MOLECULAR DISSECTION OF APOMIXIS IN BUFFELGRASS

¹ Dep. of Soil & Crop Sciences, Texas A&M Univ., College Station, TX 77843-2474

² USDA-ARS, Southern Plains Agricultural Research Center, College Station, TX 77843-2474

³ Plant Genome Mapping Laboratory, Univ. of Georgia, Athens, GA 30602

This report will summarize recent research conducted by our laboratories involving the aposporous species buffelgrass (Pennisetum ciliare (L.) Link syn. Cenchrus ciliaris L). The primary tools used were a buffelgrass mapping population segregating for method of reproduction and cDNA libraries derived from apomictic and sexual buffelgrass pistils. In efforts to discover genes important during ovule development, differential display and virtual subtraction methods identified several cDNAs that are preferentially expressed in pistils. A genetic map was established to characterize the segmental allotetraploid genome of buffelgrass. Apospory mapped to a single locus (PApo1), but sexuality failed to map as a discrete trait. Fine-mapping efforts placed additional markers in the linkage group containing PApo1. Comparative mapping to other grasses provided additional information. In preparation for QTL studies of apomixis, a PCR-based method was developed to quantitatively measure the frequency of sexual and apomictic reproduction in mixed reproductive (facultative) genotypes. The buffelgrass map supported several tenets regarding apomixis in grasses: 1) a single locus exerts major control over the trait, 2) there is suppressed recombination in this region, and 3) this locus is transmitted to progeny in non-Mendelian ratios. In addition, the genome map revealed new insights into the genetics of apomixis in buffelgrass: 1) PApo1 is governed by disomic inheritance, 2) allelic interactions at specific genome locations affect offspring survival, and 3) apomixis has either evolved independently on multiple occasions or has been rearranged among the genomes of several apomictic grasses.