ARS | Publication request: UBIQUITY OF THE ST CHLOROPLAST GENOME IN ST-CONTAINING TRITICEAE POLYPOIDS

Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 4, 2000
Publication Date: N/A

Interpretive Summary: The wheat family (Triticeae) contains numerous important forage and grain grasses. Because many of these grasses were formed from inter- species hybridization, many Triticeae species are polyploid (i.e., they contain more than the usual number of chromosomes). Researchers use this ability of inter-species hybridization to introduce desirable traits into economically important forage and grain species. However, the production of fertile offspring by inter-species hybridization is rare and researchers seek information about factors that limit the efficiency of hybrid production. One question is whether formation of fertile offspring is influenced by the choice of species for the female parent. While nuclear DNA is inherited from both parents, chloroplast DNA is generally inherited from one parent, usually the female. We examined chloroplast inheritance among polyploid Triticeae to determine whether the chloroplasts were inherited from a specific parent in naturally occurring inter-species hybridizations. We determined the sequence of a chloroplast gene to identify which parent species the chloroplast DNA came from. We found that grasses containing a certain nuclear genome (St) all inherited St chloroplast DNA. This work will be useful to scientists, academic and industry grass breeders who work on grass germplasm development for animal forage and rangeland revegetation.

Technical Abstract: We investigated cpDNA inheritance in allopolyploid Triticeae containing the St nuclear genome. The sequence of the chloroplast ndhF gene was determined for 26 allotetraploid and allohexaploid St-containing species. Nuclear genome complements for the allopolyploid species included the St genome in combination with the H, I, Ns, P, W, Y and Xm genomes. These sequences were compared with those of 5 diploid Triticeae having these nuclear genomes and with previously determined ndhF sequences for western wheatgrass (Pascopyrum smithii) and its putative progenitors. The cpDNA sequences were highly similar among diploid, allotetraploid, allohexaploid and allooctoploid Triticeae grasses containing the St nuclear genome, with 0-0.8% of the sites having substitutions between pairs of species. Neighbor-joining analysis of the sequences showed that the ndhF DNA sequences from species containing the St-nuclear genome formed a strongly supported clade within the Triticeae. The data indicated a strong preference for cpDNA inheritance from the St-nuclear genome-containing parent in hybridizations between Triticeae species. This preference was independent of the presence the H, I, Ns, P, W and Xm nuclear genomes, the geographic distribution of the species and the reproductive habit. This bias toward the St-containing parent serving as the cpDNA donor in interspecies hybridizations suggests that using the St-containing parent as the female in artificial hybridizations may be preferred.