phenotypes of constitutively expressed TFs, tissue and developmental stage specific
promoters may be used (Kasuga et al. 2004). In soybean, the expression level of
various calcium-dependent protein kinases (GmCDPKs) was studied in response to
wounding, stimulated herbivory, aphid feeding, treatment of jasmonic acid (JA),
ethylene (ET), and salicylic acid (SA) and in response to drought and abscisic acid
(ABA). Also, many GmCDPKs were induced after drought or ABA treatment
(Hettenhausen et al. 2016).
4.7.2 Role of Transcription Factors in Drought Tolerance
Transcription factors (Tfs) are DNA-binding proteins that interact with other transcriptional regulators, including chromatin remodeling/modifying proteins, to initiate or inhibit the transcription by RNA polymerase. TFs have the capacity to act as a
tool to improve the multigenic traits like drought tolerance (Rabara et al. 2014).
Multigenic control makes the development of drought-tolerant varieties a difficult
task using conventional breeding methods. TFs act as master regulators of many
physiological processes and play an important role in the regulation of gene expression under abiotic stress. Alteration in expression levels of TFs regulates the
expression of many downstream genes resulting in several different phenotypic
effects. A particular TF can control the expression of several target genes of a
specific pathway, thereby have the potential to modulate multigenic traits, such as
drought tolerance. Forty genes belonging to six major families of TFs were
upregulated during various abiotic stresses (Seki et al. 2002).
WRKY proteins are involved in the signal transduction of plant hormones, like
abscisic acid (ABA), jasmonic acid (JA), and gibberellin (GA). Expression levels of
four WRKY family of transcription factor (GmWRKY2, GmWRKY15,
GmWRKY50, and GmWRKY55) were induced in drought treatment. In this regard,
several reports strongly establish the potential of WRKY TFs as effective tool to
engineer abiotic stress tolerance, such as drought in plants (Rushton et al. 2010;
Chen et al. 2012; Rabara et al. 2013; Tripathi et al. 2013).
The potential of basic leucine zipper (bZIP) family of TFs as tools to improve
crop responses to drought was shown by heterologous expression of soybean
GmbZIP1 in Arabidopsis (Gao et al. 2011). Soybean bZIP (GmbZIP1) overexpression was shown to increase drought tolerance in Arabidopsis (Gao et al.
2011). Fifteen bZIP genes were induced by drought and salt stress (Yang et al.
2020). Among these, the expression of GmbZIP2 was significantly induced under
stress conditions. It was shown to improve drought and salt tolerance upon overexpression by enhancing the expression of stress-responsive genes, such as
GmMYB48, GmWD40, GmDHN15, GmGST1, and GmLEA. Another bZIP transcription factor, GmFDL19 has also been reported to enhance drought tolerance in
soybean (Li et al. 2017b). Chlorophyll content and activities of several antioxidant
enzymes were more in over-expressors while malonaldehyde content was lower than
wild-type plants.
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G. K. Satpute et al.
promoters may be used (Kasuga et al. 2004). In soybean, the expression level of
various calcium-dependent protein kinases (GmCDPKs) was studied in response to
wounding, stimulated herbivory, aphid feeding, treatment of jasmonic acid (JA),
ethylene (ET), and salicylic acid (SA) and in response to drought and abscisic acid
(ABA). Also, many GmCDPKs were induced after drought or ABA treatment
(Hettenhausen et al. 2016).
4.7.2 Role of Transcription Factors in Drought Tolerance
Transcription factors (Tfs) are DNA-binding proteins that interact with other transcriptional regulators, including chromatin remodeling/modifying proteins, to initiate or inhibit the transcription by RNA polymerase. TFs have the capacity to act as a
tool to improve the multigenic traits like drought tolerance (Rabara et al. 2014).
Multigenic control makes the development of drought-tolerant varieties a difficult
task using conventional breeding methods. TFs act as master regulators of many
physiological processes and play an important role in the regulation of gene expression under abiotic stress. Alteration in expression levels of TFs regulates the
expression of many downstream genes resulting in several different phenotypic
effects. A particular TF can control the expression of several target genes of a
specific pathway, thereby have the potential to modulate multigenic traits, such as
drought tolerance. Forty genes belonging to six major families of TFs were
upregulated during various abiotic stresses (Seki et al. 2002).
WRKY proteins are involved in the signal transduction of plant hormones, like
abscisic acid (ABA), jasmonic acid (JA), and gibberellin (GA). Expression levels of
four WRKY family of transcription factor (GmWRKY2, GmWRKY15,
GmWRKY50, and GmWRKY55) were induced in drought treatment. In this regard,
several reports strongly establish the potential of WRKY TFs as effective tool to
engineer abiotic stress tolerance, such as drought in plants (Rushton et al. 2010;
Chen et al. 2012; Rabara et al. 2013; Tripathi et al. 2013).
The potential of basic leucine zipper (bZIP) family of TFs as tools to improve
crop responses to drought was shown by heterologous expression of soybean
GmbZIP1 in Arabidopsis (Gao et al. 2011). Soybean bZIP (GmbZIP1) overexpression was shown to increase drought tolerance in Arabidopsis (Gao et al.
2011). Fifteen bZIP genes were induced by drought and salt stress (Yang et al.
2020). Among these, the expression of GmbZIP2 was significantly induced under
stress conditions. It was shown to improve drought and salt tolerance upon overexpression by enhancing the expression of stress-responsive genes, such as
GmMYB48, GmWD40, GmDHN15, GmGST1, and GmLEA. Another bZIP transcription factor, GmFDL19 has also been reported to enhance drought tolerance in
soybean (Li et al. 2017b). Chlorophyll content and activities of several antioxidant
enzymes were more in over-expressors while malonaldehyde content was lower than
wild-type plants.
104
G. K. Satpute et al.