Premium
Cloning and functional characterization of the Arabidopsis N ‐acetylserotonin O ‐methyltransferase responsible for melatonin synthesis
Author(s) -
Byeon Yeong,
Lee HyeJung,
Lee Hyoung Yool,
Back Kyoungwhan
Publication year - 2016
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/jpi.12289
Subject(s) - arabidopsis , biology , melatonin , gene , microbiology and biotechnology , gene cluster , biochemistry , endocrinology , mutant
The N ‐acetylserotonin O ‐methyltransferase ( ASMT ) gene encodes the enzyme that catalyzes the conversion of N ‐acetylserotonin to melatonin as the last step in melatonin biosynthesis. The first plant ASMT gene to be cloned was from rice. An orthologous gene encoding a protein with ASMT activity and only 39.7% amino acid sequence identity to the rice ASMT protein was recently isolated from apple ( Malus zumi ). The low homology of the apple ASMT sequence prompted us to screen the Arabidopsis genome for a homologous ASMT gene. The At4g35160 gene exhibited the highest sequence identity (31%) to the rice ASMT gene, followed by the At1g76790 gene with 29% sequence identity. We purified recombinant proteins expressed from the two Arabidopsis genes. The At4g35160 recombinant protein exhibited ASMT enzyme activity, but the At1g76790 recombinant protein did not; thus, we designated At4g35160 as an Arabidopsis thaliana ASMT ( At ASMT ) gene. The At ASMT protein catalyzed the conversion of N ‐acetylserotonin to melatonin and serotonin to 5‐methoxytryptamine with V max values of 0.11 and 0.29 pkat/mg protein, respectively. However, At ASMT exhibited no caffeic acid O ‐methyltransferase activity, suggesting that its function was highly specific to melatonin synthesis. At ASMT transcripts were induced by cadmium treatment in Arabidopsis followed by increased melatonin synthesis. Similar to other ASMT proteins, At ASMT was localized in the cytoplasm and its ectopic overexpression in rice resulted in increased ASMT enzyme activity and melatonin production, indicating the involvement of At ASMT in melatonin synthesis.