MOLECULAR CHARACTERIZATION OF THE APOSPORY-SPECIFIC GENOMIC REGION IN PASPALUM NOTATUM (BAHIAGRASS)

ORTIZ JPA; STEIN J; RODRIGUEZ MP; SIENA LA; PODIO M; PESSINO, SC; QUARIN CL

Wernigerode, Alemania

Congreso; 3rd International Apomixis Conference; 2007

Leibniz Institue of Plant Genetics and Crop Plant Research (IPK)

Paspalum notatum (Bahiagrass) is a perennial rhizomatous grass species widely distributed from Central to South America. It constitutes one of the most valuable natural forage grasses for the subtropical areas of Paraguay, southern Brazil and north-eastern Argentina. Natural tetraploid races (2n=4x=40) reproduce by obligated pseudogamous aposporous apomixis. Apospory in the species is controlled by a single locus which exhibits distorted segregation ratios (Martínez et al. 2001). In a recent work we developed a genetic linkage map of the species based on AFLP and RFLP molecular markers where the chromosome carrying the apospory locus (apo-locus) was identified (Stein et al. 2007). A single RFLP (rice probe C1069), 2 RAPD and 20 AFLP markers linked to the trait defined the apospory specific genomic region of the species. It showed restriction of recombination and preferential chromosome pairing (Martínez et al. 2003; Stein et al. 2004). The objective of this work was to further characterize the apospory region at the molecular level. The mapping population used was the same developed by Stein et al. (2004). It consisted of 113 individuals derived from a cross between the completely sexual tetraploid genotype Q4188 and a natural aposporous individual from accession Q4117. An estimation of the physical size of the apospory region based on mapping data indicated that it is a large chromosome fragment of about 36 Mbp. Thirteen of the markers previously found to strictly co-segregate with the apo-locus (1 RAPD and 12 AFLP) were isolated from gels, cloned and sequenced. The C1069 RFLP probe sequence was retrieved form the Rice Genome Project database. Blastn comparisons showed no homologies except for two markers: M3 (an AFLP-derived clone) exhibit homology with a Machiavelli retrotransposon Gag/Pol gene of maize (E= 5 x10-12), while rice clone C1069 corresponded to a mutator transposase-like protein (E= 0.0). Methylation-sensitive genomic hybridization with clones M3 and C1069 showed polymorphisms between the isoschizomers HpaII and MspI in both Q4188 and Q4117, indicating that the region detected are methylated in both sexual and apomictic plants. Results obtained so far denote apospory in P. notatum is controlled by a complex locus spanning over a large non-recombinant chromosomal segment, which includes non-coding sequences, retroelements and cytosine methylation.      References: Martínez et al. (2001) Hereditas 135: 19-25 Martínez et al. (2003). Molecular Breeding 12: 319-327. Stein et al. (2004) Theoretical and Applied Genetics 109: 186-191. Stein J et al. 2007. Molecular Breeding (in press)