Plant chemical genomics: gravity sensing and response

The gene families that encode the vesicle trafficking machinery in plants are highly expanded compared to those from protists and animals. As such, classical genetic screens for mutants with lesions in these genes are fraught with issues of redundancy and lethality. A chemical genomics approach can, in theory, circumvent these issues because inhibitory or stimulatory molecules may be applied at any point in development at sublethal concentrations. This chapter describes the protocols for a chemical genomics screen designed to identify components of the plant cell vesicle trafficking machinery. A two-tiered screen was designed where the primary screen assayed for chemicals that modified the gravitropic response, a process that in plant cells is intimately tied to vesicle trafficking; the secondary screen employed fluorescent marker lines that were treated with gravitropic inhibitors or inducers to assay for changes in endomembrane system morphology. We thus identified four compounds by which we can further explore the relationship between gravitropic signal transduction and vesicle trafficking.