Agriculture Reference
In-Depth Information
Overexpression of type-A
ARRs
enhances freezing tolerance in
Arabidopsis
(Shi
et al.
2012
). In contrast, another study demonstrated that type-A ARRs are nega-
tive regulators of the cold response (Jeon et al.
2010
). Although it can be assumed
that the cytokinin signalling pathway plays a negative regulatory role in freezing
tolerance, at least partially through inhibition of the ABA response, further study
will be necessary to define the exact role of cytokinin signalling, particularly for
the ARRs, in the regulation of cold signalling.
17.10.3 Ethylene and Cold Stress
Ethylene plays an important role in regulating plant responses to drought, flood-
ing, and biotic stress (Wilkinson and Davies
2010
). However, the function
of ethylene in plant responses to cold stress appears to be complex and species
dependent. Increased ethylene biosynthesis has been correlated with enhanced
chilling and freezing tolerance in several plant species, including tomato
(
Lycopersicones culentum
), cucumber (
Cucumis sativus
), and tobacco (
Nicotiana
tabacum
cv. NC89) (Wang and Adams
1982
; Ciardi et al.
1997
; Zhang and Huang
2010
). In contrast, improved cold tolerance was associated with the suppression
of ethylene biosynthesis in mung bean (
Vignaradiata
) and
Arabidopsis
(Collins
et al.
1995
; Shi et al.
2012
). In
Arabidopsis
, application of the ethylene precursor
ACC decreases freezing tolerance, whereas application of the ethylene biosynthe-
sis inhibitor AVG and the ethylene receptor antagonist AgNO
3
promote freezing
tolerance. Consistent with these findings, several ethylene-insensitive mutants,
including
etr1
-
1
,
ein4
-
1
,
ein2
-
5
,
ein3
-
1
, and
ein3 eil1
, exhibit enhanced freezing
tolerance. Genetic and biochemical analyses revealed that ethylene negatively reg-
ulates cold signalling, at least partially, through direct transcriptional control of the
COR
CBFs
and type-A
ARR
genes via EIN3 (Shi et al.
2012
) (Fig.
17.2
c).
It is known that ethylene can promote seed germination and repress seed dor-
mancy by antagonising ABA (Wilkinson and Davies
2010
). Previous studies indi-
cated that
etr1
-1 and
ein2
-
5
mutants show enhanced seed dormancy, and their
germination is hypersensitive to ABA (Chiwocha et al.
2005
; Wang et al.
2007
).
As ABA accumulates in
etr1
and
ein2
mutants (Ghassemian et al.
2000
; Chiwocha
et al.
2005
; Wang et al.
2007
), ethylene may negatively regulate ABA biosynthe-
sis during germination. Consistent with this notion, microarray data showed that a
group of genes involved in ABA signalling are upregulated in an
ein3 eil1
double
mutant (Shi et al.
2012
). Interestingly, a recent study revealed the mechanism of
how ABA inhibits root growth by increasing ethylene biosynthesis in Arabidopsis.
ABA-activated calcium-dependent protein kinases, CPK4 and CPK11 can phos-
phorylate ethylene biosynthesis synthase ACS6 and enhance its stability, thus
promoting ethylene production (Luo et al.
2014
). Although the mechanisms under-
lying the complex cross talk between ethylene, ABA, and cold signalling remain
unclear, it appears likely that the upregulation of ABA-responsive genes also con-
tributes to the freezing tolerance of ethylene-insensitive mutants.
Search WWH ::
Custom Search