Skip to main content
ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Chemistry Research » Research » Publications at this Location » Publication #172902
Title: NUCLEAR LOCALIZED CMS-ASSOCIATED ORF107 OF MITOCHONDRIAL ORIGIN IS IMPORTED INTO MITOCHONDRIA WITHOUT A TARGET SIGNAL

Author
item STOCKMEYER, KIRSTEN - CHRISTIAN-ALBRECHTS-UNIV
item Pring, Daryl
item KEMPKEN, FRANK - CHRISTIAN-ALBRECHTS-UNIV

Submitted to: Endocytobiosis and Cell Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2005
Publication Date: 1/15/2006
Citation: Stockmeyer, K., Pring, D.R., Kempken, F. 2006. Nuclear localized cms-associated orf107 of mitochondrial origin is imported into mitochondria without a target signal. Endocytobiosis and Cell Research. 16:1-8.

Interpretive Summary: Cytoplasmic male sterility (CMS) is exclusively used for hybrid sorghum seed production in the U.S. In one source of CMS we believe we know that a gene in the mitochondrion, the energy-producing part of the cell, may be causal of CMS. This probable gene is named orf107. To test this possibility that orf107 may cause CMS, it would be important to introduce the gene into the mitochondrion from the nucleus, where the majority of genetic information is stored. It was known that certain DNA sequences target, or direct, genes from the nucleus to the mitochondrion. These sequences were placed in front of orf107, and the resultant structure was introduced into tobacco cells, which are commonly used for these kinds of experiments. A fluorescing protein was added to part of the gene, which allows detection by fluorescence. When the tobacco cells were stained with a mitochondria-specific stain and examined under a microscope, we were able to see that the gene product of orf107 was indeed transported to the mitochondrion. Controls showed that orf107 without the targeting sequence also transported to the mitochondrion. These advances allow the conclusion that orf107, if introduced into the plant nucleus, would target the mitochondrion, where it might cause CMS. These advances will be of interest to molecular geneticists interested in manipulating and designing sources of CMS in higher plants.

Technical Abstract: Unique chimeric mitochondrial genes are associated with cytoplasmic male sterility (CMS) in many higher plants. It is thought that the disruption in pollen development is a consequence of mitochondrial dysfunction associated with the chimeric genes. To analyse the effect of a chimeric mitochondrial open reading frame on mitochondrial gene expression and pollen development, we introduced the CMS-associated mitochondrial orf107 from Sorghum bicolor into the tobacco nuclear genome. Constitutive expression of orf107 fused to the yeast coxIV mitochondrial targeting presequence revealed a significant reduction of plant growth and rooting ability. A similar, but less severe phenotype was observed when orf107 was expressed without a mitochondrial targeting sequence. In contrast, the same expression strategies revealed no deleterious effect in Arabidopsis thaliana. Transient expression assays employing tobacco BY2 cells provide direct evidence for import of the ORF107::GFP protein without any import sequence. Our data demonstrate that a protein of mitochondrial origin can be imported into mitochondria without the need to acquire a targeting sequence. This finding is discussed with respect to mitochondrial-nuclear gene transfer.