Investigating the phytohormone ethylene response pathway by chemical genetics.

Conventional mutant screening in forward genetics research is indispensible to understand the biological operation behind any given phenotype. However, several issues, such as functional redundancy and lethality or sterility resulting from null mutations, frequently impede the functional characterization of genetic mutants. As an alternative approach, chemical screening with natural products or synthetic small molecules that act as conditional mutagens allows for identifying bioactive compounds as bioprobes to overcome the above-mentioned issues. Ethylene is the simplest olefin and is one of the major phytohormones playing crucial roles in plant physiology. Most of the current information on how ethylene works in plants came primarily from genetic studies of ethylene mutants identified by conventional genetic screening two decades ago. However, we lack a complete picture of functional interaction among components in the ethylene pathway and cross talk of ethylene with other phytohormones. Here, we describe our methodology for using chemical genetics to identify small molecules that interfere with the ethylene response. We set up a phenotype-based screening platform and a reporter gene-based system for verification of the hit compounds identified by chemical screening. We have successfully identified small molecules affecting the ethylene phenotype in etiolated seedlings and showed that a group of structurally similar compounds are novel inhibitors of ACC synthase, a rate-limiting enzyme in the ethylene biosynthesis pathway.