Identification of the WRKY gene family in apricot and its response to drought stress

The WRKY family has been found in 14 plant species, and its members are mostly involved in plant stress resistance. Apricot (Prunus armeniaca L.) trees are extremely drought tolerant, but the molecular mechanisms have not yet been elucidated. Therefore, we investigated the WRKY gene family in apricot and analyzed the gene expression patterns in response to drought stress. A total of 56 candidate WRKY genes (PaWRKY1–56) were identified in the apricot genome. The putative proteins contain 162–1055 amino acids, with an isoelectric point of 5.0–9.68 and molecular weight of 18.76–114.2 Da. The PaWRKY family has a heptapeptide domain (WRKY) and zinc finger domain (CX5-7CX22-23HXH), which show differential variations among three groups. Group I has 12 members, with 2 WRKY and zinc finger domains located at the C and N terminus, respectively. Group II can be further divided into II-b, II-c, II-d, and II-e, with 10, 13, 6, and 7 members, respectively. Group III has eight members. Members of groups II and III have one WRKY and one zinc finger domain. Fifty-one PaWRKY genes are unevenly distributed across eight linkage groups. Only one tandem repeat event was detected, and gene duplication was identified as the main factor driving gene evolution. A total of 28 PaWRKY genes responded to the drought–rehydration treatment. In particular, drought stress up-regulated PaWRKY11/14/48 expression and down-regulated PaWRKY23 expression. The genome-wide identification, functional characterization, and evolutionary analysis of the PaWRKY family yield new insights into the role of WRKY in the drought tolerance of apricot trees.