Edinburgh, Scotland, United Kingdom - TAIR

Timing of cell division determines the relative
cell size pattern in Arabidopsis
A fundamental question in biology is how a pattern of different cell types develops
from a field of relatively uniform cells. Developmental decisions take place in a
dynamic environment, but in most cases it is not known how the growth and
proliferation of cells contribute to pattern formation. In Arabidopsis, one such
pattern is seen on the sepal epidermis where highly elongated and polypoid giant
cells are interspersed between smaller pavement cells. We have used a
combination of live imaging, image processing, modeling, and genetic
approaches to determine how this pattern is established. We predict by modeling
that the relative cell size is determined by the time at which individual cells make
a stochastic decision to exit the cell division cycle and continue to grow and
replicate their DNA without dividing, through endoreduplication. We have tested
the model using live imaging and shown that giant cells start to endoreduplicate
early during sepal development whereas the neighboring cells undergo multiple
divisions. The model predicts that the probability that cells enter endoreduplication
is a major determinant of pattern, with a higher probability causing
over-production of giant cells and a lower probability resulting in the absence of
giant cells. We show that these predicted phenotypes are produced by
overexpressing the cell cycle inhibitor KRP1 (Bemis and Torii, 2007) and loss of
function mutations in a cell cycle inhibitor gene that we name LOSS OF GIANT
CELLS FROM ORGANS (LGO), respectively. We demonstrate that the timing of
endoreduplication is perturbed accordingly. Thus in the Arabdisopsis sepal, a
key determinant of pattern formation is a stochastic decision by equivalent cells
whether to divide or endoreduplicate.
Bemis, S.M., and Torii, K.U. (2007). Dev Biol 304, 367-381.
90
C39
Saturday 15:15 - 15:30
Systems Biology
Adrienne Roeder1
Vijay Chickarmane1
Alexandre Cunha1
Boguslaw Obara2
Tigran Bacarian3
Aida Sun1
B S Manjunath2
Eric Mjolsness3
Elliot Meyerowitz1
1California Institute of
Technology
2University of California
Santa Barbara
3University of California
Irvine