Genomic divergence between Dickeya zeae strain EC2 isolated from rice and previously identified strains, suggests a different rice foot rot strain

PLoS One. 2020 Oct 20;15(10):e0240908. doi: 10.1371/journal.pone.0240908. eCollection 2020.

Abstract

Rice foot rot caused by Dickeya zeae is an important bacterial disease of rice worldwide. In this study, we identified a new strain EC2 from rice in Guangdong province, China. This strain differed from the previously identified strain from rice in its biochemical characteristics, pathogenicity, and genomic constituents. To explore genomic discrepancies between EC2 and previously identified strains from rice, a complete genome sequence of EC2 was obtained and used for comparative genomic analyses. The complete genome sequence of EC2 is 4,575,125 bp in length. EC2 was phylogenetically closest to previously identified Dickeya strains from rice, but not within their subgroup. In terms of secretion systems, genomic comparisons revealed that EC2 harbored only type I (T1SS), typeⅡ (T2SS), and type VI (T6SS) secretion systems. The flagella cluster of this strain possessed specific genomic characteristics like other D. zeae strains from Guangdong and from rice; within this locus, the genetic diversity among strains from rice was much lower than that of within strains from non-rice hosts. Unlike other strains from rice, EC2 lost the zeamine cluster, but retained the clustered regularly interspaced short palindromic repeats-1 (CRISPR-1) array. Compared to the other D. zeae strains containing both exopolysaccharide (EPS) and capsular polysaccharide (CPS) clusters, EC2 harbored only the CPS cluster, while the other strains from rice carried only the EPS cluster. Furthermore, we found strain MS1 from banana, carrying both EPS and CPS clusters, produced significantly more EPS than the strains from rice, and exhibited different biofilm-associated phenotypes. Comparative genomics analyses suggest EC2 likely evolved through a pathway different from the other D. zeae strains from rice, producing a new type of rice foot rot pathogen. These findings emphasize the emergence of a new type of D. zeae strain causing rice foot rot, an essential step in the early prevention of this rice bacterial disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Secretion Systems / genetics
  • China
  • Dickeya / classification*
  • Dickeya / genetics
  • Dickeya / isolation & purification
  • Genome, Bacterial
  • Musa / microbiology
  • Oryza / microbiology*
  • Phylogeny
  • Plant Diseases / microbiology*
  • Whole Genome Sequencing / methods*

Substances

  • Bacterial Secretion Systems

Supplementary concepts

  • Dickeya zeae

Grants and funding

This research was supported by grants from the Natural Science Foundation of Guangdong province (2015A030312002, 2016A030311017) awarded to BL and QY, National Natural Science Foundation of China (31300118) awarded to JZ, Science and Technology Project of Guangdong province (2016B020202003) awarded to HS, the Science and Technology Project of Guangzhou city (201704030120) awarded to DS, and the Special fund for scientific innovation strategy-construction of high level Academy of Agriculture Science (R2017PY-QY004, R2018QD-056) awarded to JZ. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.