Involvement of Arabidopsis Methyl Chloride Synthases in the Thiocyanate Ion Metabolism.

Abstract

Recent studies clarified that plants are the largest source of CH₃Cl, and methyl chloride synthase gene, designated as HOL, was identified in Arabidopsis. Although it is predicted that HOL methylates Cl^-, Br^-, I^-, NCS^- and HS^-, its physiological significances are still unkown.
We analyzed recombinant proteins of HOL (AtHOL1) and its homologs, AtHOL2 and AtHOL3, and demonstrated that each protein catalyzes S-adenosylmethionine-dependent methylation of Cl^-, Br^-, I^-, NCS^- and HS^-. AtHOL1 and AtHOL2 showed the highest activity with NCS^-. Analyses of the growth responses of the Arabidopsis T-DNA insertion mutants (hol1, hol2, hol3) to the substrates showed that hol1 solely increased sensitivity to NCS^-. We showed that CH₃SCN was released from homogenized Arabidopsis seedlings but not from hol1. It is known that NCS^- is produced by hydrolysis of a glucosinolate and CH₃SCN has repellent activities. These results implies that AtHOL1 is involved in the metabolism of a glucosinolate and wounding responses.