BackgroundTobacco curly shoot virus (TbCSV) is a monopartite begomovirus associated with betasatellite (Tobacco curly shoot betasatellite, TbCSB), which causes serious leaf curl disease on tomato and tobacco in China. It is interesting that TbCSV induced severe upward leaf curling in Nicotiana benthamiana, but in the presence of TbCSB, symptoms changed to be downward leaf curling. However, the mechanism of interactions between viral pathogenicity, host defense, viral-betasatellite interactions and virus-host interactions remains unclear.MethodsIn this study, RNA-seq was used to analyze differentially expressed genes (DEGs) in N. benthamiana plants infected by TbCSV (Y35A) and TbCSV together with TbCSB (Y35AB) respectively.ResultsThrough mapping to N. benthamiana reference genome, 59,814 unigenes were identified. Transcriptome analysis revealed that a total of 4081 and 3196 DEGs were identified in Y35AB vs CK (control check) and Y35A vs CK, respectively. Both GO and KEGG analyses were conducted to classify the DEGs. Ten of the top 15 GO terms were enriched in both DEGs of Y35AB vs CK and Y35A vs CK, and these enriched GO terms mainly classified into three categories including biological process, cellular component and molecular function. KEGG pathway analysis indicated that 118 and 111 pathways were identified in Y35AB vs CK and Y35A vs CK, respectively, of which nine and six pathways were significantly enriched. Three major pathways in Y35AB vs CK involved in metabolic pathways, carbon metabolism and photosynthesis, while those in Y35A vs CK were related to Ribosome, Glyoxylate and dicarboxylate metabolism and DNA replication. We observed that 8 PR genes were significantly up-regulated and 44 LRR-RLK genes were significantly differentially expressed in Y35A treatment or in Y35AB treatment. In addition, 7 and 13 genes were identified to be significantly changed in biosynthesis and signal transduction pathway of brassinosteroid (BR) and jasmonic acid (JA) respectively.ConclusionsThese results presented here would be particularly useful to further elucidate the response of the host plant against virus infection.Electronic supplementary materialThe online version of this article (10.1186/s12985-018-1044-1) contains supplementary material, which is available to authorized users.
Sclerotinia sclerotiorum (Lib.) de Bary is a devastating fungal pathogen with worldwide distribution. S. sclerotiorum is a necrotrophic fungus that secretes many cell wall-degrading enzymes (CWDEs) that destroy plant’s cell-wall components. Functional analyses of the genes that encode CWDEs will help explain the mechanisms of growth and pathogenicity of S. sclerotiorum. Here, we isolated and characterized a gene SsXyl1 that encoded an endo-β-1, 4-xylanase in S. sclerotiorum. The SsXyl1 expression showed a slight increase during the development and germination stages of sclerotia and a dramatic increase during infection. The expression of SsXyl1 was induced by xylan. The SsXyl1 deletion strains produce aberrant sclerotia that could not germinate to form apothecia. The SsXyl1 deletion strains also lost virulence to the hosts. This study demonstrates the important roles of endo-β-1, 4-xylanase in the growth and virulence of S. sclerotiorum.
Geminiviruses are single-stranded circular DNA viruses that infect many plant species and cause severe economic losses worldwide (Fauquet et al., 2003;Harrison, 1985;Navas-Castillo et al., 2011). Based on the current taxonomic criteria, geminiviruses are
Begomovirus-DNA- disease complexes induce different symptom phenotypes in their hosts. To investigate the genetic determinants of the phenotypic differences, Nicotiana spp. and tomato plants were inoculated with infectious clones of Tobacco curly shoot virus (TbCSV)/TbCSV DNA- (TbCSB) and Tomato yellow leaf curl China virus (TYLCCNV)/TYLCCNV DNA- (TYLCCNB) pseudorecombinants and showed that TYLCCNB induced characteristic vein-thickening and enation symptoms, while TbCSB only slightly exacerbated the leaf-curling symptoms, regardless of the helper virus being used. The roles of DNA--encoded C1 and a 430-nucleotide fragment containing the A-rich region and the putative C1 promoter region of the C1 gene (referred to as AP) in symptom development were further investigated by constructing hybrid satellites in which the C1 coding region or AP was exchanged between the two satellite molecules. A TYLCCNB hybrid with TbCSB C1 lost the ability to elicit the vein-thickening and enation phenotypes. TbCSB hybrids containing the TYLCCNB C1 or AP fragment failed to induce the characteristic vein thickening and enations. A TYLCCNB hybrid having the TbCSB AP fragment produced the enations, but the number of enations was less and their sizes were reduced. Differently from the phloem-specific pattern of the TYLCCNB promoter, a full-length fragment upstream of the TbCSB C1 gene confers a constitutive -glucuronidase expression pattern in transgenic tobacco plants. The above results indicate that the DNA--encoded C1 protein is the symptom determinant, but the promoter of the C1 gene has influence on symptom production.Geminiviruses are small plant viruses with circular singlestranded DNA (ssDNA) genomes that are encapsidated in unique twinned (geminate) particles. Members of the genus Begomovirus are transmitted by whiteflies (Bemisia tabaci) and infect dicotyledonous plants (42). Begomoviruses have either one or two circular ssDNA genomic components (DNA-A and DNA-B). The DNA-A component is capable of autonomous replication and encapsidation, whereas the DNA-B component encodes two proteins (BC1 and BV1) involved in movement (14). Recently, some monopartite begomoviruses have been found in association with a novel satellite DNA molecule, referred to as DNA- and now known as a betasatellite (2,5,20,22,38,45). DNA- is approximately half the size of the viral genomic DNA, and apart from a nonanucleotide sequence (TA ATATTAC), it has little sequence identity with viral genomic DNA. DNA- depends on the helper virus for replication and encapsidation and, in turn, is required for the induction of bona fide disease symptoms. DNA- bears a C1 open reading frame (ORF) on the complementary-sense strand, which is conserved among distinct betasatellites in terms of position and size. Mutational analyses and constitutive expression have shown that C1 is a strong pathogenicity/symptom determinant (7, 34, 39).Begomovirus-DNA- disease complexes are associated with a wide range of plant species and induce different sets of sympto...
Tomato yellow leaf curl China virus (TYLCCNV) Y10 isolate (Y10) and Tobacco curly shoot virus (TbCSV) Y35 isolate (Y35), both obtained from Yunnan Province, were each found to be associated with a distinct species of satellite DNA (DNA beta). Here, we demonstrate that both Y10 DNA beta (Y10beta) and Y35 DNA beta (Y35beta) were stably trans-replicated by the noncognate Begomovirus, although the noncognate DNA beta accumulated in plants at a lower level than did the cognate DNA beta. In Nicotiana benthamiana and N. glutinosa plants agroinoculated with Y10+Y10beta+Y35beta or with Y35+Y35beta+Y10beta, all components accumulated in the early stages of infection but, at later stages, the noncognate DNA beta decreased in relative concentration and was undetectable at 80 to 120 days after inoculation. The helper viruses and cognate DNA beta species persisted at higher levels throughout the experiments. When the initiation codon of the betaC1 gene of the cognate DNA beta was mutated, the dominance of the cognate over the noncognate DNA beta in mixed infections was unimpaired. These results imply that the cognate DNA beta competes with the noncognate DNA beta and that the ability for selective maintenance of DNA beta is not controlled by the betaC1 protein.
The phytohormone gibberellin (GA) is a vital plant signaling molecule that regulates plant growth and defense against abiotic and biotic stresses. To date, the molecular mechanism of the plant responses to viral infection mediated by GA is still undetermined. DELLA is a repressor of GA signaling and is recognized by the F-box protein, a component of the SCFSLY1/GID2 complex. The recognized DELLA is degraded by the ubiquitin-26S proteasome, leading to the activation of GA signaling. Here, we report that ageratum leaf curl Sichuan virus (ALCScV)-infected N. benthamiana plants showed dwarfing symptoms and abnormal flower development. The infection by ALCScV significantly altered the expression of GA pathway-related genes and decreased the content of endogenous GA in N. benthamiana. Furthermore, ALCScV-encoded C4 protein interacts with the DELLA protein NbGAI and interferes with the interaction between NbGAI and NbGID2 to prevent the degradation of NbGAI, leading to inhibition of the GA signaling pathway. Silencing of NbGAI or exogenous GA3 treatment significantly reduces viral accumulation and disease symptoms in N. benthamiana plants. The same results were obtained from experiments with the C4 protein encoded by tobacco curly shoot virus (TbCSV). Therefore, we propose a novel mechanism by which geminivirus C4 proteins control viral infection and disease symptom development by interfering with the GA signaling pathway.
Sclerotinia sclerotiorum is a destructive ascomycete plant pathogen with worldwide distribution. Extensive research on different aspects of this pathogen’s capability to cause disease will help to uncover clues about new ways to safely control Sclerotinia diseases. The thioredoxin (Trx) system consists of Trx and thioredoxin reductase (TrxR), which play critical roles in maintenance of cellular redox homeostasis. In this study, we functionally characterized a gene encoding a TrxR ( SsTrr1 ) in S. sclerotiorum . The amino acids of SsTrr1 exhibited high similarity with reported TrxRs in plant pathogens and targeted silencing of SsTrr1 lead to a decrease in TrxR activities of mycelium. SsTrr1 showed high expression levels during hyphae growth, and the levels decreased at the different stages of sclerotial development. SsTrr1 gene-silenced strains produced a smaller number of larger sclerotia on potato dextrose agar medium. The observations were consistent with the inhibitory effects on sclerotial development by the TrxR inhibitor, anrunofin. The expression of SsTrr1 showed a dramatic increase under the oxidative stress and the hyphal growth of gene-silenced strains showed more sensitivity to H 2 O 2 . SsTrr1 gene-silenced strains also showed impaired virulence in different hosts. Taken together, our results suggest that SsTrr1 encodes a TrxR that is of great important for oxidative stress tolerance, virulence, and sclerotial development of S. sclerotiorum .
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