Lyso-phosphatidylethanolamine triggers immunity against necrotrophs by promoting JA-signaling and ROS-homeostasis.

Modulation of the plant defense response by bioactive molecules is of increasing interest. However, despite plant cell lipids being one of the major cellular components, their role in plant immunity remains elusive. We found that the exogenous application of the cell-membrane localized phospholipid lyso-phosphatidylethanolamine (LPE) reprograms the plant transcript profile in favor of defense-associated genes thereby priming the plant immune system. Exogenous LPE application to different Arabidopsis accessions increases resistance against the necrotrophic pathogens, Botrytis cinerea and Cochliobolus heterostrophus. We found that the immunity-promoting effect of LPE is repealed in the jasmonic acid (JA) receptor mutant coi1, but multiplied in the JA-hypersensitive mutant feronia (fer-4). The JA-signaling repressor JAZ1 is degraded following LPE administration, suggesting that JA-signaling is promoted by LPE. Following LPE-treatment, reactive oxygen species (ROS) accumulation is affected in coi1 and fer-4. Moreover, FER signaling inhibitors of the RALF family are strongly expressed after LPE application, and RALF23 is internalized in stress granules, suggesting the LPE-mediated repression of FER-signaling by promoting RALF function. The in-situ increase of LPE-abundance in the LPE-catabolic mutants lpeat1 and lpeat2 elevates plant resistance to B. cinerea, in contrast to the endogenous LPE-deficient mutant pla2-alpha. We show that LPE increases plant resistance against necrotrophs by promoting JA-signaling and ROS-homeostasis, thereby paving the way for the LPE-targeted genomic engineering of crops to raise their ability to resist biotic threats.

Essential role of the CD docking motif of MPK4 in plant immunity, growth, and development.

MAPKs are universal eukaryotic signaling factors whose functioning is assumed to depend on the recognition of a common docking motif (CD) by its activators, substrates, and inactivators. We studied the role of the CD domain of Arabidopsis MPK4 by performing interaction studies and determining the ligand-bound MPK4 crystal structure. We revealed that the CD domain of MPK4 is essential for interaction and activation by its upstream MAPKKs MKK1, MKK2, and MKK6. Cys181 in the CD site of MPK4 was shown to become sulfenylated in response to reactive oxygen species in vitro. To test the function of C181 in vivo, we generated wild-type (WT) MPK4-C181, nonsulfenylatable MPK4-C181S, and potentially sulfenylation mimicking MPK4-C181D lines in the mpk4 knockout background. We analyzed the phenotypes in growth, development, and stress responses, revealing that MPK4-C181S has WT activity and complements the mpk4 phenotype. By contrast, MPK4-C181D cannot be activated by upstream MAPKK and cannot complement the phenotypes of mpk4. Our findings show that the CD motif is essential and is required for activation by upstream MAPKK for MPK4 function. Furthermore, growth, development, or immunity functions require upstream activation of the MPK4 protein kinase.

First Report of Fire Blight on Chinese hawthorn (Crataegus pinnatifida Bunge) Caused by Erwinia amylovora in Korea.

Fire blight is one of the destructive plant diseases caused by Erwinia amylovora and causes enormous economic losses worldwide. Fire blight was initially reported in apples, pears, and Chinese quince (Park et al. 2016; Myung et al. 2016a, 2016b) in Korea, but recent studies have reported new hosts such as apricot (Lee et al. 2021) and mountain ash (Lim et al, 2023). These reports indicate that fire blight is likely to disperse to new hosts in Korea. During the nationwide survey in June 2021, we observed typical symptoms of blossom blight and shoot blight on a Chinese hawthorn (Crataegus pinnatifida Bunge) just near an orchard (37°09'21.7"N, 127°35'02.6"E) in Icheon, Gyeonggi Province, where fire blight of Asian pear occurred. For identifying its causal agent, bacterial isolates were recovered after incubating at 28 ℃ for 24 hours on tryptic soy agar (TSA) medium (BD Difco, USA) from blighted leaves and shoots that were surface sterilized with 70% alcohol for 30 sec and homogenized in 500 µl of 10mM MgCl2. Pure cultures of white to mucoid colonies were grown on mannitol glutamate yeast extract (MGY) medium, a semi-selective medium for E. amylovora (Shrestha et al, 2003). Two isolates produced 1.5 kb amplicon through colony PCR using amsB primers (Bereswill et al. 1995). Two strains (CPFB26 and CPFB27) from the Chinese hawthorn produced amplicons identical to that from the TS3128 strain of E. amylovora, isolated from the pear tree and identified in 2016 (Park et al. 2016). For the partial 16s rRNA sequences, the total DNA of these two strains was extracted using the Wizard DNA prep kit (Promega, USA), and PCR was performed using fD1 (5'-AGAGTTTGATCCTGGCTCAG-3') and Rp2 (5'-ACGGCTACCTTGTTACGACTT-3') primer sets and further sequenced (Weisburg et al. 1991). These sequences belonged to the E. amylovora clade and were identified as E. amylovora in phylogenetic analysis (GenBank accession no. OP753569 and OP753570). Based on BLASTN analysis, CPFB26 and CPFB27 showed 99.78% similarity to the sequences of the E. amylovora strains TS3128, CFBP 1430, and ATCC 49946. To confirm pathogenicity of the isolates, 10 ㎕ bacterial suspensions (1.5 ⅹ 108 CFU/ml) was injected through the veins of the upper 2nd leaf of 3-month-old clone of apple rootstock (Malus domestica cv. M29) and incubated for six days at 28 ℃ in a chamber with 12 hours of light per day. Petioles and stems turned red hue, and the shoots finally blighted. To complete Koch's postulates, colonies were recovered on TSA medium from the inoculated apple rootstocks and verified through colony PCR for the amsB and A/B primer set (Powney et al. 2011). Hawthorn has been reported as an epidemiologically important alternate host plant of fire blight (van der Zwet et al. 2012). This study is the first to report fire blight caused by E. amylovora in Chinese hawthorn in Korea. Because Chinese hawthorn is natively distributed in Korea and is widely used as a landscaping tree (Jang et al. 2006), the findings of this study suggest that early monitoring could prevent the spread of fire blight through natural hosts.

Genome-wide profiling of long non-coding RNA of the rice blast fungus Magnaporthe oryzae during infection.

BACKGROUND: Long non-coding RNAs (lncRNAs) play essential roles in developmental processes and disease development at the transcriptional and post-transcriptional levels across diverse taxa. However, only few studies have profiled fungal lncRNAs in a genome-wide manner during host infection. RESULTS: Infection-associated lncRNAs were identified using lncRNA profiling over six stages of host infection (e.g., vegetative growth, pre-penetration, biotrophic, and necrotrophic stages) in the model pathogenic fungus, Magnaporthe oryzae. We identified 2,601 novel lncRNAs, including 1,286 antisense lncRNAs and 980 intergenic lncRNAs. Among the identified lncRNAs, 755 were expressed in a stage-specific manner and 560 were infection-specifically expressed lncRNAs (ISELs). To decipher the potential roles of lncRNAs during infection, we identified 365 protein-coding genes that were associated with 214 ISELs. Analysis of the predicted functions of these associated genes suggested that lncRNAs regulate pathogenesis-related genes, including xylanases and effectors. CONCLUSIONS: The ISELs and their associated genes provide a comprehensive view of lncRNAs during fungal pathogen-plant interactions. This study expands new insights into the role of lncRNAs in the rice blast fungus, as well as other plant pathogenic fungi.

Alternative splicing diversifies the transcriptome and proteome of the rice blast fungus during host infection.

Alternative splicing (AS) contributes to diversifying and regulating cellular responses to environmental conditions and developmental cues by differentially producing multiple mRNA and protein isoforms from a single gene. Previous studies on AS in pathogenic fungi focused on profiling AS isoforms under a limited number of conditions. We analysed AS profiles in the rice blast fungus Magnaporthe oryzae, a global threat to rice production, using high-quality transcriptome data representing its vegetative growth (mycelia) and multiple host infection stages. We identified 4,270 AS isoforms derived from 2,413 genes, including 499 genes presumably regulated by infection-specific AS. AS appears to increase during infection, with 32.7% of the AS isoforms being produced during infection but absent in mycelia. Analysis of the isoforms observed at each infection stage showed that 636 AS isoforms were more abundant than corresponding annotated mRNAs, especially after initial hyphal penetration into host cell. Many such dominant isoforms were predicted to encode regulatory proteins such as transcription factors and phospho-transferases. We also identified the genes encoding distinct proteins via AS and confirmed the translation of some isoforms via a proteomic analysis, suggesting potential AS-mediated neo-functionalization of some genes during infection. Comprehensive profiling of the pattern of genome-wide AS during multiple stages of rice-M. oryzae interaction established a foundational resource that will help investigate the role and regulation of AS during rice infection.

Genomics and Informatics, Conjoined Tools Vital for Understanding and Protecting Plant Health.

Genomics' impact on crop production continuously expands. The number of sequenced plant and microbial species and strains representing diverse populations of individual species rapidly increases thanks to the advent of next-generation sequencing technologies. Their genomic blueprints revealed candidate genes involved in various functions and processes crucial for crop health and helped in understanding how the sequenced organisms have evolved at the genome level. Functional genomics quickly translates these blueprints into a detailed mechanistic understanding of how such functions and processes work and are regulated; this understanding guides and empowers efforts to protect crops from diverse biotic and abiotic threats. Metagenome analyses help identify candidate microbes crucial for crop health and uncover how microbial communities associated with crop production respond to environmental conditions and cultural practices, presenting opportunities to enhance crop health by judiciously configuring microbial communities. Efficient conversion of disparate types of massive genomics data into actionable knowledge requires a robust informatics infrastructure supporting data preservation, analysis, and sharing. This review starts with an overview of how genomics came about and has quickly transformed life science. We illuminate how genomics and informatics can be applied to investigate various crop health-related problems using selected studies. We end the review by noting why community empowerment via crowdsourcing is crucial to harnessing genomics to protect global food and nutrition security without continuously expanding the environmental footprint of crop production.

FUSARIUM-ID v.3.0: An Updated, Downloadable Resource for Fusarium Species Identification.

Species within Fusarium are of global agricultural, medical, and food/feed safety concern and have been extensively characterized. However, accurate identification of species is challenging and usually requires DNA sequence data. FUSARIUM-ID (http://isolate.fusariumdb.org/blast.php) is a publicly available database designed to support the identification of Fusarium species using sequences of multiple phylogenetically informative loci, especially the highly informative ∼680-bp 5' portion of the translation elongation factor 1-alpha (TEF1) gene that has been adopted as the primary barcoding locus in the genus. However, FUSARIUM-ID v.1.0 and 2.0 had several limitations, including inconsistent metadata annotation for the archived sequences and poor representation of some species complexes and marker loci. Here, we present FUSARIUM-ID v.3.0, which provides the following improvements: (i) additional and updated annotation of metadata for isolates associated with each sequence, (ii) expanded taxon representation in the TEF1 sequence database, (iii) availability of the sequence database as a downloadable file to enable local BLAST queries, and (iv) a tutorial file for users to perform local BLAST searches using either freely available software, such as SequenceServer, BLAST+ executable in the command line, and Galaxy, or the proprietary Geneious software. FUSARIUM-ID will be updated on a regular basis by archiving sequences of TEF1 and other loci from newly identified species and greater in-depth sampling of currently recognized species.

The rice/maize pathogen Cochliobolus spp. infect and reproduce on Arabidopsis revealing differences in defensive phytohormone function between monocots and dicots.

The fungal genus Cochliobolus describes necrotrophic pathogens that give rise to significant losses on rice, wheat, and maize. Revealing plant mechanisms of non-host resistance (NHR) against Cochliobolus will help to uncover strategies that can be exploited in engineered cereals. Therefore, we developed a heterogeneous pathosystem and studied the ability of Cochliobolus to infect dicotyledons. We report here that C. miyabeanus and C. heterostrophus infect Arabidopsis accessions and produce functional conidia, thereby demonstrating the ability to accept Brassica spp. as host plants. Some ecotypes exhibited a high susceptibility, whereas others hindered the necrotrophic disease progression of the Cochliobolus strains. Natural variation in NHR among the tested Arabidopsis accessions can advance the identification of genetic loci that prime the plant's defence repertoire. We found that applied phytotoxin-containing conidial fluid extracts of C. miyabeanus caused necrotic lesions on rice leaves but provoked only minor irritations on Arabidopsis. This result implies that C. miyabeanus phytotoxins are insufficiently adapted to promote dicot colonization, which corresponds to a retarded infection progression. Previous studies on rice demonstrated that ethylene (ET) promotes C. miyabeanus infection, whereas salicylic acid (SA) and jasmonic acid (JA) exert a minor function. However, in Arabidopsis, we revealed that the genetic disruption of the ET and JA signalling pathways compromises basal resistance against Cochliobolus, whereas SA biosynthesis mutants showed a reduced susceptibility. Our results refer to the synergistic action of ET/JA and indicate distinct defence systems between Arabidopsis and rice to confine Cochliobolus propagation. Moreover, this heterogeneous pathosystem may help to reveal mechanisms of NHR and associated defensive genes against Cochliobolus infection.

Comparative genome analyses of four rice-infecting Rhizoctonia solani isolates reveal extensive enrichment of homogalacturonan modification genes.

BACKGROUND: Plant pathogenic isolates of Rhizoctonia solani anastomosis group 1-intraspecific group IA (AG1-IA) infect a wide range of crops causing diseases such as rice sheath blight (ShB). ShB has become a serious disease in rice production worldwide. Additional genome sequences of the rice-infecting R. solani isolates from different geographical regions will facilitate the identification of important pathogenicity-related genes in the fungus. RESULTS: Rice-infecting R. solani isolates B2 (USA), ADB (India), WGL (India), and YN-7 (China) were selected for whole-genome sequencing. Single-Molecule Real-Time (SMRT) and Illumina sequencing were used for de novo sequencing of the B2 genome. The genomes of the other three isolates were then sequenced with Illumina technology and assembled using the B2 genome as a reference. The four genomes ranged from 38.9 to 45.0 Mbp in size, contained 9715 to 11,505 protein-coding genes, and shared 5812 conserved orthogroups. The proportion of transposable elements (TEs) and average length of TE sequences in the B2 genome was nearly 3 times and 2 times greater, respectively, than those of ADB, WGL and YN-7. Although 818 to 888 putative secreted proteins were identified in the four isolates, only 30% of them were predicted to be small secreted proteins, which is a smaller proportion than what is usually found in the genomes of cereal necrotrophic fungi. Despite a lack of putative secondary metabolite biosynthesis gene clusters, the rice-infecting R. solani genomes were predicted to contain the most carbohydrate-active enzyme (CAZyme) genes among all 27 fungal genomes used in the comparative analysis. Specifically, extensive enrichment of pectin/homogalacturonan modification genes were found in all four rice-infecting R. solani genomes. CONCLUSION: Four R. solani genomes were sequenced, annotated, and compared to other fungal genomes to identify distinctive genomic features that may contribute to the pathogenicity of rice-infecting R. solani. Our analyses provided evidence that genomic conservation of R. solani genomes among neighboring AGs was more diversified than among AG1-IA isolates and the presence of numerous predicted pectin modification genes in the rice-infecting R. solani genomes that may contribute to the wide host range and virulence of this necrotrophic fungal pathogen.

Lyso-phosphatidylethanolamine primes the plant immune system and promotes basal resistance against hemibiotrophic pathogens.

BACKGROUND: Lyso-phosphatidylethanolamine (LPE) is a natural phospholipid that functions in the early stages of plant senescence. Plant innate immunity and early leaf senescence share molecular components. To reveal conserved mechanisms that link-up both processes, we tried to unravel to what extent LPE coordinates defense response and by what mode of action. RESULT: We found that LPE-treatment induces signaling and biosynthesis gene expression of the defensive hormone salicylic acid (SA). However, jasmonic acid and ethylene triggered gene induction levels are indistinguishable from the control. In accordance with gene induction for SA, oxidative stress, and reactive oxygen species (ROS) production, we detected raised in-situ hydrogen peroxide levels following LPE-application. Yet, ROS-burst assays of LPE-pretreated plants revealed a reduced release of ROS after PAMP-administration suggesting that LPE interferes with an oxidative burst. Our data refer to a priming effect of LPE on SA/ROS-associated genomic loci that encode pivotal factors in early senescence and considerably improve plant basal immunity. Thus, we challenged Arabidopsis thaliana with the hemibiotrophic pathogen Pseudomonas syringae. Consistently, we found an increased resistance in the LPE-pretreated Arabidopsis plants compared to the mock-pretreated control. CONCLUSIONS: Our results underscore a beneficial effect of LPE on plant innate immunity against hemibiotrophs. Given the resistance-promoting effect of exogenously applied LPE, this bio-agent bears the potential of being applied as a valuable tool for the genetic activation of defense-associated traits.

Harnessing Chemical Ecology for Environment-Friendly Crop Protection.

Heavy reliance on synthetic pesticides for crop protection has become increasingly unsustainable, calling for robust alternative strategies that do not degrade the environment and vital ecosystem services. There are numerous reports of successful disease control by various microbes used in small-scale trials. However, inconsistent efficacy has hampered their large-scale application. A better understanding of how beneficial microbes interact with plants, other microbes, and the environment and which factors affect disease control efficacy is crucial to deploy microbial agents as effective and reliable pesticide alternatives. Diverse metabolites produced by plants and microbes participate in pathogenesis and defense, regulate the growth and development of themselves and neighboring organisms, help maintain cellular homeostasis under various environmental conditions, and affect the assembly and activity of plant and soil microbiomes. However, research on the metabolites associated with plant health-related processes, except antibiotics, has not received adequate attention. This review highlights several classes of metabolites known or suspected to affect plant health, focusing on those associated with biocontrol and belowground plant-microbe and microbe-microbe interactions. The review also describes how new insights from systematic explorations of the diversity and mechanism of action of bioactive metabolites can be harnessed to develop novel crop protection strategies.

Transcriptome Profiling of the Rice Blast Fungus Magnaporthe oryzae and Its Host Oryza sativa During Infection.

The rice blast (fungal pathogen: Magnaporthe oryzae and host: Oryza sativa) is one of the most important model pathosystems for understanding plant-microbe interactions. Although both genome sequences were published as the first cases of pathogen and host, only a few in planta transcriptome data during infection are available. Due to technical difficulties, previously reported fungal transcriptome data are not highly qualified to comprehensively profile the expression of fungal genes during infection. Here, we report the high-quality transcriptomes of M. oryzae and rice during infection using a sheath infection-based RNA sequencing approach. This comprehensive expression profiling of the fungal pathogen and its host will provide a better platform for understanding the plant-microbe interactions at the genomic level and serve as a valuable resource for the research community.

F-box only and CUE proteins are crucial ubiquitination-associated components for conidiation and pathogenicity in the rice blast fungus, Magnaporthe oryzae.

Ubiquitination, an important process in post-translational modification, regulates various mechanisms in eukaryotes including protein degradation and interaction, cell cycle, stress response, and pathogenicity. The Skp1/Cullin/F-box and the endoplasmic reticulum-associated degradation (ERAD) complexes, RING E3 ligase complexes, are involved in ubiquitin-mediated proteolysis and protein quality control. The F-box protein has FBXO (F-box only or others), FBXW (with WD40), and FBXL (with LRR) classes depending on which interaction domain is present on the C-terminus. The ubiquitin system component cue (CUE) protein is a key factor of ERAD. However, the biological roles of FBXO and CUE proteins are largely unknown in plant pathogenic fungi including Magnaporthe oryzae. To elucidate the roles of FBXO and CUE proteins in fungal development and pathogenicity, MoFBX15 and MoCUE1 were functionally characterized in M. oryzae. Two ubiquitination-associated genes were crucial for conidiation, alkaline stress tolerance, and pathogenicity in M. oryzae. In particular, MoCUE1 was important for ER stress response and localization and translocation of cytoplasmic effectors. Moreover, ubiquitination and SUMOylation levels were decreased and transcript levels of deSUMOylation-associated genes were increased in ΔMofbx15 and ΔMocue1. This study will provide not only comprehensive understanding of the role of ubiquitination but also new insights on crosstalk between ubiquitination and SUMOylation in rice blast fungus and other fungal pathogens.

TGFam-Finder: a novel solution for target-gene family annotation in plants.

Whole-genome annotation error that omits essential protein-coding genes hinders further research. We developed Target Gene Family Finder (TGFam-Finder), an alternative tool for the structural annotation of protein-coding genes containing target domain(s) of interest in plant genomes. TGFam-Finder took considerably reduced annotation run-time and improved accuracy compared to conventional annotation tools. Large-scale re-annotation of 50 plant genomes identified an average of 150, 166 and 86 additional far-red-impaired response 1, nucleotide-binding and leucine-rich-repeat, and cytochrome P450 genes, respectively, that were missed in previous annotations. We detected significantly higher number of translated genes in the new annotations using mass spectrometry data from seven plant species compared to previous annotations. TGFam-Finder along with the new gene models can provide an optimized platform for comprehensive functional, comparative, and evolutionary studies in plants.

First Report of Rhodococcus fascians Causing Fasciation of Lilies (Lilium longiflorum Thunb.) in South Korea.

Rhodococcus fascians is a bacterium that causes growth abnormalities such as leafy galls, fasciation, and shoot proliferation in many plants, including ornamental plants. In February 2020, the Animal and Plant Quarantine Agency of South Korea detected 492,000 contaminated lily bulbs using an in-house PCR test based on the R. fascians fasD gene, and subsequently 1.3 million imported bulbs were destroyed. Because no pathogen isolation was associated with this diagnosis, there has been great cultivator demanded for bacterial isolation evidence of lily bulb infection with pathogenic R. fascians. To isolate the causal bacterium of the PCR tests, we sampled leaf, stem, and bulb tissues from 130 lilies with growth abnormality symptoms, collected from 24 South Korean mass production lily farms from June to August 2020. Supernatants of the homogenized samples were spread on mD2 medium (Kado and Heskett 1970) and incubated at 28°C for 10 days. Yellow to orange colonies were isolated into pure culture on mD2. Total DNA was extracted from cultures grown in yeast extract broth (YEB) at 28°C for 24 hours with Wizard DNA prep kit (Promega, Madison, WI, USA). PCR was performed to test for pathogenicity genes fas (A,D, and R) and att (A and R) (Putnam and Miller 2007). Colonies that produced at least one amplicon from these pathogenicity genes were analyzed by partial 16s rRNA gene sequencing to determine the corresponding species. Three strains that were isolated from the bulbs of fasciated lilies from Wanju (35°56´22.1˝N; 127°08´52.0˝E), Gwacheon (37°26´51.6˝N; 127°00´11.8˝E), and Yeongwol (37°18´45.8˝N; 128°11´05.6˝E), or W1, G3, and Y5 strains, yielded PCR products of the expected size for fas and att genes with the primer sets published in Serdani et al. (2013) and developed in this study (attAF: 5'-CCCGGCTACACGCATTCGC-3', attAR: 5'-CGAACGCGGTGTGCAGGT-3' and attRF: 5'-AGTGTCCCGTCGGCGAG-3', attRR: 5'-CGCGGCAGATCGAAGTCCT-3'). Sequences of the three strains were deposited in Genbank for fasA (accession MW122940-942), fasD (G3:MW122935 and 936), and fasR (MW122937-939); all shared 98.3 - 100% nucleotide identity to corresponding sequences from phytopathogenic R. fascians A25f (CP049745.1 Protein_ID fasA:QII09280.1, fasD:QII09282.1, and fasR:QII09277.1). The attA and attR products were only present in G3 (attA: MW122943 and attR: MW122944) and resulted in 100% identity to those of A25f (CP049745.1 Protein_ID attA:QII09269.1, attR:QII09267.1). Partial 16s rRNA gene sequences were obtained (MW064131-133) and clustered with phytopathogenic R. fascians strains D188, A21d2, and A25f. Thus we concluded that strains (W1, G3, and Y5) corresponded to R. fascians. To test the pathogenicity of these three strains, 10 seeds of garden peas for each strain were inoculated at 108 CFU/ml according to Nikolaeva et al. (2009), and the length of the main stem of each seedling was calculated 22 days post-inoculation. Seedlings inoculated with G3 and Y5 resulted in a stunted phenotype with up to 40% height reduction (p ≤ 0.001) compared to non-inoculated seedlings. As for the seedlings inoculated with W1, they exhibited as much as 15% height reduction (p ≤ 0.001). Colonies were recovered from the inoculated seedlings, identity was confirmed through colony PCR for fas and att genes. To our knowledge, this is the first report of phytopathogenic R. fascians in lilies cultivated in South Korea.

First Report of Fire Blight of Apricot (Prunus armeniaca) Caused by Erwinia amylovora in Korea.

During a survey in May 2020, symptoms of blight were observed on apricot (Prunus armeniaca cv. undetermined) in an orchard (37°06´01.5″N 127°57´44.9″E) in Chungju, South Korea, where fire blight of apple occurred. Three apricot trees in the apple orchard were heavily diseased and showed severe shoot blight and stem canker symptoms. Bacterial isolates were recovered on King's medium B from leaves and twigs that were surface-sterilized with 70% alcohol. Colonies with uniform mucoid, smooth surfaces were collected. DNA from nine isolates did not yield an amplicon in a PCR assay for detection of Erwinia pyrifoliae using primer set CPS1/CPS2c (Kim et al. 2001). Each isolate was positive in PCR assays for E. amylovora using primer sets A/B (Bereswill et al. 1992) and AJ75/76 (Llop et al. 2000) that target pEA29. Sequencing of the PCR products resulted in 99.9% (929 bp out of 930 bp) and 100% (747 bp out of 747 bp) identity with sequences of E. amylovora FB20 (GeneBank: CP050240), respectively. Amplifications of the partial 16S rRNA (GeneBank: LC557153) and hrpN (GeneBank: LC575997) genes were performed, and the products were sequenced. The primers used to amplify 16S rRNA were 518F: 5'-CCAGCAGCCGCGGTAATACG-3' and 800R: 5'-TACCAGGGTATCTAATCC-3', and those for the hrpN genes were HRPN1: 5'-ATGAGTCTGAATACAAG-3' and HRPN3c: 5'-GCTTGCCAAGTGCCATA-3'. BLAST analyses showed 99.8% (1439 bp out of 1442 bp) and 100% (1136 bp out of 1136 bp) identities, respectively, to the sequences of E. amylovora FB20. The ability of the isolates to induce a hypersensitive reaction on tobacco (Nicotiana tabacum cv. Xanthi) leaves was also evaluated. Bacterial suspensions (1.5 ⅹ 108 CFU) of 2 isolates were injected into tobacco leaves, and after 48 h, both isolates caused a hypersensitive response. To confirm pathogenicity of isolates, 3-mm-deep holes in five immature apricot (cv. Goldcot) and five immature apple (cv. Fuji) fruits were inoculated with 10 µl bacterial suspension (1.5 ⅹ 108 CFU/ml). The inoculated fruits were placed in a humid plastic box. After 7 days at 27℃, severe necrosis and bacterial ooze were present at the inoculated sites in three repeated tests. No symptoms were observed on fruits inoculated with sterile water. To complete Koch's postulates, bacteria were reisolated from the inoculated apricot and apple fruits. PCR using the specific primer sets stated above confirmed the identity as E. amylovora. Thus, based on disease symptoms, sequences, and pathogenicity, the bacterium causing blight of apricot was identified as E. amylovora. Natural infections of E. amylovora on apricot trees have been reported in the Czech Republic and Hungary (Korba and Sillerova 2011; Vegh and Palkovics 2013). Fire blight was observed in the Czech Republic on apricot trees near pear seedlings, which are highly susceptible to E. amylovora (Korba and Sillerova 2011). Natural infections of E. amylovora on Japanese plum planted adjacent to an apple orchard with severe fire blight has been reported in the United States (Mohan and Thomson 1996). Moreover, susceptibility to fire blight has been reported for apricot and Japanese plum cultivars (Mohan and Bijman 1999). To our knowledge, this the first report of fire blight of apricot caused by E. amylovora in Korea. This report is important because it provides evidence that apricot may be an overlooked reservoir for E. amylovora, in addition to apple, pear, and other rosaceous plants, in Korea. An intensive survey for additional host plants for the fire blight pathogen will be continued in Korea. This work was supported by a grant from the Agenda program (PJ01530202) of Rural Development Administration, Republic of Korea.

A High-Quality Draft Genome Sequence of Colletotrichum gloeosporioides sensu stricto SMCG1#C, a Causal Agent of Anthracnose on Cunninghamia lanceolata in China.

Colletotrichum has a broad host range and causes major yield losses of crops. The fungus Colletotrichum gloeosporioides is associated with anthracnose on Chinese fir. In this study, we present a high-quality draft genome sequence of C. gloeosporioides sensu stricto SMCG1#C, providing a reference genomic data for further research on anthracnose of Chinese fir and other hosts.

A novel approach to investigate hypoxic microenvironment during rice colonization by Magnaporthe oryzae.

Because molecular oxygen functions as the final acceptor of electrons during aerobic respiration and a substrate for diverse enzymatic reactions, eukaryotes employ various mechanisms to maintain cellular homeostasis under varying oxygen concentration. Human fungal pathogens change the expression of genes involved in virulence and oxygen-required metabolisms such as ergosterol (ERG) synthesis when they encounter oxygen limitation (hypoxia) during infection. The oxygen level in plant tissues also fluctuates, potentially creating hypoxic stress to pathogens during infection. However, little is known about how in planta oxygen dynamics impact pathogenesis. In this study, we investigated oxygen dynamics in rice during infection by Magnaporthe oryzae via two approaches. First, rice leaves infected by M. oryzae were noninvasively probed using a microscopic oxygen sensor. Second, an immunofluorescence assay based on a chemical probe, pimonidazole, was used. Both methods showed that oxygen concentration in rice decreased after fungal penetration. We also functionally characterized five hypoxia-responsive genes participating in ERG biosynthesis for their role in pathogenesis. Resulting insights and tools will help study the nature of in planta oxygen dynamics in other pathosystems.

Genomic comparisons of the laurel wilt pathogen, Raffaelea lauricola, and related tree pathogens highlight an arsenal of pathogenicity related genes.

Raffaelea lauricola is an invasive fungal pathogen and symbiont of the redbay ambrosia beetle (Xyleborus glabratus) that has caused widespread mortality to redbay (Persea borbonia) and other Lauraceae species in the southeastern USA. We compare two genomes of R. lauricola (C2646 and RL570) to seven other related Ophiostomatales species including R. aguacate (nonpathogenic close relative of R. lauricola), R. quercus-mongolicae (associated with mortality of oaks in Korea), R. quercivora (associated with mortality of oaks in Japan), Grosmannia clavigera (cause of blue stain in conifers), Ophiostoma novo-ulmi (extremely virulent causal agent of Dutch elm disease), O. ulmi (moderately virulent pathogen that cause of Dutch elm disease), and O. piceae (blue-stain saprophyte of conifer logs and lumber). Structural and functional annotations were performed to determine genes that are potentially associated with disease development. Raffaelea lauricola and R. aguacate had the largest genomes, along with the largest number of protein-coding genes, genes encoding secreted proteins, small-secreted proteins, ABC transporters, cytochrome P450 enzymes, CAZYmes, and proteases. Our results indicate that this large genome size was not related to pathogenicity but was likely lineage specific, as the other pathogens in Raffaelea (R. quercus-mongolicae and R. quercivora) had similar genome characteristics to the Ophiostoma species. A diverse repertoire of wood-decaying enzymes were identified in each of the genomes, likely used for toxin neutralization rather than wood degradation. Lastly, a larger number of species-specific, secondary metabolite, synthesis clusters were identified in R. lauricola suggesting that it is well equipped as a pathogen, which could explain its success as a pathogen of a wide range of lauraceous hosts.

Role of the Histone Acetyltransferase Rtt109 in Development and Pathogenicity of the Rice Blast Fungus.

Acetylation of histone H3 lysine 56 (H3K56) by the fungal-specific histone acetyltransferase Rtt109 plays important roles in maintaining genome integrity and surviving DNA damage. Here, we investigated the implications of Rtt109-mediated response to DNA damage on development and pathogenesis of the rice blast fungus Magnaporthe oryzae (anamorph: Pyricularia oryzae). The ortholog of Rtt109 in M. oryzae (MoRtt109) was found via sequence homology and its functionality was confirmed by phenotypic complementation of the Saccharomyces cerevisiae Rtt109 deletion strain. Targeted deletion of MoRtt109 resulted in a significant reduction in acetylation of H3K56 and rendered the fungus defective in hyphal growth and asexual reproduction. Furthermore, the deletion mutant displayed hypersensitivity to genotoxic agents, confirming the conserved importance of Rtt109 in genome integrity maintenance and genotoxic stress tolerance. Elevated expression of DNA repair genes and the results of the comet assay were consistent with constitutive endogenous DNA damage. Although the conidia produced from the mutant were not impaired in germination and appressorium morphogenesis, the mutant was significantly less pathogenic on rice leaves. Transcriptomic analysis provided insight into the factors underlying phenotypic defects that are associated with deficiency of H3K56 acetylation. Overall, our results indicate that MoRtt109 is a conserved histone acetyltransferase that affects proliferation and asexual fecundity of M. oryzae through maintenance of genome integrity and response to DNA damage.