**3. Major families of cereal TFs involved in drought response**

Transcription factors are classified into several family groups mainly based on characteristic amino acid sequences of its conserved DBDs [36, 37]. Of these, the families DREB/CBF, NAC, MYB, WRKY, bZIP, and HD-Zip are the main TFs involved in drought. Their structural features, classification, and representative family members in cereals are summarized in Table 1 and Figure 2.


It was also demonstrated that ABA can increase the transcription level of reactive oxygen species (ROS) network genes [30]. ROS are reactive oxygen–based molecules such as super‐

damage cells through membrane peroxidation and de-esterification under environmental stresses but also trigger stress endurance in plants [30]. For example, ABA has been shown to trigger the activity of cytosolic aldehyde oxidase and xanthine dehydrogenase, which sepa‐

The GA receptor GA INSENSITIVE DWARF1 (GID1) was reported from rice and is a homolog of the *Arabidopsis* GID1a/b/c [30]. GA-responsive TFs GRAS (GA insensitive [GAI], REPRESS‐ OR of *ga1-3* [RGA], and SCARECROW [SCR]) are GA signaling repressors involved in GAcontrolled plant development [30]. Subgroup of GRAS, called DELLA proteins, can interact with GID1 and lead to DELLA protein degradation. The downstream gene of DELLA TFs encoding a RING-H2 zinc finger factor XERICO is involved in ABA and GA transduction pathways under abiotic stresses [30]. Further, the DELLA protein RGL3 can be responsive to JA and interact with the JA regulator OsJAZ (jasmonic acid ZIM-domain protein) under drought [30]. Thus, DELLA proteins can be considered as the interface of ABA, GA, and JA

The regulation network of TFs plays an important role in stress-relevant hierarchic regulatory pathways. OsNAC10, a NAC TF, can up-regulate the downstream genes encoding AP2 and WRKY TFs involved in ROS detoxification and scavenging for drought response through the ABA synthesis pathway. The mechanisms of plant response to drought include cell wall development and cuticle formation [30]. The promoter region of the gene *OsNAC6* contains various recognition sites such as ABREs, MYBRS, MYCRS, W-boxes, and GCC boxes, which can be separately recognized by TFs AREB/ABF, MYB, MYC, WRKY, and ERF [33]. These TFs are likely to bind to the corresponding *cis*-elements and co-regulate the expression of *Os‐ NAC6* that participate in the ABA induction pathway and abiotic stress response in plants. In the bZIP family, the gene encoding OsbZIP12 was also found to have MYBRS, MYCRS, and W-box motifs in its promoter region, which can be recognized by TFs MYB, MYC, and WRKY, respectively [34]. Besides, OsNAC5 and OsbZip23 might co-regulate the expression of the downstream gene *OsLEA3* since both of them enhance the transcription level of *OsLEA3* [35]. OsDREB1F might interact directly/indirectly with some bZIP family members in the ABAdependent pathway that activate transcription of the ABA responsive genes *rd29B* and *RAB18* [3]. However, more in-depth studies are needed to identify these events and to explain the

**3. Major families of cereal TFs involved in drought response**

Transcription factors are classified into several family groups mainly based on characteristic amino acid sequences of its conserved DBDs [36, 37]. Of these, the families DREB/CBF, NAC, MYB, WRKY, bZIP, and HD-Zip are the main TFs involved in drought. Their structural features, classification, and representative family members in cereals are summarized in Table

2), and hydroxyl radical (OH

–

), which not only toxically

oxide (O

2 –

rately produce H

underlying mechanism.

1 and Figure 2.

), hydrogen peroxide (H

6 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

signaling pathways in response to water deficiency [30].

2 O 2 and O 2 – 2 O

in drought [32].

Transcriptional Network Involved in Drought Response and Adaptation in Cereals http://dx.doi.org/10.5772/62336 7


**Table 1.** Overview on the main cereal transcription factor family members involved in drought.

Transcriptional Network Involved in Drought Response and Adaptation in Cereals http://dx.doi.org/10.5772/62336 9

**Figure 2.** Schematic representation of domain compositions, secondary structures, and recognition sites of major drought-related TF families. The secondary structures were predicted using SWISS-MODEL (http://swissmodel.expa‐ sy.org/).

#### **3.1. DREB/CBF family**

**TF Species TFs name Cis-element recognition Downstream genes Accession/or locus number Reference**

U U U U U U U U *STZ*

U *Cor6.6, rd28A, rd29B* e.g., *NtSOD*, *NtAPX*, *NtCAT*

U *OsLEA3-1*, et al.

*LEA3, Rab16*

*LEA3-1, RAB16C*

U

e.g., *RAB21*

*OsLEA3, OsTPP1,* RAB25

*OsCAT, OsNHX1, OsMY*

*LEA3, Rab16*

Os04g21950 Os05g14370 Os02g26430 Os08g29660 Os11g29870 Os01g54600 Os01g14440 Os09g16510

EU665425 HQ700327 EU665430 KR827395 CAD60651 AK072062

U Os02g09830 Os05g0569300 [92]

AK103188 Os06g45140 Os09g13570 Os09g28310

KJ562868,

KJ806555-KJ806560 [84]

HQ166718

U AK365526.1 AK251589.1 AK359622.1 AK374525.1 AK359391.1 AK365082.1 AK249686.1 AK368116.1 AK369418.1 AK372616.1 AK359129.1

U NM\_001158672 [89]

GRMZM5G858197 [88]

HQ328839 *GRMZM2G448607* [88]

*GRMZM2G103647* [88]

AY224440 AF145728 JX514832

[90]

 D

 U

 U

[27]

[104]

[108]

 D Rice, *Arabidopsis*

 U

 D

[134]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

[86]

 D

 D

 U

 D

 D

 D

 D

 D

 D

 D

 D

 D

 D

 D

 D

 D

 Tobacco

N N N N N N N N N N N N N N N *Arabidopsis*

N N Rice Rice

Drought, salt, osmotic stress

Drought

Drought

Drought, salt

Drought

Drought, salt

[98]

[24]

[25]

[25, 93]

 D

 D

 D

 I

 D

[81]

[78]

[81]

[81]

[81]

[81]

[81]

[81]

[82]

[83]

[82]

[111]

[133]

[23, 92]

[34]

[91]

 D

 D

 D

 U

 D

 U

 Tobacco

N Rice Rice Rice Rice Rice

Rice Rice Rice *Arabidopsis*

Drought, salt, freezing stress

Drought, salt, cold

Drought

Drought

Drought

Drought

Drought

Drought, cold

Drought

Drought

Drought

Drought

Drought

Drought

Drought

Drought, heat, salt

Drought

 Drought, heat, hydrogen peroxide

Drought, cold

Drought, salt

Drought

Drought, salt, osmotic stresses

Drought

Drought, salt

Drought

Drought

Drought

 D

 U

 Tobacco *Arabidopsis*

 D

 U

 U

 U

 U

 U

 U

 D

 U

N *Arabidopsis*

N N N N N N *Arabidopsis*

Drought, cold

Drought, disease

Drought, cold, flood

Drought, cold, flood

Drought, cold, flood

Drought, cold, flood

Drought, cold, flood

Drought, cold, flood

Drought, salt

Drought, salinity

Drought, salt, freezing

 stress

8 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

OsWRKY42 U

OsWRKY45 U

OsWRKY50 U

OsWRKY53 U

OsWRKY78 U

OsWRKY84 U

OsWRKY96 U

OsWRKY100 U

TaWRKY2 U

TaWRKY10 U

TaWRKY19 U

TaWRKY44 (TTGACC/ TTAACC)

Barley Hv-WRKY38 U

Rice

**Table 1.** Overview on the main cereal transcription factor family members involved in drought.

bZIP

Barley

 DRE

e.g., *rd29B, RAB18, HIS1-3*

U U U U U

e.g., *Atrd29A, AtRD20, Atrd29B*

U U U U U U U U U U U U U U U U

OsbZip23 ABRE

OsbZip12 ABRE

OsbZip16 ABRE

OsbZip45 ABRE

OsbZip46 ABRE

OsbZIP52/ RISBZ5 G-box

OsbZip71 ABRE or

OsbZip72 ABRE

Wheat TabZip60 ABRE

TaABP1 U

HvbZip13 U

HvbZip15 U

HvbZip18 U

HvbZip20 U

HvbZip23 U

HvbZip29 U

HvbZip34 U

HvbZip40 U

HvbZip42 U

HvbZip49 U

HvbZip52 U

HvbZip53 U

HvbZip77 U

ZmbZip17 U

ZmbZip37 U

ZmbZip72 ABRE

ZmbZip74 U

ZmbZip112 U

Rice Oshox22 CAAT (G/C)

OsHox4 U

Maize Zmhdz10 CAATAATTG

U, Unknown; D, ABA-dependent; I, ABA-independent; N, No transgenic.

HD-Zip

 ATTG

Maize

WRKY

Wheat

Rice

**ABA (D/I) Transgenic plants Stress inducible/tolerance** 

The DREB/CBF family is a member of the AP2/EREBF superfamily of TFs, responsive to several stresses including drought [3, 8]. A cDNA encoding the first identified DREB/CBF family member CBF1 was isolated from *Arabidopsis thaliana* and characterized by Stockinger et al. [38]. DREB/CBF TFs possess about 60 amino acid long AP2 DBD which specifically recognizes a dehydration-responsive C-repeat (DRE/CRT) *cis*-element. The AP2 is a highly conserved domain of DREB family members. It contains two conserved motifs: the YRG and RAYD motifs. The YRG motif is considered to determine DNA binding and the RAYD motif, which forms an α-helix on the C-terminus, is supposed to play a role in PPI [39]. Drought responsive DREB TFs were also found in other plant species such as *Brassica napus* [40], *Triticum aesti‐ vum* [41], *Atriplex hortensis* [17], and *Oryza sativa* [42].

Many reported drought-inducible cereal DREBs were shown to be regulators improving stress endurance. In wheat, the gene *TaDREB1* [41] was induced by drought, salt, and cold. The transgenic barely containing *TaDREB2* and *TaDREB3* [13] showed improved tolerance in drought and low temperature conditions. In rice, 13 transcriptional factors including seven DREB1 types (OsDREB1A, 1B, 1C, 1D, 1E, 1F, and 1G) and six DREB2 types (OsDREB2A, 2B, 2C, 2D, 2E, and OsAB14) [43] were isolated and analyzed. The overexpression of OsDREB1A [1] and OsDREB1F [3] resulted in transgenic *Arabidopsis* and rice plants with higher tolerance to salt, drought, and low temperature. OsDREB1G, 2A, and 2B were identified to be strong candidates in drought responsive pathways, while OsDREB1E could slightly improve the drought survival rate in transgenic rice [44, 45]. In different wheat cultivars, TaDREB1 was demonstrated to be inducible by drought, salt, low temperature, and ABA [41]. TaDREB2 and TaDREB3 significantly improved frost and drought tolerance in transgenic barley and wheat [13]. In maize, ZmDREB1A [11], –2A [94], and ZmDREB2.7 [46] contributed to drought tolerance. In barley, the gene *HvDREB1* [47] was induced by drought, salt, and low tempera‐ ture, while the constitutive expression of HvCBF4 [48] increased the survival rate of transgenic rice under drought.
