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Tea is one of the most popular healthy and non-alcoholic beverages worldwide. Tea anthracnose is a disease in tea mature leaves and ultimately affects yield and quality. Colletotrichum camelliae is a dominant fungal pathogen in the tea field that infects tea plants in China. The pathogenic factors of fungus and the susceptible factors in the tea plant are not known. In this work, we performed molecular and genetic studies to observe a cerato-platanin protein CcCp1 from C. camelliae, which played a key role in fungal pathogenicity. △CcCp1 mutants lost fungal virulence and reduced the ability to produce conidia. Transcriptome and metabolome were then performed and analysed in tea-susceptible and tea-resistant cultivars, Longjing 43 and Zhongcha 108, upon C. camelliae wild-type CCA and △CcCp1 infection, respectively. The differentially expressed genes and the differentially accumulated metabolites in tea plants were clearly overrepresented such as linolenic acid and linoleic acid metabolism, glycerophospholipid metabolism, phenylalanine biosynthesis and metabolism, biosynthesis of flavonoid, flavone and flavonol etc. In particular, the accumulation of jasmonic acid was significantly increased in the susceptible cultivar Longjing 43 upon CCA infection, in the fungal CcCp1 protein dependent manner, suggesting the compound involved in regulating fungal infection. In addition, other metabolites in the glycerophospholipid and phenylalanine pathway were observed in the resistant cultivar Zhongcha 108 upon fungal treatment, suggesting their potential role in defense response. Taken together, this work indicated C. camelliae CcCp1 affected the tea plant lipid metabolism pathway to promote disease while the lost function of CcCp1 mutants altered the fungal virulence and plant response.

Background Tea, which is produced from new shoots of existing tea plants (Camellia sinensis), is one of the most popular, non-alcoholic, healthy beverages worldwide. Colletotrichum camelliae is one of the dominant fungal pathogens of tea. The interaction of C. camelliae with tea could be a useful pathosystem to elucidate various aspects of woody, medicinal plant-fungal interactions. Currently, many studies characterizing resistance or virulence and aggressiveness use lesion size at the infection sites on the leaves to quantify the growth of the pathogen. However, this method does not offer the sensitivity needed for the robust quantification of small changes in aggressiveness or the accurate quantification of pathogen growth at the early stages of infection. Results A quantitative real-time polymerase chain reaction (qRT-PCR) assay was developed for the quantification of C. camelliae growth on tea plant. This method was based on the comparison of fungal DNA in relation to plant biomass. This assay was used to investigate the phenotypes of tea plant cultivars in response to C. camelliae infection. Two cultivars, Zhongcha 108 (ZC108) and Longjing 43 (LJ43), were tested with this method. ZC108 was previously reported as an anthracnose-resistant cultivar against C. camelliae, while LJ43 was susceptible. The traditional lesion measurement method showed that both cultivars were susceptible to a virulent strain of C. camelliae, while the qRT-PCR approach indicated that very little fungal growth occurred in the anthracnose-resistant cultivar ZC108. The observed results in this study were consistent with previously published research. In addition, the DNA-based real-time PCR method was applied for analysis of pathogenic differences in general C. camelliae isolates and among several Colletotrichum spp that infect tea. Conclusions This study showed that the DNA-based qRT-PCR technique is rapid, highly sensitive and easily applicable for routine experiments and could be used in screening for resistant tea plant cultivars or to identify differences in pathogen aggressiveness within and among Colletotrichum species.

Additional file 2: Figure S1. Amplification results of target genes using DNA inputs from different organisms. M: DL2000 DNA Ladder (2000, 1000, 750, 500, 250, 100 bp); a Amplification results of GAPDH using DNA from Colletotrichum camelliae CCA (1), C. camelliae CCB (2), C. camelliae LS_19 (3), C. camelliae ZJ1A5 (4), C. camelliae ZJ1A8 (5), C. camelliae HB1A4 (6), C. fructicola SX_6 (7), C. siamense E-8–1 (8), C. fioriniae ZJ1A2 (9), Pseudopestalotiopsis camelliae-sinensis HUN1A3 (10), Neopestalotiopsis sp. YN1A5 (11), Magnaporthe oryzae (12) and tea cultivar LJ43 DNA control (13). b Amplification results of ITS using DNA from Colletotrichum camelliae CCA (1), C. camelliae CCB (2), C. camelliae LS_19 (3), C. camelliae ZJ1A5 (4), C. camelliae ZJ1A8 (5), C. camelliae HB1A4 (6), C. fructicola SX_6 (7), C. siamense E-8–1 (8), C. fioriniae ZJ1A2 (9), Pseudopestalotiopsis camelliae-sinensis HUN1A3 (10), Neopestalotiopsis sp. YN1A5 (11), Magnaporthe oryzae (12) and tea cultivar LJ43 DNA control (13).

Additional file 1: Table S1. Geographical distribution of tea pathogens used in this research.

The large WRKY transcription factor family is mainly involved in regulating plant immune responses. Arabidopsis WRKY33 is a key transcriptional regulator of hormonal and metabolic processes towards Botrytis cinerea strain 2100 infection and is essential for resistance. In contrast to B. cinerea strain 2100, the strain B05.10 is virulent on wild-type (WT) Col-0 Arabidopsis plants highlighting the genetic diversity within this pathogen species. We analysed how early WRKY33-dependent responses are affected upon infection with strain B05.10 and found that most of these responses were strongly dampened during this interaction. Ectopic expression of WRKY33 resulted in complete resistance towards this strain indicating that virulence of B05.10, at least partly, depends on suppressing WRKY33 expression/protein accumulation. As a consequence, the expression levels of direct WRKY33 target genes, including those involved in the biosynthesis of camalexin, were also reduced upon infection. Concomitantly, elevated levels of the phytohormone abscisic acid (ABA) were observed. Molecular and genetic studies revealed that ABA negatively influences defence to B05.10 and effects jasmonic acid/ethylene (JA/ET) and salicylic acid (SA) levels. Susceptibility/resistance was determined by the antagonistic effect of ABA on JA, and this crosstalk required suppressing WRKY33 functions at early infection stages. This indicates that B. cinerea B05.10 promotes disease by suppressing WRKY33-mediated host defences.

The tea plant [Camellia sinensis (L.) O. Kuntze] is one of the most important leaf crops, and it is widely used for the production of non-alcoholic beverages worldwide. Tea also has a long history of medicinal use. Colletotrichum camelliae Massee is one of the dominant fungal pathogens that infects tea leaves and causes severe tea anthracnose disease. To analyze the molecular biology of C. camelliae, the quantification of pathogen gene expression by the RT-qPCR method is necessary. Reliable RT-qPCR results require the use of stable reference genes for data normalization. However, suitable reference genes have not been reported in C. camelliae thus far. In this study, 12 candidate genes (i.e., CcSPAC6B12.04c, CcWDR83, Cchp11, Ccnew1, CcHplo, CcRNF5, CcHpcob, CcfaeB-2, CcYER010C, CcRNM1, CcUP18, and CcACT) were isolated from C. camelliae and assessed as potential reference genes. The expression stability of these genes in C. camelliae during spore germination and mycelial growth and interaction with host plants was first evaluated using several statistical algorithms, such as geNorm, NormFinder, and Bestkeeper. A web-based analysis program, Refinder, was then used to find the most suitable reference genes. Our results indicated that Cenew1, CcHplo, and CcSPAC6B12.04c were the most stable reference genes in C. camelliae under all conditions. Our work provided the most suitable reference genes for future studies performed to quantify the target gene expression levels of C. camelliae.

Background Tea, which is produced from new shoots of existing tea plants (Camellia sinensis), is one of the most popular, non-alcoholic, healthy beverages worldwide. Colletotrichum camelliae is one of the dominant fungal pathogens of tea. The interaction of C. camelliae with tea could be a useful pathosystem to elucidate various aspects of woody, medicinal plant-fungal interactions. Currently, many studies characterizing resistance or virulence and aggressiveness use lesion size at the infection sites on the leaves to quantify the growth of the pathogen. However, this method does not offer the sensitivity needed for the robust quantification of small changes in aggressiveness or the accurate quantification of pathogen growth at the early stages of infection. Results A quantitative real-time polymerase chain reaction (qRT-PCR) assay was developed for the quantification of C. camelliae growth on tea plant. This method was based on the comparison of fungal DNA in relation to plant biomass. This assay was used to investigate the phenotypes of tea plant cultivars in response to C. camelliae infection. Two cultivars, Zhongcha 108 (ZC108) and Longjing 43 (LJ43), were tested with this method. ZC108 was previously reported as an anthracnose-resistant cultivar against C. camelliae, while LJ43 was susceptible. The traditional lesion measurement method showed that both cultivars were susceptible to a virulent strain of C. camelliae, while the qRT-PCR approach indicated that very little fungal growth occurred in the anthracnose-resistant cultivar ZC108. The observed results in this study were consistent with previously published research. In addition, the DNA-based real-time PCR method was applied for analysis of pathogenic differences in general C. camelliae isolates and among several Colletotrichum spp that infect tea. Conclusions This study showed that the DNA-based qRT-PCR technique is rapid, highly sensitive and easily applicable for routine experiments and could be used in screening for resistant tea plant cultivars or to identify differences in pathogen aggressiveness within and among Colletotrichum species.

The large WRKY transcription factor family is mainly involved in regulating plant immune responses. Arabidopsis WRKY33 is a key transcriptional regulator of hormonal and metabolic processes towards Botrytis cinerea strain 2100 infection and is essential for resistance. In contrast to B. cinerea strain 2100, the strain B05.10 is virulent on wild-type (WT) Col-0 Arabidopsis plants highlighting the genetic diversity within this pathogen species. We analysed how early WRKY33-dependent responses are affected upon infection with strain B05.10 and found that most of these responses were strongly dampened during this interaction. Ectopic expression of WRKY33 resulted in complete resistance towards this strain indicating that virulence of B05.10, at least partly, depends on suppressing WRKY33 expression/protein accumulation. As a consequence, the expression levels of direct WRKY33 target genes, including those involved in the biosynthesis of camalexin, were also reduced upon infection. Concomitantly, elevated levels of the phytohormone abscisic acid (ABA) were observed. Molecular and genetic studies revealed that ABA negatively influences defence to B05.10 and effects jasmonic acid/ethylene (JA/ET) and salicylic acid (SA) levels. Susceptibility/resistance was determined by the antagonistic effect of ABA on JA, and this crosstalk required suppressing WRKY33 functions at early infection stages. This indicates that B. cinerea B05.10 promotes disease by suppressing WRKY33-mediated host defences.

Rapid and massive transcriptional reprogramming upon pathogen recognition is the decisive step in plant–phytopathogen interactions. Plant transcription factors (TFs) are key players in this process but they require a suite of other context-specific co-regulators to establish sensory transcription regulatory networks to bring about host immunity. Molecular, genetic and biochemical studies, particularly in the model plants Arabidopsis and rice, are continuously uncovering new components of the transcriptional machinery that can selectively impact host resistance toward a diverse range of pathogens. Moreover, detailed studies on key immune regulators, such as WRKY TFs and NPR1, are beginning to reveal the underlying mechanisms by which defense hormones influence the function of these factors. Here we provide a short update on such recent developments.

The Arabidopsis mutant wrky33 is highly susceptible to Botrytis cinerea. We identified >1680 Botrytis-induced WRKY33 binding sites associated with 1576 Arabidopsis genes. Transcriptional profiling defined 318 functional direct target genes at 14 hr post inoculation. Comparative analyses revealed that WRKY33 possesses dual functionality acting either as a repressor or as an activator in a promoter-context dependent manner. We confirmed known WRKY33 targets involved in hormone signaling and phytoalexin biosynthesis, but also uncovered a novel negative role of abscisic acid (ABA) in resistance towards B. cinerea 2100. The ABA biosynthesis genes NCED3 and NCED5 were identified as direct targets required for WRKY33-mediated resistance. Loss-of-WRKY33 function resulted in elevated ABA levels and genetic studies confirmed that WRKY33 acts upstream of NCED3/NCED5 to negatively regulate ABA biosynthesis. This study provides the first detailed view of the genome-wide contribution of a specific plant transcription factor in modulating the transcriptional network associated with plant immunity. DOI: http://dx.doi.org/10.7554/eLife.07295.001, eLife digest Crop yields can be badly affected by diseases caused by some fungi and other microbes. One fungus called Botrytis cinerea is able to infect many different species of crop plants—including tomatoes and grapes—and can cause severe damage both before and after harvest. This fungus belongs to a group of microbes that kill the plant cells they invade and then extract the nutrients from the dead cells. Some plants are able to resist infection by B. cinerea and researchers have identified several proteins that are involved in this resistance. One such protein is called WRKY33, which is able to bind to DNA to regulate the activity of particular genes. However, it was not clear exactly which genes were involved in the response to B. cinerea. Arabidopsis thaliana is a small flowering plant that is often used in research. Mutant A. thaliana plants lacking WRKY33 are very susceptible to infection with B. cinerea. Here, Liu et al. use several genetic techniques to find out which genes WRKY33 regulates when A. thaliana plants are exposed to the fungus. The experiments indicate that WRKY33 can alter the activity of over 300 genes. Some of these genes had previously been shown to be targets of WRKY33 and are involved in cell responses to plant hormones and the production of an antimicrobial molecule called camalexin. Liu et al. also show that two genes called NCED3 and NCED5—which are required for the production of a plant hormone called abscisic acid—are repressed by WRKY33. Mutant plants lacking WRKY33 had increased levels of abscisic acid and further experiments suggested that the repression of NCED3 and NCED5 by WRKY33 is important to resistance against the fungus. Liu et al.'s findings provide the first detailed view of which genes in A. thaliana are regulated by WRKY33 when the plant is exposed to B. cinerea. A future challenge is to understand how blocking the production of abscisic acid protects plants against B. cinerea and other similar fungi. DOI: http://dx.doi.org/10.7554/eLife.07295.002

The Arabidopsis thaliana transcription factor WRKY33 is a key transcriptional regulator of plant responses towards B. cinerea strain 2100 infection, and is essential for resistance. To elucidate the critical molecular components involved, global mapping of WRKY33-regulated target genes was performed by integrating ChIP-seq data of WRKY33 binding sites with RNA-seq results of 14h B. cinerea-induced and WRKY33-dependent gene expression profiles. Comparative gene expression analysis between resistant wild-type Columbia-0 and susceptible wrky33 mutant plants revealed that B. cinerea 2100-induced WRKY33 has both transcriptional activator and repressor roles in regulating hundreds of target genes with distinct molecular functions, but mainly acts as a transcriptional repressor. Genome-wide analysis confirmed previously known WRKY33 targets involved in ethylene and jasmonic acid hormone signaling and phytoalexin biosynthesis, but also uncovered new vital components affecting the complex regulatory circuitry affecting resistance towards Botrytis. In particular, the abscisic acid (ABA) biosynthetic genes NCED3 and NCED5 were identified as key targets of WRKY33-mediated resistance towards this necrotroph. Further genetic, biochemical and molecular studies confirmed that WRKY33 acts upstream of NCED3 and NCED5 to negatively regulate ABA biosynthesis and signaling. These results reveal a novel role of WRKY33 in modulating host immunity by repressing part of the ABA hormone regulatory network. Comparative analysis of WRKY33 function between the B. cinerea avirulent strain 2100 and the virulent strain B05.10 revealed that Botrytis-induced WRKY33 gene expression and protein accumulation are significantly lower in B. cinerea B05.10 infected WT plants than in plants challenged with strain 2100. As a consequence, the expression levels of WRKY33-regulated target genes involved in the biosynthesis of antifungal camalexin and JA/ET related defense signaling are clearly reduced upon B05.10 infection. However, WRKY33-overexpression lines were clearly resistant to B05.10. These data strongly suggest that WRKY33-dependent early immune responses in WT plants were negatively affected by B. cinerea virulent strain B05.10. Further analysis of Arabidopsis ABA deficiency mutants in combination with B. cinerea B05.10 BcABA mutants revealed that, as is the case for strain 2100, Arabidopsis-derived ABA negatively regulates plant immune responses to B05.10. Elevated JA/ET levels were observed in nced3 nced5 double mutants, suggesting that ABA antagonizes JA/ET signaling upon B05.10 infection. This ABA antagonism of JA/ET signaling was dependent on WRKY33. In conclusion, this thesis provides novel insights into the role of WRKY33 in modulating host immunity towards both an avirulent and a virulent strain of the necrotrph B. cinerea.

A thermostable superoxide dismutase [(SOD) EC 1.15.1.1] from a Thermoascus aurantiacus var. levisporus was purified to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) homogeneity by a series of column chromatographies. The molecular mass of a single band of the enzyme was estimated to be 16.8 kDa by SDS-PAGE. The molecular mass was estimated to be 33.2 kDa by gel filtration on Sephacryl S-100, indicating that the enzyme was composed of two identical subunits of 16.8 kDa each. N-terminal amino acid sequencing (seven residues) yielded VKAVAVL. Using RACE-PCR, a Cu, Zn-SOD gene was cloned from T. aurantiacus var. levisporus. The sequence was 705 bp and contained a 468 bp ORF encoding a Cu, Zn-SOD of 155 amino acid residues.

Background Lipoxygenase (LOXs) is a large family of plant enzymes that catalyse the hydroperoxidation of free polyunsaturated fatty acids into diverse biologically active compounds, collectively named phyto-oxylipins. Although multiple isoforms of LOXs have been identified in a wide range of annual herbaceous plants, the genes encoding these enzymes in perennial woody plants have not received as much attention. In Camellia sinensis (L.) O. Kuntze, no LOX gene of any type has been isolated, and its possible role in tea plant development, senescence, and defence reaction remains unknown. The present study describes the isolation, characterization, and expression of the first tea plant LOX isoform, namely CsLOX1, and seeks to clarify the pattern of its expression in the plant's defence response as well as in flower opening and senescence. Results Based on amino acid sequence similarity to plant LOXs, a LOX was identified in tea plant and named CsLOX1, which encodes a polypeptide comprising 861 amino acids and has a molecular mass of 97.8 kDa. Heterologous expression in yeast analysis showed that CsLOX1 protein conferred a dual positional specificity since it released both C-9 and C-13 oxidized products in equal proportion and hence was named 9/13-CsLOX1. The purified recombinant CsLOX1 protein exhibited optimum catalytic activity at pH 3.6 and 25°C. Real-time quantitative PCR analysis showed that CsLOX1 transcripts were detected predominantly in flowers, up-regulated during petal senescence, and down-regulated during flower bud opening. In leaves, the gene was up-regulated following injury or when treated with methyl jasmonate (MeJA), but salicylic acid (SA) did not induce such response. The gene was also rapidly and highly induced following feeding by the tea green leafhopper Empoasca vitis, whereas feeding by the tea aphid Toxoptera aurantii resulted in a pattern of alternating induction and suppression. Conclusions Analysis of the isolation and expression of the LOX gene in tea plant indicates that the acidic CsLOX1 together with its primary and end products plays an important role in regulating cell death related to flower senescence and the JA-related defensive reaction of the plant to phloem-feeders.