50:	The Arabidopsis VAR2 variegation locus defines an FtsH homolog that functions in early thylakoid membrane biogenesis.

Authors:	Chen, Meng(A)Choi, YangDo(A)Voytas, Daniel, F.(B)Rodermel, Steven, R.(A)
Affiliations:	(A): Department of Botany, Iowa State University, Ames, IA 50011 (B): Department of Zoology/Genetics, Iowa State University, Ames, IA 50011 (C): Interdepartmental Plant Physiology Major, Iowa State University, Ames, IA 50011
Presenter:	Chen, Meng , mengc@iastate.edu

Chloroplasts are highly coordinated with their host cells in differentiation and development. In order to better elucidate the mechanisms involved in nuclear-chloroplast interactions, we have been characterizing nuclear gene-induced variegation mutants. In Arabidopsis, only four loci have been identified to give rise to a variegation phenotype. They are im, chm, var1, and var2. Two of them (im and var2) have been studied in our lab. Var2 is a nuclear mutation affecting chloroplast development. While cotyledons appear normal, true leaves of var2 first emerge as yellow, then turn into green-white sectors. The green sectors contain cells with normal chloroplasts, whereas the white sectors contain cells with abnormal plastids lacking internal membrane structures. Var2 was cloned by chromosome walking, and seven var2 alleles have been sequenced. Sequence analyses indicate that VAR2 is a FtsH-like zinc and ATP dependent-protease. It has two transmembrane domains at its N-terminus and an ATP binding site and a zinc binding site at its C-terminus. Chloroplast import experiments using in vitro translated VAR2 protein indicated that VAR2 is localized on the thylakoid membrane with its C-terminus facing the stroma. Northern and Western bolts suggested that VAR2 is only expressed in photosynthetic tissues. VAR2 is highly homologous to PFTF from red pepper. It has been suggested that PFTF is involved in vesicle fusion and/or protein translocation during chromoplast differentiation (P. Hugueney et al., 1995, Proc Natl Acad Sci U S A 92, 5630-4). We conclude that VAR2 functions in early thylakoid membrane biogenesisas a factor that mediates vesicle fusion events. A mechanism of variegation will be presented.