Current Investigations

Our current investigations on CMS in B. napus are directed towards cloning and characterization of the two native restorer genes (termed Rfn and Rfp). We have devised novel methods for targeted genetic and physical mapping of the complex B. napus genome and have used this methodology to construct a high resolution genetic map of the Rfp region (7) and to identify and characterize a B. napus bacterial artificial chromosome (BAC) that covers the genetically-defined restorer region from the Rfn genotype. We are currently attempting to clone and characterize corresponding candidate genes from the Rfp genotype. Experiments aimed at identifying the restorer genes through genetic transformation experiments as well in further fine genetic mapping are in progress.

In 2003 (5), we showed that the nuclear restorer gene Rfo specified a protein encoding multiple, pentatricopeptide repeats (PPRs). Such proteins represent a family of eukaryotic proteins that has undergone a very high degree of expansion in the land plant lineage. Many PPR proteins have been shown to be involved in diverse aspects of organelle post-transcriptional gene expression and to function by specifically binding target RNAs. Studies in other laboratories have revealed that nuclear restorer genes in other plant species also specify PPR proteins, and in fact, that restorers appear to represent a distinct clade of PPR proteins. We first suggested that that related PPR genes within a species appear to be under positive or diversifying evolutionary selective pressure (6), a notion consistent with the intragenomic arms race hypothesis. This prediction has since been born out by analysis of diverse sequenced plant genomes by other investigators; thus, it seems likely that this arms race has been going on throughout the evolutionary history of flowering plants.

In addition to our studies on CMS in B. napus, we are, with collaborators at the Institut Nationale de Recherche Agronomique (INRA) in France, investigating how the Rfo protein recognizes its mitochondrial mRNA target. A second international collaboration, in this case with researchers in Biology at McGill, at the Volcani Institute in Israel and the University of Western Australia, is directed towards understanding the mode of action of nuclear genes termed maturases that encode proteins that are necessary for the splicing of specific introns in plant mitochondrial genes of the model plant Arabidopsis thaliana.

Selected references from my laboratory, as cited above:
5. Brown, G.G. et al. (2003). The radish Rfo restorer gene of Ogura cytoplasmic male sterility encodes a protein with multiple pentatricopeptide repeats. Plant J. 35: 262-272.
6. Geddy, R.G. and Brown, G.G. (2007). Genes encoding pentatricopeptide repeat (PPR) proteins are not conserved in location in plant genomes and may be subject to diversifying selection. BMC Genomics 8: Article 30.
7. Formanova, N., Stollar R., Geddy, R.G., Mahé, L., Laforest, M., Landry, B.S. and Brown, G.G. (2010). High-resolution mapping of the Brassica napus Rfp restorer locus using Arabidopsis-derived molecular markers. Theor. Appl. Genet. 120: 843-851.