|SONG, XIANLIANG - SHANDONG AGRICULTURAL UNIVERSITY|
Submitted to: Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2014
Publication Date: 4/22/2014
Citation: Thyssen, G.N., Song, X., Naoumkina, M.A., Kim, H.J., Fang, D.D. 2014. Independent replication of mitochondrial genes supports the transcriptional program in developing fiber cells of cotton (Gossypium hirsutum L.). Gene. 544:41-48.
Interpretive Summary: The mitochondrial is the factory in a plant cell to produce energy for plant growth and development. It has its own chromosome and genes. In this research, we investigated the relationship between mitochondrial gene copy numbers and expression levels and cotton fiber development. First, we surveyed mitochondrial gene copy number and gene expression in cotton leaves and fibers of development stages. Next, we used this information to select 14 of the 35 protein coding mitochondrial genes for more detailed analysis. We collected RNA and DNA from cotton fiber cells at five developmental time points from a short fiber mutant Li2 and its wild type (WT) near isogenic line (NIL, almost identical) DP5690, and determined the copy number and relative expression level for each of the selected mitochondrial genes. Mitochondrial gene copy number and expression levels were low at the fiber elongation stage. As secondary cell wall biosynthesis began in developing fibers, the expression levels and copy numbers of mitochondrial genes involved in energy production and respiration were up-regulated in WT DP5690. However, the short fiber mutant Li2, failed to increase expression of these genes, which include three subunits of ATP synthase, and two cytochrome genes. At the same time, Li2 failed to increase the copy numbers of these highly expressed genes.
Technical Abstract: The mitochondrial genomes of flowering plants exist both as a "master circle" chromosome and as numerous subgenomic sublimons that are generated by intramolecular recombination. Differential stability or replication of these sublimons allows individual mitochondrial gene copy numbers to vary independently between different cell types and developmental stages. Our objective was to determine the relationship between mitochondrial gene copy number and transcript abundance in the elongating fiber cells of Upland cotton (Gossypium hirsutum L.). We compared RNA and DNA from cotton fiber cells at five developmental time points from early elongation through secondary cell wall thickening from the Ligon-lintless 2 (Li2) short fiber mutant and its wild type near isogenic line (NIL) DP5690. Mitochondrial gene copy number decreased from 3 to 8-DPA in the developing cotton fiber cells while transcript levels remained low. As secondary cell wall biosynthesis began in developing fibers, the expression levels and copy numbers of mitochondrial genes involved in energy production and respiration were up-regulated in wild type cotton DP5690. However, the short fiber mutant Li2, failed to increase expression of these genes, which include three subunits of ATP synthase, atp1, atp8 and atp9 and two cytochrome genes cox1 and cob. At the same time, Li2 failed to increase the copy numbers of these highly expressed genes. Surprisingly, we found that when mitochondrial genes were highly transcribed, they also had very high copy numbers. This observation suggests that in developing cotton fibers, increased mitochondrial sublimon replication may support increases in gene transcription.