Light Regulated CoWRKY15 Acts on CoSQS Promoter to Promote Squalene Synthesis in Camellia oleifera Seeds

Squalene synthase (SQS) is the most direct key enzyme regulating squalene synthesis. To better understand the regulatory mechanisms of squalene biosynthesis, a 1423-bp long promoter region of the <i>CoSQS</i> gene was isolated from <i>Camellia oleifera</i>. Plant CARE and PLACE analysis affirmed the existence of the core promoter elements such as TATA and CAAT boxes and transcription factor binding sites like W-box and MYB in the isolated sequence. Exogenous factors regulating the <i>CoSQS</i> promoter were obtained by using Yeast one-hybrid screening, and the key transcription factor CoWRKY15 was found. AOS (Antibody Optimization System) analysis showed that CoWRKY15 had the highest interactions with a confidence level of 0.9026. Bioinformatics analysis showed that CoWRKY15 belonged to class 2 of the <i>WRKY</i> gene family. The results of subcellular localization showed that CoWRKY15 functioned in the nucleus. The results of CoWRKY15 promoter analysis showed that 8 out of 14 cis-elements with annotatable functions were related to the light response. The region of the <i>CoSQS</i> promoter that interacts with CoWRKY15 is -186 bp~-536 bp. The histochemical assay and squalene content suggested that the <i>CoSQS</i> promoter could drive the expression of GUS gene and specific promotion of <i>CoSQS</i> expression. It was found that CoWRKY15 could act on the -186 bp~-536 bp <i>CoSQS</i> promoter to regulate the expression of <i>CoSQS</i> and the content of squalene in <i>C. oleifera</i> seed kernels.