NLR-associating transcription factor bHLH84 and its paralogs function redundantly in plant immunity

PLoS Pathog. 2014 Aug 21;10(8):e1004312. doi: 10.1371/journal.ppat.1004312. eCollection 2014 Aug.

Abstract

In plants and animals, nucleotide-binding and leucine-rich repeat domain containing (NLR) immune receptors are utilized to detect the presence or activities of pathogen-derived molecules. However, the mechanisms by which NLR proteins induce defense responses remain unclear. Here, we report the characterization of one basic Helix-loop-Helix (bHLH) type transcription factor (TF), bHLH84, identified from a reverse genetic screen. It functions as a transcriptional activator that enhances the autoimmunity of NLR mutant snc1 (suppressor of npr1-1, constitutive 1) and confers enhanced immunity in wild-type backgrounds when overexpressed. Simultaneously knocking out three closely related bHLH paralogs attenuates RPS4-mediated immunity and partially suppresses the autoimmune phenotypes of snc1, while overexpression of the other two close paralogs also renders strong autoimmunity, suggesting functional redundancy in the gene family. Intriguingly, the autoimmunity conferred by bHLH84 overexpression can be largely suppressed by the loss-of-function snc1-r1 mutation, suggesting that SNC1 is required for its proper function. In planta co-immunoprecipitation revealed interactions between not only bHLH84 and SNC1, but also bHLH84 and RPS4, indicating that bHLH84 associates with these NLRs. Together with previous finding that SNC1 associates with repressor TPR1 to repress negative regulators, we hypothesize that nuclear NLR proteins may interact with both transcriptional repressors and activators during immune responses, enabling potentially faster and more robust transcriptional reprogramming upon pathogen recognition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / immunology
  • Arabidopsis Proteins / immunology*
  • Gene Expression Regulation, Plant
  • Gene Knockout Techniques
  • Immunoprecipitation
  • Microscopy, Confocal
  • Plant Immunity / immunology*
  • Plants, Genetically Modified
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transcription Factors / immunology*

Substances

  • Arabidopsis Proteins
  • Transcription Factors

Grant support

This research is supported from financial funds from the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery program and the William Cooper Endowment Fund from UBC Botany Department. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.