Abstract
Recent studies clarified that tropical and subtropical forests are the largest source of CH3Cl emitted to the atmosphere. Although a methyl chloride synthase gene, designated as HARMLESS TO OZONE LAYER/HOL/AtHOL1, was identified in Arabidopsis, its physiological significance has not been reported yet. Our biochemical analyses of the recombinant proteins of AtHOL1 and its homologs, AtHOL2 and AtHOL3, revealed that each protein had S-adenosyl-L-methionine-dependent methyltransferase activities. The enzymatic analyses with possible physiological substrates indicated that the activities of all AtHOL proteins for Cl- were much lower than that of AtHOL1 for NCS-. We demonstrated that NCS- was produced in response to wounding and almost all of NCS- was derived from indole glucosinolate in Arabidopsis. Our reverse genetic analyses showed that CH3SCN was produced by AtHOL1 upon wounding treatment. These results suggested that AtHOL1 was involved in indole glucosinolate metabolism rather than methyl chloride synthesis.
