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P. Costantino - The role of the DAG transcription factors in Arabidopsis seed germination
afb triple and quadruple mutants, anther dehiscence
and pollen maturation occur earlier than in the wild
type, causing the release of mature pollen grains
before the completion of filament elongation. We
also assessed the contribution of auxin transport to
late stamen developmental processes. Our results
suggest that auxin synthesized in anthers plays a
major role in coordinating anther dehiscence and
pollen maturation, while auxin transport contributes
to the independent regulation of preanthesis filament
elongation.
Root meristem
Plant postembryonic development takes place in
the meristems, where stem cells self-renew and
produce daughter cells that differentiate and give
rise to different organ structures. For the maintenance
of meristems, the rate of differentiation of
daughter cells must equal the generation of new
cells: how this is achieved is a central question in
plant development. In the Arabidopsis root meristem,
stem cells surround a small group of organizing
cells, the quiescent center. Together they form
a stem cell niche, whose position and activity
depends on the combinatorial action of a small
number of genes as well as on polar auxin transport.
In contrast, the mechanisms controlling
meristematic cell differentiation remain unclear.
We demonstrated that cytokinins control the rate
of meristematic cell differentiation and thus determine
root meristem size via a two-component
receptor histidine kinase-transcription factor signaling
pathway. Analysis of the root meristems of
cytokinin mutants, spatial cytokinin depletion, and
exogenous cytokinin application indicated that
cytokinins act in a restricted region of the root
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meristem, where they antagonize a noncellautonomous
cell-division signal, and we provided
evidence that this signal is auxin.
Subsequently, by means of a comprehensive genetic
and molecular analysis, we showed that a primary
cytokinin-response transcription factor, ARR1, activates
the gene SHY2, a repressor of auxin signaling
that negatively regulates the PIN auxin transport
facilitator genes: thereby, cytokinin causes auxin
redistribution, prompting cell differentiation.
Conversely, auxin mediates degradation of the SHY2
protein, sustaining PIN activities and cell division.
Thus, the cell differentiation and division balance
necessary for controlling root meristem size and root
growth is the result of the interaction between
cytokinin and auxin through a simple regulatory circuit
converging on the SHY2 gene.
Selected publications
Dello Ioio R, Scaglia Linhares F, Scacchi E,
Casamitjana-Martinez E, Heidstra R, Costantino P,
Sabatini S. Cytokinins determine Arabidopsis root
meristem size by controlling cell differentiation. Curr
Biol. 2007, 17:678-82.
Cecchetti V, Altamura MM, Falasca G, Costantino
P, Cardarelli M. Auxin regulates Arabidopsis anther
dehiscence, pollen maturation and filament elongation.
Plant Cell 2008, 20:1760-74.
Dello Ioio R, Nakamura K, Moubayidin L, Perilli S,
Taniguchi M, Morita M, Aoyama T, Costantino P,
Sabatini S. A genetic framework for the control of
cell division and differentiation in the root meristem.
Science 2008, 322:1380-4.