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Marja Timmermans: "Patterning the Leaf by Small RNA and Lipid Signals"

Wann 23.04.2012
von 16:15 bis 17:00
Wo Zoology Lecture Hall, Hauptstr. 1, 79104 Freiburg
Kontakttelefon +49 761 203 6969
Teilnehmer Open to the public
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Marja Timmermans
Cold Spring Harbor Laboratory, NY, USA

Patterning the Leaf by Small RNA and Lipid Signals

Establishment of dorsoventral (adaxial-abaxial) polarity is essential for the outgrowth and patterning of leaves, and thereby an important innovation in the evolution of plants. We have shown that leaf polarity is established through a cascade of opposing small RNAs in which miR390 triggers the biogenesis of a second class of small RNAs, the tasiR-ARFs, which in turn regulate the accumulation of miR166. Importantly, through localization of key tasiR-ARF biogenesis components we showed that these small RNAs accumulate outside their defined domain of biogenesis on the upper side of leaves. Movement of tasiR-ARF creates a gradient of accumulation across the leaf that maintains the polarized accumulation of the abaxial (ventral) determinant ARF3. Likewise, miR166 traffics from its site of biogenesis in the abaxial epidermis to restrict expression of HD-ZIPIII transcription factors to the upper domain of the leaf. Our observations indicate that leaves are partitioned into adaxial and abaxial domains via a novel patterning mechanism involving small RNAs that act as mobile morphogen-like instructive signals. Mathematical modelling predicts that the opposing small RNA gradients generated through mobility are uniquely suited to create robust patterning boundaries. This model is supported by our recent observations, which will be presented. In a further effort to identify positional signals required for the specification of this important developmental axis, we are utilizing biochemical and chemical genomics approaches to identify compounds that bind the START lipid-binding domain of HD-ZIPIII proteins and regulate their activity. Results from these studies will be presented along with progress made toward uncovering the endogenous START domain-bound ligand.