Biology Reference
In-Depth Information
SPL
genes and other genes involved in flowering, but have no effect on the
expression of miR156 (
Jung et al., 2012, 2011; Wang et al., 2009; Yu et al.,
2012
)(
Fig. 5.2
).
One of the ways in which miR156 represses flowering is through its
effect on miR172, a miRNA that represses several AP2-like transcription
factors that inhibit flowering. High levels of miR172 promote flowering
by repressing the expression of these floral repressors (reviewed in
(
Zhu & Helliwell, 2011
). miR172 is strongly upregulated when adult plants
are transferred from SD to LD (
Jung et al., 2007; Schmid et al., 2003
), but its
expression also increases early in development in the absence of a LD stim-
ulus (
Wu et al., 2009
). This early increase in miR172 is complementary
to the decrease in miR156 expression, and is thought to be a consequence
of this decrease because plants overexpressing miR156 have reduced levels
of miR172, whereas plants with reduced levels of miR156 have elevated
levels of mIR172 (
Jung et al., 2011; Wu et al., 2009
). miR156 represses
miR172 through its effect on the expression of
SPL9
,
SPL10
, and related
SPL
genes. Transgenic plants expressing miR156-resistant SPL9 transcripts
under the regulation of the endogenous
SPL9
promoter have elevated
levels of miR172 and flower early (
Wang et al., 2009; Wu et al., 2009
). This
Adult
Juvenile
miR156
miR156
SPL9 etc
SPL9 etc
miR172b
miR172b
Long days
Long days
AP2-like
AP2-like
GA
GA
SOC1
SOC1
FT
FT
LFY
LFY
FUL
SPL3, 4, 5
FUL
SPL3, 4, 5
AP1
AP1
Flower
Flower
Figure 5.2 miR156 controls reproductive competence by repressing the expression of
genes required for flower production. The pathways illustrated here are based on val-
idated miRNA-target interactions and transcription factor binding studies described in
the text. Black indicates genes that are expressed; gray represents repressed genes.
