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SUMMARY:The influence of salicylic acid and jasmonic acid on expression of
  RNA-dependent RNA polymerase 1 in Arabidopsis - Lydia Hunter
DTSTART:20120531T143000Z
DTEND:20120531T150000Z
UID:TALK36399@talks.cam.ac.uk
CONTACT:Suzy Stoodley
DESCRIPTION:Cellular RNA dependent RNA polymerases (RDRs) promote the ampl
 ification of RNA silencing and RDRs1 and 6 have been shown to play roles i
 n anti-viral silencing in plants.  In tobacco RDR1 transcript levels are i
 ncreased in response to a number of factors including treatment with salic
 ylic acid (SA)\, an important signal in induced pathogen resistance.  This
  has led to suggestions that RDR1 activity contributes to SA-induced resis
 tance to viruses.  However\, despite the apparent importance of RDR1\, its
  regulation by defensive signal transduction pathways has not been investi
 gated in detail.  My PhD project investigates the role of RDR1 in reducing
  viral accumulation in potato plants\, which was covered in some detail in
  my first year talk\, and the regulation of RDR1 expression by plant defen
 ce pathways in Arabidopsis\, which will be the focus of my third year pres
 entation.  By conducting detailed time-course experiments I have demonstra
 ted that SA and methyljasmonic acid (MeJA)\, a derivative of jasmonic acid
  (JA)\, another important defensive signal\, both induce transient gene ex
 pression of AtRDR1\, and with very similar kinetics. Wounding Arabidopsis 
 leaves also induces RDR1 expression\, which is consistent with regulation 
 of RDR1 expression by JA.  The results are surprising because the SA- and 
 JA-dependent signalling pathways are often antagonistic and induce distinc
 t sets of genes.   Working with Arabidopsis mutant lines harbouring defect
 s in defensive signalling I have found that full SA-induced RDR1 expressio
 n is dependent on the transcriptional activator  ‘non-expressor of patho
 genesis-related genes 1’ (NPR1).  Thus\, the mechanism governing increas
 ed RDR1 transcription appears to be similar to that involved in the regula
 tion of many other SA-induced defence-related genes.  However\, the induct
 ion of increased RDR1 transcript accumulation following MeJA is unaltered 
 in coronatine-insensitive 1 (coi1) mutant plants.  This is surprising beca
 use the majority of JA-dependent genes are dependent on the functioning of
  COI1 (a Skp1-Cullin1-F box) protein that mediates perception of JA.  I wi
 ll discuss my ongoing work on the interplay of SA\, JA and potentially oth
 er signals in the regulation of this enigmatic component of RNA silencing.
LOCATION:Department of Plant Sciences\, Large Lecture Theatre
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