RSB Directors Seminar: Regulation and significance of halide and thiol methylation in plants

Presented by ANU College of Health & Medicine

Chloromethane is a major carrier of chlorine in Earth’s atmosphere and thus participates in influencing the integrity of ozone layer. Biogenic emissions constitute the predominant source of chloromethane in the atmosphere. A likely route for the biosynthesis of this gas is direct enzymatic methylation of Cl– ions, which has been also viewed as a Cl– detoxification mechanism among halophytic organisms. Our attempts to dissect this pathway and to understand its molecular regulation, physiological role and ecological significance, led to the discovery of a novel class of plant enzymes – thiol methyltransferases (TMTs) – and the genes encoding these. Although TMTs can methylate both halide (including Cl–) and thiol ions, in reality, their primary natural function appears to be the methylation of thiols released upon the hydrolysis of glucosinolates – a family of defensive compounds in several plant genera, especially the mustard family. The volatile products of these methylation reactions have putative roles in plant-insect and plant-pathogen interactions. Notwithstanding the natural function of TMTs, it may be possible to harness their catalytic properties to methylate Cl– ions to chloromethane gas, and thereby use them to improve salinity tolerance of valuable crops via detoxification of Cl–. This presentation will provide a retrospective of our research in the area and explore potential avenues for future work.