Integrated mRNA and Small RNA Sequencing for Analyzing Leaf Spot Pathogen Didymella segeticola and Its Host, Tea (Camellia sinensis), During Infection.

Leaf spot on tea plants (Camellia sinensis [L.] Kuntze), caused by the fungus Didymella segeticola (Q. Chen) Q. Chen, Crous & L. Cai (syn. Phoma segeticola), negatively affects the productivity and quality of tea leaves in Guizhou Province, China. Although the genome sequence of D. segeticola has been published, no data on the transcriptome or microRNAs (miRNAs) of the pathogen or host during infection are available. Here, we report on the high-quality transcriptome and miRNA sequences of both D. segeticola and tea during infection, using the Illumina HiSeq 4000 or HiSeq 2500 platforms. Comprehensive expression profiling of the fungal pathogen and its host will provide a resource for future research into trait-specific genes of the pathogen and the host as well as on host-pathogen interactions and on disease resistance mechanisms.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Integrated mRNA and Small RNA Sequencing for Analyzing Tea Leaf Spot Pathogen Lasiodiplodia theobromae, Under In Vitro Conditions and the Course of Infection.

Lasiodiplodia theobromae is a phytopathogenic fungus, which can cause many different diseases on different crops. The pathogen can cause leaf spot on tea plants (Camellia sinensis), which negatively affects the productivity and quality of tea leaves in tea plantations in Guizhou Province, China. Although the genome sequence of L. theobromae has been published, no data on the transcriptome or small RNA sequences of L. theobromae under in vitro conditions and the course of infection of tea leaf are available. Here, we report the high-quality transcriptome and small RNA sequences of L. theobromae in vitro conditions and the course of infection of tea leaf using the platform of Illumina HiSeq. This comprehensive expression profiling of the fungal pathogen will provide a valuable resource for future research on trait-specific genes of the pathogen, host-pathogen interactions, and disease resistance in the host.

Antifungal Activity and Possible Mode of Action of Ningnanmycin Against Tea Gray Blight Disease Pathogen Pseudopestalotiopsis camelliae-sinensis.

Gray blight is a serious disease of tea (Camellia sinensis) for which there is currently no effective control or preventive measure apart from fungicides. Screening for effectiveness of a natural antimicrobial against this pathogen and identifying its mode of action could contribute to the management of this disease. Antifungal activity of the antimicrobial ningnanmycin (NNM) from Streptomyces noursei var. xichangensis against the pathogen causing gray blight disease, Pseudopestalotiopsis camelliae-sinensis strain GZHS-2017-010, was confirmed in vitro by the mycelial growth rate method. Optical microscopy, scanning electron microscopy, and transmission electron microscopy were used to observe morphological changes in hyphae of P. camelliae-sinensis treated with NNM. RNA sequencing, bioinformatics, and quantitative real-time PCR were used to identify genes in the hyphae that were differentially expressed in response to treatment with NNM. Thirty-eight genes from 16 pathways, known as targets of antifungal agents, were used to investigate gene expression in hyphae at the half-maximal effective concentration (EC50), EC30, and EC70 for 1, 7, or 14 h. The results indicated that NNM can inhibit the growth of hyphae in vitro, with an EC50 of 75.92 U/ml, inducing morphological changes in organelles, septa, and extracellular polysaccharides, targeting ribosomes to disturb translation in protein synthesis and influencing some biosynthetic functions of the hyphae.

First Report of Epicoccum nigrum Causing Brown Leaf Spot in Tea in Guizhou Province, China.

Brown leaf spots were observed on tea [Camellia sinensis (L.) Kuntze] in Sinan County (27.74 °N, 108.35 °E) and Kaiyang County (27.96 °N, 107.34 °E), Guizhou Province, China, from 2018 to 2020. For the leaf spots with the typical symptoms, the disease incidence was estimated to range between 56% and 61%, respectively. The disease severity was estimated to range from 39 to 43 across 12 tea plantations, respectively. The disease initially occurred at the margins of leaf tips, and the lesions expanded gradually, being dark brown and irregularly shaped and became necrotic. To identify the causal organism, two leaves from each of 15 tea twigs, one or two per plantation, were detached from 8- or 10-year-old tea plants on each of 12 plantations. Samples taken from the lesion margins were sterilized with 75% ethanol followed by 0.5% NaOCl, placed on potato dextrose agar (PDA), and then incubated at 25oC in darkness for 5 days (Wang et al. 2020). For each sample, hyphal tips from the margin of a growing colony were successively transferred to fresh PDA, and pure cultures were obtained. Three representative strains were grown on PDA, malt extract agar (MEA), and oatmeal agar (OA) plates. The colonies had smooth margins and abundant mycelia on all three media, with the colony colors being from gray to light purple on PDA, white on MEA, and purplish-red on OA at 5 days post-inoculation. At 20 days post-inoculation on MEA, stromata began to gradually form, which were droplet-like, 100 to 2,000 µm in diameter, and semi-immersed on the medium's surface. Black sporodochia were produced on the surfaces of stromata. Conidiophores were aggregated in sporodochia, densely compacted, and dark brown. Conidia were globose or pyriform, dark, multicellular, and measured 22.95 ± 3.59 × 19.82 ± 3.13 µm (n = 50) in diameter. The morphological characteristics of the mycelia and reproductive structures of the strains were identical to those of Epicoccum nigrum. The internal transcribed spacer (ITS) region of rDNA, and the partial 28S large subunit rDNA (LSU), RNA polymerase II second largest subunit (RPB2), and beta-tubulin (TUB) genes of these strains were amplified using the primers V9G/ITS4 (De Hoog and Gerrits van den Ende 1998; White et al. 1990), LR0R/LR5 (Rehner and Samuels 1994), RPB2-5F2/fRPB2-7cR (Sung et al. 2007), and TUB2Fd/TUB4Rd (Woudenberg et al. 2009), respectively, and deposited in GenBank (accession no. MW646378, MW291537, MW602293, and MW602295 for ITS, LSU, RBP2, and TUB, respectively). A maximum parsimony phylogenetic analysis indicated that the representative strains clustered with E. nigrum CBS 173.73 (Chen et al. 2017). Pathogenicity tests were performed on 5-year-old potted tea and on 10-year-old C. sinensis cv. Fuding-dabaicha in the field. Mycelial plugs (6-mm diam.) and a conidial suspension (106 conidial/mL) were applied on punctured leaves using a sterile needle and non-punctured leaves. Inoculation with only a PDA plug or sterile water served as controls. Brown spots appeared on the wounded sites of tea leaves at 2 days post-inoculation. No symptoms were observed on the non-wounded leaves or wounded leaves inoculated with PDA plugs lacking mycelia. The re-isolated pathogen from diseased plants was identical to the purified strain ACCC39731 used for inoculation, with re-isolation frequency being 85.0%. To our knowledge, this is the first report of E. nigrum causing leaf spot on tea plants in China, and our findings will be useful for its management and further research.

Whole Genome Sequence and Gene Annotation Resource for Didymella bellidis Associated with Tea Leaf Spot.

Didymella bellidis is a phytopathogenic fungus that causes leaf spot on tea plants (Camellia sinensis), which negatively affects the productivity and quality of tea leaves in Guizhou Province, China. D. bellidis isolate GZYQYQX2B was sequenced using Pacific Biosciences and Illumina technologies, and assembled into a whole genome of 35.5 Mbp. Transcripts of D. bellidis isolate GZYQYQX2B were predicted from the assembled genome and were further validated by RNA sequence data. In total, 10,731 genes were predicted by integrating three approaches, namely ab initio and homology-based gene prediction, as well as transcriptomics data. The whole-genome sequence of D. bellidis will provide a resource for future research on trait-specific genes of the pathogen and host-pathogen interactions.

First report of Alternaria longipes causing leaf spot on tea in China.

Tea [Camellia sinensis (L.) Kuntze)] have been widely planted in Guizhou Province in recent years, and the cultivation area in the region ranks first among all the provinces or cities in China. Leaf spot disease was an important disease of tea in Kaiyang county, Guizhou Province, which mainly damaged young leaves and shoot of tea and led to a huge loss of the production of tea. The spots initially represented brown and round, and then the diameter of the spot was 4-6 mm during later period, with the color of the center in the spot changing white. Tea leaf spot disease always occurs in early spring and the region with 1300 m altitude. From 2016 to 2019, disease incidence of leaves was estimated at 84% to 92%, and the disease severity on a plant basis was determined to be 64% to 76%, depending on the field. To identify the causal agent of the foliar disease, pieces of the lesion margins were surface sterilized with 75% ethanol for 30 s, followed by 0.5% sodium hypochlorite for 5 min, rinsed with sterile water three times, plated on potato dextrose agar (PDA) and incubated in the dark at 25C for 3 to 5 d. The hyphal tips from the margins of the growing colonies were successively picked and transferred to fresh PDA plates to purify the isolates. The result indicated that the isolates on PDA represented initially round form, and white mycelium. The reverse sides of the isolates firstly displayed light yellow on PDA. Conidiophores represent dark brown, geniculate. Brown conidia, narrow ovoid, length: 22.9 ± 4.5 µm, width: 11.1 ± 1.7 µm, with 4 to 8 transverse septa and with conspicuously ornamented walls. The gene of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (Berbee et al. 1999) and the Alternaria allergen 1 (Alt a1) (Hong et al. 2005) of three strains were amplified, sequenced and deposited in Genbank. Maximum parsimony phylogenetic analysis based on concatenated sequences of combined GAPDH (1-583) and Alt a 1 (588-1065) indicated that the strain AXLKY_2019_010 was identical to reference strain Alternaria longipes strain EGS 30-033, and the clade was supported by 96% bootstrap values. According to the Koch's postulate, the tea leaves were inoculated with PDA plugs with actively growing mycelia using the methods of the puncture, cut and unwound under the laboratory conditions and the natural conditions. Slight yellow spots were gradually formed after 2 d post-inoculation on the inoculated leaves, and the color of the center of the spot changed to be white. With the prolonging of inoculation time, the size of lesion represented to be slightly enlarged. PDA plugs without mycelia were used as a control, and the control group showed no symptoms. The same isolates were consistently reisolated from inoculated leaves. A. longipes can cause leaf blight of carrots in Israel (Vintal et al. 2002), leaf spot of potato in Pakistan (Shoaib et al. 2014) and leaf spot of Atractylodes macrocephala in China (Tan et al. 2012). To our knowledge, this is the first report of A. longipes causing leaf spot on tea in China and our findings will be useful for its management and for further research.

Transcriptomic, Biochemical, and Morphological Study Reveals the Mechanism of Inhibition of Pseudopestalotiopsis camelliae-sinensis by Phenazine-1-Carboxylic Acid.

Gray blight disease is one of the most destructive diseases of tea plants and occurs widely in the tea-growing areas of the world. It is caused by several fungal phytopathogens, of which Pseudopestalotiopsis camelliae-sinensis is the main pathogen in China. The environmentally friendly antimicrobial, phenazine-1-carboxylic acid (PCA), a metabolite of the natural soil-borne bacteria Pseudomonas spp., can inhibit a range of fungal crop diseases. In this study, we determined that PCA was active against Ps. camelliae-sinensis in vitro. We studied the mode of action of PCA on hyphae using a microscopic investigation, transcriptomics, biochemical methods, and molecular docking. The results of scanning and transmission electron microscopy indicated that PCA caused developmental deformity of mycelia and organelle damage, and it significantly decreased the accumulation of exopolysaccharides on the hyphal surface. The transcriptome revealed that 1705 and 1683 differentially expressed genes of Ps. camelliae-sinensis treated with PCA were up-regulated or down-regulated, respectively, with genes associated with ribosome biogenesis, oxidative phosphorylation, and encoding various proteins of N-glycan biosynthesis being significantly up-regulated. Up-regulation of nine genes related to N-glycan biosynthesis of Ps. camelliae-sinensis in response to PCA treatment was confirmed by reverse transcription qPCR. The enzymatic activity of catalase and superoxide dismutase of hyphae was significantly decreased by PCA treatment. Our results indicated that exposure to PCA resulted in expression changes in oxidoreductase genes, accumulation of reactive oxygen species, and decreased activity of catalase, with concomitant damage to the fungal cell membrane and cell wall.