Submitted to: Sexual Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2005
Publication Date: 3/2/2006
Citation: Pring, D.R., Tang, H.V., Chase, C.D., Miripant, M.N. 2006. Microspore gene expression associated with cytoplasmic male sterility and fertility restoration in sorghum. Sexual Plant Reproduction. 19:25-35. Interpretive Summary: Hybrids of many crop crops, including sorghum, are dependent on the use of cytoplasmic male sterility (CMS) for efficient seed production. No pollen are produced on male-sterile plants, and hybrids are produced by pollinating these plants with normal, fertile plants. These fertile plants also restore fertility to the hybrid, thus allowing seed to be produced in farmer's fields. An important goal is to locate and identify these fertility restorer genes in sorghum, so that they can be quickly incorporated into important lines and manipulated to make seed production more efficient. We attacked this problem by using modern molecular biology tools and very young pollen, named microspores, to learn the earliest responses to the fertility restoration genes. We made DNA, the unit of inheritance, from transcripts of the early genes we detected and analyzed them by sequencing. Several interesting potential genes were found, but none have been identified as to specific function in higher plants to date. These data will allow us to recover the complete sequences of the candidate genes and allow mapping the genes on the physical map of sorghum. These observations will be of interest to geneticists and others involved in research on CMS and in basic reproduction processes of higher plants.
Technical Abstract: An approach to identify differential gene expression associated with the restoration of male fertility in sorghum lines carrying the IS1112C male-sterile cytoplasm was developed utilizing cDNA-AFLP transcript profiling applied to early-mid microspores. Near-isogenic male-sterile, normal male-fertile, and fertility-restored BC7F3 lines in the Tx398 and Tx7000 backgrounds, and a marker-selected BC11F3 in the Tx398 background, were examined. The fertility-restored lines were homozygous for the restoring alleles at the two required loci. We visualized a finite number of expressed sequences unique to, or dramatically up-regulated in the fertility restored lines, validating the utility of the approach. Restoration-associated transcripts differed between the Tx398 and Tx7000 backgrounds, indicating nuclear background-specific expression patterns and reactions to restoration. Analyses of four homozygous single-gene conversion recombinant inbred lines suggest that expression of certain visualized transcripts may be dependent on presence of one or both of the two genes required for fertility restoration. Sequences of the restoration-associated transcripts showed similarity with EST's whose cellular function has not been ascertained. Gene product abundance of several mitochondrial genes was unaltered in a near-isogenic sterile line exhibiting a significant number of alterations in expressed nuclear genes relative to a normal male-fertile line.