A partial loss-of-function mutation in an Arabidopsis RNA polymerase III subunit leads to pleiotropic defects

J Exp Bot. 2016 Apr;67(8):2219-30. doi: 10.1093/jxb/erw020. Epub 2016 Feb 10.


Plants employ five DNA-dependent RNA polymerases (Pols) in transcription. One of these polymerases, Pol III, has previously been reported to transcribe 5S rRNA, tRNAs, and a number of small RNAs. However, in-depth functional analysis is complicated by the fact that knockout mutations in Pol subunits are typically lethal. Here, we report the characterization of the first known viable Pol III subunit mutant,nrpc7-1 This mutant was originally isolated from a forward genetic screen designed to identify enhancers of the autoimmune mutantsnc1, which contains a gain-of-function mutation in a nucleotide-binding leucine-rich repeat (NLR) immune receptor-encoding gene. Thenrpc7-1mutation occurs in an intron-exon splice site and results in intron retention in someNRPC7transcripts. There is a global disruption in RNA equilibrium innrpc7-1, exemplified by the altered expression of a number of RNA molecules, some of which are not reported to be transcribed by Pol III. There are developmental defects associated with the mutation, as homozygous mutant plants are dwarf, have stunted roots and siliques, and possess serrated leaves. These defects are possibly due to altered small RNA stability or activity. Additionally, thenrpc7-1mutation confers anNLR-specific alternative splicing defect that correlates with enhanced disease resistance, highlighting the importance of alternative splicing in regulating NLR activity. Altogether, these results reveal novel roles for Pol III in maintaining RNA homeostasis, adjusting the expression of a diverse suite of genes, and indirectly modulating gene splicing. Future analyses using thenrpc7-1mutant will be instrumental in examining other unknown Pol III functions.

Keywords: Alternative splicing; Arabidopsis; NRPC7; Pol III; RNA polymerase III; Rpc25.; plant immunity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics*
  • Arabidopsis / immunology
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism
  • Base Sequence
  • Cell Nucleus / metabolism
  • Chromosomes, Plant / genetics
  • Cloning, Molecular
  • Genetic Pleiotropy*
  • Mutation / genetics*
  • Plant Immunity
  • Protein Subunits / genetics*
  • Protein Subunits / metabolism
  • RNA Polymerase III / genetics*
  • RNA Polymerase III / metabolism
  • RNA Splicing / genetics
  • RNA, Plant / metabolism
  • Subcellular Fractions / metabolism


  • Arabidopsis Proteins
  • Protein Subunits
  • RNA, Plant
  • RNA Polymerase III