Ostersetzer, O., Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Kato, Y., Research Institute for Bioresources, Okayama University, Kurashiki, Okayama, 710-0046, Japan
Adam, Z., Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel
Sakamoto, W., Research Institute for Bioresources, Okayama University, Kurashiki, Okayama, 710-0046, Japan

Arabidopsis contains four Lon protease-like proteins (AtLon1-AtLon4), predicted to be localized in different cellular organelles, including mitochondria, peroxisomes and plastids. A notable question is whether Lon is present in chloroplasts, since it is absent from cyanobacteria and thus appears to have been lost during the evolution of photosynthetic organisms. Based on in vivo transient assays, we found that AtLon4 is dually targeted to both mitochondria and chloroplasts. Furthermore, immunoblot analysis localized AtLon4 to the thylakoids. Thus, in spite of its absence from basal photosynthetic organisms, our results suggest the presence of Lon in plant plastids. © The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved.