Development of hop transcriptome to support research into host-viroid interactions

PLoS One. 2017 Sep 8;12(9):e0184528. doi: 10.1371/journal.pone.0184528. eCollection 2017.

Abstract

Viroids, the smallest known pathogens, unable to encode any proteins, can cause severe diseases in their host plants. One of the proposed mechanisms of their pathogenicity includes silencing the host's genes via viroid-derived small RNAs, which are products of the host's immune response to the viroid's double stranded RNA. Humulus lupulus (hop) plants are hosts to several viroids; two of them, HLVd and CBCVd, are interesting models for studying host-viroid interactions, due to the symptomless infection of the former and severe stunting disease caused by the latter. To study these interactions, we constructed a deep hop NGS transcriptome based on 35 Gb paired-end sequencing data assembled into over 74 Mb of contigs. These transcripts were used for in-silico prediction of target transcripts of vd-sRNA of the two aforementioned viroids, using two different software tools. Prediction models revealed that 1062 and 1387 hop transcripts share nucleotide similarities with HLVd- and CBCVd-derived small RNAs, respectively, so they could be silenced in an RNA interference process. Furthermore, we selected 17 transcripts from 4 groups of targets involved in the metabolism of plant hormones, small RNA biogenesis, transcripts with high complementarity with viroid-derived small RNAs and transcripts targeted by CBCVd-derived small RNAs with high cellular concentrations. Their expression was monitored by reverse transcription quantitative PCR performed using leaf, flower and cone samples. Additionally, the expression of 5 pathogenesis related genes was monitored. Expression analysis confirmed high expression levels of four pathogenesis related genes in leaves of HLVd and CBCVd infected hop plants. Expression fluctuations were observed for the majority of targets, with possible evidence of downregulation of GATA transcription factor by CBCVd- and of linoleate 13S-lipoxygenase by HLVd-derived small RNAs. These results provide a deep transcriptome of hop and the first insights into complex viroid-hop plant interactions.

MeSH terms

  • Computational Biology / methods
  • Gene Expression Profiling
  • Gene Ontology
  • High-Throughput Nucleotide Sequencing
  • Host-Pathogen Interactions / genetics*
  • Humulus / genetics*
  • Molecular Sequence Annotation
  • Plant Diseases / genetics*
  • Plant Diseases / virology*
  • Transcriptome*
  • Viroids / genetics*

Grants and funding

This work was supported by J4-4153, Slovenian Research Agency - ARRS, http://www.sicris.si/public/jqm/prj.aspx?lang=eng&opdescr=search&opt=2&subopt=400&code1=cmn&code2=auto&psize=10&hits=1&page=1&count=&search_term=J4-4153&id=6974&slng=&order_by=; P4-0077, Slovenian Research Agency - ARRS, http://www.sicris.si/public/jqm/prg.aspx?lang=eng&opdescr=search&opt=2&subopt=700&code1=cmn&code2=auto&psize=10&hits=3&page=1&count=1&id=9741&slng=eng&search_term=P4-0077&order_by=; 1000-11-310098, Slovenian Research Agency - ARRS; 2321-12-210006, Administration of the Republic of Slovenia for Food Safety, Veterinary and Plant Protection.