Biology Reference
In-Depth Information
of CS2, H3K27me3-enriched, domains that rarely span more than one or two
genes (
Roudier et al., 2011; Turck et al., 2007; Zhang, Clarenz, et al., 2007
)is
in sharp contrast to the large patches of H3K27me3, which encompass several
genes reported in
Drosophila
and mammals (
Bernstein et al., 2006; Schwartz
et al., 2006; Tolhuis et al., 2006
). This suggests organism-specific variations
in the use of otherwise conserved mechanisms.
Further refinement in the classification of
Arabidopsis
chromatin states
can be expected, possibly as a result of the analysis of additional chromatin
marks and proteins but also, and more importantly, through an increase in
the cellular resolution of epigenomic maps. This is clearly a necessary step for
determining the dynamics of chromatin states in a developmental context,
which is of key importance to reveal the functional impact of chromatin-
level regulation during organogenesis and development.
3. CHROMATIN-BASED PROCESSES DURING
VEGETATIVE DEVELOPMENT
While many regulators of chromatin-associated pathways have been
characterized in
Arabidopsis
, their specific impact during development
remains poorly understood in many cases. Extensive analysis of the role
of PcG proteins has shown that PRC2-mediated gene repression affects
most developmental transitions in
Arabidopsis
(Reviewed in
Bemer &
Grossniklaus, 2012; Holec & Berger, 2012; Zheng & Chen, 2011
). More-
over, loss of PRC2 or PRC1 activities leads to dedifferentiation and active
proliferation as well as to an unbalance between division and differentiation
in meristems (
Aichinger, Villar, Di Mambro, Sabatini, & Kohler, 2011;
Bouyer et al., 2011; Bratzel et al., 2010; Schubert et al., 2006
), which sug-
gests that, like in metazoans, PcG proteins are central regulators of cell fate
acquisition and maintenance in plants (Reviewed in
Hennig & Derkacheva,
2009; K¨hler & Hennig, 2010
). Among all developmental transitions,
flowering has crystallized many research efforts that are starting to provide
a refined understanding of how the environment affects gene expression,
either transiently or over longer periods.
3.1. Aligning developmental transitions with seasonal changes
of the environment
The transition to flowering is a major developmental switch in the plant life
cycle. Regulation of flowering time in response to seasonal changes is critical
for reproductive success, as it ensures the completion of seed production in
