Genetic code expansion and synthetic genetic circuits that can count for precision control of plant and microbial gene expression

Jennifer Brophy presents two methods for programming when and where genes are expressed in plants and their associated microbes. One creates a chemical signal using the noncanonical amino acid O-methyl-L-tyrosine. Engineered Arabidopsis, tomato and poplar produce the signal, while engineered Bacillus subtilis and soil bacteria respond by activating gene expression. Restricting signal production to selected plant tissues allows local control of microbial activity. The second approach builds a genetic circuit that counts successive branching events in roots. It produces different expression patterns at different branch orders, helping researchers distinguish the contributions of roots that otherwise have similar molecular identities. Together, the approaches support experiments on plant development and the engineering of plant–microbe partnerships.