Effects of chlorantraniliprole on the development, fecundity and prey consumption of a non-specific predator, Rhynocoris fuscipes (Hemiptera: Reduviidae).

Transplant treatment with chlorantraniliprole (CAP) is a proactive approach to protect transplanted plants from pests during early establishment and has been comprehensively applied in tobacco fields in Guangdong Province, China. However, it is not known whether the high dose of CAP in transplant treatments has lethal or sublethal effects on the generalist predator Rhynocoris fuscipes Fabricius (Hemiptera: Reduviidae). To address this concern, the mortalities of R. fuscipes were assessed when 2nd instar larvae of R. fuscipes were in direct contact with or consuming CAP and when their eggs were exposed to CAP. Furthermore, 2nd instar nymphs R. fuscipes were long-term exposed to CAP until they reached adulthood, and their life table parameters were determined. After exposure to CAP, the activity of detoxification enzymes (P450, CaeE and GST) and the functional respond of R. fuscipes to their preys Agrotis ipsilon larvae were determined. In this study, CAP at all concentrations did not significantly increase the mortality of 2nd instar of R. fuscipes nymphs in comparison with the control. The detoxification enzyme (P450, CarE and GST) activities and the number of A. ipsilon larvae consumed by R. fuscipes in the transplant treatment were not affected by CAP after 3-d or long-term exposure. These results indicated that CAP was harmless to R. fuscipes according to IOBC protocols. However, during the treatment of 2nd instar nymphs with a label rate of 15 g AI/ha and a 5× label rate of 75 g AI/ha, CAP significantly prolonged the pre-adult and pre-oviposition periods, and treated adults had lower oviposition. Attention should be given to the time interval between transplant treatment and the release of this biocontrol agent into the field to minimize the impact of CAP on the predator R. fuscipes.

Phosphatidyl Ethanolamine Binding Protein FLOWERING LOCUS T-like 12 (OsFTL12) Regulates the Rice Heading Date under Different Day-Length Conditions.

Plant FLOWERING LOCUS T-Like (FTL) genes often redundantly duplicate on chromosomes and functionally diverge to modulate reproductive traits. Rice harbors thirteen FTL genes, the functions of which are still not clear, except for the Hd3a and RFT genes. Here, we identified the molecular detail of OsFTL12 in rice reproductive stage. OsFTL12 encoding protein contained PEBP domain and localized into the nucleus, which transcripts specifically expressed in the shoot and leaf blade with high abundance. Further GUS-staining results show the OsFTL12 promoter activity highly expressed in the leaf and stem. OsFTL12 knock-out concurrently exhibited early flowering phenotype under the short- and long-day conditions as compared with wild-type and over-expression plants, which independently regulates flowering without an involved Hd1/Hd3a and Ehd1/RFT pathway. Further, an AT-hook protein OsATH1 was identified to act as upstream regulator of OsFTL12, as the knock-out OsATH1 elevated the OsFTL12 expression by modifying Histone H3 acetylation abundance. According to the dissection of OsFTL12 molecular functions, our study expanded the roles intellectual function of OsFTL12 in the mediating of a rice heading date.

First Report of Fusarium Root Rot of Tobacco Caused by Fusarium fujikuroi in Guangdong Province, China.

From March to June 2022, Fusarium tobacco root rot broke out in Shaoguan Guangdong Province, China, affecting approximately 15% of tobacco production fields, with an incidence of 24% to 66%. In the early stage, the lower leaves showed chlorosis, and the roots became black. In the later stage, the leaves became browned and withered, the root cortices were broken and shed, and only a small number of roots were left. Eventually, the entire plant died. Six diseased plant samples (cv. yueyan 97) from Shaoguan (113.8°E, 24.8°N) were collected as test materials. The diseased root tissues (4×4 mm) were surface-sterilized using 75% ethanol for 30 s and 2% NaOCl for 10 min, rinsed 3 times with sterile water and incubated for 4 days on potato dextrose agar (PDA) medium at 25 °C. Fungal colonies were subcultured on fresh PDA, grown for the next 5 d and purified by single-spore separation. Eleven isolates with similar morphological characteristics were obtained. Their colonies were white and fluffy, and the bottoms of the culture plates were pale pink after 5 days of incubation. The macroconidia were slender, slightly curved and measured 18.54~45.85 µm×2.35~3.84 µm (n=50), with 3 to 5 septa. The microconidia were oval or spindle shaped, with one to two cells, and measured 5.56~16.76 µm×2.32~3.86 µm (n=50). Chlamydospores were absent. Such characteristics are typical of the genus Fusarium (Booth C, 1971). The SGF36 isolate was chosen for further molecular analysis. The TEF-1α and ß-tubulin genes (Pedrozo et al.2015) were amplified. Based on a phylogenetic tree (neighbor-joining method and 1,000 bootstrap values) obtained using multiplex alignments of concatenations of these two genes from 18 Fusarium species, SGF36 was grouped into a clade with Fusarium fujikuroi strain 12-1 (MK443268.1/MK443267.1) and F. fujikuroi isolate BJ-1 (MH263736.1/MH263737.1). To further identity the isolate, five additional gene sequences (rDNA-ITS (OP862807.1), RPB2, histone 3, calmodulin, and mitochondrial small subunit) (Pedrozo et al.2015), were subjected to BLAST searches in GenBank, and the results indicated that they were most similar to F. fujikuroi sequences, with sequence identities greater than 99%. The phylogenetic tree obtained using six genes except mitochondrial small subunit gene showed that SGF36 was grouped together with four F. fujikuroi strains to form a single clade. Pathogenicity was determined by the inoculation of wheat grains with fungi in potted tobacco plants. The SGF36 isolate was inoculated onto sterilized wheat grains, which were then incubated at 25 °C for 7 d. Thirty wheat grains with fungi were added to 200 g of sterilized soil, which was then mixed well and placed into pots. One six-leaf-stage tobacco seedling (cv. yueyan 97) was planted in each pot. A total of 20 tobacco seedlings were treated. Another 20 control seedlings were treated with wheat grains without fungi. All seedlings were placed in a greenhouse at 25 °C with 90% relative humidity. After 5 d, the leaves of all inoculated seedlings showed chlorosis, and the roots became discolored. No symptoms were observed in the controls. The fungus was reisolated from symptomatic roots and confirmed to be F. fujikuroi based on the TEF-1α gene sequence. No F. fujikuroi isolates were recovered from control plants. F. fujikuroi was previously reported to be associated with rice bakanae disease (Ram et al., 2018), soybean root rot (Zhao et al., 2020) and cotton seedling wilt (Zhu et al., 2020). To our knowledge, this is the first report of F. fujikuroi causing root wilt on tobacco in China. The identification of the pathogen may help to establish appropriate measures for controlling this disease.

Petunia hybrida is a New Host of Pectobacterium brasiliense Associated with Soft Rot Disease in China.

Petunia hybrida is commonly cultivated for ornamental use in urban parks greening and street embellishment in China. In March 2022, 60% of P. hybrida plants cv. Wave Purple (n≈1800) from an ornamental plant nursery under natural conditions in Tianhe district (N 113°21'21", E 23°9'3.5"), Guangzhou, Guangdong Province, China, were affected with soft rot disease. The distribution of the disease was generally uniform. Infected plants initially exhibit small water-soaked lesions at the base of the stem, which then extended to the leaves. Eventually the diseased plant collapsed and died. Nine diseased plants were collected, and affected tissues cut into small fragments (5 × 5 mm), which were disinfested in 75% ethanol (30 s) and 2% sodium hypochlorite (60 s), followed by three rinses with sterile distilled water. The sterilized sections were macerated in 200 µl sterile water, and streaked on Luria-Bertani (LB) agar medium and incubated at 28°C for 48 h. Single colonies were restreaked three times to obtain purified isolation. Sixteen bacterial strains with similar morphology were isolated, and their colonies were yellowish white, round, and convex with smooth surfaces on LB agar plate. The representative strain BDQ1 was selected for further analyses and the 16S rDNA gene (GenBank Accession ON982467) were amplified using primer pair 27F/1492R, revealed above 99% sequence identity with some Pectobacterium brasiliense isolates (GenBank Accession Nos. CP046380(1421/1422), MN393966(1419/1422), and CP020350(1419/1422)) using BLASTn. A multilocus phylogenetic analysis by neighbor-joining method (1,000 bootstrap values) based on six housekeeping gene sequences of gyrA (GenBank Accession No. ON995454), icdA (ON995455), mdh (ON995456), mtlD (ON995457), proA (ON995458), and rpoS genes (ON995459) (Ma et al. 2007; Waleron et al., 2008). The results of phylogenetic analysis showed BDQ1 strain belong to the P. brasiliense clade. Pathogenicity tests were performed on ten healthy P. hybrida cv. Wave Purple plants by injecting 10 µl of bacterial suspensions of BDQ1 (108 CFU/ml) into the stems; another 10 healthy control plants were injected with 10 µl of sterile water. All plants were grown at 25-30°C and 60% humidity in natural light/dark cycle. After 3 d, all inoculated plants showed soft rot symptoms resembling to those observed in the nursery, while control plants remained healthy. Bacteria were successfully reisolated from the symptomatic tissues and identified to be P. brasiliense by PCR mentioned above. P. brasiliense is considered a very aggressive pathogen, which has been reported in Eurasia and Africa (Oulghazi et al. 2021). To our knowledge, this is the first report of P. brasiliense causing bacterial soft rot on P. hybrida in China. This pathogen may pose threat to P. hybrida production in area with warmand humid climate in China. The current study expands the known host range of P. brasiliense and helped raise attention on controlling pathogen spread.

Antimicrobial Activity of Natural Plant Compound Carvacrol Against Soft Rot Disease Agent Dickeya zeae.

Dickeya zeae is a globally important bacterial pathogen that has been reported to cause severe soft rot diseases in several essential food crops, including bananas, rice, maize, and potatoes. Carvacrol, a hydrophobic terpene component, is found in aromatic plants of the Labiatae family and various essential oils. However, little work has been done on its antimicrobial potential against D. zeae. This study aimed to evaluate the antimicrobial activity and the functional mechanism of carvacrol against D. zeae. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of carvacrol against D. zeae were 0.1 mg/mL and 0.2 mg/mL, respectively. Carvacrol affected the cell membrane of D. zeae, as revealed by decreased intracellular ATP concentration, nucleic acid leakage, and decreased membrane potential. Scanning electron microscopy (SEM) micrographs confirmed that D. zeae cell membranes were damaged by carvacrol. Furthermore, a significant inhibition of D. zeae swimming motility and biofilm formation was observed following treatments with carvacrol at sub-inhibitory concentrations, indicating a significantly negative effect on these virulence factors. Accordingly, the tissue infection test revealed that carvacrol significantly reduced the pathogenicity of D. zeae. In a pot experiment, inoculated banana seedlings displayed remarkably lesser disease symptoms following treatment with carvacrol, and the control efficiency for banana soft rot was 32.0% at 14 days post-inoculation. To summarize, carvacrol exhibits strong antimicrobial activity against D. zeae and great potential applications in the control of D. zeae-associated crop diseases.

First report of Curvularia gladioli causing leaf spots on Gladiolus gandavensis in China.

Gladiolus (Gladiolus gandavensis Van Houtte) is a perennial plant in the family Iridaceae, which shows sword-shaped leaves and spikes of brilliantly colored irregular flowers arising from corms. It is one of the most important fresh cut flowers and is widely cultivated worldwide, including in China. In September 2020, white pinpoints were first observed on gladiolus leaves in Jiangmen City, Guangdong Province, China. The white spots eventually turned brown. The lesions then developed into oval to circular spots, which were surrounded with an obvious yellow halo. The spots expanded and coalesced, causing leaf blight. These symptoms were observed on approximately 10% of gladiolus plants in fields measuring ca. 70 ha. Symptomatic leaves were sampled from fields, surface sterilized in 75% ethanol for 30 s, submerged in a 2% NaOCl solution for 10 min, and rinsed three times with sterile water. The samples were then cut into pieces (5 × 5 mm) and incubated for 4 d on potato dextrose agar (PDA) at 25°C. A representative fungal colony was subcultured onto new PDA and grown for another 7 d, and its mycelium appeared to be grayish-black and villiform. This strain was named as Cg_TS. Its conidiophores were simple, septate, cylindrical in shape, and moderate brown in color. They occurred singly or in groups. They were straight or slightly flexuous and ranged in size from 57.0 to 80.0 µm × 4.0 to 8.0 µm. Conidia were 3-distoseptate and curved at the third cell from the base. The third cell was swollen to one side and larger than other cells. These conidia ranged in size from 23.5 to 32.0 µm × 11.5 to 16.0 µm. These morphological characteristics were consistent with the description of Curvularia gladioli Boerema & Hamers (Boerema and Hamers 1989). Using primer pair ITS1 and ITS4, PCR was applied to amplify the internal transcribed spacer (ITS) region of rDNA. This sequence (GenBank accession No. MW426196.1) was subjected to BLAST in GenBank, suggesting that it was most similar to C. gladioli sequences, LT631345.1 and HG778987.1, with both of 99.49% of similarity. To fulfill Koch's postulates, healthy two-month-old gladiolus plants were used for pathogenicity testing, and the leaves were wounded by pressing slightly with a pipette tip. Mycelium disks (3 mm diameter) were applied onto wounded leaves of 10 plants. Another 10 healthy plants were inoculated with PDA disks which served as control. Inoculated samples were placed in a greenhouse at 25°C and 90% relative humidity. After 3 d, brown leaf spots appeared on all of pathogen-inoculated leaves. The symptoms were consistent with those initially observed and C. gladioli was re-isolated from the symptomatic tissue. Identification was confirmed by morphological observation and ITS sequencing. Control leaves remained symptomless. The curvularia fungus was firstly reported on gladiolus in Florida in 1947 and spread globally via infected corms (Torre et al. 2015), it was also reported to cause leaf spots on gladiolus in Brazil in 2013 (Torres et al. 2013). Although C. gladioli had been recorded as a Curvularia species occurring in China (Zhang et al. 2006), it was not reported to cause leaf spots on gladiolus in Guangdong Province and elsewhere in China. To our knowledge, this is the first report of Curvularia gladioli causing leaf spots on gladiolus in China. Identification of this pathogen will help develop diagnostic methods for corms and seedlings, and may lead to the development of appropriate chemical management strategies.

Genomic analysis of the Phalaenopsis pathogen Dickeya sp. PA1, representing the emerging species Dickeya fangzhongdai.

BACKGROUND: Dickeya sp. strain PA1 is the causal agent of bacterial soft rot in Phalaenopsis, an important indoor orchid in China. PA1 and a few other strains were grouped into a novel species, Dickeya fangzhongdai, and only the orchid-associated strains have been shown to cause soft rot symptoms. METHODS: We constructed the complete PA1 genome sequence and used comparative genomics to explore the differences in genomic features between D. fangzhongdai and other Dickeya species. RESULTS: PA1 has a 4,979,223-bp circular genome with 4269 predicted protein-coding genes. D. fangzhongdai was phylogenetically similar to Dickeya solani and Dickeya dadantii. The type I to type VI secretion systems (T1SS-T6SS), except for the stt-type T2SS, were identified in D. fangzhongdai. The three phylogenetically similar species varied significantly in terms of their T5SSs and T6SSs, as did the different D. fangzhongdai strains. Genomic island (GI) prediction and synteny analysis (compared to D. fangzhongdai strains) of PA1 also indicated the presence of T5SSs and T6SSs in strain-specific regions. Two typical CRISPR arrays were identified in D. fangzhongdai and in most other Dickeya species, except for D. solani. CRISPR-1 was present in all of these Dickeya species, while the presence of CRISPR-2 varied due to species differentiation. A large polyketide/nonribosomal peptide (PK/NRP) cluster, similar to the zeamine biosynthetic gene cluster in Dickeya zeae rice strains, was discovered in D. fangzhongdai and D. solani. The D. fangzhongdai and D. solani strains might recently have acquired this gene cluster by horizontal gene transfer (HGT). CONCLUSIONS: Orchid-associated strains are the typical members of D. fangzhongdai. Genomic analysis of PA1 suggested that this strain presents the genomic characteristics of this novel species. Considering the absence of the stt-type T2SS, the presence of CRISPR loci and the zeamine biosynthetic gene cluster, D. fangzhongdai is likely a transitional form between D. dadantii and D. solani. This is supported by the later acquisition of the zeamine cluster and the loss of CRISPR arrays by D. solani. Comparisons of phylogenetic positions and virulence determinants could be helpful for the effective quarantine and control of this emerging species.

Characterization of Canna yellow mottle virus in a New Host, Alpinia purpurata, in Hawaii.

Canna yellow mottle virus (CaYMV) is an important badnavirus infecting Canna spp. worldwide. This is the first report of CaYMV in flowering ginger (Alpinia purpurata) in Hawaii, where it is associated with yellow mottling and necrosis of leaves, vein streaking, and stunted plants. We have sequenced CaYMV in A. purpurata (CaYMV-Ap) using a combination of next-generation sequencing and traditional Sanger sequencing techniques. The complete genome of CaYMV-Ap was 7,120 bp with an organization typical of other Badnavirus species. Our results indicated that CaYMV-Ap was present in the episomal form in infected flowering ginger. We determined that this virus disease is prevalent in Hawaii and could potentially have significant economic impact on the marketing of A. purpurata as cut flowers. There is a potential concern that the host range of CaYMV-Ap may expand to include other important tropical plants.

Anandins A and B, Two Rare Steroidal Alkaloids from a Marine Streptomyces anandii H41-59.

Anandins A (1) and B (2), two rare steroidal alkaloids, were isolated from the fermentative broth of a marine actinobacteria Streptomyces anandii H41-59. The gross structures of the two alkaloids were elucidated by spectroscopic methods including HR-ESI-MS, and NMR. Their absolute configurations were confirmed by single-crystal X-ray diffraction analysis and comparison of their experimental and calculated electronic circular dichroism spectra, respectively. Anandin A exhibited a moderate inhibitory effect against three human cancer cell lines MCF-7, SF-268, and NCI-H460 with IC50 values of 7.5, 7.9, 7.8 µg/mL, respectively.

Deep sequencing of banana bract mosaic virus from flowering ginger (Alpinia purpurata) and development of an immunocapture RT-LAMP detection assay.

Banana bract mosaic virus (BBrMV) has never been reported in banana plants in Hawaii. In 2010, however, it was detected in a new host, flowering ginger (Alpinia purpurata). In this study, we characterize the A. purpurata isolate and study its spread in flowering ginger in Hawaii. A laboratory study demonstrated that BBrMV could be transmitted from flowering ginger to its natural host, banana, therefore raising a serious concern about the potential risk to the rapidly growing banana industry of Hawaii. To quickly monitor this virus in the field, we developed a robust immunocapture reverse transcription loop-mediated isothermal amplification (IC-RT-LAMP) assay. Deep sequencing of the BBrMV isolate from A. purpurata revealed a single-stranded RNA virus with a genome of 9,713 nt potentially encoding a polyprotein of 3,124 aa, and another predicted protein, PIPO, in the +2 reading-frame shift. Most of the functional motifs in the Hawaiian isolate were conserved among the genomes of isolates from one found in the Philippines and India. However, the A. purpurata isolate had an amino acid deletion in the Pl protein that was most similar to the Philippine isolate. Phylogenetic analysis of an eastern Pacific subpopulation that included A. purpurata was closest in genetic distance to a Southeast Asian subpopulation, suggesting frequent gene flow and supporting the hypothesis that the A. purpurata isolate arrived in Hawaii from Southeast Asia.

Dickeya fangzhongdai was prevalent and caused taro soft rot when coexisting with the Pectobacterium complex, with a preference for Araceae plants.

Bacterial soft rot caused by coinfection with Dickeya spp. and Pectobacterium spp. in hosts can cause successive changes in fields, and it is difficult to prevent the spread of and control the infection. Pectobacterium spp. are prevalent in the growing areas of tuberous crops, including taro and potato. Recently, Dickeya fangzhongdai has emerged as a virulent pathogen in taro. To determine the prevalence status of the causal agents and evaluate the potential spreading risks of D. fangzhongdai, screening and taxonomic classification were performed on phytopathogenic bacteria collected from different taro-growing areas in Guangdong Province, China, and biological and genomic characteristics were further compared among typical strains from all defined species. The causative agents were verified to be phytobacterial strains of D. fangzhongdai, Pectobacterium aroidearum and Pectobacterium colocasium. P. aroidearum and P. colocasium were found to form a complex preferring Araceae plants and show intensive genomic differentiation, indicating their ancestor had adapted to taro a long time prior. Compared with Pectobacterium spp., D. fangzhongdai was more virulent to taro corms under conditions of exogenous infection and more adaptable at elevated temperatures. D. fangzhongdai strains isolated from taro possessed genomic components of additional T4SSs, which were accompanied by additional copies of the hcp-vgrG genes of the T6SS, and these contributed to the expansion of their genomes. More gene clusters encoding secondary metabolites were found within the D. fangzhongdai strains than within the Pectobacterium complex; interestingly, distinct gene clusters encoding zeamine and arylpolyene were both most similar to those in D. solani that caused potato soft rot. These comparisons provided genomic evidences for that the newly emerging pathogen was potentially equipped to compete with other pathogens. Diagnostic qPCR verified that D. fangzhongdai was prevalent in most of the taro-growing areas and coexisted with the Pectobacterium complex, while the plants enriching D. fangzhongdai were frequently symptomatic at developing corms and adjacent pseudostems and caused severe symptoms. Thus, the emerging need for intensive monitoring on D. fangzhongdai to prevent it from spreading to other taro-growing areas and to other tuberous crops like potato; the adjustment of control strategies based on different pathopoiesis characteristics is recommended.

Silica nanoparticles conferring resistance to bacterial wilt in peanut (Arachis hypogaea L.).

Peanut bacterial wilt (PBW) caused by the pathogen Ralstonia solanacearum severely affects the growth and yield potential of peanut crop. In this study, we synthesized silica nanoparticles (SiO2 NPs), a prospective efficient management approach to control PBW, and conducted a hydroponic experiment to investigate the effects of different SiO2 NPs treatments (i.e., 0, 100, and 500 mg L-1 as NP0, NP100, and NP500, respectively) on promoting plant growth and resistance to R. solanacearum. Results indicated that the disease indices of NP100 and NP500 decreased by 51.5 % and 55.4 % as compared with NP0 under R. solanacearum inoculation, respectively, while the fresh and dry weights and shoot length of NP100 and NP500 increased by 7.62-42.05 %, 9.45-32.06 %, and 2.37-17.83 %, respectively. Furthermore, SiO2 NPs induced an improvement in physio-biochemical enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and lipoxygenase) which eliminated the excess production of hydrogen peroxide, superoxide anions, and malondialdehyde to alleviate PBW stress. Notably, the targeted metabolomic analysis indicated that SiO2 NPs enhanced salicylic acid (SA) contents, which involved the induction of systemic acquired resistance (SAR). Moreover, the transcriptomic analysis revealed that SiO2 NPs modulated the expression of multiple transcription factors (TFs) involved in the hormone pathway, such as AHLs, and the identification of hormone pathways related to plant defense responses, such as the SA pathway, which activated SA-dependent defense mechanisms. Meanwhile, the up-regulated expression of the SA-metabolism gene, salicylate carboxymethyltransferase (SAMT), initiated SAR to promote PBW resistance. Overall, our findings revealed that SiO2 NPs, functioning as a plant elicitor, could effectively modulate physiological enzyme activities and enhance SA contents through the regulation of SA-metabolism genes to confer the PBW resistance in peanuts, which highlighted the potential of SiO2 NPs for sustainable agricultural practices.

Hemiactinomycin, an undescribed intermediate of actinomycin biosynthesis from an actinomycetes strain Streptomyces antibioticus H41-55.

Hemiactinomycin (1), an intermediate derivative of actinomycin biosynthesis, together with three known actinomycins (2-4) , were isolated from the ethanolic extract of Streptomyces antibioticus H41-55 fermentation mycelium by using various column chromatography. The structure of the derivative was established by extensive spectroscopic analysis, including HRESIMS, 1D, and 2D NMR spectroscopy. In addition, the anti-inflammatory activities of all the isolates were tested. The derivative (1) showed inhibiting NO release activities in LPS-induced RAW 264.7 macrophages with the IC50 values of 15.41 ± 0.66 µM.

Genomic Comparisons and Phenotypic Diversity of Dickeya zeae Strains Causing Bacterial Soft Rot of Banana in China.

Bacterial soft rot of banana, caused by Dickeya zeae, is spreading rapidly in important banana growing areas in China and seriously threatens banana production. In this study, we sequenced the high-quality complete genomes of three typical banana strains, MS1 (size: 4,831,702-bp; genome coverages: 538x), MS_2014 (size: 4,740,000-bp; genome coverages: 586x) and MS_2018 (size: 4,787,201-bp; genome coverages: 583x), isolated in 2009, 2014, and 2018, respectively. To determine their genomic and phenotypic diversity with respect to their hosts of origin, they were compared with other D. zeae strains, including another representative banana strain MS2 from China. The sequenced strains were similar in utilization of carbon source and chemical substrates, and general genomic features of GC content, and tRNA and rRNA regions. They were also conserved in most virulence determinants, including gene-encoding secretion systems, plant cell wall degrading enzymes, and exopolysaccharides. We further explored their genomic diversity in the predicted genomic islands (GIs). These GIs were rich in integrases and transposases, where some genomic dissimilarity was observed in the flagellar gene cluster and several secondary metabolite gene clusters. Different constituents of core biosynthetic modules were found within the bacteriocin and aryl polyene (APE) pigment gene clusters, and the strains from banana showed different phenotypes with respect to antibiosis effects and colony pigmentation. Additionally, clustered regularly interspaced short palindromic repeat (CRISPR) and prophage elements, such as type I-F and III-A CRISPR arrays and an intact prophage of MS1-P5, contributed to bacterial diversity. Phylogenetic tree analysis and genome-genome nucleotide comparison confirmed the genomic divergence among the strains isolated from banana. Considering these characteristics, MS2 and MS_2014 probably diverged later than MS1, while MS_2018 was different and more similar to foreign strains isolated from other hosts in several characteristics. Strain MS_2018 caused severe symptoms on banana varieties previously considered moderately resistant or moderately susceptible, including varieties of Cavendish (Musa AAA) and Plantain (Musa ABB). Our study of genomic and phenotypic diversity raises public attention to the risk of spreading new pathogenic variants within banana growing regions and supports development of predictive strategies for disease control.

Genomic divergence between Dickeya zeae strain EC2 isolated from rice and previously identified strains, suggests a different rice foot rot strain.

Rice foot rot caused by Dickeya zeae is an important bacterial disease of rice worldwide. In this study, we identified a new strain EC2 from rice in Guangdong province, China. This strain differed from the previously identified strain from rice in its biochemical characteristics, pathogenicity, and genomic constituents. To explore genomic discrepancies between EC2 and previously identified strains from rice, a complete genome sequence of EC2 was obtained and used for comparative genomic analyses. The complete genome sequence of EC2 is 4,575,125 bp in length. EC2 was phylogenetically closest to previously identified Dickeya strains from rice, but not within their subgroup. In terms of secretion systems, genomic comparisons revealed that EC2 harbored only type I (T1SS), typeⅡ (T2SS), and type VI (T6SS) secretion systems. The flagella cluster of this strain possessed specific genomic characteristics like other D. zeae strains from Guangdong and from rice; within this locus, the genetic diversity among strains from rice was much lower than that of within strains from non-rice hosts. Unlike other strains from rice, EC2 lost the zeamine cluster, but retained the clustered regularly interspaced short palindromic repeats-1 (CRISPR-1) array. Compared to the other D. zeae strains containing both exopolysaccharide (EPS) and capsular polysaccharide (CPS) clusters, EC2 harbored only the CPS cluster, while the other strains from rice carried only the EPS cluster. Furthermore, we found strain MS1 from banana, carrying both EPS and CPS clusters, produced significantly more EPS than the strains from rice, and exhibited different biofilm-associated phenotypes. Comparative genomics analyses suggest EC2 likely evolved through a pathway different from the other D. zeae strains from rice, producing a new type of rice foot rot pathogen. These findings emphasize the emergence of a new type of D. zeae strain causing rice foot rot, an essential step in the early prevention of this rice bacterial disease.

CONSTANS-Like 9 (OsCOL9) Interacts with Receptor for Activated C-Kinase 1(OsRACK1) to Regulate Blast Resistance through Salicylic Acid and Ethylene Signaling Pathways.

In a previous transcriptome analysis of early response genes in rice during Magnaporthe oryzae infection, we identified a CONSTANS-like (COL) gene OsCOL9. In the present study, we investigated the functional roles of OsCOL9 in blast resistance. OsCOL9 belonged to group II of the COL protein family, and it contained a BB-box and a C-terminal CCT (CONSTANS, COL and TOC1) domain. OsCOL9 was found in the nucleus of rice cells, and it exerted transcriptional activation activities through its middle region (MR). Magnaporthe oryzae infection induced OsCOL9 expression, and transgenic OsCOL9 knock-out rice plants showed increased pathogen susceptibility. OsCOL9 was a critical regulator of pathogen-related genes, especially PR1b, which were also activated by exogenous salicylic acid (SA) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene (ET). Further analysis indicated that OsCOL9 over-expression increased the expressions of phytohormone biosynthetic genes, NPR1, WRKY45, OsACO1 and OsACS1, which were related to SA and ET biosynthesis. Interestingly, we found that OsCOL9 physically interacted with the scaffold protein OsRACK1 through its CCT domain, and the OsRACK1 expression was induced in response to exogenous SA and ACC as well as M. oryzae infection. Taken together, these results indicated that the COL protein OsCOL9 interacted with OsRACK1, and it enhanced the rice blast resistance through SA and ET signaling pathways.

4-Coumarate-CoA Ligase-Like Gene OsAAE3 Negatively Mediates the Rice Blast Resistance, Floret Development and Lignin Biosynthesis.

Although adenosine monophosphate (AMP) binding domain is widely distributed in multiple plant species, detailed molecular functions of AMP binding proteins (AMPBPs) in plant development and plant-pathogen interaction remain unclear. In the present study, we identified an AMPBP OsAAE3 from a previous analysis of early responsive genes in rice during Magnaporthe oryzae infection. OsAAE3 is a homolog of Arabidopsis AAE3 in rice, which encodes a 4-coumarate-Co-A ligase (4CL) like protein. A phylogenetic analysis showed that OsAAE3 was most likely 4CL-like 10 in an independent group. OsAAE3 was localized to cytoplasm, and it could be expressed in various tissues. Histochemical staining of transgenic plants carrying OsAAE3 promoter-driven GUS (ß-glucuronidase) reporter gene suggested that OsAAE3 was expressed in all tissues of rice. Furthermore, OsAAE3-OX plants showed increased susceptibility to M. Oryzae, and this finding was attributable to decreased expression of pathogen-related 1a (PR1) and low level of peroxidase (POD) activity. Moreover, OsAAE3 over-expression resulted in increased content of H2O2, leading to programmed cell-death induced by reactive oxygen species (ROS). In addition, OsAAE3 over-expression repressed the floret development, exhibiting dramatically twisted glume and decreased fertility rate of anther. Meanwhile, the expressions of lignin biosynthesis genes were significantly decreased in OsAAE3-OX plants, thereby leading to reduced lignin content. Taken together, OsAAE3 functioned as a negative regulator in rice blast resistance, floret development, and lignin biosynthesis. Our findings further expanded the knowledge in functions of AMBPs in plant floret development and the regulation of rice-fungus interaction.