LACCASE is Necessary for Root Development in Salvia miltiorrhiza

Laccases are multicopper-containing glycoproteins related to monolignol oxidation and polymerization. These properties indicate that laccases are involved in the formation of important medicinal phenolic acid compounds in Salvia miltiorrhiza such as salvianolic acid B (SAB), which is used for cardiovascular disease treatment. To date, 29 laccases have been found in S. miltiorrhiza, some of which influence the synthesis of phenolic acids. Because of the functional redundancy of laccase genes, their roles in S. miltiorrhiza are poorly understood. In this study, the CRISPR/Cas9 system was first used for dual gene locus targeting in S. miltiorrhiza to knock out multiple laccase family genes. The development of the roots was retarded, and root microstructure was abnormal in laccase mutant lines. Additionally, the accumulation of phenolic acid compounds as well as lignin was dramatically reduced. This study suggests that SmLACs are necessary for root development and phenolic acid compound metabolism in S. miltiorrhiza.