Role of transporters in plant disease resistance

Regulation of sucrose metabolism, sugar transport and pentose phosphate pathway by PacC in apple fruit colonized by Penicillium expansum

A critical transcription factor, PacC, modulates the expression of fungal pH signaling. Although PacC-mediated environmental pH has been reported to regulate the growth and pathogenicity of postharvest pathogens, the involvement of PacC in sucrose metabolism, sugar transport, and the pentose phosphate pathway (PPP) in different zones of decayed fruit remains unclear. Our work showed that the inoculation with a PePacC deletion strain of Penicillium expansum (ΔPePacC) accelerated sucrose catabolism and glucose and fructose accumulation in different zones of apple fruit. This was attributed to an increase in sucrose metabolism enzyme activities and up-regulation of the sugar transporter protein-related gene expression. Moreover, ΔPePacC inoculation increased the PPP-related enzyme activities and the levels of nicotinamide adenine dinucleotide phosphate (NADPH) and NADP+. In conclusion, PacC modulates sucrose metabolism, sugar transport, and the PPP in apple fruit by mediating dynamic changes in environmental pH, thereby enhancing fruit disease resistance.

The role of sugar transporters in the battle for carbon between plants and pathogens

In photosynthetic cells, plants convert carbon dioxide to sugars that can be moved between cellular compartments by transporters before being subsequently metabolized to support plant growth and development. Most pathogens cannot synthesize sugars directly but have evolved mechanisms to obtain plant-derived sugars as C resource for successful infection and colonization. The availability of sugars to pathogens can determine resistance or susceptibility. Here, we summarize current progress on the roles of sugar transporters in plant-pathogen interactions. We highlight how transporters are manipulated antagonistically by both host and pathogens in competing for sugars. We examine the potential application of this target in resistance breeding and discuss opportunities and challenges for the future.

Lr34/Yr18/Sr57/Pm38 confers broad-spectrum resistance to fungal diseases via sinapyl alcohol transport for cell wall lignification in wheat

The widely recognized pleiotropic adult plant resistance gene Lr34 encodes an ATP-binding cassette transporter and plays an important role in breeding wheat for enhanced resistance to multiple fungal diseases. Despite its significance, the mechanisms underlying Lr34-mediated pathogen defense remain largely unknown. Our study demonstrates that wheat lines carrying the Lr34res allele exhibit thicker cell walls and enhanced resistance to fungal penetration compared to those without Lr34res. Transcriptome and metabolite profiling revealed that the lignin biosynthetic pathway is suppressed in lr34 mutants, indicating a disruption in cell wall lignification. Additionally, we discovered that lr34 mutant lines are hypersensitive to sinapyl alcohol, a major monolignol crucial for cell wall lignification. Yeast accumulation and efflux assays confirmed that the LR34 protein functions as a sinapyl alcohol transporter. Both genetic and virus-induced gene silencing experiments demonstrated that the disease resistance conferred by Lr34 can be enhanced by incorporating the TaCOMT-3B gene, which is responsible for the biosynthesis of sinapyl alcohol. Collectively, our findings provide novel insights into the role of Lr34 in disease resistance through mediating sinapyl alcohol transport and cell wall deposition, and highlight the synergistic effect of TaCOMT-3B and Lr34 against multiple fungal pathogens by mediating cell wall lignification in adult wheat plants.

Systematic Investigation of Aluminum Stress-Related Genes and Their Critical Roles in Plants

Aluminum (Al) stress is a dominant obstacle for plant growth in acidic soil, which accounts for approximately 40-50% of the world's potential arable land. The identification and characterization of Al stress response (Al-SR) genes in Arabidopsis, rice, and other plants have deepened our understanding of Al's molecular mechanisms. However, as a crop sensitive to acidic soil, only eight Al-SR genes have been identified and functionally characterized in maize. In this review, we summarize the Al-SR genes in plants, including their classifications, subcellular localizations, expression organs, functions, and primarily molecular regulatory networks. Moreover, we predict 166 putative Al-SR genes in maize based on orthologue analyses, facilitating a comprehensive understanding of the impact of Al stress on maize growth and development. Finally, we highlight the potential applications of alleviating Al toxicity in crop production. This review deepens our understanding of the Al response in plants and provides a blueprint for alleviating Al toxicity in crop production.

Comparative transcriptome analysis of resistant and susceptible watermelon genotypes reveals the role of RNAi, callose, proteinase, and cell wall in squash vein yellowing virus resistance

Watermelon (Citrullus lanatus) is the third largest fruit crop in the world in term of production. However, it is susceptible to several viruses. Watermelon vine decline (WVD), caused by whitefly-transmitted squash vein yellowing virus (SqVYV), is a disease that has caused over $60 million in losses in the US and continues to occur regularly in southeastern states. Understanding the molecular mechanisms underlying resistance to SqVYV is important for effective disease management. A time-course transcriptomic analysis was conducted on resistant (392291-VDR) and susceptible (Crimson Sweet) watermelon genotypes inoculated with SqVYV. Significantly higher levels of SqVYV were observed over time in the susceptible compared to the resistant genotype. The plasmodesmata callose binding protein (PDCB) gene, which is responsible for increased callose deposition in the plasmodesmata, was more highly expressed in the resistant genotype than in the susceptible genotype before and after inoculation, suggesting the inhibition of cell-to-cell movement of SqVYV. The potential role of the RNA interference (RNAi) pathway was observed in the resistant genotype based on differential expression of eukaryotic initiation factor (eIF), translin, DICER, ribosome inactivating proteins, RNA-dependent RNA polymerase (RDR), and Argonaute (AGO) genes after inoculation. The significant differential expression of hormone-related genes, including those involved in the ethylene, jasmonic acid, auxin, cytokinin, gibberellin, and salicylic acid signaling pathways, was observed, emphasizing their regulatory roles in the defense response. Genes regulating pectin metabolism, cellulose synthesis, cell growth and development, xenobiotic metabolism, and lignin biosynthesis were overexpressed in the susceptible genotype, suggesting that alterations in cell wall integrity and growth processes result in disease symptom development. These findings will be helpful for further functional studies and the development of SqVYV-resistant watermelon cultivars.

AGC kinases OXI1 and AGC2-2 regulate camalexin secretion and disease resistance by phosphorylating transporter PDR6

Plant transporters regulating the distribution of secondary metabolites play critical roles in defending against pathogens, insects, and interacting with beneficial microbes. The phosphorylation of these transporters can alter their activity, stability, and intracellular protein trafficking. However, the regulatory mechanism underlying this modification remains elusive. In this study, we discovered two orthologs of mammalian PKA, PKG, and PKC (AGC) kinases, oxidative signal-inducible 1 (OXI1) and its closest homologue, AGC subclass 2 member 2 (AGC2-2; 75% amino acid sequence identity with OXI1), associated with the extracellular secretion of camalexin and Arabidopsis (Arabidopsis thaliana) resistance to Pseudomonas syringae, and Botrytis cinerea. These kinases can undergo in vitro kinase reactions with three pleiotropic drug resistance (PDR) transporters: PDR6, PDR8, and PDR12. Moreover, our investigation confirmed PDR6 interaction with OXI1 and AGC2-2. By performing LC-MS/MS and parallel reaction monitoring, we identified the phosphorylation sites on PDR6 targeted by these kinases. Notably, chitin-induced PDR6 phosphorylation at specific residues, namely S31, S33, S827, and T832. Additional insights emerged by expressing dephosphorylated PDR6 variants in a pdr6 mutant background, revealing that the target residues S31, S33, and S827 promote PDR6 efflux activity, while T832 potentially contributes to PDR6 stability within the plasma membrane. The findings of this study elucidate partial mechanisms involved in the activity regulation of PDR-type transporters, providing valuable insights for their potential application in future plant breeding endeavors.

Integrated transmission electron microscopy and proteomic analyses reveal the cytoarchitectural response to cucumber mosaic virus infection in tobacco

Cucumber mosaic virus (CMV) causes huge economic losses to agriculture every year; thus, understanding the mechanism of plant resistance to CMV is imperative. In this study, an integrated analysis of transmission electron microscopy (TEM) observations and proteomic results was used to identify cytoarchitectural differences in Nicotiana tabacum cv. NC82 (susceptible) and cv. Taiyan 8 (T.T.8; resistant) following infection with CMV. The TEM observations showed that the structure of the chloroplasts and mitochondria was severely damaged at the late stage of infection in NC82. Moreover, the chloroplast stroma and mitochondrial cristae were reduced and disaggregated. However, in T.T.8, organelle structure remained largely intact Selective autophagy predominated in T.T.8, whereas non-selective autophagy dominated in NC82, resembling cellular disorder. Proteomic analysis of T.T.8 revealed differentially expressed proteins (DEPs) mostly associated with photosynthesis, respiration, reactive oxygen species (ROS) scavenging, and cellular autophagy. Biochemical analyses revealed that ROS-related catalase, autophagy-related disulfide isomerase, and jasmonic acid and antioxidant secondary metabolite synthesis-related 4-coumarate:CoA ligase (Nt4CL) exhibited different trends and significant differences in expression in the two cultivars after CMV inoculation. Furthermore, mutant phenotyping verified that reduced Nt4CL expression impaired resistance in T.T.8. The identified DEPs are crucial for maintaining intracellular homeostatic balance and likely contribute to the mechanism of CMV resistance in tobacco. These findings increase our understanding of plant cytological mechanisms conferring resistance to CMV infection.

Molecular characterization of genes involved in tolerance of cadmium in Triticum aestivum (L.) under Cd stress

The NRAMPs (natural resistance-associated macrophage proteins) are major transporters for the absorption and transport of metals like Pb, Zn, Mn, Fe, and Cd in plants. While NRAMP gene family members have been extensively studied as metal transporters in model and other plants, little information has been reported on their role in Triticum aestivum, particularly in response to Cd stress. Current study reported 13 NRAMP candidates in the genome of T. aestivum. Phylogenetic analysis divided these into three clades. Motif and gene structure study showed that members in the same clades shared the same location and pattern, which further supported the phylogenetic analysis. The analysis of cis-acting elements in promoter sequences of NRAMP genes in wheat identified stress-responsive transcription factor binding sites. Multiple sequence alignment identified the conservation of important residues. Based on RNA-seq and qRT-PCR analysis, Cd stress-responsive variations of TaNRAMP gene expression were reported. This study provides comprehensive data to understand the TaNRAMP gene family, its features, and its expression, which will be a helpful framework for functional research.

Comparative Transcriptomic Analysis of Wheat Cultivars in Response to Xanthomonas translucens pv. cerealis and Its T2SS, T3SS, and TALEs Deficient Strains

Xanthomonas translucens pv. cerealis causes bacterial leaf streak disease on small grain cereals. Type II and III secretion systems (T2SS and T3SS) play a pivotal role in the pathogenicity of the bacterium, while no data are available on the transcriptomic profile of wheat cultivars infected with either wild type (WT) or mutants of the pathogen. In this study, WT, TAL-effector mutants, and T2SS/T3SS mutants of X. translucens pv. cerealis strain NXtc01 were evaluated for their effect on the transcriptomic profile of two wheat cultivars, 'Chinese Spring' and 'Yangmai-158', using Illumina RNA-sequencing technology. RNA-Seq data showed that the number of differentially expressed genes (DEGs) was higher in Yangmai-158 than in Chinese Spring, suggesting higher susceptibility of Yangmai-158 to the pathogen. In T2SS, most suppressed DEGs were related to transferase, synthase, oxidase, WRKY, and bHLH transcription factors. The gspD mutants showed significantly decreased disease development in wheat, suggesting an active contribution of T2SS in virulence. Moreover, the gspD mutant restored full virulence and its multiplication in planta by addition of gspD in trans. In the T3SS-deficient strain, downregulated DEGs were associated with cytochrome, peroxidases, kinases, phosphatases, WRKY, and ethylene-responsive transcription factors. In contrast, upregulated DEGs were trypsin inhibitors, cell number regulators, and calcium transporter. Transcriptomic analyses coupled with quantitative real-time-PCR indicated that some genes are upregulated in Δtal1/Δtal2 compared with the tal-free strain, but no direct interaction was observed. These results provide novel insight into wheat transcriptomes in response to X. translucens infection and pave the way for understanding host-pathogen interactions.

Structures and coordination chemistry of transporters involved in manganese and iron homeostasis

A repertoire of transporters plays a crucial role in maintaining homeostasis of biologically essential transition metals, manganese, and iron, thus ensuring cell viability. Elucidating the structure and function of many of these transporters has provided substantial understanding into how these proteins help maintain the optimal cellular concentrations of these metals. In particular, recent high-resolution structures of several transporters bound to different metals enable an examination of how the coordination chemistry of metal ion-protein complexes can help us understand metal selectivity and specificity. In this review, we first provide a comprehensive list of both specific and broad-based transporters that contribute to cellular homeostasis of manganese (Mn2+) and iron (Fe2+ and Fe3+) in bacteria, plants, fungi, and animals. Furthermore, we explore the metal-binding sites of the available high-resolution metal-bound transporter structures (Nramps, ABC transporters, P-type ATPase) and provide a detailed analysis of their coordination spheres (ligands, bond lengths, bond angles, and overall geometry and coordination number). Combining this information with the measured binding affinity of the transporters towards different metals sheds light into the molecular basis of substrate selectivity and transport. Moreover, comparison of the transporters with some metal scavenging and storage proteins, which bind metal with high affinity, reveal how the coordination geometry and affinity trends reflect the biological role of individual proteins involved in the homeostasis of these essential transition metals.

Characterization and co-expression analysis of ATP-binding cassette transporters provide insight into genes related to cannabinoid transport in Cannabis sativa L

Plant ATP-binding cassette (ABC) transporters contribute the transport of diverse secondary metabolites. However, their roles in cannabinoid trafficking are still unsolved in Cannabis sativa. In this study, 113 ABC transporters were identified and characterized in C. sativa from their physicochemical properties, gene structure, and phylogenic relationship, as well as spatial gene expression patterns. Eventually, seven core transporters were proposed including one member in ABC subfamily B (CsABCB8) and six ABCG members (CsABCG4, CsABCG10, CsABCG11, CsABCG32, CsABCG37, and CsABCG41), harboring potential in participating cannabinoid transport, by combining phylogenetic and co-expression analysis from the gene and metabolite level. The candidate genes exhibited a high correlation with cannabinoid biosynthetic pathway genes and the cannabinoid content, and they were highly expressed where cannabinoids appropriately biosynthesized and accumulated. The findings underpin further research on the function of ABC transporters in C. sativa, especially in unveiling the mechanisms of cannabinoid transport to boost systematic and targeted metabolic engineering.

Physiological and biochemical regulation of tobacco by oxathiapiprolin under Phytophthora nicotianae infection

As a fungicide, oxathiapiprolin has excellent effects on diseases caused by oomycetes. Fungicides generally protect crops by inhibiting pathogens, but little research has addressed the effects of fungicides on crops. This study combined transcriptomic and metabolomic analyses to systematically analyze the physiological regulatory mechanisms of oxathiapiprolin on tobacco under Phytophthora nicotianae infection. The results showed that under P. nicotianae infection, tobacco's photosynthetic rate and antioxidant enzyme activity increased after the application of oxathiapiprolin. Omics results showed that the genes related to carbon metabolism, disease-resistant proteins, and amino acid synthesis were highly expressed, and the amino acid content increased in tobacco leaves. This study is the first comprehensive investigation of the physiological regulatory effects of oxathiapiprolin on tobacco in response to P. nicotianae infection. These findings provide a basis for the balance between regulating tobacco growth and development and enhancing disease resistance under the stimulation of oxathiapiprolin and provide new research and development opportunities for identifying new disease-resistance genes and the development of high-yielding disease-resistant crop varieties.

Whole genome sequence of Cryptosphaeria pullmanensis, an important pathogenic fungus potentially threatening crop and forestry production

Many fungal members of the Diatrypaceae family are pathogenic towards plants and are widely distributed globally. Cryptosphaeria pullmanensis is a pathogenic fungus that infects populus and walnut trees, causing their death. We sequenced the genome of C. pullmanensis based on a combination of Nanopore PromethION and Illumina NovaSeq PE150 platforms, and functionally annotated the sequences using a number of open-access databases. This is the first report of the genome-scale assembly and annotation for C. pullmanensis, the first species of the genus Cryptosphaeria to be sequenced. We obtained 13 contigs with an N50 contig size of 7,095,780 bp, a GC content ratio of 43.23% and a genome size of 56.72 Mb with 10,474 putative coding genes. Comparative genomic analysis against the genomes of seven Ascomycetes fungal strains was performed. Among the seven species tested, the Eutypa lata genome displayed the highest similarity to the C. pullmanensis genome in terms of collinearity and homologous gene content. This study has provided a genetic resource that offers extensive information and a framework for future investigations into the transcriptome, proteome, and metabonome of C. pullmanensis to understand its molecular pathogenesis.

Unlocking the potentials of nitrate transporters at improving plant nitrogen use efficiency

Nitrate ( NO 3 - ) transporters have been identified as the primary targets involved in plant nitrogen (N) uptake, transport, assimilation, and remobilization, all of which are key determinants of nitrogen use efficiency (NUE). However, less attention has been directed toward the influence of plant nutrients and environmental cues on the expression and activities of NO 3 - transporters. To better understand how these transporters function in improving plant NUE, this review critically examined the roles of NO 3 - transporters in N uptake, transport, and distribution processes. It also described their influence on crop productivity and NUE, especially when co-expressed with other transcription factors, and discussed these transporters' functional roles in helping plants cope with adverse environmental conditions. We equally established the possible impacts of NO 3 - transporters on the uptake and utilization efficiency of other plant nutrients while suggesting possible strategic approaches to improving NUE in plants. Understanding the specificity of these determinants is crucial to achieving better N utilization efficiency in crops within a given environment.

Transcriptomic Analysis Revealed Key Defense Genes and Signaling Pathways Mediated by the Arabidopsis thaliana Gene SAD2 in Response to Infection with Pseudomonas syringae pv. Tomato DC3000

Nucleocytoplasmic transport receptors play key roles in the nuclear translocation of disease resistance proteins, but the associated mechanisms remain unclear. The Arabidopsis thaliana gene SAD2 encodes an importin β-like protein. A transgenic Arabidopsis line overexpressing SAD2 (OESAD2/Col-0) showed obvious resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) compared to the wild type (Col-0), but the knockout mutant sad2-5 was susceptible. Transcriptomic analysis was then performed on Col-0, OESAD2/Col-0, and sad2-5 leaves at 0, 1, 2, and 3 days post-inoculation with Pst DC3000. A total of 1825 differentially expressed genes (DEGs) were identified as putative biotic stress defense genes regulated by SAD2, 45 of which overlapped between the SAD2 knockout and overexpression datasets. Gene Ontology (GO) analysis indicated that the DEGs were broadly involved in single-organism cellular metabolic processes and in response to stimulatory stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) biochemical pathway analysis revealed that many of the DEGs were associated with the biosynthesis of flavonoids and other specialized metabolites. Transcription factor analysis showed that a large number of ERF/AP2, MYB, and bHLH transcription factors were involved in SAD2-mediated plant disease resistance. These results provide a basis for future exploration of the molecular mechanisms associated with SAD2-mediated disease resistance and establish a set of key candidate disease resistance genes.

Association mapping for broomrape resistance in sunflower

INTRODUCTION

Sunflower breeding for resistance to the parasitic plant sunflower broomrape (Orobanche cumana Wallr.) requires the identification of novel resistance genes. In this research, we conducted a genome-wide association study (GWAS) to identify QTLs associated with broomrape resistance.

METHODS

The marker-trait associations were examined across a germplasm set composed of 104 sunflower accessions. They were genotyped with a 600k AXIOM® genome-wide array and evaluated for resistance to three populations of the parasite with varying levels of virulence (races EFR, FGV, and GTK) in two environments.

RESULTS AND DISCUSSION

The analysis of the genetic structure of the germplasm set revealed the presence of two main groups. The application of optimized treatments based on the general linear model (GLM) and the mixed linear model (MLM) allowed the detection of 14 SNP markers significantly associated with broomrape resistance. The highest number of marker-trait associations were identified on chromosome 3, clustered in two different genomic regions of this chromosome. Other associations were identified on chromosomes 5, 10, 13, and 16. Candidate genes for the main genomic regions associated with broomrape resistance were studied and discussed. Particularly, two significant SNPs on chromosome 3 associated with races EFR and FGV were found at two tightly linked SWEET sugar transporter genes. The results of this study have confirmed the role of some QTL on resistance to sunflower broomrape and have revealed new ones that may play an important role in the development of durable resistance to this parasitic weed in sunflower.

Comparative transcriptome analysis reveals that ATP synthases regulate Fusarium oxysporum virulence by modulating sugar transporter gene expressions in tobacco

Fusarium oxysporum is a main causative agent of tobacco root rot, severely affecting tobacco growth. Here, 200 F. oxysporum strains were isolated and examined for their virulence toward tobacco plants. These strains were divided into disease class 1-3 (weak virulence), 4-6 (moderate virulence), and 7-9 (strong virulence). To understand the virulence mechanism of F. oxysporum, a comparative transcriptome study was performed using weak, moderate, and strong virulence-inducing strains. The results showed that expression levels of 1,678 tobacco genes were positively correlated with virulence levels, while expression levels of 3,558 genes were negatively associated with virulence levels. Interestingly, the expression levels of ATP synthase genes were positively correlated with F. oxysporum virulence. To verify whether ATP synthase gene expression is associated with F. oxysporum virulence, 5 strains each of strong, moderate, and weak virulence-inducing strains were tested using qRT-PCR. The results confirmed that ATP synthase gene expression is positively correlated with virulence levels. Knock-out mutants of ATP synthase genes resulted in a relatively weak virulence compared to wild-type as well as the inhibition of F. oxysporum-mediated suppression of NtSUC4, NtSTP12, NtHEX6, and NtSWEET, suggesting that ATP synthase activity is also associated with the virulence. Taken together, our analyses show that ATP synthases are key genes for the regulation of F. oxysporum virulence and provide important information for understanding the virulence mechanism of F. oxysporum in tobacco root rot.

The Pathogen-Induced MATE Gene TaPIMA1 Is Required for Defense Responses to Rhizoctonia cerealis in Wheat

The sharp eyespot, mainly caused by the soil-borne fungus Rhizoctonia cerealis, is a devastating disease endangering production of wheat (Triticum aestivum). Multi-Antimicrobial Extrusion (MATE) family genes are widely distributed in plant species, but little is known about MATE functions in wheat disease resistance. In this study, we identified TaPIMA1, a pathogen-induced MATE gene in wheat, from RNA-seq data. TaPIMA1 expression was induced by Rhizoctonia cerealis and was higher in sharp eyespot-resistant wheat genotypes than in susceptible wheat genotypes. Molecular biology assays showed that TaPIMA1 belonged to the MATE family, and the expressed protein could distribute in the cytoplasm and plasma membrane. Virus-Induced Gene Silencing plus disease assessment indicated that knock-down of TaPIMA1 impaired resistance of wheat to sharp eyespot and down-regulated the expression of defense genes (Defensin, PR10, PR1.2, and Chitinase3). Furthermore, TaPIMA1 was rapidly induced by exogenous H₂O₂ and jasmonate (JA) treatments, which also promoted the expression of pathogenesis-related genes. These results suggested that TaPIMA1 might positively regulate the defense against R. cerealis by up-regulating the expression of defense-associated genes in H₂O₂ and JA signal pathways. This study sheds light on the role of MATE transporter in wheat defense to Rhizoctonia cerealis and provides a potential gene for improving wheat resistance against sharp eyespot.

Structure and Function of Rhizosphere Soil and Root Endophytic Microbial Communities Associated With Root Rot of Panax notoginseng

Panax notoginseng (Burk.) F. H. Chen is a Chinese medicinal plant of the Araliaceae family used for the treatment of cardiovascular and cerebrovascular diseases in Asia. P. notoginseng is vulnerable to root rot disease, which reduces the yield of P. notoginseng. In this study, we analyzed the rhizosphere soil and root endophyte microbial communities of P. notoginseng from different geographical locations using high-throughput sequencing. Our results revealed that the P. notoginseng rhizosphere soil microbial community was more diverse than the root endophyte community. Rhodopseudomonas, Actinoplanes, Burkholderia, and Variovorax paradoxus can help P. notoginseng resist the invasion of root rot disease. Ilyonectria mors-panacis, Pseudomonas fluorescens, and Pseudopyrenochaeta lycopersici are pathogenic bacteria of P. notoginseng. The upregulation of amino acid transport and metabolism in the soil would help to resist pathogens and improve the resistance of P. notoginseng. The ABC transporter and gene modulating resistance genes can improve the disease resistance of P. notoginseng, and the increase in the number of GTs (glycosyltransferases) and GHs (glycoside hydrolases) families may be a molecular manifestation of P. notoginseng root rot. In addition, the complete genomes of two Flavobacteriaceae species and one Bacteroides species were obtained. This study demonstrated the microbial and functional diversity in the rhizosphere and root microbial community of P. notoginseng and provided useful information for a better understanding of the microbial community in P. notoginseng root rot. Our results provide insights into the molecular mechanism underlying P. notoginseng root rot and other plant rhizosphere microbial communities.

NtSWEET1 promotes tobacco resistance to Fusarium oxysporum-induced root rot disease

Sugars Will Eventually be Exported Transporter (SWEET) is a newly characterized family of sugar transporters, which plays critical roles in plant-pathogen interactions. However, the function of SWEET in tobacco and its interaction with Fusarium oxysporum, a causal agent of root rot, remain unclear. This study aimed to dissect the function of NtSWEETs in tobacco root rot using stem bases from tobacco plants inoculated with F. oxysporum. RNA-sequencing (RNA-Seq) analysis was performed, and the results indicated that Sucrose Transporter 4 (NtSUC4), Sugar Transporter 12 (NtSTP12), Hexose Transporter 6 (NtHEX6), NtSWEET1, NtSWEET3b, and NtSWEET12 were downregulated by infection with F. oxysporum. The expression of NtSWEET1, but not of NtSUC4, NtSTP12, NtHEX6, NtSWEET3b, or NtSWEET12, was suppressed at all the time points tested after inoculation with F. oxysporum. The NtSWEET1-green fluorescent protein was localized on the plasma membrane and possessed the ability to transport glucose, fructose and galactose. Compared with the wild-type plants, NtSWEET1 RNAi plants were more susceptible to root rot, indicating that NtSWEET1 positively regulated the defense of tobacco against root rot. This study identified the role of SWEETs in tobacco and their interaction with F. oxysporum. The results might be useful in protecting tobacco plants from root rot.

Trichoderma-Induced Ethylene Responsive Factor MsERF105 Mediates Defense Responses in Malus sieversii

Trichoderma can induce plant hormone signal pathways mediating plant defenses, resulting in broad-spectrum resistance to phytopathogens. Herein, Malus sieversii seedlings were treated with Trichoderma biofertilizer and/or Alternaria alternata f. sp. mali, and transcriptome analysis revealed significant differential expression. There was a high similarity between the transcriptome expression profiles of Trichoderma-induced and A. alternata-infected M. sieversii samples for genes related to jasmonic acid (JA), ethylene, and salicylic acid (SA) signaling pathways. Additionally, Trichoderma biofertilizer activated numerous disease-resistant genes (ERF, NAC, bHLH, and STK) and defense response genes (DRP, ABC, and HSP). Among transcription factors, members of the ERF family were the most differentially expressed (18 ERFs), indicating that they may be closely related to defense responses. Among ERFs, differential expression of MsERF105 was the most significant (upregulated 27.6-fold compared to controls). MsERF105 was heterologously expressed in PdPap poplar (Populus davidiana × Populus alba var. pyramidalis Louche), and following infection with A. alternata (Aal), transgenic PdPap-MsERF105s plants displayed lower malondialdehyde (downregulated 41.4%) and reactive oxygen species (ROSs) levels, and higher reductase activities, especially superoxide dismutase (SOD; upregulated 77.5% compared to PdPap-ROK2 plants). Furthermore, the lesion areas of PdPap-MsERF105s leaves were significantly smaller (0.2%) than those of PdPap-ROK2 leaves (∼26.0%), and the cell membrane integrity was superior for PdPap-MsERF105s leaves. Thus, MsERF105 enhanced the resistance of PaPap poplar to Aal, presumably because MsERF105 activates the expression of PR1 and PDF1.2. In conclusion, Trichoderma biofertilizer modulated the differential expression of numerous disease resistance genes and defense response genes in M. sieversii in response to pathogen attack, and MsERF105 played important roles in this process.

Regulatory Roles of Small Non-coding RNAs in Sugar Beet Resistance Against Beet curly top virus

Beet curly top virus (BCTV) mediated yield loss in sugar beets is a major problem worldwide. The circular single-stranded DNA virus is transmitted by the beet leafhopper. Genetic sources of BCTV resistance in sugar beet are limited and commercial cultivars rely on chemical treatments versus durable genetic resistance. Phenotypic selection and double haploid production have resulted in sugar beet germplasm (KDH13; 13 and KDH4-9; 4) that are highly resistant to BCTV. The molecular mechanism of resistance to the virus is unknown, especially the role of small non-coding RNAs (sncRNAs) during early plant-viral interaction. Using the resistant lines along with a susceptible line (KDH19-17; 19), we demonstrate the role of sugar beet microRNAs (miRNAs) in BCTV resistance during early infection stages when symptoms are not yet visible. The differentially expressed miRNAs altered the expression of their corresponding target genes such as pyruvate dehydrogenase (EL10Ac1g02046), carboxylesterase (EL10Ac1g01087), serine/threonine protein phosphatase (EL10Ac1g01374), and leucine-rich repeats (LRR) receptor-like (EL10Ac7g17778), that were highly expressed in the resistant lines versus susceptible lines. Pathway enrichment analysis of the miRNA target genes showed an enrichment of genes involved in glycolysis/gluconeogenesis, galactose metabolism, starch, and sucrose metabolism to name a few. Carbohydrate analysis revealed altered glucose, galactose, fructose, and sucrose concentrations in the infected leaves of resistant versus susceptible lines. We also demonstrate differential regulation of BCTV derived sncRNAs in the resistant versus susceptible lines that target sugar beet genes such as LRR (EL10Ac1g01206), 7-deoxyloganetic acid glucosyltransferase (EL10Ac5g12605), and transmembrane emp24 domain containing (EL10Ac6g14074) and altered their expression. In response to viral infection, we found that plant derived miRNAs targeted BCTV capsid protein/replication related genes and showed differences in expression among resistant and susceptible lines. The data presented here demonstrate the contribution of miRNA mediated regulation of metabolic pathways and cross-kingdom RNA interference (RNAi) in sugar beet BCTV resistance.