AUTHOR=Ma Ruifang , Xiao Ying , Lv Zongyou , Tan Hexin , Chen Ruibing , Li Qing , Chen Junfeng , Wang Yun , Yin Jun , Zhang Lei , Chen Wansheng 

TITLE=AP2/ERF Transcription Factor, Ii049, Positively Regulates Lignan Biosynthesis in Isatis indigotica through Activating Salicylic Acid Signaling and Lignan/Lignin Pathway Genes

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01361

DOI=10.3389/fpls.2017.01361

ISSN=1664-462X

ABSTRACT=<p>Lignans, such as lariciresinol and its derivatives, have been identified as effective antiviral ingredients in <italic>Isatis indigotica</italic>. Evidence suggests that the APETALA2/ethylene response factor (AP2/ERF) family might be related to the biosynthesis of lignans in <italic>I. indigotica</italic>. However, the special role played by the AP2/ERF family in the metabolism and its underlying putative mechanism still need to be elucidated. One novel AP2/ERF gene, named <italic>Ii049</italic>, was isolated and characterized from <italic>I. indigotica</italic> in this study. The quantitative real-time PCR analysis revealed that <italic>Ii049</italic> was expressed highest in the root and responded to methyl jasmonate, salicylic acid (SA) and abscisic acid treatments to various degrees. Subcellular localization analysis indicated that <italic>Ii049</italic> protein was localized in the nucleus. Knocking-down the expression of <italic>Ii049</italic> caused a remarkable reduction of lignan/lignin contents and transcript levels of genes involved in the lignan/lignin biosynthetic pathway. <italic>Ii049</italic> bound to the coupled element 1, RAV1AAT and CRTAREHVCBF2 motifs of genes <italic>IiPAL</italic> and <italic>IiCCR</italic>, the key structural genes in the lignan/lignin pathway. Furthermore, <italic>Ii049</italic> was also essential for SA biosynthesis, and SA induced lignan accumulation in <italic>I. indigotica</italic>. Notably, the transgenic <italic>I. indigotica</italic> hairy roots overexpressing <italic>Ii049</italic> showed high expression levels of lignan/lignin biosynthetic genes and SA content, resulting in significant accumulation of lignan/lignin. The best-engineered line (OVX049-10) produced 425.60 μg·g<sup>−1</sup> lariciresinol, an 8.3-fold increase compared with the wild type production. This study revealed the function of <italic>Ii049</italic> in regulating lignan/lignin biosynthesis, which had the potential to increase the content of valuable lignan/lignin in economically significant medicinal plants.</p>