Transcriptome-wide identification of WRKY transcription factors and their expression profiles under different stress in <i>Cynanchum thesioides</i>

Abstract

<i>Cynanchum thesioides (Freyn) K. Schum.</i> is an important economic and medicinal plant widely distributed in northern China. WRKY transcription factors (TFs) play important roles in plant growth, development and regulating responses. However, there is no report on the <i>WRKY</i> genes in <i>Cynanchum thesioides</i>. A total of 19 WRKY transcriptome sequences with complete ORFs were identified as WRKY transcriptome sequences by searching for WRKYs in RNA sequencing data. Then, the <i>WRKY</i> genes were classified by phylogenetic and conserved motif analysis of the WRKY family in <i>Cynanchum thesioides</i> and <i>Arabidopsis thaliana</i>. qRT-PCR was used to determine the expression patterns of 19 <i>CtWRKY</i> genes in different tissues and seedlings of <i>Cynanchum thesioides</i> under plant hormone (ABA and ETH) and abiotic stresses (cold and salt). The results showed that 19 <i>CtWRKY</i> genes could be divided into groups I-III according to their structure and phylogenetic characteristics, and group II could be divided into five subgroups. The prediction of <i>CtWRKY</i> gene protein interactions indicates that <i>CtWRKY</i> is involved in many biological processes. In addition, the <i>CtWRKY</i> gene was differentially expressed in different tissues and positively responded to abiotic stress and phytohormone treatment, among which <i>CtWRKY9</i>, <i>CtWRKY18,</i> and <i>CtWRKY19</i> were significantly induced under various stresses. This study is the first to identify the <i>WRKY</i> gene family in <i>Cynanchum thesioides</i>, and the systematic analysis lays a foundation for further identification of the function of <i>WRKY</i> genes in <i>Cynanchum thesioides</i>.