Dr. Richard Vierstra
The Environmental & Plant Biology Colloquium Series presents Dr. Richard Vierstra, on “Autophagy, the Master of Selective Recycling” on Friday, March 27, at 11:50 a.m. in Porter 104.
Vierstra is a Full Professor with the Laboratory of Genetics at the University of Wisconsin-Madison.
Abstract: Autophagy-mediated turnover plays an essential role in cellular housekeeping by removing damaged organelles and unwanted cytoplasmic constituents, and is critical for plant defense and robust nutrient recycling, especially during nitrogen and fixed-carbon starvation. This “self eating” is mediated by a conjugation system that modifies a pair of ubiquitin-like proteins ATG12 and ATG8 to eventually form an autophagic vesicle coated with the ATG8-phosphatidylethanolamine (PE) adduct. The ATG8-PE serves two purposes, one is to help direct the transport of autophagic vesicles to the vacuole for breakdown, and the other is to serve as a docking platform for a suite of ATG8-interacting proteins that selectively tether appropriate cargo within the vesicle lumen before enclosure. Using an extensive collection of atg mutants in Arabidopsis, we have characterized the pathway responsible for ATG8/12 conjugation and the kinase cascade that connects metabolic and environmental cues to the formation and transport of autophagic vesicles. A key regulatory step is controlled by the ATG1 kinase complex that works downstream of the TOR signaling system and ATG8/12 modification. It is not only necessary for vacuolar deposition of autophagic bodies but also becomes a substrate through the interaction of several subunits with ATG8, thus providing feedback control on autophagic turnover. In addition to bulk turnover, we found that the ATG system is responsible for the turnover of organelles like mitochondria and chloroplasts, and large cytoplasmic complexes such as 26S proteasomes or ribosomes when dysfunctional or no longer needed. Proteasome turnover appears to be mediated by prior ubiquitylation of numerous core subunits, which are then recognized by the dual ubiquitin/ATG8 receptor RPN10. Using maize as a model, we have also begun to describe the roles of ATG8-mediated autophagy in crops. Our initial genetic studies revealed a key role in productivity by mobilizing nitrogen when limiting to developing seeds. (Work supported by the NSF Plant Genome Research Program.)
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