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SUMMARY:Small RNAs as morphogen-like signals in the patterning of leaves -
  Marja Timmerman\, Cold Spring Harbor Laboratory
DTSTART:20140428T100000Z
DTEND:20140428T110000Z
UID:TALK52282@talks.cam.ac.uk
CONTACT:37580
DESCRIPTION:Establishment of adaxial-abaxial (top/bottom) polarity is esse
 ntial for the flattened outgrowth and patterning of leaves\, and forms a k
 ey innovation in the evolution of land plants. We have shown that this pol
 ar axis is established through a cascade of opposing small RNAs in which m
 iR390 triggers the biogenesis of a second class of small RNAs\, the tasiR-
 ARFs\, which in turn regulate the accumulation of miR166. Importantly\, we
  showed that tasiR-ARF traffics from cell to cell. Movement of tasiR-ARF c
 reates a gradient of accumulation across the leaf that dissipates towards 
 the abaxial/bottom side. This gradient is interpreted into a sharp on-off 
 domain of expression of the target and abaxial cell fate determinant ARF3.
  Likewise\, miR166 traffics from its site of biogenesis in the bottom epid
 ermal layer to restrict expression of adaxial determinants\, the HD-ZIPIII
  transcription factors\, to the upper domain of the leaf. Mathematical mod
 elling predicts that the opposing small RNA gradients generated through mo
 bility are uniquely suited to create sharply defined and robust patterning
  boundaries. This model is supported by our recent observations\, which wi
 ll be presented. Our observations indicate that leaves are partitioned int
 o top and bottom domains via a novel patterning mechanism involving opposi
 ng gradients of small RNAs that act as mobile morphogen-like instructive s
 ignals.
LOCATION:Large Lecture Theatre\, Department of Plant Sciences
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