DSSS - Making a flat leaf: Pre-patterning, morphogenic small RNAs, and Turing dynamics
- Date: Feb 14, 2025
- Time: 03:00 PM - 04:00 PM (Local Time Germany)
- Speaker: Prof. Marja Timmermans
- Center for Plant Molecular Biology, University of Tübingen
- Location: NO.002, MPI für Intelligente Systeme

As the principal photosynthetic organ, a leaf
commonly develops as a thin, flat lamina optimized for light capture and gas
exchange. The
flat geometry appears deceptively simple. In reality, its production poses an unusual and mechanistically
challenging problem; namely, how to create a stable dorsoventral (top-bottom) boundary within the plane
of a long and wide, but shallow, structure that grows orders of magnitude in size. We
have shown that the spatial information needed to specify dorsal (top) versus ventral
(bottom) fate is provided by a pre-pattern at the shoot stem cell niche
responsible for all post-embryonic shoot growth. This pre-pattern converts a
uniform signaling input from the organogenic hormone auxin into a ARF-dependent
binary response output to distinguish dorsal from ventral identity. As the leaf
primordium emerges from the pre-patterned niche environment, the initial
polarity resolves into an intricate system of transcription
factor interactions that
reinforce either dorsal or ventral cell fate. Their
spatial arrangement at the organ level is further governed by mobile small RNAs
that act as morphogens and generate sharply defined domains
of target gene expression through an intrinsic threshold-based readout
of their accumulation gradients. Our most recent
findings show that this gene regulatory network follows the organizing
principles of a Turing system. Dorsoventral polarity is thus propagated by a
self-organizing system of small RNA - transcription factor interactions.
This system dynamically adapts to internal and external perturbations to sustain
the robust polarity boundary in planar leaves, but at the same time provides
flexibility to support morphological diversity.