Abstract
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.
Highlights
Capsicum (Capsicum spp.) is a genus in Solanaceae, a family that contains economically important crops including potato and tomato
Molecular responses of host plants to impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV) tospovirus infections were reported using microarrays derived from expressed sequence tags
TSWV infection led to the up-regulation of chitin response genes and down-regulation of genes involved in DNA replication, chromatin biogenesis and cytokinesis compared to mock plants [31]
Summary
Capsicum (Capsicum spp.) is a genus in Solanaceae, a family that contains economically important crops including potato and tomato. Capsicum is attacked by various pathogens and pests that can cause extensive losses in production Pathogens, such as Xanthomonas spp., Phytophthora spp, Colletotrichum spp., chili leaf curl virus, tomato spotted wilt virus (TSWV) and groundnut bud necrosis virus (GBNV) have been reported to cause major diseases in capsicum [2,3,4]. CaCV is a tentative species in the genus Tospovirus, family Bunyaviridae [11] It contains a tripartite single strand RNA genome with negative and ambisense polarity which codes for RNA-dependent RNA polymerase, two structural proteins, nucleocapsid and glycoproteins and two non-structural proteins with proposed suppressor of RNA silencing and movement protein functions [12]. CaCV protein that triggers susceptibility or resistance responses in host plants remains unresolved
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