De novo Transcriptome Analysis Revealed the Putative Pathway Genes Involved in Biosynthesis of Moracins in Morus alba L.

Moracins, a kind of 2-phenyl-benzofuran compound from Moraceae, serve as phytoalexins with antimicrobial, anti-inflammatory, antitumor, and antidiabetes activities and respond to biotic and abiotic stresses, while their biosynthetic pathway and regulatory mechanism remain unclear. Here, we report a de novo transcriptome sequencing for different tissues of seedlings, as well as leaves under different stresses, in M. alba L. A total of 88 282 unigenes were assembled with an average length of 937 bp, and 82.2% of them were annotated. On the basis of the differential expression analysis and enzymatic activity assays in vitro, moracins were traced to the phenylpropanoid pathway, and a putative biosynthetic pathway of moracins was proposed. Unigenes coding key enzymes in the pathway were identified and their expression levels were verified by real-time quantitative reverse transcription PCR (qRT-PCR). Particularly, a p-coumaroyl CoA 2'-hydroxylase was presumed to be involved in the biosynthesis of stilbenes and deoxychalcones in mulberry. Additionally, the transcription factors that might participate in the regulation of moracin biosynthesis were obtained by coexpression analysis. These results shed light on the putative biosynthetic pathway of moracins, providing a basis for further investigation in functional characterization and transcriptional regulation of moracin biosynthesis in mulberry.