Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2002
Publication Date: 4/18/2002
Citation: JESSUP, R.W., BURSON, B.L., BUROW, G.B., WANG, Y.W., CHANG, C., LI, Z., PATERSON, A.H., HUSSEY, M.A. DISOMIC INHERITANCE, SUPPRESSED RECOMBINATION, AND ALLELIC INTERACTIONS GOVERN APOSPORY IN BUFFELGRASS AS REVEALED BY GENOME MAPPING. CROP SCIENCE. 2002. V. 42. P. 1694-1988. Interpretive Summary: Molecular tools are being used to learn more about the genetics of important traits in plants. One trait that has received considerable attention is an asexual or vegetative type of reproduction known as apomixis. In this type of reproduction, seed are produced without fertilization and the plants that develop from apomictic seed are identical lto the female parent. Thus, apomixis is nature's way of cloning plants by seed. The reason why there is so much interest in apomixis is that it can be used to permanently fix hybrid vigor in hybrids and this would greatly increase yields of food crops. Unfortunately, apomixis does not naturally occur in important grain and food crops but it occurs in many of the warm- season grasses. Therefore, molecular tools will have be used to transfer the gene controlling apomixis from these grasses to the important crops. Buffelgrass is an excellent grass to use for this purpose because more is known about the genetics of apomixis in it than any other species. In thi study, a genetic map of buffelgrass was constructed to determine the location of the apomixis gene on the buffelgrass chromosomes. The apomixis gene was mapped to a location on one of the buffelgrass chromosomes. This is the first step in eventually being able to transfer apomixis from buffelgrass to important food crops.
Technical Abstract: Molecular tools have not identified the gene(s) governing apomixis or successfully transferred the trait to important, sexually reproducing food crops. Several molecular studies addressing apomixis in grasses have used interspecific and intergeneric hybridizations. The resulting loss of F1 individuals from these wide crosses, caused by unfavorable interactions between the gametes, zygote, embryo, endosperm, and/ or maternal tissue, could have eliminated recombinant genotypes with valuable information towards linkage analyses of the trait. Buffelgrass (Pennisetum ciliare (L.) Link syn. Cenchrus ciliaris L.), a polymorphic species with interfertile apomictic and sexual genotypes, offers an opportunity to genetically map apomixis utilizing intraspecific hybrids with euploid genomes. This study reports a linkage map of the apospory region in buffelgrass. Apospory, classified by progeny testing and cytologically observing megagametophytes, mapped to a single locus in the apomictic parent's genome. Two buffelgrass cDNAs (pPAP3A07 and pPAP8C08) and three previously reported apospory markers (UGT197, QH8, and OPC4) were tightly linked (1.4 cM) to the trait. As a tetraploid species (2n=4x=36), four copies of each chromosome are expected in buffelgrass. A single homolog and two homeologs were identified for the chromosome carrying apospory, indicating the formation of two bivalents during meiosis and the disomic inheritance of apospory in buffelgrass. Allelic bridges between the parents revealed suppressed recombination in the apospory linkage group. Segregation distortion between a marker on the sexual parent's homolog to the apospory linkage group and a marker on a separate maternal linkage group suggested specific allelic combinations in female gametes affect