AUTHOR=Li Qing , Feng Jingxian , Chen Liang , Xu Zhichao , Zhu Yingjie , Wang Yun , Xiao Ying , Chen Junfeng , Zhou Yangyun , Tan Hexin , Zhang Lei , Chen Wansheng 

TITLE=Genome-Wide Identification and Characterization of Salvia miltiorrhiza Laccases Reveal Potential Targets for Salvianolic Acid B Biosynthesis

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00435

DOI=10.3389/fpls.2019.00435

ISSN=1664-462X

ABSTRACT=<p>Laccases are widely distributed in plant kingdom catalyzing the polymerization of lignin monolignols. Rosmarinic acid (RA) has a lignin monolignol-like structure and is converted into salvianolic acid B (SAB), which is a representatively effective hydrophilic compound of a well-known medicinal plant <italic>Salvia miltiorrhiza</italic> and also the final compound of phenolic acids metabolism pathway in the plant. But the roles of laccases in the biosynthesis of SAB are poorly understood. This work systematically characterizes <italic>S. miltiorrhiza</italic> laccase (SmLAC) gene family and identifies the SAB-specific candidates. Totally, 29 laccase candidates (SmLAC1-SmLAC29) are found to contain three signature Cu-oxidase domains. They present relatively low sequence identity and diverse intron–exon patterns. The phylogenetic clustering of laccases from <italic>S. miltiorrhiza</italic> and other ten plants indicates that the 29 SmLACs can be divided into seven groups, revealing potential distinct functions. Existence of diverse <italic>cis</italic> regulatory elements in the <italic>SmLAC</italic>s promoters suggests putative interactions with transcription factors. Seven <italic>SmLAC</italic>s are found to be potential targets of miR397. Putative glycosylation sites and phosphorylation sites are identified in SmLAC amino acid sequences. Moreover, the expression profile of <italic>SmLAC</italic>s in different organs and tissues deciphers that 5 <italic>SmLAC</italic>s (<italic>SmLAC7/8/20/27/28</italic>) are expressed preferentially in roots, adding the evidence that they may be involved in the phenylpropanoid metabolic pathway. Besides, silencing of <italic>SmLAC7</italic>, <italic>SmLAC20</italic> and <italic>SmLAC28</italic>, and overexpression of <italic>SmLAC7</italic> and <italic>SmLAC20</italic> in the hairy roots of <italic>S. miltiorrhiza</italic> result in diversification of SAB, signifying that <italic>SmLAC7</italic> and <italic>SmLAC20</italic> take roles in SAB biosynthesis. The results of this study lay a foundation for further elucidation of laccase functions in <italic>S. miltiorrhiza</italic>, and add to the knowledge for SAB biosynthesis in <italic>S. miltiorrhiza</italic>.</p>