Variations of five eIF4E genes across cassava accessions exhibiting tolerant and susceptible responses to cassava brown streak disease

PLoS One. 2017 Aug 3;12(8):e0181998. doi: 10.1371/journal.pone.0181998. eCollection 2017.

Abstract

Cassava (Manihot esculenta) is an important tropical subsistence crop that is severely affected by cassava brown streak disease (CBSD) in East Africa. The disease is caused by Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Both have a (+)-sense single-stranded RNA genome with a 5' covalently-linked viral protein, which functionally resembles the cap structure of mRNA, binds to eukaryotic translation initiation factor 4E (eIF4E) or its analogues, and then enable the translation of viral genomic RNA in host cells. To characterize cassava eIF4Es and their potential role in CBSD tolerance and susceptibility, we cloned five eIF4E transcripts from cassava (accession TMS60444). Sequence analysis indicated that the cassava eIF4E family of proteins consisted of one eIF4E, two eIF(iso)4E, and two divergent copies of novel cap-binding proteins (nCBPs). Our data demonstrated experimentally the coding of these five genes as annotated in the published cassava genome and provided additional evidence for refined annotations. Illumina resequencing data of the five eIF4E genes were analyzed from 14 cassava lines tolerant or susceptible to CBSD. Abundant single nucleotide polymorphisms (SNP) and biallelic variations were observed in the eIF4E genes; however, most of the SNPs were located in the introns and non-coding regions of the exons. Association studies of non-synonymous SNPs revealed no significant association between any SNP of the five eIF4E genes and the tolerance or susceptibility to CBSD. However, two SNPs in two genes were weakly associated with the CBSD responses but had no direct causal-effect relationship. SNPs in an intergenic region upstream of eIF4E_me showed a surprising strong association with CBSD responses. Digital expression profile analysis showed differential expression of different eIF4E genes but no significant difference in gene expression was found between susceptible and tolerant cassava accessions despite the association of the intergenic SNPs with CBSD responses.

MeSH terms

  • Disease Resistance / genetics
  • Disease Resistance / immunology*
  • Eukaryotic Initiation Factor-4E / genetics*
  • Genetic Variation / genetics*
  • Host-Pathogen Interactions
  • Manihot / growth & development
  • Manihot / immunology*
  • Manihot / virology
  • Plant Diseases / immunology*
  • Plant Diseases / virology
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / growth & development
  • Plants, Genetically Modified / immunology*
  • Potyviridae / physiology*
  • RNA, Viral / genetics

Substances

  • Eukaryotic Initiation Factor-4E
  • RNA, Viral

Grants and funding

This project is supported in part by Bill and Melinda Gates Foundation Challenge Exploration Grant OPP1068522 to ZX and Natural Science Foundation of China Grant 31461143016 to ZL, ZX, and XZ. One of the coauthors (SR) is affiliated with Genus plc, DeForest, WI, USA. Genus plc provided support only in the form of salaries for author SR, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of this author are articulated in the ‘author contributions’ section.