AabHLH112, a bHLH transcription factor, positively regulates sesquiterpenes biosynthesis in Artemisia annua

Abstract

The bHLH transcription factors play important roles in the regulation of plant growth, development, and secondary metabolism. β-Caryophyllene, <i>epi</i>-cedrol, and β-farnesene, three kinds of sesquiterpenes mainly found in plants, are widely used as spice in the food industry and biological pesticides in agricultural production. Furthermore, they also have a significant value in the pharmaceutical industry. However, there is currently a lack of knowledge on the function of bHLH family TFs in β-caryophyllene, <i>epi</i>-cedrol, and β-farnesene biosynthesis. Here, we found that AabHLH112 transcription factor had a novel function to positively regulate β-carophyllene, <i>epi</i>-cedrol, and β-farnesene biosynthesis in <i>Artemisia annua</i>. Exogenous MeJA enhanced the expression of <i>AabHLH112</i> and genes of β-caryophyllene synthase (<i>CPS</i>), <i>epi-</i>cedrol synthase (<i>ECS</i>), and β-farnesene synthase (<i>BFS</i>), as well as sesquiterpenes content. Dual-LUC assay showed the activation of <i>AaCPS, AaECS</i>, and <i>AaBFS</i> promoters were enhanced by AabHLH112. Yeast one-hybrid assay showed AabHLH112 could bind to the G-box (CANNTG) <i>cis</i>-element in promoters of both <i>AaCPS</i> and <i>AaECS.</i> In addition, overexpression of <i>AabHLH112</i> in <i>A. annua</i> significantly elevated the expression levels of <i>AaCPS</i>, <i>AaECS</i>, and <i>AaBFS</i> as well as the contents of β-caryophyllene, <i>epi</i>-cedrol, and β-farnesene, while suppressing <i>AabHLH112</i> expression by RNAi reduced the expression of the three genes and the contents of the three sesquiterpenes. These results suggested that <i>AabHLH112</i> is a positive regulator of β-caryophyllene, <i>epi</i>-cedrol, and β-farnesene biosynthesis in <i>A. annua</i>.