**1. Introduction**

Changing environmental factors, such as abiotic stresses, influence plant growth and development [1]. Among them, drought and heat stresses seriously threaten crop productivity and quality. Plants must respond appropriately to changing environmental challenges to survive. Thus, it is important to explore the stress response mechanisms of plants and to enhance their tolerance to drought and heat to increase crop productivity without expanding cultivated land [2].

Environmental stresses initiate transcription factor (TF)-mediated expression of a variety of genes in plants, including bZIP, AP2/EREBP, MYB/MYC, NAC and WRKY [1,3–6]. WRKY TFs are identified by their conserved DNA-binding WRKY domains (WRKYGQK) in N-termini, and a zinc -finger motif (C-X4-5-C-X22-23-H-X1-H or C-X7-C-X23-H-X1-C) in C-termini [7,8]. It has been reported that WRKYs participated in defense responses by binding to the W-box located in the promoters of plant defense-related genes [9–11]. Another study found that 15 WRKY rice genes were induced by infection with the pathogen *Magnaporthe grisea* [12]. Statistically, 13 rice WRKY genes have regulated resistance against pathogens [13–17].

Recently, studies have revealed the involvement of the WRKY family in plant responses to abiotic stresses [18,19]. For example, *ABO3/WRKY63* took part in responses to abscisic acid (ABA) and drought stress in *Arabidopsis*. *AtWRKY57*-overexpressing *Arabidopsis* exhibited improved tolerance to drought by combining the promoter sequences of *NCED3* through the ABA pathway [20]. Overexpression of *OsWRKY30* enhanced resistance to drought stress in rice by the phosphorylation process of mitogen-activated protein kinases (MAPKs) [11]. *TaWRKY2* is a nuclear-located protein, and overexpression of *TaWRKY2* in *Arabidopsis* led to enhanced tolerance to drought and salt stresses by improving the expressions of *STZ* and *RD29B*; moreover, the exogenous expression of *TaWRKY19* in *Arabidopsis* not only conferred resistance to salt and drought, but also improved freezing tolerance [21]. In addition, *CmWRKY10*-overexpression in chrysanthemum revealed enhanced resistance to drought stress by regulating stress-related genes [19].

Maize (*Zea mays*) is a major food and economic crop. A few studies on the genome-wide analysis of WRKYs in maize have been reported in recent years. Wei et al. (2012) identified 136 WRKY proteins encoded by 119 *ZmWRKY* genes in maize, and Zhang et al. (2017) identified three additional new *ZmWRKY* genes and analyzed the gene expression profiles of *ZmWRKYs* using data from microarray, three RNA-seq studies, and the results of RT-PCR, which improved knowledge of WRKYs in maize [22,23]. In this paper, we performed drought-treated *de novo* transcriptome sequencing of maize (SRP144573) to investigate potential drought-tolerant WRKY genes in the maize genome. We identified a drought-responsive WRKY gene, *ZmWRKY106*, (Gene ID: GRMZM2G013391), which was named by Wei et al. (2012) and Zhang et al. (2017) [22,23]. The exogenous expression of *ZmWRKY106* in *Arabidopsis* led to enhanced tolerance of drought and heat.
