Genome-wide characterisation and expression profiling of the LBD family in Salvia miltiorrhiza reveals the function of LBD50 in jasmonate signaling and phenolic biosynthesis

Jasmonates (JAs) regulate growth, development, and secondary metabolism in many economically significant crops. The lateral organ boundaries domain (LBD) protein family is a class of plant-specific transcription factors involved in the regulation of lateral organ development and jasmonate signaling. However, the functions of LBD genes in Salvia miltiorrhiza Bunge, an emerging model medicinal plant, are unclear. In this study, a total of 51 LBD transcription factor genes were identified in the genome of S. miltiorrhiza, and were classified by phylogenetic analysis into seven subfamilies. The expression profile revealed that 10 of the LBD genes are tissue-specific and JA-inducible. Of the 51 LBD transcription factor genes, 11 % (six out of 51) were potentially involved in the biosynthesis of tanshinones or phenolic acids. Correlation analysis showed that the expression of SmLBD9, SmLBD13, SmLBD21, and SmLBD50 were observably regulated in JA zim domain (JAZ) proteins transgenic S. miltiorrhiza, indicating their critical roles in the JA signaling pathway. Further functional analysis indicated that the overexpression of SmLBD50 inhibited the synthesis of total phenolics, total flavonoids, and anthocyanins in S. miltiorrhiza. Consistent with these phytochemical changes, the expression of phenolic biosynthetic genes was also stimulated. Yeast two-hybrid (Y2H) assays indicated that the SmLBD50 protein interacts with SmJAZ1, SmMYB36/97, SmbHLH37 and SmMYC2a/2b, four important transcription factors involved in JA signaling. In conclusion, our study off ;ers the first genome-wide overview and annotation of the LBD transcription factor family in S. miltiorrhiza and provides a foundation for understanding the molecular basis and regulatory mechanisms of SmLBD50 in relation to the JA response and phenolic metabolism in S. miltiorrhiza.