Two-dimensional patterning by a trapping/depletion mechanism: the role of TTG1 and GL3 in Arabidopsis trichome formation.
Trichome patterning in Arabidopsis serves as a model system to study how single cells are selected within a field of initially equivalent cells. Current models explain this pattern by an activator-inhibitor feedback loop. Here, we report that also a newly discovered mechanism is involved by which patterning is governed by the removal of the trichome-promoting factor TRANSPARENT TESTA GLABRA1 (TTG1) from non-trichome cells. We demonstrate by clonal analysis and misexpression studies that Arabidopsis TTG1 can act non-cell-autonomously and by microinjection experiments that TTG1 protein moves between cells. While TTG1 is expressed ubiquitously, TTG1-YFP protein accumulates in trichomes and is depleted in the surrounding cells. TTG1-YFP depletion depends on GLABRA3 (GL3), suggesting that the depletion is governed by a trapping mechanism. To study the potential of the observed trapping/depletion mechanism, we formulated a mathematical model enabling us to evaluate the relevance of each parameter and to identify parameters explaining the paradoxical genetic finding that strong ttg1 alleles are glabrous, while weak alleles exhibit trichome clusters.
Botanical Institute III, University of Cologne, Köln, Germany, 2 Department of Biology, University of Freiburg, Freiburg, Germany.
Daniel
D
Bouyer
Florian
F
Geier
Friedrich
F
Kragler
Arp
A
Schnittger
Martina
M
Pesch
Katja
K
Wester
Rachappa
R
Balkunde
Jens
J
Timmer
Christian
C
Fleck
Martin
M
Hülskamp
D017360:Arabidopsis / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D019521:Body Patterning / Q000502:physiology; D017343:Genes, Plant; D008954:Models, Biological; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D010940:Plant Proteins; C417284:GL3 protein, Arabidopsis; C121067:TTG1 protein, Arabidopsis