Alterations in subtelomeric tandem repeats during early stages of allopolyploidy in wheat

Abstract

The genomic content of the subtelomeric repeated sequences Spelt1 and Spelt52 was studied by dot, Southern, and in situ hybridization in 11 newly synthesized amphiploids of Aegilops and Triticum, and data were compared with the parental plants. Spelt1 had reduced copy numbers in the first generation of three synthetic amphiploids, but two others did not change; Spelt52 was amplified in nine amphiploids and did not change in two. In the second allopolyploid generation, Spelt1 copy number did not change, whereas there was amplification of Spelt52 in some allopolyploids and decreases in others. Neither allopolyploidy level nor the direction of the cross affected the patterns of change in the newly synthesized amphiploids. Changes did not result from intergenomic recombination because similar alterations were noticed in allopolyploids with and without Ph1, a gene that suppresses homoeologous pairing. No differences in Spelt1 and Spelt52 tandem organization were found by Southern hybridization. The significance of these data are discussed in relation to the establishment of newly formed allopolyploids.

Rapid and Repeatable Elimination of a Parental Genome-Specific DNA Repeat (pGc1R-1a) in Newly Synthesized Wheat Allopolyploids

“…Nevertheless, because of the phenomenology, we note that there are at least two lines proposed scarcity, if not absence, of homeologous recomof apparent difference between the elimination of lowbinations under allopolyploid conditions in the Aegilopscopy and repetitive sequences. The first difference lies Triticum complex (Feldman et al 1997;Ozkan et al 2001; in possible causes for the elimination of the two types Salina et al 2004), the purging of unfavorable genic of DNA sequences. Probably due to technical reasons for interactions cannot be accomplished by Mendelian segdetection, the results of both this study and previously regation (Rieseberg 2001).…”

“…Probably due to technical reasons for interactions cannot be accomplished by Mendelian segdetection, the results of both this study and previously regation (Rieseberg 2001). Therefore, it is conceivable reported works (Daud and Gustafson 1996; Pestsova that the drastic elimination of the parental-specific, yet et al 1998; Salina et al 2004) on the elimination of dispensable, DNA repeats would lead to a more harmorepetitive DNA elements following allopolyploidization nious cellular environment and hence might improve are confined to genome-specific sequences, i.e., sefertility in newly formed wheat allopolyploids. It should quences present in only one of the parental species.…”

Mapping PrBn and Other Quantitative Trait Loci Responsible for the Control of Homeologous Chromosome Pairing in Oilseed Rape (Brassica napus L.) Haploids

“…It is certainly not a matter of chance that most if not all allopolyploids exhibit a diploid-like meiotic behavior and disomic inheritance at meiosis with only homologous chromosomes being associated as bivalents at metaphase I. Current knowledge suggests that the meiotic diploidization, which has occurred upon hybridization in polyploid species, is probably achieved by two complementary mechanisms: (1) the structural divergence between homeologous chromosomes that may already exist at the diploid stage and be accentuated through sequence elimination upon allopolyploidization (Feldman et al 1997;Salina et al 2004) and (2) the involvement of genes that suppress homeologous pairing (reviewed in Jenczewski and Alix 2004). For instance, the Ph1 locus is required to prevent homeologous pairing in allopolyploid wheat (Riley and 1 Chapman 1958;Sears and Okamoto 1958), as evidenced by the formation of numerous bivalents and multivalents at metaphase I of meiosis in nulli-5B haploids of wheat.…”

Estudios citogenéticos evolutivos del género Zea

“…Teniendo en cuenta los resultados obtenidos, se podría considerar que el Género Zea podría haber tenido el siguiente mecanismo evolutivo (  Translocaciones entre cromosomas no homólogos (Weber y Alexander, 1972)  Divergencia estructural de los cromosomas homólogos por eliminación de secuencias cromosómicas (Feldman et al, 1997;Salina et al, 2004), dando lugar a cromosomas homeólogos de distinto tamaño, como los observados en el trihíbrido entre Z. mays, Z. diploperennis y Z. luxurians.…”

“… Reordenamientos y cambio de función de los genes provenientes de un ancestro en común (Feldman et al, 1997;Salina et al, 2004). Este mecanismo pudo dar lugar a características fenotípicas nuevas como por ejemplo la clorantia en los híbridos entre el maíz y los teosintes.…”