Geoscience Reference
In-Depth Information
function (Lago et al., 2005).
Arabidopsis
TAF10 mutants,
with reduced expression, are more sensitive to salt stress,
whereas overexpression of TAF10 increased seed germina-
tion rate upon osmotic stress (Gao et al., 2006), suggesting that
TAF10 is involved in osmotic stress responses. A mutation in
Arabidopsis
TAF12B results in failure to induce a subset of
ethylene-regulated genes in etiolated seedlings (Robles et al.,
2007).
Arabidopsis
TAF12B protein also regulates a set of
genes involved in late signalling processes governing a range
of cytokinin responses, including cell proliferation and differ-
entiation (Kubo et al., 2011).
the mediator
Another way by which activators and co-activators may recruit
RNA Pol II to a promoter is by interacting with a multi-protein
complex, the mediator (Blazek et al., 2005; Kidd et al., 2011;
Mathur et al., 2011). The mediator was first discovered in
yeast after the finding that purified activators and components
of the general transcription machinery were not sufficient for
regulated
in vitro
transcription. The activator-dependent tran-
scription also required the addition of crude yeast extracts,
and the unknown component mediating the missing function
was named the mediator (Kelleher et al., 1990; Flanagan et al.,
1991). This complex is required for regulated transcription of
nearly all RNA Pol II-dependent genes in
Saccharomyces
cerevisiae
and functions as a bridge between regulatory pro-
teins and the basal RNA Pol II transcription machinery, as
a regulator of the phosphorylation status of the C-terminal
domain (CTD) and possibly as a modulator of the chromatin
structure. The mediator complex in plants was found to com-
prise 27 subunits, 21 of which were conserved between plants
and other eukaryotes (Backstrom et al., 2007). In
Arabidopsis
,
mediator subunits have essential roles, including plant growth
and development. For example, STRUWWELPETER (SWP)/
MED14 controls the cell number during primordia initiation
and also regulates the duration of cell proliferation in aerial
organs (Autran et al., 2002). The mediator subunits MED12-
MED13 have been shown to regulate developmental timing
during embryo patterning (Gillmor et al., 2010). Phytochrome
and flowering time1 (PFT1)/MED25 is known to play a key
role in light signalling and flowering time (Inigo et al., 2012;
Klose et al., 2012). MED25 also plays the essential role in
JA-mediated pathogen defence (Kidd et al., 2009), drought
and salt stress (Elfving et al., 2011) and JA and ABA signal-
ling (Chen et al., 2012).
