A compound enzyme, comprising L-histidine methylase, halogen methyltransferase and trimethylhistidine sulfurylase. L-histidine is catalyzed by L-histidine methylase and halogen methyltransferase to obtain trimethylhistidine, and then is catalyzed by trimethylhistidine sulfurase to obtain the L-ergothioneine. The method can realize conversion from L-histidine to L-ergothioneine only in two steps. Moreover, SAM enzyme is regenerated, such that the usage amount of the SAM enzyme is greatly reduced. Therefore, the method greatly reduces the raw material cost. Moreover, the method is high in reaction concentration (about 30 g/L), simple in process and good in industrial production prospect.

A gene related to biosynthesis of ergothioneine is provided. Based on five synthesis genes of ergothioneine in Mycobacteroides abscessus, only an encoding sequence of each of the five genes is retained, and a gene structure of an encoding region in each gene is optimized to obtain genes related to the biosynthesis of the ergothioneine that are stably expressed in rice. These genes have sequences set forth in SEQ ID NO: 1 to SEQ ID NO: 5, and encoded proteins thereof have amino acid sequences set forth in SEQ ID NO: 6 to SEQ ID NO: 10. The gene is transferred into rice to construct a transgenic rice molecular farm to produce the ergothioneine. As a molecular farm, rice seeds do not contain alkaloids or allergens that are harmful to the human body. Moreover, biosynthesized ergothioneine shows the advantages of easy extraction and processing and of low production cost.