Biology Reference
In-Depth Information
In this respect, COLDAIR, rather than COOLAIR, appears to be function-
ally equivalent to HOTAIR in the regulation of
FLC
during vernalization.
However, HOTAIR also recruits the H3K4me2 demethylase LSD1, which
contributes to gene silencing (
Tsai et al., 2010
). Similarly, COOLAIR partic-
ipates in the recruitment of the H3K4me2/3 demethylase FLD, one of the
Arabidopsis
LSD1 homologue, which is also involved in
FLC
repression via
the autonomous pathway. Taken together, these observations therefore sug-
gest an intriguing evolutionary twist whereby two lncRNA instead of one
would coordinate two independent pathways at
FLC
through the recruitment
of synergistic chromatin-modifying activities.
Targeted recruitment of PRC2 via a lncRNA, either directly or indirectly,
has also been proposed tobe involved inX-chromosome inactivation in female
mammals (Reviewed in
Augui, Nora, &Heard, 2011
) and thus may be a con-
served mechanism in metazoans. It remains to be determined whether such a
mechanism is widespread in plants.
4. THE CENTRAL ROLE OF EPIGENETICS IN PLANT
REPRODUCTIVE DEVELOPMENT
Chromatin-based regulations are an essential determinant of repro-
ductive development in plants. Unlike animals, plants do not set aside germ
cells early in development. Instead, plant germ cells differentiate from
somatic cells following a prolonged vegetative life and produce multicellular
gametophytes that contain the gametes (
Fig. 6.2
). In the ovules, usually a
single archesporial (germ) cell differentiates from maternal somatic tissues.
It undergoes meiosis to produce four spores, only one of which survives.
In the majority of flowering plants, the surviving spore goes through three
rounds of nuclear division without cytokinesis. Subsequent cellularization
and differentiation result in a seven-celled embryo sac (female gametophyte)
comprising two gametic cells, the haploid egg and the homodiploid central
cells (generated from two haploid nuclei), as well as five accessory cells, two
synergids, involved in interaction with the male gametophyte and three
antipodal cells of unknown functions. Similarly, the male gametophyte
(the pollen grain) is produced in the anthers following the late definition
of the male germ cells and comprises one accessory (vegetative) cell and
two sperm cells derived from a single haploid spore. Fertilization of the
egg cell by one of the sperm cells gives rise to the zygote, while fertilization
of the central cell by the second sperm cell produces the endosperm, an
embryo-supporting tissue. Embryo and endosperm develop in a coordinated
manner together with surrounding maternal integuments, forming the seed.
