An object of the present invention is to identify an enzyme having activity of synthesizing dihydrotentoxin that is a tentoxin precursor and an enzyme having activity of synthesizing tentoxin using dihydrotentoxin as a substrate. The present invention concerns a tentoxin synthesis-related gene encoding a protein comprising the amino acid sequence of SEQ ID NO: 16 and having activity of nonribosomal peptide synthesis of dihydrotentoxin and a tentoxin synthesis-related gene encoding a protein comprising the amino acid sequence of SEQ ID NO: 18 and having activity of converting dihydrotentoxin to tentoxin.