Abstract

Virus infection may cause a multiplicity of symptoms in their host including discoloration, distortion and growth retardation. Hibiscus chlorotic ringspot virus (HCRSV) infection was studied using kenaf (Hibiscus cannabinus L.), a non-wood fiber-producing crop in this study. Infection by HCRSV reduced the fiber yield and concomitant economic value of kenaf. We investigated kenaf growth retardation and fluctuations of four selected miRNAs after HCRSV infection. Vegetative growth (including plant height, leaf size and root development) was severely retarded. From the transverse and radial sections of the mock and HCRSV-infected kenaf stem, the vascular bundles of HCRSV-infected plants were severely disrupted. In addition, four conserved plant developmental and defence related microRNAs (miRNAs) (miR165, miR167, miR168 and miR171) and their respective target genes phabulosa (PHB), auxin response factor 8 (ARF8), argonaute 1 (AGO1) and scarecrow-like protein 1 (SCL1) displayed variation in expression levels after HCRSV infection. Compared with the mock inoculated kenaf plants, miR171 and miR168 and their targets SCL1 and AGO1 showed greater fluctuations after HCRSV infection. As HCRSV upregulates plant SO transcript in kenaf and upregulated AGO1 in HCRSV-infected plants, the expression level of AGO1 transcript was further investigated under sulfite oxidase (SO) overexpression or silencing condition. Interestingly, the four selected miRNAs were also up- or down-regulated upon overexpression or silencing of SO. Plant growth retardation and fluctuation of four conserved miRNAs are correlated to HCRSV infection.

Highlights

  • Hibiscus chlorotic ringspot virus (HCRSV) belongs to the genus Carmovirus, family Tombusviridae [1]

  • Kenaf plant growth retardation and four selected plant conserved developmental related miRNAs were investigated after HCRSV infection

  • Previously investigated in Cucumber mosaic virus (CMV)- and Tomato aspermy virus (TAV)-infected plants. Their selected miRNAs displayed fluctuations after CMV and TAV infections, the changes of their target mRNAs were comparable, suggesting a similar mechanism in perturbing miRNA pathways [20]

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Summary

Introduction

Hibiscus chlorotic ringspot virus (HCRSV) belongs to the genus Carmovirus, family Tombusviridae [1] It is an icosahedral, positive sense single-stranded RNA plant virus. It is well studied that the targets of miR165, miR167, miR168 and miR171 are phabulosa (PHB), auxin response factor 8 (ARF8), argonaute 1 (AGO1) and scarecrow-like protein 1 (SCL1) respectively, playing essential roles in regulating plant development [18,19,20,21]. Since plant growth retardation was related to certain plant developmental genes expression profiles which are regulated by miRNAs, the four selected plant conserved developmental related miRNAs (miR165, miR167, miR168 and miR171) were investigated after HCRSV infection. This study showed that the plant developmental related miRNAs fluctuated after HCRSV infection, which displayed plant growth retardation. Analyzing the plant developmental related miRNAs will improve the understanding of viral infection and present strategies to prevent infection in future

Materials and Methods
4: Virus inoculation
5: RNA extraction and cDNA synthesis
8: Cloning of four conserved miRNAs and their respective target genes
9: RACE PCR to amplify the complete sequence of AGO1 from kenaf
1: Morphology of HCRSV-infected kenaf plants
2: Disruption of vascular bundle formation in HCRSVinfected kenaf stem
4: Upregulation of the transcript level of AGO1 after SO overexpression
Findings
Discussion
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