Gene regulatory networks elucidating huanglongbing disease mechanisms

PLoS One. 2013 Sep 25;8(9):e74256. doi: 10.1371/journal.pone.0074256. eCollection 2013.

Abstract

Next-generation sequencing was exploited to gain deeper insight into the response to infection by Candidatus liberibacter asiaticus (CaLas), especially the immune disregulation and metabolic dysfunction caused by source-sink disruption. Previous fruit transcriptome data were compared with additional RNA-Seq data in three tissues: immature fruit, and young and mature leaves. Four categories of orchard trees were studied: symptomatic, asymptomatic, apparently healthy, and healthy. Principal component analysis found distinct expression patterns between immature and mature fruits and leaf samples for all four categories of trees. A predicted protein - protein interaction network identified HLB-regulated genes for sugar transporters playing key roles in the overall plant responses. Gene set and pathway enrichment analyses highlight the role of sucrose and starch metabolism in disease symptom development in all tissues. HLB-regulated genes (glucose-phosphate-transporter, invertase, starch-related genes) would likely determine the source-sink relationship disruption. In infected leaves, transcriptomic changes were observed for light reactions genes (downregulation), sucrose metabolism (upregulation), and starch biosynthesis (upregulation). In parallel, symptomatic fruits over-expressed genes involved in photosynthesis, sucrose and raffinose metabolism, and downregulated starch biosynthesis. We visualized gene networks between tissues inducing a source-sink shift. CaLas alters the hormone crosstalk, resulting in weak and ineffective tissue-specific plant immune responses necessary for bacterial clearance. Accordingly, expression of WRKYs (including WRKY70) was higher in fruits than in leaves. Systemic acquired responses were inadequately activated in young leaves, generally considered the sites where most new infections occur.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Citrus / genetics*
  • Citrus / microbiology
  • Gene Regulatory Networks*
  • Plant Diseases / genetics*
  • Polymerase Chain Reaction
  • Transcriptome

Grants and funding

This research was funded by grants obtained from the Citrus Research and Development Foundation in Florida and the Citrus Research Board of California. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.