Submitted to: Sexual Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2004
Publication Date: 3/1/2004
Citation: Pring, D.R., Tang, H.V. 2004. Transcript profiling of male-fertile and male-sterile sorghum indicates extensive alterations in gene expression during microgametogensis. Sexual Plant Reproduction. 16:289-297. Interpretive Summary: Cytoplasmic male sterility in grain sorghum is required for hybrid seed production. In use, one parent of a cross to generate a hybrid is male-sterile, and is grown adjacent to male pollinators; any seed formed on the sterile plant is hybrid. Fertility restorer (Rf) genes are used to insure that the resulting hybrid is fertile. The identification and isolation of these important Rf genes would allow directed incorporation into agronomic lines, expanding the diversity of hybrid production. We exploited a new molecular tool, transcript profiling, to search for evidence of action of the Rf genes. We isolated very young and nearly mature pollen from fertile and sterile lines, and from a sterile line restored to fertility. Transcripts, the functional part of the plant genome, were isolated and fractionated by transcript profiling procedures. Normal pollen undergoes dramatic changes in the expression of genes during maturation, and patterns in the male-sterile line were markedly altered. Very young pollen shows fewer variations between fertile and sterile lines, and Rf genes restore most normal functions. Novel Rf-associated expressed genes were identified. About 12,000 genes are expressed in very young pollen. These studies established the utility of transcript processing in examining the complexity of gene expression in pollen, and identified a number of candidates for Rf genes or pathways affected by Rf genes. The data have impact in designing critical approaches to cytoplasmic male sterility, and will be value to geneticists and molecular biologists.
Technical Abstract: Male-sterile sorghum carrying the IS1112C cytoplasm represents an unusual example of aberrant microgametogenesis wherein microspores develop into inviable pollen that remain physically intact until anther exsertion. These inviable pollen are characterized by absence of starch deposition, yet fluoresce with the vital stain fluoroscein diacetate. cDNA-AFLP transcript profiling was utilized to examine differential gene expression in near-isogenic male-fertile and male-sterile plants at a late stage representing young-nearly mature pollen, spanning the terminal 96 hrs of pollen development, and an early stage representing early-mid microspores to early pollen, 7-11 days prior to anthesis. The transition from early to late stages is characterized by changes in abundance of nearly 33% of shared transcripts, and early- or late-specific expression of about 10% of transcripts. Male-sterile plants exhibit extensive changes in regulatory patterns characteristic of fertile plants, including premature expression of late-specific, and prolonged expression of early-specific, transcripts. Many late-specific transcripts in male-fertile plants are not expressed in male-sterile plants, which also express transcripts not detected in fertile plants. Genome-wide transcriptome patterns indicate the expression of an estimated 12,000 genes in early-mid microspores. The abundance of at least 15% of these transcripts is altered in male-sterile plants. A near-isogenic line restored to male fertility is characterized by apparent normalized expression of most of these transcripts. The development of the microgametophyte is thus characterized by dynamic programmed changes in gene expression, and the expression of male sterility compounds these changes in a complex manner.