Keren, I., Institute of Plant Sciences, Agricultural Research Organizaion (ARO), Volcani Center, Bet Dagan 50250, Israel, Department of Plant Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Tal, L., Institute of Plant Sciences, Agricultural Research Organizaion (ARO), Volcani Center, Bet Dagan 50250, Israel, Department of Plant Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Des Francs-Small, C.C., Australian Research Council (ARC), Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
Araújo, W.L., Max Planck Institute for Molecular Plant Physiology, Am Mühlenberg 1, D14476 Potsdam-Golm, Germany, Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-000 Viçosa, Brazil
Shevtsov, S., Institute of Plant Sciences, Agricultural Research Organizaion (ARO), Volcani Center, Bet Dagan 50250, Israel
Shaya, F., Institute of Plant Sciences, Agricultural Research Organizaion (ARO), Volcani Center, Bet Dagan 50250, Israel
Fernie, A.R., Max Planck Institute for Molecular Plant Physiology, Am Mühlenberg 1, D14476 Potsdam-Golm, Germany
Small, I., Australian Research Council (ARC), Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
Ostersetzer-Biran, O., Institute of Plant Sciences, Agricultural Research Organizaion (ARO), Volcani Center, Bet Dagan 50250, Israel

Mitochondrial genomes (mtDNAs) in angiosperms contain numerous group II-type introns that reside mainly within protein-coding genes that are required for organellar genome expression and respiration. While splicing of group II introns in non-plant systems is facilitated by proteins encoded within the introns themselves (maturases), the mitochondrial introns in plants have diverged and have lost the vast majority of their intron-encoded ORFs. Only a single maturase gene (matR) is retained in plant mtDNAs, but its role(s) in the splicing of mitochondrial introns is currently unknown. In addition to matR, plants also harbor four nuclear maturase genes (nMat 1 to 4) encoding mitochondrial proteins that are expected to act in the splicing of group II introns. Recently, we established the role of one of these proteins, nMAT2, in the splicing of several mitochondrial introns in Arabidopsis. Here, we show that nMAT1 is required for trans-splicing of nad1 intron 1 and also functions in cis-splicing of nad2 intron 1 and nad4 intron 2. Homozygous nMat1 plants show retarded growth and developmental phenotypes, modified respiration activities and altered stress responses that are tightly correlated with mitochondrial complex I defects. © 2012 The Authors.