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Roberto Espinoza Corral (Lundquist Lab)

Date & Location: September 10, 2019, at 12p; Room 168 Plant Biology Building

Subject: Analysis of the protein oligomeric state of dynamic plastoglobule lipoprotein particles of Arabidopsis thaliana

Abstract: The photosynthetically active thylakoid membranes of plant chloroplasts contain associated lipoprotein particles called plastoglobules. These plastoglobules are derived from – and remain attached to – the thylakoid, comprising a distinct population of protein and lipid. While their importance to plant growth and development is highlighted by their dynamic morphology under stresses or developmental transitions and their ubiquity amongst photosynthetic species, their precise role(s) remain unclear.

We suggest that the plastoglobule serves in part as a platform for metabolic channeling by drawing pathway enzymes into close physical proximity. To test this hypothesis, we have compared the oligomeric state of the A. thaliana plastoglobule proteome under unstressed and light-stressed conditions by separating proteins by BN-PAGE and analyzing gel slices of increasing native molecular mass by mass spec-based proteomics. We identify multiple proteins present in high molecular mass complexes and propose interactions amongst several plastoglobule proteins based on co-migration on the BN-PAGE gel. Comparison of the two environmental conditions reveals a dynamic oligomeric state, suggesting creation and formation of distinct complexes in response to differing requirements of the plant. We selected a protein kinase that migrates in a high molecular weight complex specifically under light stress for T-DNA mutant studies. Characterization of the mutant demonstrates impairment in the transition from vegetative to reproductive growth, emphasizing the plastoglobules role in developmental transitions. In vitro kinase assays reveal critical residues required for kinase activity and phenotypic complementation. We propose a model of plastoglobule function that synthesizes our discoveries.

Speaker Lab: Dr. Peter K Lindquist