Methyl Jasmonate- and Salicylic Acid-Induced Transcription Factor ZjWRKY18 Regulates Triterpenoid Accumulation and Salt Stress Tolerance in Jujube

Abstract

Triterpenoids are important, pharmacologically active substances in jujube (<i>Ziziphus jujuba</i> Mill.), and play an important role in the plant's resistance to abiotic stress. However, regulation of their biosynthesis, and the underlying mechanism of their balance with stress resistance, remain poorly understood. In this study, we screened and functionally characterized the <i>ZjWRKY18</i> transcription factor, which is associated with triterpenoid accumulation. The transcription factor is induced by methyl jasmonate and salicylic acid, and its activity was observed by gene overexpression and silencing experiments, combined with analyses of transcripts and metabolites. <i>ZjWRKY18</i> gene silencing decreased the transcription of triterpenoid synthesis pathway genes and the corresponding triterpenoid content. Overexpression of the gene promoted the biosynthesis of jujube triterpenoids, as well as triterpenoids in tobacco and <i>Arabidopsis thaliana</i>. In addition, <i>ZjWRKY18</i> binds to W-box sequences to activate promoters of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and farnesyl pyrophosphate synthase, suggesting that <i>ZjWRKY18</i> positively regulates the triterpenoid synthesis pathway. Overexpression of <i>ZjWRKY18</i> also increased tolerance to salt stress in tobacco and <i>Arabidopsis thaliana</i>. These results highlight the potential use of <i>ZjWRKY18</i> to improve triterpenoid biosynthesis and salt stress tolerance in plants, and provide a strong basis for metabolic engineering to improve the content of triterpenoids and breeding of jujube varieties that are resistant to stress.