Four NAC family TFs (GmNAC4, GmNAC25, GmNAC29, and GmNAC72)
were reported to be increased significantly in drought stress. In another study,
28 dehydration-responsive GmNAC genes were analyzed and it was revealed that
eight of these genes were found to be induced in drought-tolerant soybean varieties
under drought conditions (Hussain et al. 2017). Also, four of these (GmNAC4,
GmNAC5, GmNAC20, and GmNAC21) were more dehydration resistant than
others. The NAC family TFs are also proposed to be master regulators of various
metabolic pathways in plants and have potential to manipulate the drought tolerance
in transgenic plants.
ERF TFs are plant-specific TFs regulating a number of developmental and stressrelated processes (Dietz et al. 2010). The AP2/ERF family consists of several
subfamilies: the AP2, ERF, dehydration responsive element binding protein
(DREB), and RAV (Mizoi et al. 2012). Several studies have reported that DREB
TFs have potential to engineer drought tolerance. GmDREB2 improved salt and
drought tolerance in Arabidopsis (Chen et al. 2007a). Two different types of
transgenic soybean plants over-expressing AtDREB1D gene under constitutive
and ABA-inducible promoters were raised. The transgenic plants showed increased
drought tolerance by maintaining higher membrane stability (Guttikonda et al.
2014).
Transgenic soybean harboring GmDREB6 transcription factor was raised and the
expression of P5CS gene and proline content was studied (Nguyen et al. 2019).
Under normal condition, proline content was slightly higher in the transgenic plants.
However, under salt stress the proline content increased to a large extent in transgenic plants. GmDREB6 has been proposed to bind GT-1 region in the promoter of
P5CS gene and activate its expression (Zhang et al. 2013). Expression level of
soybean DREB TF was studied in drought-sensitive and drought-tolerant cultivars.
Also, the expression level of some known DREB regulated target genes were also
investigated under water stress conditions (Stolf-Moreira et al. 2010). The droughttolerant genotype had increased expression of aquaporin (Gmpip1), defensin
(Gmdefensin), and galactinol synthase (Gmgols) under drought stress conditions.
In soybean, an R1 MYB transcription factor, GmMYB176, is reported to regulate
isoflavone synthesis by affecting the expression of GmCHS8. GmMYB118 was
significantly regulated by salt and drought treatment, and over-expression of
GmMYB118 improved tolerance to drought and salt in both Arabidopsis and
soybean. GmMYB expression was induced by drought, salt, ABA, and H 2 O 2 . The
transgenic lines over-expressing GmMYB84 exhibited enhanced drought tolerance
than WT plants. The over-expressors have longer primary root length, greater
proline and ROS content, higher antioxidant enzyme activity, lower dehydration
rate, and reduced MDA content (Wang et al. 2017). The activities of antioxidant
enzymes were induced by ROS in over-expressor lines. The GmMYB84 was shown
to bind the cis elements in the promoter of GmRBOHB1 and GmRBOHB2 which
results in increased ROS levels leading to increased root growth under drought stress
conditions (Wang et al. 2017). In addition, several members of bHLH, SRS, VOZ,
NFYA family of transcription factors are shown to be involved in regulation of
expression of various abiotic stress-related genes in soybean.
4 Breeding and Molecular Approaches for Evolving Drought-Tolerant Soybeans
105
were reported to be increased significantly in drought stress. In another study,
28 dehydration-responsive GmNAC genes were analyzed and it was revealed that
eight of these genes were found to be induced in drought-tolerant soybean varieties
under drought conditions (Hussain et al. 2017). Also, four of these (GmNAC4,
GmNAC5, GmNAC20, and GmNAC21) were more dehydration resistant than
others. The NAC family TFs are also proposed to be master regulators of various
metabolic pathways in plants and have potential to manipulate the drought tolerance
in transgenic plants.
ERF TFs are plant-specific TFs regulating a number of developmental and stressrelated processes (Dietz et al. 2010). The AP2/ERF family consists of several
subfamilies: the AP2, ERF, dehydration responsive element binding protein
(DREB), and RAV (Mizoi et al. 2012). Several studies have reported that DREB
TFs have potential to engineer drought tolerance. GmDREB2 improved salt and
drought tolerance in Arabidopsis (Chen et al. 2007a). Two different types of
transgenic soybean plants over-expressing AtDREB1D gene under constitutive
and ABA-inducible promoters were raised. The transgenic plants showed increased
drought tolerance by maintaining higher membrane stability (Guttikonda et al.
2014).
Transgenic soybean harboring GmDREB6 transcription factor was raised and the
expression of P5CS gene and proline content was studied (Nguyen et al. 2019).
Under normal condition, proline content was slightly higher in the transgenic plants.
However, under salt stress the proline content increased to a large extent in transgenic plants. GmDREB6 has been proposed to bind GT-1 region in the promoter of
P5CS gene and activate its expression (Zhang et al. 2013). Expression level of
soybean DREB TF was studied in drought-sensitive and drought-tolerant cultivars.
Also, the expression level of some known DREB regulated target genes were also
investigated under water stress conditions (Stolf-Moreira et al. 2010). The droughttolerant genotype had increased expression of aquaporin (Gmpip1), defensin
(Gmdefensin), and galactinol synthase (Gmgols) under drought stress conditions.
In soybean, an R1 MYB transcription factor, GmMYB176, is reported to regulate
isoflavone synthesis by affecting the expression of GmCHS8. GmMYB118 was
significantly regulated by salt and drought treatment, and over-expression of
GmMYB118 improved tolerance to drought and salt in both Arabidopsis and
soybean. GmMYB expression was induced by drought, salt, ABA, and H 2 O 2 . The
transgenic lines over-expressing GmMYB84 exhibited enhanced drought tolerance
than WT plants. The over-expressors have longer primary root length, greater
proline and ROS content, higher antioxidant enzyme activity, lower dehydration
rate, and reduced MDA content (Wang et al. 2017). The activities of antioxidant
enzymes were induced by ROS in over-expressor lines. The GmMYB84 was shown
to bind the cis elements in the promoter of GmRBOHB1 and GmRBOHB2 which
results in increased ROS levels leading to increased root growth under drought stress
conditions (Wang et al. 2017). In addition, several members of bHLH, SRS, VOZ,
NFYA family of transcription factors are shown to be involved in regulation of
expression of various abiotic stress-related genes in soybean.
4 Breeding and Molecular Approaches for Evolving Drought-Tolerant Soybeans
105