Identification of Methylosome Components as Negative Regulators of Plant Immunity Using Chemical Genetics

Mol Plant. 2016 Dec 5;9(12):1620-1633. doi: 10.1016/j.molp.2016.10.006. Epub 2016 Oct 15.


Nucleotide-binding leucine-rich repeat (NLR) proteins serve as immune receptors in both plants and animals. To identify components required for NLR-mediated immunity, we designed and carried out a chemical genetics screen to search for small molecules that can alter immune responses in Arabidopsis thaliana. From 13 600 compounds, we identified Ro 8-4304 that was able to specifically suppress the severe autoimmune phenotypes of chs3-2D (chilling sensitive 3, 2D), including the arrested growth morphology and heightened PR (Pathogenesis Related) gene expression. Further, six Ro 8-4304 insensitive mutants were uncovered from the Ro 8-4304-insensitive mutant (rim) screen using a mutagenized chs3-2D population. Positional cloning revealed that rim1 encodes an allele of AtICln (I, currents; Cl, chloride; n, nucleotide). Genetic and biochemical analysis demonstrated that AtICln is in the same protein complex with the methylosome components small nuclear ribonucleoprotein D3b (SmD3b) and protein arginine methyltransferase 5 (PRMT5), which are required for the biogenesis of small nuclear ribonucleoproteins (snRNPs) involved in mRNA splicing. Double mutant analysis revealed that SmD3b is also involved in the sensitivity to Ro 8-4304, and the prmt5-1 chs3-2D double mutant is lethal. Loss of AtICln, SmD3b, or PRMT5 function results in enhanced disease resistance against the virulent oomycete pathogen Hyaloperonospora arabidopsidis Noco2, suggesting that mRNA splicing plays a previously unknown negative role in plant immunity. The successful implementation of a high-throughput chemical genetic screen and the identification of a small-molecule compound affecting plant immunity indicate that chemical genetics is a powerful tool to study whole-organism plant defense pathways.

Keywords: TNL; autoimmunity; chemical genetics; methylosome; plant immunity; small molecule screening.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / immunology*
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Autoimmunity / genetics
  • Autoimmunity / physiology
  • Disease Resistance / genetics
  • Disease Resistance / physiology
  • Gene Expression Regulation, Plant
  • Plant Immunity / genetics
  • Plant Immunity / physiology*
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / immunology
  • Plants, Genetically Modified / metabolism
  • Protein-Arginine N-Methyltransferases / genetics
  • Protein-Arginine N-Methyltransferases / metabolism


  • Arabidopsis Proteins
  • Protein-Arginine N-Methyltransferases