Rf8-mediated T-urf13 transcript accumulation coincides with a pentatricopeptide repeat cluster on maize chromosome 2L

Authors: MEYER, JULIE - Iowa State University; PEI, DEQING - Iowa State University; Wise, Roger

Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2011
Publication Date: 8/29/2011
Citation: Meyer, J.M., Pei, D., Wise, R.P. 2011. Rf8-mediated T-urf13 transcript accumulation coincides with a pentatricopeptide repeat cluster on maize chromosome 2L. The Plant Genome. 4(3):283-299.

Interpretive Summary: Maize hybrids have a significant yield advantage over open-pollinated varieties. One way of producing hybrid seed efficiently is through the use of cytoplasmic male-sterile (CMS) germplasm. Since CMS plants do not produce viable pollen, they are unable to cross pollinate other plants. This is an advantage because it eliminates the need for the time and labor intensive task of hand emasculation of the inbred lines. Most CMS systems also have restorer genes that correct the defect of male sterility. By using a combination of characterized cytoplasmic male-sterile plants and plants that contain nuclear restorer genes, one can produce hybrid seed effectively. However, our understanding of the way restoration occurs has been hampered by the lack of information on the mechanism by which nuclear restorer genes function. In T-cytoplasm maize, CMS results from the action of the URF13 mitochondrial pore-forming protein, encoded by the unique T-urf13 mitochondrial gene. Full or partial restoration of fertility to T-cytoplasm maize is mediated by the Rf2a nuclear gene, in combination with one of three other genes: Rf1, Rf8, or Rf*. Rf2a encodes a mitochondrial aldehyde dehydrogenase, whereas Rf1, Rf8, and Rf* are all associated with T-urf13 mitochondrial transcript processing activity. This manuscript describes the genetic and physical mapping of Rf8 and Rf* to a 4.55 Mb region on 2L that contains ten pentatricopeptide repeat (PPR) encoding genes in the B73 5b.60 genome assembly. Positioning the Rf8 gene on the maize genome sequence will promote research by scientists that work in mechanisms of nuclear-cytoplasmic interactions, pollen development, and molecular breeding, thus leading to better plant performance.

Technical Abstract: Cytoplasmic male sterility (CMS) is a maternally inherited inability to produce functional pollen. In T-cytoplasm maize, CMS results from the action of the URF13 mitochondrial pore-forming protein, encoded by the unique T-urf13 mitochondrial gene. Full or partial restoration of fertility to T-cytoplasm maize is mediated by the Rf2a nuclear gene, in combination with one of three other genes: Rf1, Rf8, or Rf*. Rf2a encodes a mitochondrial aldehyde dehydrogenase, whereas Rf1, Rf8, and Rf* are associated with the accumulation of distinctive T-urf13 mitochondrial transcripts. RNA processing activity associated with Rf8 maps within a 4.55 Mb region on 2L that contains ten pentatricopeptide repeat (PPR) encoding genes in the B73 5b.60 genome assembly. Genetic linkage analysis also indicated that Rf* is positioned within this PPR cluster, as well as Rf3, which restores S-cytoplasm maize. Partially male-fertile plants segregated for the presence or absence of the Rf8-associated, T-urf13 1.42/0.42-kb transcripts, indicating that the RNA processing event associated with these transcripts is not necessary for anther exertion. In addition, a statistically significant delay in flowering was observed between partially male-fertile and mostly male-fertile plants. Taken together, these new results indicate that Rf8-mediated male fertility is under the control of more than one nuclear locus.