Agriculture Reference
In-Depth Information
Gene expression analysis by reverse northern blot has shown that two selected candidate
wheat bHLHs (
bHLH2
: CA599618 and
bHLH3
: CJ685625] are affected by salt stress in a tolerant
wheat cultivar. The BLASTx results showed that both have a homologue in wheat,
bHLH94
(E
value=5e
-85
for bHLH2 and E value=5e
-102
for bHLH3]. AtAIB was another homologue for
bHLH3 from
Arabidopsis
involved in the regulation of ABA signaling in
Arabidopsis
and plays
a role in drought tolerance and ABA treatment response [37, 59]. The high homology (E
value=2e
-5
1] between these orthologues and the result of reverse northern blot hybridizations
in that research indicate that these two bHLH gene may have an important function in
tolerance to salt stress in wheat [59].
4. WRKY transcription factors
WRKY transcription factors have been studied in plants extensively in the last two decades.
First Ishiguro and Nakamura [23] identified a WRKY protein in sweet potato (
Ipomoea
batatas
); since then many other members of this TF family have been cloned and functionally
characterized in plants, including wild oats (
Avena
fatua
) [62], parsley (
Petroselinum
crispum
)
[63], tobacco (
Nicotiana
tabacum
) [8, 19, 34, 61],
Arabidopsis
thaliana
[12], potato (
Solanum
tuberosum
) [5, 14], orchardgrass (
Dactylis glomerata
) [2], winter bittersweet nightshade
(
Solanum
dulcamara
) [22], desert legume (
Retama
raetam
) [55], barley (
Hordeum
vulgare
) [66], rice
(
Oryza sativa
) [41], cotton (
Gossypium
arboreum
) [77], and coconut (
Cocos
nucifera
) [44]. More
recently, WRKY family TFs were also identified in lower plants including ferns (
Ceratopteris
richardii
), mosses (
Physcomitrella
patens
) [4], a smile mode (
Dictyostelium
discoideum
) and the
protist (
Giardia
lamblia
) [81, 73].
A WRKY domain of about 60 amino acids is a characteristic of WRKY proteins. This domain
comprises the absolutely conserved sequence WRKYGQK followed by a zinc finger motif. The
WRKY domain binds to the W box ([T][T]TGAC[C/T]) of target gene promoters to modulate
transcription [10, 73]. It should be mentioned that in spite of the strong conservation of their
DNA-binding domain, the overall structures of WRKY TFs are highly divergent. WRKY TF
family members are grouped into three distinct groups based on the number and type of the
WRKY domains which might also reflect their different functions [59]. WRKY TFs with two
WRKY domains belong to group I and members of group II and group III possess one WRKY
domain. Group I and group II have a C2H2 zinc finger motif, while in group III, the WRKY
domain contains a C2HC motif. WRKY TFs can then be further classified into different
subgroups based on their phylogenetic clades. The WRKY family is one of the TF families for
which the regulatory role in biotic and abiotic stresses has been demonstrated in plants. These
include infection of bacteria, fungi, oomycetes and viruses, treatment with salicylic acid (SA)
or H
2
O
2
, mechanical stimulation, drought, cold, wounding, high-salinity and UV radiation.
Most WRKY TFs of group III play a role in plant defense signaling pathways. Some members
of the WRKY family may have key functions in plant development, such as embryo develop‐
ment, fruit maturation, tannin synthesis in the seed coat, maturation of root cells, morpho‐
genesis of trichomes, senescence, and dormancy. Furthermore, some of WRKY family
Search WWH ::
Custom Search