing downstream genes associated with pathogen resistance and abiotic stress response. This paper provides a comprehensive overview of the current advancements in plant ADF gene research and suggests that the identification of plant ADF family genes across a broader spectrum, thorough analysis of ADF gene regulation in stress resistance of plants, and manipulation of ADF genes through genome-editing techniques to enhance plant stress resistance are crucial avenues for future investigation in this field.

Arabidopsis thaliana Subclass I ACTIN DEPOLYMERIZING FACTORs Regulate Nuclear Organization and Gene Expression

ACTIN DEPOLYMERIZING FACTOR (ADF) is a conserved protein that regulates the organization and dynamics of actin microfilaments. Eleven ADFs in the Arabidopsis thaliana genome are grouped into four subclasses, and subclass I ADFs, ADF1-4, are all expressed throughout the plant. Previously, we showed that subclass I ADFs function in the regulation of the response against powdery mildew fungus as well as in the regulation of cell size and endoreplication. Here, we report a new role of subclass I ADFs in the regulation of nuclear organization and gene expression. Through microscopic observation of epidermal cells in mature leaves, we found that the size of chromocenters in both adf4 and transgenic lines where expression of subclass I ADFs is downregulated (ADF1-4Ri) was reduced compared with that of wild-type Col-0. Arabidopsis thaliana possesses eight ACTIN (ACT) genes, among which ACT2, -7 and -8 are expressed in vegetative organs. The chromocenter size in act7, but not in the act2/8 double mutant, was enlarged compared with that in Col-0. Microarray analysis revealed that 1,818 genes were differentially expressed in adf4 and ADF1-4Ri. In particular, expression of 22 nucleotide-binding leucine-rich repeat genes, which are involved in effector-triggered plant immunity, was reduced in adf4 and ADF1-4Ri. qRT-PCR confirmed the altered expressions shown with microarray analysis. Overall, these results suggest that ADF regulates various aspects of plant physiology through its role in regulation of nuclear organization and gene expression. The mechanism how ADF and ACT regulate nuclear organization and gene expression is discussed.

Actin-Depolymerizing Factor Gene Family Analysis Revealed That CsADF4 Increased the Sensitivity of Sweet Orange to Bacterial Pathogens

The actin-depolymerizing factor (ADF) gene family regulates changes in actin. However, the entire ADF family in the sweet orange Citrus sinensis has not been systematically identified, and their expressions in different organs and biotic stress have not been determined. In this study, through phylogenetic analysis of the sweet orange ADF gene family, seven CsADFs were found to be highly conserved and sparsely distributed across the four chromosomes. Analysis of the cis-regulatory elements in the promoter region showed that the CsADF gene had the potential to impact the development of sweet oranges under biotic or abiotic stress. Quantitative fluorescence analysis was then performed. Seven CsADFs were differentially expressed against the invasion of Xcc and CLas pathogens. It is worth noting that the expression of CsADF4 was significantly up-regulated at 4 days post-infection. Subcellular localization results showed that CsADF4 was localized in both the nucleus and the cytoplasm. Overexpression of CsADF4 enhanced the sensitivity of sweet orange leaves to Xcc. These results suggest that CsADFs may regulate the interaction of C. sinensis and bacterial pathogens, providing a way to further explore the function and mechanisms of ADF in the sweet orange.

Genome-wide identification of actin-depolymerizing factor gene family and their expression patterns under various abiotic stresses in soybean (Glycine max)

The actin-depolymerizing factor (ADF) encoded by a family of genes is highly conserved among eukaryotes and plays critical roles in the various processes of plant growth, development, and stress responses via the remodeling of the architecture of the actin cytoskeleton. However, the ADF family and the encoded proteins in soybean (Glycine max) have not yet been systematically investigated. In this study, 18 GmADF genes (GmADF1 - GmADF18) were identified in the soybean genome and were mapped to 14 different chromosomes. Phylogenetic analysis classified them into four groups, which was confirmed by their structure and the distribution of conserved motifs in the encoded proteins. Additionally, 29 paralogous gene pairs were identified in the GmADF family, and analysis of their Ka/Ks ratios indicated their purity-based selection during the evolutionary expansion of the soybean genome. The analysis of the expression profiles based on the RNA-seq and qRT-PCR data indicated that GmADFs were diversely expressed in different organs and tissues, with most of them responding actively to drought- and salt-induced stresses, suggesting the critical roles played by them in various biological processes. Overall, our study shows that GmADF genes may play a crucial role in response to various abiotic stresses in soybean, and the highly inducible candidate genes could be used for further functional studies and molecular breeding in soybean.

VILLIN2 regulates cotton defense against Verticillium dahliae by modulating actin cytoskeleton remodeling

The active structural change of actin cytoskeleton is a general host response upon pathogen attack. This study characterized the function of the cotton (Gossypium hirsutum) actin-binding protein VILLIN2 (GhVLN2) in host defense against the soilborne fungus Verticillium dahliae. Biochemical analysis demonstrated that GhVLN2 possessed actin-binding, -bundling, and -severing activities. A low concentration of GhVLN2 could shift its activity from actin bundling to actin severing in the presence of Ca2+. Knockdown of GhVLN2 expression by virus-induced gene silencing reduced the extent of actin filament bundling and interfered with the growth of cotton plants, resulting in the formation of twisted organs and brittle stems with a decreased cellulose content of the cell wall. Upon V. dahliae infection, the expression of GhVLN2 was downregulated in root cells, and silencing of GhVLN2 enhanced the disease tolerance of cotton plants. The actin bundles were less abundant in root cells of GhVLN2-silenced plants than in control plants. However, upon infection by V. dahliae, the number of actin filaments and bundles in the cells of GhVLN2-silenced plants was raised to a comparable level as those in control plants, with the dynamic remodeling of the actin cytoskeleton appearing several hours in advance. GhVLN2-silenced plants exhibited a higher incidence of actin filament cleavage in the presence of Ca2+, suggesting that pathogen-responsive downregulation of GhVLN2 could activate its actin-severing activity. These data indicate that the regulated expression and functional shift of GhVLN2 contribute to modulating the dynamic remodeling of the actin cytoskeleton in host immune responses against V. dahliae.

Burkholderia gladioli strain KJ-34 exhibits broad-spectrum antifungal activity

INTRODUCTION

Plant pathogens are one of the major constraints on worldwide food production. The antibiotic properties of microbes identified as effective in managing plant pathogens are well documented.

METHODS

Here, we used antagonism experiments and untargeted metabolomics to isolate the potentially antifungal molecules produced by KJ-34.

RESULTS

KJ-34 is a potential biocontrol bacterium isolated from the rhizosphere soil of rice and can fight multiple fungal pathogens (i.e. Ustilaginoidea virens, Alternaria solani, Fusarium oxysporum, Phytophthora capsica, Corynespora cassiicola). The favoured fermentation conditions are determined and the fermentation broth treatment can significantly inhibit the infection of Magnaporthe oryzae and Botryis cinerea. The fermentation broth suppression ratio is 75% and 82%, respectively. Fermentation broth treatment disrupted the spore germination and led to malformation of hyphae. Additionally, we found that the molecular weight of antifungal products were less than 1000 Da through semipermeable membranes on solid medium assay. To search the potentially antifungal molecules that produce by KJ-34, we used comparative and bioinformatics analyses of fermentation broth before and after optimization by mass spectrometry. Untargeted metabolomics analyses are presumed to have a library of antifungal agents including benzoylstaurosporine, morellin and scopolamine.

DISCUSSION

These results suggest that KJ-34 produced various biological control agents to suppress multiple phytopathogenic fungi and showed a strong potential in the ecological technologies of prevention and protection.

Live-Cell Imaging of Cytoskeletal Responses and Trafficking During Fungal Elicitation

Understanding the mechanisms driving plant defense responses holds the promise to provide new means to reinforce plant defense both through agrochemicals and targeted genetic improvement. The capability to quantify impacts of phytopathogens on subcellular dynamics is particularly important when elucidating the role of specific virulence mechanisms that make contributions toward infection success but do not individually alter disease outcome. Acquiring these data requires an investigator to achieve the successful handling of both plant and microbe prior to observation and an appreciation of the challenges in acquiring images under these conditions. In this chapter we describe a protocol to support the observation of cytoskeletal dynamics surrounding sites of fungal interaction, specifically the powdery mildew Blumeria graminis f.sp. hordei on the surface of Arabidopsis thaliana. Furthermore, we also describe a procedure to expose etiolated (dark-grown) hypocotyls to a molecular pattern to activate defense responses in the absence of a phytopathogen with the aim of observing localized actin-dependent trafficking.

The Cytoskeleton in Plant Immunity: Dynamics, Regulation, and Function

The plant cytoskeleton, consisting of actin filaments and microtubules, is a highly dynamic filamentous framework involved in plant growth, development, and stress responses. Recently, research has demonstrated that the plant cytoskeleton undergoes rapid remodeling upon sensing pathogen attacks, coordinating the formation of microdomain immune complexes, the dynamic and turnover of pattern-recognizing receptors (PRRs), the movement and aggregation of organelles, and the transportation of defense compounds, thus serving as an important platform for responding to pathogen infections. Meanwhile, pathogens produce effectors targeting the cytoskeleton to achieve pathogenicity. Recent findings have uncovered several cytoskeleton-associated proteins mediating cytoskeletal remodeling and defense signaling. Furthermore, the reorganization of the actin cytoskeleton is revealed to further feedback-regulate reactive oxygen species (ROS) production and trigger salicylic acid (SA) signaling, suggesting an extremely complex role of the cytoskeleton in plant immunity. Here, we describe recent advances in understanding the host cytoskeleton dynamics upon sensing pathogens and summarize the effectors that target the cytoskeleton. We highlight advances in the regulation of cytoskeletal remodeling associated with the defense response and assess the important function of the rearrangement of the cytoskeleton in the immune response. Finally, we propose suggestions for future research in this area.

Potential Targets for CRISPR/Cas Knockdowns to Enhance Genetic Resistance Against Some Diseases in Wheat (Triticum aestivum L.)

Wheat is one of the most important food crops worldwide. Even though wheat yields have increased considerably in recent years, future wheat production is predicted to face enormous challenges due to global climate change and new versions of diseases. CRISPR/Cas technology is a clean gene technology and can be efficiently used to target genes prone to biotic stress in wheat genome. Herein, the published research papers reporting the genetic factors corresponding to stripe rust, leaf rust, stem rust, powdery mildew, fusarium head blight and some insect pests were critically reviewed to identify negative genetic factors (Susceptible genes) in bread wheat. Out of all reported genetic factors related to these disease, 33 genetic factors (S genes) were found as negative regulators implying that their down-regulation, deletion or silencing improved disease tolerance/resistance. The results of the published studies provided the concept of proof that these 33 genetic factors are potential targets for CRISPR/Cas knockdowns to improve genetic tolerance/resistance against these diseases in wheat. The sequences of the 33 genes were retrieved and re-mapped on the latest wheat reference genome IWGSC RefSeq v2.1. Phylogenetic analysis revealed that pathogens causing the same type of disease had some common conserved motifs and were closely related. Considering the significance of these disease on wheat yield, the S genes identified in this study are suggested to be disrupted using CRISPR/Cas system in wheat. The knockdown mutants of these S genes will add to genetic resources for improving biotic stress resistance in wheat crop.

GhADF6-mediated actin reorganization is associated with defence against Verticillium dahliae infection in cotton

Several studies have revealed that actin depolymerizing factors (ADFs) participate in plant defence responses; however, the functional mechanisms appear intricate and need further exploration. In this study, we identified an ADF6 gene in upland cotton (designated as GhADF6) that is evidently involved in cotton's response to the fungal pathogen Verticillium dahliae. GhADF6 binds to actin filaments and possesses actin severing and depolymerizing activities in vitro and in vivo. When cotton root (the site of the fungus invasion) was inoculated with the pathogen, the expression of GhADF6 was markedly down-regulated in the epidermal cells. By virus-induced gene silencing analysis, the down-regulation of GhADF6 expression rendered the cotton plants tolerant to V. dahliae infection. Accordingly, the abundance of actin filaments and bundles in the root cells was significantly higher than that in the control plant, which phenocopied that of the V. dahliae-challenged wild-type cotton plant. Altogether, our results provide evidence that an increase in filament actin (F-actin) abundance as well as dynamic actin remodelling are required for plant defence against the invading pathogen, which are likely to be fulfilled by the coordinated expressional regulation of the actin-binding proteins, including ADF.

Biostimulant impacts of Glutacetine® and derived formulations (VNT1 and VNT4) on the bread wheat grain proteome

Nitrogen (N) fertilizer is essential to ensure grain yield and quality in bread wheat. Improving N use efficiency is therefore crucial for wheat grain protein quality. In the present work, we analysed the effects on the winter wheat grain proteome of biostimulants containing Glutacetine® or two derived formulations (VNT1 and 4) when mixed with urea-ammonium-nitrate fertilizer. A large-scale quantitative proteomics analysis of two wheat flour fractions produced a dataset of 4369 identified proteins. Quantitative analysis revealed 9, 39 and 96 proteins with a significant change in abundance after Glutacetine®, VNT1 and VNT4 treatments, respectively, with a common set of 11 proteins that were affected by two different biostimulants. The major effects impacted proteins involved in (i) protein synthesis regulation (mainly ribosomal and binding proteins), (ii) defence and responses to stresses (including chitin-binding protein, heat shock 70 kDa protein 1 and glutathione S-transferase proteins), (iii) storage functions related to gluten protein alpha-gliadins and starch synthase and (iv) seed development with proteins implicated in protease activity, energy machinery, and the C and N metabolism pathways. Altogether, our study showed that Glutacetine®, VNT1 and VNT4 biostimulants positively affected protein composition related to grain quality. Data are available via ProteomeXchange with identifier PXD021513. SIGNIFICANCE: We performed a large-scale quantitative proteomics study of the total protein extracts from flour samples to determine the effect of Glutacetine®-based biostimulants treatment on the protein composition of bread wheat grain. To our knowledge, only a few studies in the literature have applied proteomic approaches to study bread wheat grains and in particular to investigate the effect of biostimulants on the grain proteome of this cereal crop. In addition, most approaches used fractional extraction of proteins to target reserve proteins followed electrophoresis which leads to low identification rate of proteins. We identified and quantified a large protein dataset of 4369 proteins and determined ontological class of proteins affected by biostimulants treatments. Our proteomics investigation revealed the important role of these new biostimulants in achieving significant changes in protein synthesis regulation, storage functions, protease activity, energy machinery, C and N metabolism pathways and responses to biotic and abiotic stresses in grain.

Wheat Thioredoxin (TaTrxh1) Associates With RD19-Like Cysteine Protease TaCP1 to Defend Against Stripe Rust Fungus Through Modulation of Programmed Cell Death

Thioredoxins (Trxs) function within the antioxidant network through modulation of one or more redox reactions involved in oxidative-stress signaling. Given their function in regulating cellular redox, Trx proteins also fulfill key roles in plant immune signaling. Here, TaTrxh1, encoding a subgroup h member of the Trx family, was identified and cloned in wheat (Triticum aestivum), which was rapidly induced by Puccinia striiformis f. sp. tritici invasion and salicylic acid (SA) treatment. Overexpression of TaTrxh1 in tobacco (Nicotiana benthamiana) induced programmed cell death. Silencing of TaTrxh1 in wheat enhanced susceptibility to P. striiformis f. sp. tritici in different aspects, including reactive oxygen species accumulation and pathogen-responsive or -related gene expression. Herein, we observed that the cellular concentration of SA was significantly reduced in TaTrxh1-silenced plants, indicating that TaTrxh1 possibly regulates wheat resistance to stripe rust through a SA-associated defense signaling pathway. Using a yeast two-hybrid screen to identify TaTrxh1-interacting partners, we further show that interaction with TaCP1 (a RD19-like cysteine protease) and subsequent silencing of TaCP1 reduced wheat resistance to P. striiformis f. sp. tritici. In total, the data presented herein demonstrate that TaTrxh1 enhances wheat resistance against P. striiformis f. sp. tritici via SA-dependent resistance signaling and that TaTrxh1 interaction with TaCP1 is required for wheat resistance to stripe rust.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Genome-Wide Identification and Low Temperature Responsive Pattern of Actin Depolymerizing Factor (ADF) Gene Family in Wheat (Triticum aestivum L.)

The actin depolymerizing factor (ADF) gene family, which is conserved in eukaryotes, is important for plant development, growth, and stress responses. Cold stress restricts wheat growth, development, and distribution. However, genome-wide identification and functional analysis of the ADF family in wheat is limited. Further, because of the promising role of ADF genes in cold response, there is need for an understanding of the function of this family on wheat under cold stress. In this study, 25 ADF genes (TaADFs) were identified in the wheat genome and they are distributed on 15 chromosomes. The TaADF gene structures, duplication events, encoded conversed motifs, and cis-acting elements were investigated. Expression profiles derived from RNA-seq data and real-time quantitative PCR analysis revealed the tissue- and temporal-specific TaADF expression patterns. In addition, the expression levels of TaADF13/16/17/18/20/21/22 were significantly affected by cold acclimation or freezing conditions. Overexpression of TaADF16 increased the freezing tolerance of transgenic Arabidopsis, possibly because of enhanced ROS scavenging and changes to the osmotic regulation in cells. The expression levels of seven cold-responsive genes were up-regulated in the transgenic Arabidopsis plants, regardless of whether the plants were exposed to low temperature. These findings provide fundamental information about the wheat ADF genes and may help to elucidate the regulatory effects of the encoded proteins on plant development and responses to low-temperature stress.

GhVLN4 is involved in multiple stress responses and required for resistance to Verticillium wilt

As structural and signaling platform in plant cell, the actin cytoskeleton is regulated by diverse actin binding proteins (ABPs). Villins are one type of major ABPs responsible for microfilament bundling, which have proved to play important roles in plant growth and development. However, the function of villins in stress tolerance is poorly understood. Here, we report the function of cotton GhVLN4 in Verticillium wilt resistance and abiotic stress tolerance. The expression of GhVLN4 was up-regulated by gibberellin, ethylene, ABA, salicylic acid, jasmonate, NaCl, PEG, and Verticillium dahliae treatment, suggesting the involvement of GhVLN4 in multiple stress and hormone responses and signaling. Virus-induced gene silencing GhVLN4 made cotton more susceptible to V. dahliae characterized by the preferential colonization and rapid growth of the fungus in both phloem and xylem of the infected stems. Arabidopsis overexpressing GhVLN4 exhibited higher resistance to V. dahliae, salt and drought than the wild-type plants. The enhanced resistance to V. dahliae is likely related to the upregulated components in SA signaling pathway; the improved tolerance to salt and drought is characterized by upregulation of the components both in ABA- related and ABA-independent signal pathways, along with altered stomatal aperture under drought. Our findings demonstrate that GhVLN4 may play important roles in regulating plant tolerance to both biotic and abiotic stresses.

Multidimensional analysis of actin depolymerising factor family in pigeon pea under different environmental stress revealed specific response genes in each subgroup

Actin depolymerising factor (ADF) is an actin binding protein that is ubiquitous in animal and plant cells. It plays an important role in plant growth and development, as well as resistance to biotic and abiotic stress. The research of plant ADF family has been restricted to Arabidopsis thaliana (L.) Heynh. and some herb crops, but no woody cash crops have been reported to date. All members of the Cajanus cajan (L.) Millsp. ADF (CcADF) family were identified from the pigeon pea genome, and distributed among the four subfamilies by phylogenetic analysis. CcADFs were relatively conservative in gene structure evolution, protein structure and functional expression, and different CcADFs showed specific expression patterns under different treatments. The expression characteristics of several key CcADFs were revealed by analysing the stress response pattern of CcADFs and the time series RNA-seq of aluminium stress. Among them, CcADF9 in the first subgroup specifically responded to aluminium stress in the roots; CcADF3 in the second subgroup intensively responded to fungal infection in the leaves; and CcADF2 in the fourth subgroup positively responded to various stress treatments in different tissues. This study extended the relationship between plant ADF family and aluminium tolerance, as well as adding to the understanding of CcADF family in woody crops.

Arabidopsis REM16 acts as a B3 domain transcription factor to promote flowering time via directly binding to the promoters of SOC1 and FT

Actin depolymerizing factor (ADF) is a key modulator for dynamic organization of actin cytoskeleton. Interestingly, it was found that the ADF1 gene silencing delays flowering, but its mechanism remains unclear. In this study, ADF1 was used as a bait to screen its interacting proteins by the yeast two-hybrid (Y2H) system. One of them, the REM16 transcription factor was identified. As one of the AP2/B3-like transcriptional factor family members, the REM16 contains two B3 domains and its transcript levels kept increasing during the floral transition stage. Overexpression of REM16 accelerates flowering while silencing of REM16 delays flowering. Gene expression analysis indicated that the key flowering activation genes such as CONSTANS (CO), FLOWERING LOCUS T (FT), LEAFY (LFY) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC1) were upregulated in the REM16 overexpression lines, while the transcription of the flowering suppression gene FLOWERING LOCUS C (FLC) was decreased. In contrast, the REM16 gene silencing lines contained lower transcript levels of the CO, FT, LFY and SOC1 but higher transcript levels of the FLC compared with the wild-type plants. It was proved that REM16 could directly bind to the promoter regions of SOC1 and FT by in vitro and in vivo assays. Genetic analysis supported that REM16 acts upstream of SOC1 and FT in flowering pathways. All these studies provided strong evidence demonstrating that REM16 promotes flowering by directly activating SOC1 and FT.

Linkage mapping and genome-wide association study reveals conservative QTL and candidate genes for Fusarium rot resistance in maize

BACKGROUND

Fusarium ear rot (FER) caused by Fusarium verticillioides is a major disease of maize that reduces grain yield and quality globally. However, there have been few reports of major loci for FER were verified and cloned.

RESULT

To gain a comprehensive understanding of the genetic basis of natural variation in FER resistance, a recombinant inbred lines (RIL) population and one panel of inbred lines were used to map quantitative trait loci (QTL) for resistance. As a result, a total of 10 QTL were identified by linkage mapping under four environments, which were located on six chromosomes and explained 1.0-7.1% of the phenotypic variation. Epistatic mapping detected four pairs of QTL that showed significant epistasis effects, explaining 2.1-3.0% of the phenotypic variation. Additionally, 18 single nucleotide polymorphisms (SNPs) were identified across the whole genome by genome-wide association study (GWAS) under five environments. Compared linkage and association mapping revealed five common intervals located on chromosomes 3, 4, and 5 associated with FER resistance, four of which were verified in different near-isogenic lines (NILs) populations. GWAS identified three candidate genes in these consistent intervals, which belonged to the Glutaredoxin protein family, actin-depolymerizing factors (ADFs), and AMP-binding proteins. In addition, two verified FER QTL regions were found consistent with Fusarium cob rot (FCR) and Fusarium seed rot (FSR).

CONCLUSIONS

These results revealed that multi pathways were involved in FER resistance, which was a complex trait that was controlled by multiple genes with minor effects, and provided important QTL and genes, which could be used in molecular breeding for resistance.

Genome-Wide Identification and Characterization of Actin-Depolymerizing Factor (ADF) Family Genes and Expression Analysis of Responses to Various Stresses in Zea Mays L

Actin-depolymerizing factor (ADF) is a small class of actin-binding proteins that regulates the dynamics of actin in cells. Moreover, it is well known that the plant ADF family plays key roles in growth, development and defense-related functions. Results: Thirteen maize (Zea mays L., ZmADFs) ADF genes were identified using Hidden Markov Model. Phylogenetic analysis indicated that the 36 identified ADF genes in Physcomitrella patens, Arabidopsis thaliana, Oryza sativa japonica, and Zea mays were clustered into five groups. Four pairs of segmental genes were found in the maize ADF gene family. The tissue-specific expression of ZmADFs and OsADFs was analyzed using microarray data obtained from the Maize and Rice eFP Browsers. Five ZmADFs (ZmADF1/2/7/12/13) from group V exhibited specifically high expression in tassel, pollen, and anther. The expression patterns of 13 ZmADFs in seedlings under five abiotic stresses were analyzed using qRT-PCR, and we found that the ADFs mainly responded to heat, salt, drought, and ABA. Conclusions: In our study, we identified ADF genes in maize and analyzed the gene structure and phylogenetic relationships. The results of expression analysis demonstrated that the expression level of ADF genes was diverse in various tissues and different stimuli, including abiotic and phytohormone stresses, indicating their different roles in plant growth, development, and response to external stimulus. This report extends our knowledge to understand the function of ADF genes in maize.

The tomato Arp2/3 complex is required for resistance to the powdery mildew fungus Oidium neolycopersici

The actin-related protein 2/3 complex (Arp2/3 complex), a key regulator of actin cytoskeletal dynamics, has been linked to multiple cellular processes, including those associated with response to stress. Herein, the Solanum habrochaites ARPC3 gene, encoding a subunit protein of the Arp2/3 complex, was identified and characterized. ShARPC3 encodes a 174-amino acid protein possessing a conserved P21-Arc domain. Silencing of ShARPC3 resulted in enhanced susceptibility to the powdery mildew pathogen Oidium neolycopersici (On-Lz), demonstrating a role for ShARPC3 in defence signalling. Interestingly, a loss of ShARPC3 coincided with enhanced susceptibility to On-Lz, a process that we hypothesize is the result of a block in the activity of SA-mediated defence signalling. Conversely, overexpression of ShARPC3 in Arabidopsis thaliana, followed by inoculation with On-Lz, showed enhanced resistance, including the rapid induction of hypersensitive cell death and the generation of reactive oxygen. Heterologous expression of ShARPC3 in the arc18 mutant of Saccharomyces cerevisiae (i.e., ∆arc18) resulted in complementation of stress-induced phenotypes, including high-temperature tolerance. Taken together, these data support a role for ShARPC3 in tomato through positive regulation of plant immunity in response to O. neolycopersici pathogenesis.

Battlefield Cytoskeleton: Turning the Tide on Plant Immunity

The plant immune system comprises a complex network of signaling processes, regulated not only by classically defined immune components (e.g., resistance genes) but also by a suite of developmental, environmental, abiotic, and biotic-associated factors. In total, it is the sum of these interactions-the connectivity to a seemingly endless array of environments-that ensures proper activation, and control, of a system that is responsible for cell surveillance and response to threats presented by invading pests and pathogens. Over the past decade, the field of plant pathology has witnessed the discovery of numerous points of convergence between immunity, growth, and development, as well as overlap with seemingly disparate processes such as those that underpin plant response to changes in the environment. Toward defining how immune signaling is regulated, recent studies have focused on dissecting the mechanisms that underpin receptor-ligand interactions, phospho-regulation of signaling cascades, and the modulation of host gene expression during infection. As one of the major regulators of these immune signaling cascades, the plant cytoskeleton is the stage from which immune-associated processes are mobilized and oriented and, in this role, it controls the movement of the organelles, proteins, and chemical signals that support plant defense signaling. In short, the cytoskeleton is the battlefield from which pathogens and plants volley virulence and resistance, transforming resistance to susceptibility. Herein, we discuss the role of the eukaryotic cytoskeleton as a platform for the function of the plant immune system.

Understanding Cytoskeletal Dynamics During the Plant Immune Response

The plant cytoskeleton is a dynamic framework of cytoplasmic filaments that rearranges as the needs of the cell change during growth and development. Incessant turnover mechanisms allow these networks to be rapidly redeployed in defense of host cytoplasm against microbial invaders. Both chemical and mechanical stimuli are recognized as danger signals to the plant, and these are perceived and transduced into cytoskeletal dynamics and architecture changes through a collection of well-recognized, previously characterized players. Recent advances in quantitative cell biology approaches, along with the powerful molecular genetics techniques associated with Arabidopsis, have uncovered two actin-binding proteins as key intermediaries in the immune response to phytopathogens and defense signaling. Certain bacterial phytopathogens have adapted to the cytoskeletal-based defense mechanism during the basal immune response and have evolved effector proteins that target actin filaments and microtubules to subvert transcriptional reprogramming, secretion of defense-related proteins, and cell wall-based defenses. In this review, we describe current knowledge about host cytoskeletal dynamics operating at the crossroads of the molecular and cellular arms race between microbes and plants.

Plant-microbe interactions: organelles and the cytoskeleton in action

Contents Summary 1012 I. Introduction 1012 II. The endomembrane system in plant-microbe interactions 1013 III. The cytoskeleton in plant-microbe interactions 1017 IV. Organelles in plant-microbe interactions 1019 V. Inter-organellar communication in plant-microbe interactions 1022 VI. Conclusions and prospects 1023 Acknowledgements 1024 References 1024 SUMMARY: Plants have evolved a multilayered immune system with well-orchestrated defense strategies against pathogen attack. Multiple immune signaling pathways, coordinated by several subcellular compartments and interactions between these compartments, play important roles in a successful immune response. Pathogens use various strategies to either directly attack the plant's immune system or to indirectly manipulate the physiological status of the plant to inhibit an immune response. Microscopy-based approaches have allowed the direct visualization of membrane trafficking events, cytoskeleton reorganization, subcellular dynamics and inter-organellar communication during the immune response. Here, we discuss the contributions of organelles and the cytoskeleton to the plant's defense response against microbial pathogens, as well as the mechanisms used by pathogens to target these compartments to overcome the plant's defense barrier.

TaARPC3, Contributes to Wheat Resistance against the Stripe Rust Fungus

The actin cytoskeleton participates in numerous cellular processes, including less-characterized processes, such as nuclear organization, chromatin remodeling, transcription, and signal transduction. As a key regulator of actin cytoskeletal dynamics, the actin related protein 2/3 complex (Arp2/3 complex) controls multiple developmental processes in a variety of tissues and cell types. To date, the role of the Arp2/3 complex in plant disease resistance signaling is largely unknown. Herein, we identified and characterized wheat ARPC3, TaARPC3, which encodes the C3 subunit of the Arp2/3 complex. Expression of TaARPC3 in the arc18 mutant of Saccharomyces cerevisiae Δarc18 resulted in complementation of stress-induced phenotypes in S. cerevisiae, as well as restore wild-type cell shape malformations. TaARPC3 was found predominantly to be localized in the nucleus and cytoplasm when expressed transiently in wheat protoplast. TaARPC3 was significantly induced in response to avirulent race of Puccinia striiformis f. sp. tritici (Pst). Knock-down of TaARPC3 by virus-induced gene silencing resulted in a reduction of resistance against Pst through a specific reduction in actin cytoskeletal organization. Interestingly, this reduction was found to coincide with a block in reactive oxygen species (ROS) accumulation, the hypersensitive response (HR), an increase in TaCAT1 mRNA accumulation, and the growth of Pst. Taken together, these findings suggest that TaARPC3 is a key subunit of the Arp2/3 complex which is required for wheat resistance against Pst, a process that is associated with the regulation of the actin cytoskeleton.