The Role of Transcription Factors in Wheat Under Different Abiotic Stresses - Abiotic Stress: Plant Responses and Applications in Agriculture - page 373

member of R2R3MYB) has shown that there is a high homology between this gene and
AtMYB59 in Arabidopsis (E value=4e -6 0]. It has been shown that AtMYB59 expression increases
in response to phytohormones including jasmonic acid, SA, gibberellic acid and ethylene,
especially in leaf and stem tissues [38, 39, 59]. But its expression level in roots and inflorescences
was lower than in other organs, showing its role in hormonal signal pathways in response to
biotic stresses and plant defense against pathogen attacks [38, 39, 59].
Full-length cDNA is an important resource for isolating the functional genes in wheat.
Recently, Zhang et al. [83] analyzed a group of MYB genes that respond to one or more stress
treatments. They isolated 60 full-length cDNA sequences encoding wheat MYB proteins. A
phylogenetic tree with wheat, rice, and Arabidopsis MYB proteins was constructed to examine
their evolutionary relationships and the putative functions of wheat MYB proteins based on
Arabidopsis MYB proteins with known functions. Tissue-specific analysis and abiotic stress
response expression profiles were carried out to find potential genes that participate in the
stress signal transduction pathway, including the analysis of transgenic Arabidopsis plants
expressing the MYB gene, TaMYB32 [83].
Recently, Qin et al. [56] identified a new R2R3-type MYB transcription factor gene, TaMYB33 ,
from wheat ( T. aestivum ). This gene was induced by ABA, NaCl, and PEG treatments, and its
promoter sequence contains the putative ABRE, MYB and other abiotic stress-related cis-
elements. Ectopic over-expression of this gene in Arabidopsis significantly enhanced its
tolerance to drought and NaCl treatments, but not to LiCl and KCl stresses. The expression of
two genes, AtP5CS (involved in proline synthesis) and AtZAT12 (a C2H2 zinc finger tran‐
scription factor that is involved in regulating ascorbate peroxidase expression), was induced
in the TaMYB33 -expressing transgenic Arabidopsis lines. This suggests that TaMYB33 promotes
the ability for ROS scavenging and osmotic pressure balance reconstruction. TaMYB33 over-
expression lines displayed up-regulation of AtAAO3 along with down-regulation of AtABF3
and AtABI1 , indicating that ABA synthesis was elevated while its signaling was constrained.
The authors concluded that TaMYB33 enhances salt and drought tolerance partially via an
improved ability for ROS detoxification and osmotic balance reconstruction [57].
TaMYB56 (on chromosomes 3B and 3D) in wheat was identified as a cold stress-related gene
by Zhang et al. [82]. The expression levels of TaMYB56-B and TaMYB56-D were strongly
induced by cold stress, but slightly induced by salt stress in wheat. Detailed characterization
of the Arabidopsis transgenic plants that overexpressed TaMYB56-B revealed that TaMYB56-B
is possibly involved in the responses of plants to freezing and salt stresses. The expression of
some cold stress-responsive genes, such as DREB1A/CBF3 and COR15a , were found to be
elevated in the TaMYB56-B -overexpressing Arabidopsis plants compared to wild-type [82].
TaMYB3R1 is another MYB gene which has been shown to be potentially involved in wheat
response to drought, salt and cold stress. Cai et al. [6] cloned TaMYB3R1 from wheat ( T.
aestivum ). TaMYB3R1 amino acid sequence shares high identity to other plant MYB3R proteins.
Subcellular localization experiments in onion epidermal cells proved that TaMYB3R1 was
present in the nucleus. Trans-activation assays in yeast cells confirmed that TaMYB3R1 was
a TF that required the C-terminal region to activate the expression of reporter gene. DNA-
binding tests showed the MSA cis-element-binding activity of TaMYB3R1. TaMYB3R1