JAGGED controls growth anisotropyand coordination between cell sizeand cell cycle during plant organogenesis.
BACKGROUND
In all multicellular organisms, the links between patterning genes, cell growth, cell cycle, cell size homeostasis, and organ growth are poorly understood, partly due to the difficulty of dynamic, 3D analysis of cell behavior in growing organs. A crucial step in plant organogenesis is the emergence of organ primordia from the apical meristems. Here, we combined quantitative, 3D analysis of cell geometry and DNA synthesis to study the role of the transcription factor JAGGED (JAG), which functions at the interface between patterning and primordium growth in Arabidopsis flowers.


RESULTS
The floral meristem showed isotropic growth and tight coordination between cell volume and DNA synthesis. Sepal primordia had accelerated cell division, cell enlargement, anisotropic growth, and decoupling of DNA synthesis from cell volume, with a concomitant increase in cell size heterogeneity. All these changes in growth parameters required JAG and were genetically separable from primordium emergence. Ectopic JAG activity in the meristem promoted entry into S phase at inappropriately small cell volumes, suggesting that JAG can override a cell size checkpoint that operates in the meristem. Consistent with a role in the transition from meristem to primordium identity, JAG directly repressed the meristem regulatory genes BREVIPEDICELLUS and BELL 1 in developing flowers.


CONCLUSIONS
We define the cellular basis for the transition from meristem to organ identity and identify JAG as a key regulator of this transition. JAG promotes anisotropic growth and is required for changes in cell size homeostasis associated with accelerated growth and the onset of differentiation in organ primordia.
Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
Katharina
K
Schiessl
Swathi
S
Kausika
Paul
P
Southam
Max
M
Bush
Robert
R
Sablowski
D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D048429:Cell Size; D035264:Flowers / Q000166:cytology* / Q000254:growth & development* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D018519:Meristem / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; C097235:BEL1 protein, Arabidopsis; D018797:Cell Cycle Proteins; D018398:Homeodomain Proteins; C484013:JAGGED protein, Arabidopsis; D014157:Transcription Factors