First Report of Stem and Foliage Blight of Chrysanthemum morifolium cv. Fubaiju Caused by Stagonosporopsis chrysanthemi in China.

Chrysanthemum (Chrysanthemum morifolium cv. Fubaiju) is used as medicinal herb (Chen et al. 2020). In October 2021, a leaf spot disease was observed on leaves of C. morifolium in Huanggang, Hubei province. Disease incidence was approximately 40%. Leaf lesions manifested as necrotic spots, coalesced, and expanded to form brown-black spots, leading to wilting of the leaves. On stems, the lesions manifested as dark brown necrotic spots. To identify the pathogen, 29 pieces (5 × 5 mm) from lesion margins were surface sterilized in 1% NaOCl and rinsed three times with sterile water. The pieces were transferred onto potato dextrose agar (PDA) for incubation at 25℃ for 3 d in the dark. Fifteen fungal colonies were successfully isolated. The colony morphology with flat wavy edge, sparse aerial mycelia, and surface olivaceous black were observed at 7 days post incubation. Subglobular pycnidia were brown with a short beak, and pycnidia diameters were thick (212 to 265 × 189 to 363 µm, n = 20). Ovoid conidia were aseptate and hyaline, conidia diameters were thick (4.0 to 9.8 × 1.8 to 4.7 µm, n = 100). The morphological characters of these isolates were consistent with those of Stagonosporopsis chrysanthemi (Zhao et al. 2021). Pure culture of representative HGNU2021-18 isolated from the diseased leaves subjected to molecular identification. Sequences of the rDNA internal transcribed spacer (ITS) region, 28S large subunit ribosomal RNA (LSU), ß-tubulin (TUB2), actin (ACT), and partial RNA polymerase II largest subunit (RPB2) genes were amplified from genomic DNA of isolate HGNU2021-18 using the following primer pairs: ITS1/ITS4 (White et al. 1990), LR0R/LR5 (Rehner et al. 1994), Btub2Fd/Btub4Rd (Woudenberg et al. 2009), ACT512F/ACT783R (Carbone et al.1999), and RPB2-5F2 (Sung et al. 2007)/fRPB2-7cR (Liu et al. 1999), respectively. The PCR products were purified and then sequenced by Sangon Biotech (China). Nucleotide sequences of ITS (544 bp, OM346748), LSU (905 bp, OM758418), TUB2 (563 bp, OM945724), ACT (294 bp, OM793715), and RPB2 (957 bp, OM793716) amplified from the isolate HGNU2021-18 were subjected to BLASTn analysis. The results showed that ITS, LSU, TUB2, ACT, and RPB2 shared 100.00%, 99.45%, 99.20%, 100.00%, and 100.00% sequence identity to the five published sequences (MW810272.1, MH869953.1, MW815129.1, JN251973.1, and MT018012.1, respectively) of the S. chrysanthemi isolate CBS 500.63. Phylogenetic analysis of the multilocus sequences of ITS, LSU, RPB2, ACT, and TUB2 belonging to different Stagonosporopsis species was performed in MEGA 7.0 (Chen et al. 2015). Isolate HGNU2021-18 was placed in a clade with S. chrysanthemi with 99% bootstrap support. Thus, the results of morphological and molecular analyses indicated that the disease symptoms on chrysanthemum plants were caused by S. chrysanthemi. Under conditions of 25°C and 85% relative humidity, pathogenicity test was performed on 2-month-old healthy plants using isolate HGNU2021-18. The leaves were inoculated with 5 mm diameter mycelial plugs or with sterile agar plugs (control). Six plants were used in each treatment. Disease symptoms were observed on treated plants at 2 weeks post inoculation which were those previously observed in the field, while the control plants remained symptomless. The pathogen was re-isolated from the diseased plants, and S. chrysanthemi was confirmed as the causal pathogen. This is the first report of S. chrysanthemi causing stem and foliage blight of chrysanthemum in China.

The Dynamic Changes of Brassica napus Seed Microbiota across the Entire Seed Life in the Field.

The seed microbiota is an important component given by nature to plants, protecting seeds from damage by other organisms and abiotic stress. However, little is known about the dynamic changes and potential functions of the seed microbiota during seed development. In this study, we investigated the composition and potential functions of the seed microbiota of rapeseed (Brassica napus). A total of 2496 amplicon sequence variants (ASVs) belonging to 504 genera in 25 phyla were identified, and the seed microbiota of all sampling stages were divided into three groups. The microbiota of flower buds, young pods, and seeds at 20 days after flowering (daf) formed the first group; that of seeds at 30 daf, 40 daf and 50 daf formed the second group; that of mature seeds and parental seeds were clustered into the third group. The functions of seed microbiota were identified by using PICRUSt2, and it was found that the substance metabolism of seed microbiota was correlated with those of the seeds. Finally, sixty-one core ASVs, including several potential human pathogens, were identified, and a member of the seed core microbiota, Sphingomonas endophytica, was isolated from seeds and found to promote seedling growth and enhance resistance against Sclerotinia sclerotiorum, a major pathogen in rapeseed. Our findings provide a novel perspective for understanding the composition and functions of microbiota during seed development and may enhance the efficiency of mining beneficial seed microbes.

Transcriptional activator UvXlnR is required for conidiation and pathogenicity of rice false smut fungus Ustilaginoidea virens.

Transcription factors play critical roles in diverse biological processes in fungi. XlnR, identified as a transcriptional activator that regulates the expression of the extracellular xylanase genes in fungi, has not been extensively studied for its function in fungal development and pathogenicity in rice false smut fungus Ustilaginoidea virens. In this study, we characterized UvXlnR in U. virens and established that the full-length, N- and C-terminal forms of the UvXlnR have the ability to activate transcription. The study further demonstrated that UvXlnR plays crucial roles in various aspects of U. virens biology. Deletion of UvXlnR affected growth, conidiation, and stress response. UvXlnR mutants also exhibited reduced pathogenicity, which could be partially attributed to the reduced expression of xylanolytic genes and extracellular xylanase activity of U. virens during the infection process. Our results indicate that UvXlnR is involved in regulating growth, conidiation, stress response, and pathogenicity.

A Glycosyl Hydrolase 5 Family Protein Is Essential for Virulence of Necrotrophic Fungi and Can Suppress Plant Immunity.

Phytopathogenic fungi normally secrete large amounts of CWDEs to enhance infection of plants. In this study, we identified and characterized a secreted glycosyl hydrolase 5 family member in Sclerotinia sclerotiorum (SsGH5, Sclerotinia sclerotiorum Glycosyl Hydrolase 5). SsGH5 was significantly upregulated during the early stages of infection. Knocking out SsGH5 did not affect the growth and acid production of S. sclerotiorum but resulted in decreased glucan utilization and significantly reduced virulence. In addition, Arabidopsis thaliana expressing SsGH5 became more susceptible to necrotrophic pathogens and basal immune responses were inhibited in these plants. Remarkably, the lost virulence of the ΔSsGH5 mutants was restored after inoculating onto SsGH5 transgenic Arabidopsis. In summary, these results highlight that S. sclerotiorum suppresses the immune responses of Arabidopsis through secreting SsGH5, and thus exerts full virulence for successful infection.

The schizotrophic lifestyle of Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum is a cosmopolitan and typical necrotrophic phytopathogenic fungus that infects hundreds of plant species. Because no cultivars highly resistant to S. sclerotiorum are available, managing Sclerotinia disease caused by S. sclerotiorum is still challenging. However, recent studies have demonstrated that S. sclerotiorum has a beneficial effect and can live mutualistically as an endophyte in graminaceous plants, protecting the plants against major fungal diseases. An in-depth understanding of the schizotrophic lifestyle of S. sclerotiorum during interactions with plants under different environmental conditions will provide new strategies for controlling fungal disease. In this review, we summarize the pathogenesis mechanisms of S. sclerotiorum during its attack of host plants as a destructive pathogen and discuss its lifestyle as a beneficial endophytic fungus.

Botrytis cinerea type II inhibitor of apoptosis BcBIR1 enhances the biocontrol capacity of Coniothyrium minitans.

Apoptosis-like programmed cell death is associated with fungal development, ageing, pathogenicity and stress responses. Here, to explore the potential of Botrytis cinerea type II inhibitor of apoptosis (IAP) BcBIR1 in elevating the biocontrol efficacy of Coniothyrium minitans, the BcBIR1 gene was heterologously expressed in C. minitans. Results indicated that the strains expressing BcBIR1 had higher rates of conidiation, mycelial growth and biomass growth than the wild-type strain. Moreover, BcBIR1 was found to inhibit apoptosis, indicating its role as an IAP in C. minitans. Under various abiotic stresses, the growth rates of BcBIR1-expressing strains were significantly higher than that of the wild-type strain. Moreover, the conidial survival rate of the BcBIR1-expressing strains treated with ultraviolet irradiation was enhanced. In antifungal activity assay, the culture filtrates of BcBIR1-expressing strains displayed a stronger inhibitory effect on B. cinerea and Sclerotinia sclerotiorum than the wild-type strain. The study also found that BcBIR1 expression increased the mycoparasitism against the sclerotia, but not the hyphae of S. sclerotiorum. Taken together, these results suggest that BcBIR1 enhances vegetative growth, conidiation, anti-apoptosis activity, abiotic stress resistance, antifungal activity and mycoparasitism in C. minitans. As an IAP, BcBIR1 may improve the control capacity of C. minitans against S. sclerotiorum.

The Transcription Factor SsZNC1 Mediates Virulence, Sclerotial Development, and Osmotic Stress Response in Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum is a fungal pathogen with a broad range of hosts, which can cause diseases and pose a great threat to many crops. Fungal-specific Zn2Cys6 transcription factors (TFs) constitute a large family prevalent among plant pathogens. However, the function of Zn2Cys6 TFs remains largely unknown. In this study, we identified and characterized SsZNC1, a Zn2Cys6 TF in S. sclerotiorum, which is involved in virulence, sclerotial development, and osmotic stress response. The expression of SsZNC1 was significantly up-regulated in the early stages of S. sclerotiorum infection on Arabidopsis leaves. The target deletion of SsZNC1 resulted in reduced virulence on Arabidopsis and oilseed rape. In addition, sclerotial development ability and growth ability under hyperosmotic conditions of SsZNC1 knockout transformants were reduced. A transcriptomic analysis unveiled its regulatory role in key cellular functions, including cellulose catabolic process, methyltransferase activity, and virulence, etc. Together, our results indicated that SsZNC1, a core regulatory gene involved in virulence, sclerotial development and stress response, provides new insight into the transcription regulation and pathogenesis of S. sclerotiorum.

Two sirtuin proteins, Hst3 and Hst4, modulate asexual development, stress tolerance, and virulence by affecting global gene expression in Beauveria bassiana.

Beauveria bassiana is a widely used entomopathogenic fungus in insect biological control applications. In this study, we investigated the role of two sirtuin homologs, BbHst3 and BbHst4, in the biological activities and pathogenicity of B. bassiana. Our results showed that deletion of BbHst3 and/or BbHst4 led to impaired sporulation, reduced (~50%) conidial production, and decreased tolerance to various stresses, including osmotic, oxidative, and cell wall-disturbing agents. Moreover, BbHst4 plays dominant roles in histone H3-K56 acetylation and DNA damage response, while BbHst3 is more responsible for maintaining cell wall integrity. Transcriptomic analyses revealed significant changes (>1,500 differentially expressed genes) in gene expression patterns in the mutant strains, particularly in genes related to secondary metabolism, detoxification, and transporters. Furthermore, the ΔBbHst3, ΔBbHst4, and ΔBbHst3ΔBbHst4 strains exhibited reduced virulence in insect bioassays, with decreased (~20%) abilities to kill insect hosts through topical application and intra-hemocoel injection. These findings highlight the crucial role of BbHst3 and BbHst4 in sporulation, DNA damage repair, cell wall integrity, and fungal infection in B. bassiana. Our study provides new insights into the regulatory mechanisms underlying the biological activities and pathogenicity of B. bassiana and emphasizes the potential of targeting sirtuins for improving the efficacy of fungal biocontrol agents.IMPORTANCESirtuins, as a class of histone deacetylases, have been shown to play important roles in various cellular processes in fungi, including asexual development, stress response, and pathogenicity. By investigating the functions of BbHst3 and BbHst4, we have uncovered their critical contributions to important phenotypes in Beauveria bassiana. Deletion of these sirtuin homologs led to reduced conidial yield, increased sensitivity to osmotic and oxidative stresses, impaired DNA damage repair processes, and decreased fungal virulence. Transcriptomic analyses showed differential expression of numerous genes involved in secondary metabolism, detoxification, transporters, and virulence-related factors, potentially uncovering new targets for manipulation and optimization of fungal biocontrol agents. Our study also emphasizes the significance of sirtuins as key regulators in fungal biology and highlights their potential as promising targets for the development of novel antifungal strategies.

Protist ubiquitin ligase effector PbE3-2 targets cysteine protease RD21A to impede plant immunity.

Clubroot, caused by the soil-borne protist pathogen Plasmodiophora brassicae, is one of the most devastating diseases of Brassica oil and vegetable crops worldwide. Understanding the pathogen infection strategy is crucial for the development of disease control. However, because of its obligate biotrophic nature, the molecular mechanism by which this pathogen promotes infection remains largely unknown. P. brassicae E3 ubiquitin ligase 2 (PbE3-2) is a Really Interesting New Gene (RING)-type E3 ubiquitin ligase in P. brassicae with E3 ligase activity in vitro. Yeast (Saccharomyces cerevisiae) invertase assay and apoplast washing fluid extraction showed that PbE3-2 harbors a functional signal peptide. Overexpression of PbE3-2 in Arabidopsis (Arabidopsis thaliana) resulted in higher susceptibility to P. brassicae and decreases in chitin-triggered reactive oxygen species burst and expression of marker genes in salicylic acid signaling. PbE3-2 interacted with and ubiquitinated host cysteine protease RESPONSIVE TO DEHYDRATION 21A (RD21A) in vitro and in vivo. Mutant plants deficient in RD21A exhibited similar susceptibility and compromised immune responses as in PbE3-2 overexpression plants. We show that PbE3-2, which targets RD21A, is an important virulence factor for P. brassicae. Two other secretory RING-type E3 ubiquitin ligases in P. brassicae performed the same function as PbE3-2 and ubiquitinated RD21A. This study reveals a substantial virulence functional role of protist E3 ubiquitin ligases and demonstrates a mechanism by which protist E3 ubiquitin ligases degrade host immune-associated cysteine proteases to impede host immunity.

Characterization of a novel hypovirus isolated from the phytopathogenic fungus Colletotrichum camelliae.

Some members of genus Colletotrichum are important plant pathogens. Here, we report a novel positive single-stranded RNA virus, Colletotrichum camelliae hypovirus 1 (CcHV1), from strain GXNN11-2 of Colletotrichum camelliae. The complete genome of CcHV1 is 9907 nucleotides (nt) in length and contains a single large open reading frame (ORF) from nt 352 to 9006. This ORF encodes a polyprotein with four conserved domains, namely UDP-glycosyltransferase, RNA-dependent RNA polymerase (RdRp), peptidase, and DEAD-like helicase. The CcHV1 polyprotein shares the highest similarity with Fusarium concentricum hypovirus 1. Phylogenetic analysis indicated that CcHV1 clustered with members of the genus Betahypovirus within the family Hypoviridae. This is the first report of a hypovirus in a member of the genus Colletotrichum.

Overexpression of chitinase PbChia1 from Plasmodiophora brassicae improves broad-spectrum disease resistance of Arabidopsis.

Chitinase plays an important role in plant resistance against chitin-containing pathogens through hydrolysis of chitin. Clubroot caused by Plasmodiophora brassicae is a major disease for cruciferous crops and vegetables worldwide. The cell wall of P. brassicae resting spores contains chitin. Chitinase is regarded as capable of improving plant resistance to fungal diseases. However, there has been no report about the function of chitinase in P. brassicae. Here, wheat germ agglutinin staining and commercial chitinase treatment demonstrated that chitin is a functional component in P. brassicae. In addition, Chitinase PbChia1 was identified by chitin pull-down assay combined with LC-MS/MS. PbChia1 was found to be a typical secreted chitinase, which could bind chitin with chitinase activity in vitro. PbChia1 could significantly decrease the resting spores of P. brassicae and therefore relieve the severity of clubroot symptom, with a biocontrol effect of 61.29%. Overexpression of PbChia1 in Arabidopsis thaliana improved its resistance to P. brassicae, increased host survival rate and seed yield, enhanced PAMPs-triggered reactive oxygen species burst, MAPK activation and expression of immune-related genes. PbChia1 transgenic plants also showed resistance to other pathogens, such as biotrophic bacterium Pst DC3000, necrotrophic fungi Sclerotinia sclerotiorum and Rhizoctonia solani. These findings indicate that chitinase PbChia1 is a candidate gene that can confer broad-spectrum disease resistance in breeding.

Selenium-mediated Cr(VI) reduction and SeNPs synthesis accelerated Bacillus cereus SES to remediate Cr contamination.

Microbial biotransformation of Cr(VI) is a sustainable approach to reduce Cr(VI) toxicity and remediate Cr(VI) contamination. In this study, Bacillus cereus SES with the capability of reducing both Cr(VI) and Se(IV) was isolated, and the effect of Se supplementation on Cr(VI) reduction by Bacillus cereus SES was investigated. Se(IV) addition enabled 2.6-fold faster Cr(VI) reduction, while B. cereus SES reduced 96.96% Se(IV) and produced more selenium nanoparticles (SeNPs) in the presence of Cr(VI). Co-reduction products of B. cereus SES on Cr(VI) and Se(IV) were SeNPs adsorbed with Cr(III). The relevant mechanisms were further revealed by proteomics. Se(IV) supplementation mediated the synthesis of Cr(VI) reductants and stress-resistant substances, thus enhancing Cr(VI) resistance and promoting Cr(VI) reduction. Meanwhile, high Se(IV) reduction rate was associated with Cr(VI)-induced electron transport processes, and Cr(VI) mediated the up-regulation of flagellar assembly, protein export and ABC transporters pathways to synthesis and export more SeNPs. Furthermore, Se combined with B. cereus SES had the potential to reduce the toxicity of Cr(VI) via reducing the bioavailability of Cr and improving the bioavailability of Se in soil. Results suggested that Se could be an efficient strategy to enhance the remediation of B. cereus SES on Cr contamination.

Suppressing Structural Relaxation in Nanoscale Antimony to Enable Ultralow-Drift Phase-Change Memory Applications.

Phase-change random-access memory (PCRAM) devices suffer from pronounced resistance drift originating from considerable structural relaxation of phase-change materials (PCMs), which hinders current developments of high-capacity memory and high-parallelism computing that both need reliable multibit programming. This work realizes that compositional simplification and geometrical miniaturization of traditional GeSbTe-like PCMs are feasible routes to suppress relaxation. While to date, the aging mechanisms of the simplest PCM, Sb, at nanoscale, have not yet been unveiled. Here, this work demonstrates that in an optimal thickness of only 4 nm, the thin Sb film can enable a precise multilevel programming with ultralow resistance drift coefficients, in a regime of ≈10-4 -10-3 . This advancement is mainly owed to the slightly changed Peierls distortion in Sb and the less-distorted octahedral-like atomic configurations across the Sb/SiO2 interfaces. This work highlights a new indispensable approach, interfacial regulation of nanoscale PCMs, for pursuing ultimately reliable resistance control in aggressively-miniaturized PCRAM devices, to boost the storage and computing efficiencies substantially.

Molecular characterization of a novel fungal alphaflexivirus reveals potential inter-species horizontal gene transfer.

Sclerotinia sclerotiorum is a notorious phytopathogenic fungus that harbors diverse mycoviruses. A novel positive-sense single-stranded RNA virus, Sclerotinia sclerotiorum alphaflexivirus 2 (SsAFV2), was isolated from the hypovirulent strain 32-9 of S. sclerotiorum, and its complete genome was determined. The SsAFV2 genome contains 7,162 nucleotides (nt), excluding the poly (A) structure, and is composed of four open reading frames (ORF1-4). ORF1 encodes a polyprotein that contains three conserved domains: methyltransferase, helicase, and RNA-dependent RNA polymerase (RdRp). The ORF3 putative encodes coat proteins (CP), with ORF2 and ORF4 encoding hypothetical proteins of unknown functions. Phylogenetic analysis revealed that SsAFV2 clustered with Botrytis virus X (BVX) based on multiple alignments of helicase, RdRp, and CP, but the methyltransferase of SsAFV2 was most closely related to Sclerotinia sclerotiorum alphaflexivirus 1, suggesting that SsAFV2 is a new member of the Botrexvirus genus within the Alphaflexiviridae family, and also revealed the occurrence of potential inter-species horizontal gene transfer events within the Botrexvirus genus during the evolutionary process. Our results contribute to the current knowledge regarding the evolution and divergence of Botrexviruses.

Schizotrophic Sclerotinia sclerotiorum-Mediated Root and Rhizosphere Microbiome Alterations Activate Growth and Disease Resistance in Wheat.

Sclerotinia sclerotiorum, a widespread pathogen of dicotyledons, can grow endophytically in wheat, providing protection against Fusarium head blight and stripe rust and enhancing wheat yield. In this study, we found that wheat seed treatment with strain DT-8, infected with S. sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1) and used as a "plant vaccine" for brassica protection, could significantly increase the diversity of the fungal and bacterial community in rhizosphere soil, while the diversity of the fungal community was obviously decreased in the wheat root. Interestingly, the relative abundance of potential plant growth-promoting rhizobacteria (PGPR) and biocontrol agents increased significantly in the DT-8-treated wheat rhizosphere soil. These data might be responsible for wheat growth promotion and disease resistance. These results may provide novel insights for understanding the interaction between the schizotrophic microorganism and the microbiota of plant roots and rhizosphere, screening and utilizing beneficial microorganisms, and further reducing chemical pesticide utilization and increasing crop productivity. IMPORTANCE Fungal pathogens are seriously threatening food security and natural ecosystems; efficient and environmentally friendly control methods are essential to increase world crop production. S. sclerotiorum, a widespread pathogen of dicotyledons, can grow endophytically in wheat, providing protection against Fusarium head blight and stripe rust and enhancing wheat yield. In this study, we discovered that S. sclerotiorum treatment increased the diversity of the soil fungal and bacterial community in rhizosphere soil, while the diversity of the fungal community was obviously decreased in the wheat root. More importantly, the relative abundance of potential PGPR and bio-control agents increased significantly in the S. sclerotiorum-treated wheat rhizosphere soil. The importance of this work is that schizotrophic S. sclerotiorum promotes wheat growth and enhances resistance against fungal diseases via changes in the structure of the root and rhizosphere microbiome.

Rapeseed Domestication Affects the Diversity of Rhizosphere Microbiota.

Rhizosphere microbiota is important for plant growth and health. Domestication is a process to select suitable plants to satisfy the needs of humans, which may have great impacts on the interaction between the host and its rhizosphere microbiota. Rapeseed (Brassica napus) is an important oilseed crop derived from the hybridization between Brassica rapa and Brassica oleracea ~7500 years ago. However, variations in rhizosphere microbiota along with rapeseed domestication remain poorly understood. Here, we characterized the composition and structure of the rhizosphere microbiota among diverse rapeseed accessions, including ten B. napus, two B. rapa, and three B. oleracea accessions through bacterial 16S rRNA gene sequencing. B. napus exhibited a higher Shannon index and different bacterial relative abundance compared with its wild relatives in rhizosphere microbiota. Moreover, artificial synthetic B. napus lines G3D001 and No.2127 showed significantly different rhizosphere microbiota diversity and composition from other B. napus accessions and their ancestors. The core rhizosphere microbiota of B. napus and its wild relatives was also described. FAPROTAX annotation predicted that the synthetic B. napus lines had more abundant pathways related to nitrogen metabolism, and the co-occurrence network results demonstrated that Rhodoplanes acted as hub nodes to promote nitrogen metabolism in the synthetic B. napus lines. This study provides new insights into the impacts of rapeseed domestication on the diversity and community structure of rhizosphere microbiota, which may highlight the contribution of rhizosphere microbiota to plant health.

Duality of immune recognition by tomato and virulence activity of the Ralstonia solanacearum exo-polygalacturonase PehC.

Ralstonia solanacearum is a devastating soil-borne bacterial pathogen capable of infecting many plant species, including tomato (Solanum lycopersicum). However, the perception of Ralstonia by the tomato immune system and the pathogen's counter-defense strategy remain largely unknown. Here, we show that PehC, a specific exo-polygalacturonase secreted by Ralstonia, acts as an elicitor that triggers typical immune responses in tomato and other Solanaceous plants. The elicitor activity of PehC depends on its N-terminal epitope, and not on its polygalacturonase activity. The recognition of PehC specifically occurs in tomato roots and relies on unknown receptor-like kinase(s). Moreover, PehC hydrolyzes plant pectin-derived oligogalacturonic acids (OGs), a type of damage-associated molecular pattern (DAMP), which leads to the release of galacturonic acid (GalA), thereby dampening DAMP-triggered immunity (DTI). Ralstonia depends on PehC for its growth and early infection and can utilize GalA as a carbon source in the xylem. Our findings demonstrate the specialized and dual functions of Ralstonia PehC, which enhance virulence by degrading DAMPs to evade DTI and produce nutrients, a strategy used by pathogens to attenuate plant immunity. Solanaceous plants have evolved to recognize PehC and induce immune responses, which highlights the significance of PehC. Overall, this study provides insight into the arms race between plants and pathogens.

Neofusicoccum actinidiae and Neofusicoccum guttata, Two New Species Causing Kiwifruit Rot in China.

Kiwi is a popular fruit consumed worldwide. A number of fungal pathogens have been reported to cause postharvest rot of kiwifruit, and Botryosphaeriaceae species are the major causal agents of the disease. In this study, 18 isolates belonging to the genus Neofusicoccum (family Botryosphaeriaceae) were isolated from 247 symptomatic kiwifruits of the cultivars Jinyan, Jintao, and Jinkui collected from orchards in Hubei and Jiangxi provinces, China. Among the isolates, three grouped with various known Neofusicoccum parvum isolates, whereas the remaining 15 formed two independent clades. On the basis of further phylogenetic analyses with concatenated sequences of ITS and three genes encoding translation elongation factor 1-alpha (TEF), ß-tubulin (TUB), and DNA-dependent RNA polymerase II subunit (RPB2), as well as morphological characteristics, two new species, N. actinidiae and N. guttata, were proposed. Their pathogenicity to kiwi, apple, and citrus fruits was also confirmed.

Characterization of a Fungal Virus Representing a Novel Genus in the Family Alphaflexiviridae.

Sclerotinia sclerotiorum is an ascomycetous fungus and hosts various mycoviruses. In this study, a novel fungal alphaflexivirus with a special genomic structure, named Sclerotinia sclerotiorum alphaflexivirus 1 (SsAFV1), was cloned from a hypovirulent strain, AHS31. Strain AHS31 was also co-infected with two botourmiaviruses and two mitoviruses. The complete genome of SsAFV1 comprised 6939 bases with four open reading frames (ORFs), a conserved 5'-untranslated region (UTR), and a poly(A) tail in the 3' terminal; the ORF1 and ORF3 encoded a replicase and a coat protein (CP), respectively, while the function of the proteins encoded by ORF2 and ORF4 was unknown. The virion of SsAFV1 was flexuous filamentous 480-510 nm in length and 9-10 nm in diameter. The results of the alignment and the phylogenetic analysis showed that SsAFV1 is related to allexivirus and botrexvirus, such as Garlic virus X of the genus Allexivirus and Botrytis virus X of the genus Botrevirus, both with 44% amino-acid (aa) identity of replicase. Thus, SsAFV1 is a novel virus and a new genus, Sclerotexvirus, is proposed to accommodate this novel alphaflexivirus.