Poster: Protein targeting & vesicular trafficking

Abs # 660: Multiple domains of atTic110 are essential for protein import into chloroplasts in Arabidopsis

Presenter:	Inaba, Takehito , tinaba@nsm.umass.edu
Authors	Inaba, Takehito  (A)   Li, Ming  (A)   Ewers, Carolin  (A)   Schnell, Danny J (A)
Affiliations:	(A): University of Massachusetts

Most chloroplast proteins are synthesized in the cytosol and imported into chloroplasts. After recognition by receptors at the chloroplast surface, the preproteins are translocated into the organelle by multimeric translocons at the outer and inner envelope, designated Toc and Tic complexes, respectively. Although the activities and functions of the Toc components have been extensively investigated, the nature of each Tic components remains to be established. Tic110 was the first Tic component identified and represents a major constituent of active Tic complexes. It is an integral inner envelope membrane protein consisting of two predicted transmembrane helices and a large hydrophilic carboxyl-terminal region. We have demonstrated that the hydrophilic domain of Tic110 is soluble, located at the stromal side of the chloroplast inner envelope and directly binds to preproteins. However, how Tic110 coordinates stromal events during protein transport in vivo remains unclear. To elucidate the in vivo mechanism of Tic110, we isolated an Arabidopsis knockout mutant for Tic110. We demonstrate that Arabidopsis Tic110, atTic110, has essential roles for early embryogenesis as well as vegetative growth. Analysis of transgenic Arabidopsis over-expressing truncated atTic110 suggests that separable domains on atTic110 have distinctive but essential functions in vivo. We will discuss the possible role of each domain in protein import into chloroplasts.