Research Molecular Biologist / Adj. Professor USDA-ARS/Cornell University
Plastids are found ubiquitously in plants and perform various critical functions for plant growth and development. Sophisticated machineries are developed to mediate the import of nucleus-encoded proteins into plastids. While the key translocons at the outer (TOC) and inner (TIC) membranes of chloroplasts are defined, proteins that interact with the core machinery to facilitate preprotein import are continuously being discovered. A DnaJ-like chaperone ORANGE (OR) protein is known to regulate carotenoid biosynthesis as well as plastid biogenesis and development. In this study, we found that OR physically interacts with several Tic proteins including Tic20, Tic40, and Tic110 in the classic TIC core complex of the chloroplast import machinery. Knocking out or and its homologous gene or-like greatly affects the import efficiency of representative photosynthetic and non-photosynthetic preproteins. Consistent with the direct interactions of OR with Tic proteins, the effect of OR occurs at translocation at the inner envelope membrane (i.e. at the TIC complex). OR is able to reduce Tic40 protein turnover rate through its chaperone activity, like its reported function on other target proteins. Moreover, OR was found to suppress the interaction between Tic40 and Tic110. It also reduces the binding of preproteins to Tic110 to aid their release for translocation and processing. Our findings suggest that OR plays a new and regulatory role in facilitating the later stage of plastid preprotein translocation to regulate plastid preprotein import, a process essential for chloroplast biogenesis and development.
Coauthors: Hui Yuan – Cornell University;Emily Pawlowski – Michigan State University;Danny Schnell – Michigan State University