Generic tools for conditionally altering protein abundance and phenotypes on demand.

Conditional gene expression and modulating protein stability under physiological conditions are important tools in biomedical research. They led to a thorough understanding of the roles of many proteins in living organisms. Current protocols allow for manipulating levels of DNA, mRNA, and of functional proteins. Modulating concentrations of proteins of interest, their post-translational processing, and their targeted depletion or accumulation are based on a variety of underlying molecular modes of action. Several available tools allow a direct as well as rapid and reversible variation right on the spot, i.e., on the level of the active form of a gene product. The methods and protocols discussed here include inducible and tissue-specific promoter systems as well as portable degrons derived from instable donor sequences. These are either constitutively active or dormant so that they can be triggered by exogenous or developmental cues. Many of the described techniques here directly influencing the protein stability are established in yeast, cell culture and in vitro systems only, whereas the indirectly working promoter-based tools are also commonly used in higher eukaryotes. Our major goal is to link current concepts of conditionally modulating a protein of interest's activity and/or abundance and approaches for generating cell and tissue types on demand in living, multicellular organisms with special emphasis on plants.