Abstract
Viroids are smallest known pathogen that consist of non-capsidated, single-stranded non-coding RNA replicons and they exploits host factors for their replication and propagation. The severe stunting disease caused by Citrus bark cracking viroid (CBCVd) is a serious threat, which spreads rapidly within hop gardens. In this study, we employed comprehensive transcriptome analyses to dissect host-viroid interactions and identify gene expression changes that are associated with disease development in hop. Our analysis revealed that CBCVd-infection resulted in the massive modulation of activity of over 2000 genes. Expression of genes associated with plant immune responses (protein kinase and mitogen-activated protein kinase), hypersensitive responses, phytohormone signaling pathways, photosynthesis, pigment metabolism, protein metabolism, sugar metabolism, and modification, and others were altered, which could be attributed to systemic symptom development upon CBCVd-infection in hop. In addition, genes encoding RNA-dependent RNA polymerase, pathogenesis-related protein, chitinase, as well as those related to basal defense responses were up-regulated. The expression levels of several genes identified from RNA sequencing analysis were confirmed by qRT-PCR. Our systematic comprehensive CBCVd-responsive transcriptome analysis provides a better understanding and insights into complex viroid-hop plant interaction. This information will assist further in the development of future measures for the prevention of CBCVd spread in hop fields.
Highlights
Viroids are small, single-stranded, circular, highly structured, non-protein-coding infectiousRNAs with genomes ranging in size from 250 to 401 nt [1]
Our results indicated that the Citrus bark cracking viroid (CBCVd)-infection in hop results in the significant differential modulation of miRNAs that are involved in several hormone pathways and transcriptional factors involved in the regulation of metabolism, growth and development [18]
After the dormancy period (14-month), dot-blot hybridization and ssRT-qPCR displayed the similar trend of excess of minus strand over plus strand in all nine symptomatic plants, which was corroborated with our previous studies suggesting that
Summary
RNAs with genomes ranging in size from 250 to 401 nt [1]. The viroid genome is approximately tenfold smaller than the smallest RNA virus and they solely depend on their own RNA, host factors, and host enzymatic machinery for autonomous replication and movement [2,3]. Viruses 2018, 10, 570 acid-based pathogens, which make them alluring models to study structure-function relationship in RNA [4]. They are cosmopolitan in distribution and are the etiologic agents of diverse diseases affecting monocots and dicots, herbaceous and woody, and agronomic and ornamental plants [5]. Viroid-induced symptoms range from necrosis to less severe developmental disorders, including leaf chlorosis, stunting, flowering alterations, and fruit and seed deformations [2]. The International Committee on Taxonomy of Viruses (ICTV) classified 32 viroid species, whereas the NCBI
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