The Role of Transcription Factors in Wheat Under Different Abiotic Stresses - Abiotic Stress: Plant Responses and Applications in Agriculture - page 372

is 50-53 amino acids in length and contains three regularly-distributed tryptophan (or
phenylalanine) residues, which can together form a hydrophobic core. Each MYB repeat forms
three α-helices: the two that are located at the C-terminus adopt a variation of the helix-turn-
helix (HLH) conformation that recognizes and binds to the DNA major groove at the specific
recognition site such as C/TAACG/TG [51, 52].
Since the first plant MYB gene, C1 , was isolated in Zea mays [54], research concerning different
aspects of the MYB gene family, including gene number, sequence characterization, evolution,
and potential functions, has been widely conducted in plants [9, 16, 72]. So far, large numbers
of MYB genes have been identified in different plant species, comprising 204 members in
Arabidopsis , 218 members in rice, 279 members in grapevine, 197 members in poplar, and 180
members in Brachypodium [9, 70, 72].
MYB proteins are involved in many significant physiological and biochemical processes,
including the regulation of primary and secondary metabolism, the control of cell development
and the cell cycle, the participation in defense and response to various biotic and abiotic
stresses, and hormone synthesis and signal transduction [16, 83].
Extensive studies of the MYB gene family in various plant species have provided a better
understanding of this gene family; however, little is known about this gene family in bread
wheat [83].
We previously analyzed the expression levels of ten MYB TF genes from wheat ( Triticum
aestivum ) in two recombinant inbred lines contrasting in their salt tolerance in response to salt
or drought stress via quantitative RT-PCR [58]. A potential new MYB gene ( TaMYBsdu 1] was
significantly up-regulated in leaves and roots of wheat plants subjected to long-term drought
stress. Furthermore, TaMYBsdu1 showed higher transcript abundance in the salt-tolerant
genotype than in the susceptible genotype under salt stress. These data suggested that
TaMYBsdu1 is a potentially important regulator for wheat adaptation to both salt and drought
stresses [58].
In other work, two putative MYB genes, MYB2 (DQ353858.1] and MYB3 (CJ920766] were up-
regulated in a tolerant variety (Mahouti) under salt stress conditions but down-regulated in
the susceptible cultivar (Chinese Spring), MYB2 . Sequence analysis with the BLASTx and Plant
Gene Ontology assignment showed that MYB2 is a part of TaMYB1 (E value=6e -15 5]. The results
of a study by Lee et al. [36] show that TaMYB1 is involved in abiotic stresses responses in wheat.
The expression of this gene increases during oxygen deficiency (flooding), PEG treatment
(drought) and salt increases, especially in roots. In addition, its transcript gradually increases
in starting ABA and PEG treatments [36]. In research conducted by Mott and Wang [46] on
comparative transcriptome analysis of salt-tolerant wheat germplasm lines using wheat
genome arrays, it was found that TaMYB1 was one of the up-regulated genes with 34 times
higher expression levels under stress condition relative to the control. Functional analysis of
the MYB2 homologue in Arabidopsis , AtMYB44 (E value=1e -5 9], showed that this gene was up-
regulated in response to drought, salt, cold and ABA treatments, especially in stomata guard
cells and vascular tissue. Transgenic plants overexpressing this gene showed more tolerance
to mentioned stresses compared to wide-type plants [28]. Homology analysis of MYB3 (a