The Role of Transcription Factors in Wheat Under Different Abiotic Stresses - Abiotic Stress: Plant Responses and Applications in Agriculture - page 375

also differentially expressed following wound stress response [22]. The potato StNAC gene
shows induced expression in responses to Phytophthora infestans infection and wounding
treatment [23]. Barley plants with the HvNAC6 gene knocked down show penetration
resistance in epidermal cells when inoculated with virulent isolates of Blumeria graminis f. sp.
hordei [25]. Overexpression of rice OsNAC4 resulted in hypersensitive response (HR) cell death;
and in the OsNAC4 knocked down lines, HR cell death was markedly decreased in response
to the avirulent bacterial strain ( Acidovorax avenae N1141] [67]. Therefore, it seems that plant
NAC TFs play multiple roles in defense responses to pathogen attack as well as exogenous
stimuli [74].
Although these transcription factors can bind to the same core NAC recognition sequence,
recent reports have shown that the different NAC TFs have different functions in plant
development. In addition, NAC proteins can form homo- or hetero-dimers. Stress-responsive
NAC TFs can be used for improving stress tolerance in transgenic plants, although the mode
of action appears complex in plants. Recent reports support the notion of substantial crosstalk
between plant growth and stress responses. In rice, Kikuchi et al. [33] characterized the
molecular properties of eight NAC genes ( OsNAC1 to OsNAC 8].
In contrast to Arabidopsis , the NAC regulon may have additional roles in monocot plants.
Important future tasks will, therefore, lie in the comparative analysis of gene expression
patterns and the identification of their target genes to determine the function of these genes in
plant development and tolerance to abiotic and biotic stresses [49].
Xia et al. [74] reported the full-length cDNA sequence of a novel wheat ( T. aestivum ) NAC TF,
TaNAC8 , (using in silico cloning, reverse transcription PCR and 3' rapid amplification of cDNA
ends PCR methods. TaNAC8 shows strong homology to rice OsNAC8 with an N-terminal
NAC domain and a trans-membrane helices motif in the C-terminus. Yeast one hybrid assays
confirmed that TaNAC8's C-terminal region acted as transcriptional activator. Inoculation of
wheat with an incompatible isolate of the stripe rust pathogen Puccinia striiformis f. sp. tritici
or treatments with MeJA or ethylene led to increased TaNAC8 transcription in leaves 24 h post
inoculation/treatment. However, SA and ABA had no significant effect on gene expression.
Abiotic stress treatments, including high salinity, PEG and low-temperature, also induced
TaNAC8 expression, suggesting that TaNAC8 may function as a transcriptional activator
involved in wheat defense responses to both abiotic and biotic stresses [74].
Mao et al. [42] obtained a fragment of TaNAC2 from suppression subtractive cDNA libraries
of wheat treated with PEG, and its full-length cDNA was obtained by screening a full-length
wheat cDNA library. Gene expression pro fi ling indicated that TaNAC2 was involved in
response to drought, salt, cold, and ABA treatment. Overexpression of TaNAC2 in Arabidop‐
sis resulted in enhanced tolerances to drought, salt, and freezing stresses which coincided with
enhanced expression of abiotic stress-response genes and several physiological indices [42].
TaNAC4 encodes another NAC TF in wheat high homology with rice OsNAC4 [73]. Functional
analysis using onion epidemical cells and yeast one-hybrid assays confirmed that TaNAC4
functions as a transcriptional activator. TaNAC4 expression was induced in wheat leaves by in‐
fection with stripe rust, and also by MeJA, ABA and ethylene treatments. However, SA had no