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Effects of Elevated Temperature on the Susceptibility of Capsicum Plants to Capsicum Chlorosis Virus Infection.

ABSTRACT: Capsicum, an important vegetable crop in Queensland, Australia, is vulnerable to both elevated temperatures and capsicum chlorosis virus (CaCV). Thus, it is imperative to understand the genetic responses of capsicum plants (Capsicum annuum) to CaCV under elevated temperature conditions. Here, we challenged susceptible plants (cv. Yolo Wonder) with CaCV and investigated the effects of elevated temperature on symptom expression, the accumulation of virus-derived short interfering RNA (vsiRNA) and viral RNA, and the expression of plant defense-associated genes. CaCV-inoculated plants initially showed more severe symptoms and higher viral concentrations at a higher temperature (HT, 35 °C) than at ambient temperature (AT, 25 °C). However, symptom recovery and reduced viral RNA accumulation were seen in the CaCV-infected plants grown at HT at later stages of infection. We also observed that HT enhanced the accumulation of vsiRNAs and that, concurrently, RNA interference (RNAi)-related genes, including Dicer-like2 (DCL2), DCL4, RNA-dependent RNA polymerase 1 (RdRp1), RdRp6, and Argonaute2 (AGO2), were upregulated early during infection. Moreover, continuous high levels of vsiRNAs were observed during later stages of CaCV infection at HT. Overall, our investigation suggests that HT facilitates CaCV replication during early infection stages. However, this appears to lead to an early onset of antiviral RNA silencing, resulting in a subsequent recovery from CaCV in systemic leaves.

SUBMITTER: Tsai WA

PROVIDER: S-EPMC8879237 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature

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Effects of Elevated Temperature on the Susceptibility of Capsicum Plants to Capsicum Chlorosis Virus Infection.

Tsai Wei-An WA Shafiei-Peters Jonathan R JR Mitter Neena N Dietzgen Ralf G RG

Pathogens (Basel, Switzerland) 20220202 2

Capsicum, an important vegetable crop in Queensland, Australia, is vulnerable to both elevated temperatures and capsicum chlorosis virus (CaCV). Thus, it is imperative to understand the genetic responses of capsicum plants (<i>Capsicum annuum</i>) to CaCV under elevated temperature conditions. Here, we challenged susceptible plants (cv. Yolo Wonder) with CaCV and investigated the effects of elevated temperature on symptom expression, the accumulation of virus-derived short interfering RNA (vsiRN ...[more]

PMID: 35215143

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Project description:BackgroundCapsicum chlorosis virus (CaCV) is an emerging pathogen of capsicum, tomato and peanut crops in Australia and South-East Asia. Commercial capsicum cultivars with CaCV resistance are not yet available, but CaCV resistance identified in Capsicum chinense is being introgressed into commercial Bell capsicum. However, our knowledge of the molecular mechanisms leading to the resistance response to CaCV infection is limited. Therefore, transcriptome and expression profiling data provide an important resource to better understand CaCV resistance mechanisms.Methodology/principal findingsWe assembled capsicum transcriptomes and analysed gene expression using Illumina HiSeq platform combined with a tag-based digital gene expression system. Total RNA extracted from CaCV/mock inoculated CaCV resistant (R) and susceptible (S) capsicum at the time point when R line showed a strong hypersensitive response to CaCV infection was used in transcriptome assembly. Gene expression profiles of R and S capsicum in CaCV- and buffer-inoculated conditions were compared. None of the genes were differentially expressed (DE) between R and S cultivars when mock-inoculated, while 2484 genes were DE when inoculated with CaCV. Functional classification revealed that the most highly up-regulated DE genes in R capsicum included pathogenesis-related genes, cell death-associated genes, genes associated with hormone-mediated signalling pathways and genes encoding enzymes involved in synthesis of defense-related secondary metabolites. We selected 15 genes to confirm DE expression levels by real-time quantitative PCR.Conclusion/significanceDE transcript profiling data provided comprehensive gene expression information to gain an understanding of the underlying CaCV resistance mechanisms. Further, we identified candidate CaCV resistance genes in the CaCV-resistant C. annuum x C. chinense breeding line. This knowledge will be useful in future for fine mapping of the CaCV resistance locus and potential genetic engineering of resistance into CaCV-susceptible crops.

Project description:Thrips palmi is a widely distributed major agricultural pest in the tropics and subtropics, causing significant losses in cucurbit and solanaceous crops through feeding damage and transmission of tospoviruses. Thrips palmi is a vector of capsicum chlorosis virus (CaCV) in Australia. The present understanding of transmission biology and potential effects of CaCV on T. palmi is limited. To gain insights into molecular responses to CaCV infection, we performed RNA-Seq to identify thrips transcripts that are differentially-abundant during virus infection of adults. De-novo assembly of the transcriptome generated from whole bodies of T. palmi adults generated 166,445 contigs, of which ~24% contained a predicted open reading frame. We identified 1,389 differentially-expressed (DE) transcripts, with comparable numbers up- (708) and down-regulated (681) in virus-exposed thrips compared to non-exposed thrips. Approximately 59% of these DE transcripts had significant matches to NCBI non-redundant proteins (Blastx) and Blast2GO identified provisional functional categories among the up-regulated transcripts in virus-exposed thrips including innate immune response-related genes, salivary gland and/or gut-associated genes and vitellogenin genes. The majority of the immune-related proteins are known to serve functions in lysosome activity and melanisation in insects. Most of the up-regulated oral and extra-oral digestion-associated genes appear to be involved in digestion of proteins, lipids and plant cell wall components which may indirectly enhance the likelihood or frequency of virus transmission or may be involved in the regulation of host defence responses. Most of the down-regulated transcripts fell into the gene ontology functional category of 'structural constituent of cuticle'. Comparison to DE genes responsive to tomato spotted wilt virus in Frankliniella occidentalis indicates conservation of some thrips molecular responses to infection by different tospoviruses. This study assembled the first transcriptome in the genus Thrips and provides important data to broaden our understanding of networks of molecular interactions between thrips and tospoviruses.

Project description:Tospoviruses are among the most devastating viruses of horticultural and field crops. Capsicum chlorosis virus (CaCV) has emerged as an important pathogen of capsicum and tomato in Australia and South-east Asia. Present knowledge about CaCV protein functions in host cells is lacking. We determined intracellular localization and interactions of CaCV proteins by live plant cell imaging to gain insight into the associations of viral proteins during infection. Proteins were transiently expressed as fusions to autofluorescent proteins in leaf epidermal cells of Nicotiana benthamiana and capsicum. All viral proteins localized at least partially in the cell periphery suggestive of cytoplasmic replication and assembly of CaCV. Nucleocapsid (N) and non-structural movement (NSm) proteins localized exclusively in the cell periphery, while non-structural suppressor of silencing (NSs) protein and Gc and Gn glycoproteins accumulated in both the cell periphery and the nucleus. Nuclear localization of CaCV Gn and NSs is unique among tospoviruses. We validated nuclear localization of NSs by immunofluorescence in protoplasts. Bimolecular fluorescence complementation showed self-interactions of CaCV N, NSs and NSm, and heterotypic interactions of N with NSs and Gn. All interactions occurred in the cytoplasm, except NSs self-interaction was exclusively nuclear. Interactions of a tospoviral NSs protein with itself and with N had not been reported previously. Functionally, CaCV NSs showed strong local and systemic RNA silencing suppressor activity and appears to delay short-distance spread of silencing signal. Cell-to-cell movement activity of NSm was demonstrated by trans-complementation of a movement-defective tobamovirus replicon. CaCV NSm localized at plasmodesmata and its transient expression led to the formation of tubular structures that protruded from protoplasts. The D155 residue in the 30K-like movement protein-specific LxD/N50-70G motif of NSm was critical for plasmodesmata localization and movement activity. Compared to other tospoviruses, CaCV proteins have both conserved and unique properties in terms of in planta localization, interactions and protein functions which will effect viral multiplication and movement in host plants.

Dataset Information

Effects of Elevated Temperature on the Susceptibility of Capsicum Plants to Capsicum Chlorosis Virus Infection.

Publications

Effects of Elevated Temperature on the Susceptibility of Capsicum Plants to Capsicum Chlorosis Virus Infection.

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