Body of Abstract: Targeted protein degradation is a potential strategy to capture the dynamics of fast cellular processes or to characterize the function of essential proteins. Targeted protein degradation has been used in non-plant cell biology exploit plant biological mechanisms such as the activity of photoreceptors for optogenetics or auxin-mediated ubiquitination in auxin degrons. It follows that these are not applicable for plants as light and auxin are very strong signals for plant cells. Plants are well adapted to quickly target proteins for degradation via polyubiquitination as several plant hormones are perceived by E3 ligases with exquisite specificity. E3 ubiquitin ligases mediate target protein recognition and ubiquitylation, and they comprise a large and diverse family of proteins in eukaryotes. Polyubiquitinated proteins are typically targeted for degradation via the proteasome, autophagy or vacuole targeting.
We developed a system for targeted protein degradation in plants. This system is based on the specific and well-characterized interaction between a non-plant E3 ligase and its target. This ligase-target interaction is well characterized and modular, which made it ideal for targeted degradation of chimeric protein fusions. A specific domain of the target, or “degron”, is sufficient to target a chimeric protein for degradation. Experiments using transient expression in Nicotiana showed that i) chimeric E3 ligase fusions are stable and active in plants, ii) degron fusions to GFP or other plant proteins are stable in the absence of the E3 ligase, iii) E3 ligase fusions efficiently degrade proteins containing the new degron sequence, and iv) target protein degradation can be induced by transcriptional control of the E3 ligase. Mutations in the degron or the catalytic site of the E3 ligase abolish protein degradation, indicating a good level of specificity. We will present proof-of concept results that showed potential of this technology for future applications in plant cell biology.