Submitted to: Current Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2001
Publication Date: N/A
Interpretive Summary: Grain sorghum production in the U.S. relies exclusively on the use of cytoplasmic male sterility (CMS) for efficient seed production and maximizing yields of hybrid lines. To understand the mechanisms of CMS, USDA, ARS, scientists in the Crop Genetics and Environmental Research Unit at Gainesville, Florida, are evaluating the basis of CMS in the sorghum line IS1112C. A possible basis for sterility was described for this source of CMS. In this case messenger RNA (mRNA) from the mitochondrion, a major energy-producing part of the cell, was shown to be modified in sterile plants. The gene involved, named atp6, is important to proper function. The modification is named RNA editing, where the sequence of the mRNA is altered, changing the gene protein product. Previously it was found that pollen from sterile plants were unable to properly edit the mRNA. This was an important lead in understanding CMS and the design of experiments to engineer the trait. This observation was re-examined in field conditions, where the sterility and fertility traits are stable. The extent of the loss of editing capability was examined in two sets of fertile and sterile plants, and young and maturing pollen was examined using a variety of approaches. There was essentially no loss of RNA editing capability in the sterile plants. Thus altered RNA editing is not a factor in male sterility conferred by the IS1112C sorghum line, and can be disregarded.
A dramatic reduction of mitochondrial atp6 transcript editing capability in sorghum anthers and pollen has been invoked as a factor in the loss of viability of the male gametophyte in lines carrying the IS1112C male-sterile cytoplasm. We initiated an examination of transcript editing of sorghum atp6 during pollen biogenesis, in developing microspores and pollen of normal, male-fertile and near-isogenic male-sterile lines, in a field environment. Transcript editing in steady-state cDNA populations from two male fertile lines indicated an average of about 90% editing among 15 sites examined, from microspores through maturing pollen. Parallel samples from two male-sterile lines demonstrated a minor but detectable reduction in editing efficiency, most evident in nearly-mature pollen and pollen from exserted anthers. However, editing efficiency in these cells averaged about 80%, substantially higher than the 20% previously observed. Thus the male-sterile lines retain substantial atp6 editing efficiency in an environment wherein the sterility and fertility restoration traits are stably expressed. We conclude that the drastically reduced editing of atp6 transcripts in anthers and pollen of sorghum carrying the IS11121C male-sterile cytoplasm is not demonstrable under Florida field conditions, and thus not a factor in male sterility in this system.