Submitted to: Nucleic Acids Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/1998
Publication Date: N/A
Citation: Interpretive Summary: Hybrid grain sorghum production in the U.S. is dependent on the use of cytoplasmic male sterility (cms). Currently only one source of cms is used. Agricultural Research Service scientists in Gainesville, FL, have been examining an alternative source. To examine the usefulness of this source, the mechanism by which sterility is expressed, and how seed set can be assured for the farmer, is critical. We have identified a gene that appears to cause cms, and a gene that restores fertility for seed production. Genes are transcribed into messenger RNA (mRNA) before a gene product can be made. We have shown that a restorer gene functions by cutting mRNA such that very little of the gene product might be expected. We found that "RNA editing", a process by which the genetic code of a gene is changed in mRNA, may be required for action of the fertility restorer gene. Sorghum lines used for seed production must therefore "edit" the mRNA if the plants are to set seed, and all lines examined did indeed "edit" the mRNA. We have therefore established a probable basis for male sterility and one mechanism by which seed set is obtained for production. Only a few examples are known about how cms, and the restoration of fertility, might function in plants. These advances may allow geneticists and plant breeders to better understand the development of cms for use in the production of hybrid plants.
Technical Abstract: Processing of transcripts of sorghum mitochondrial orf107, a chimeric open reading frame associated with cytoplasmic male sterility, is conferred by the nuclear gene Rf3. The processing activity cleaves 75% of orf107 transcripts internally, and is obligatory for fertility restoration. Two orf107 transcript editing sites, 77 and 79 bp 5' to the processing site, are 81% and 61% edited in rf3rf3 lines, while these sites are 41% and 10% edited in the remaining 25% of whole-length transcripts in an Rf3Rf3 line. RNA editing and processing efficiency in F1 progeny were similar to the Rf3Rf3 parent. Analyses of backcross progeny indicated that all non-processing, rf3rf3 lines were characterized by high editing efficiency. Rf3rf3 backcross progeny, however, exhibited editing efficiencies intermediate to the F1 and the recurrent parent, indicating that the genetic regulation of editing may be complex. We postulate that highly edited transcripts within the population are quickly processed in lines carrying Rf3, generating a residual population of poorly edited transcripts. Thus action of Rf3 has no direct affect on RNA editing, but may be dependent on a substrate of highly edited transcripts. These data indicate a possible novel role of transcript editing in gene regulation through influencing the efficiency of transcript processing.