Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/19/2007
Publication Date: 9/15/2007
Citation: Jauhar, P.P., Dogramaci, M. 2007. Chromosome pairing in durum wheat haploids with and without ph1b of bread wheat. Euphytica. Published on-line 9-15-07 published 12-23-07 paper form 12-23-07 Volume 159 #3: 353-358 Interpretive Summary: Durum or macaroni wheat evolved in nature as a hybrid between two related grasses and has two complete sets of chromosomes (a complete set is a genome), designated AA and BB. The chromosomes of the two genomes are genetically similar and can compensate for each other’s absence, and therefore are potentially capable of pairing with one another. However, a gene called Ph1 acts like a "policeman" and permits pairing only between homologous (identical) chromosomes. This Ph1-exercised disciplinary control makes durum wheat and its successor, bread wheat (with three sets of chromosomes AA, BB, and DD), stable and successful species. However, the occurrence of homoeologous pairing (i.e., pairing between chromosomes of wheat and those of wild species) is imperative for alien gene transfer into wheat. Mutants of the Ph1 gene, in the form of deletions, are available in bread wheat (ph1b) and durum wheat (ph1c). Because of the absence of the policeman Ph1, illegitimate pairing can take place in bread wheat haploids (plants with half the chromosome number) possessing ph1b and in durum haploid haploids possessing ph1c. Now by crossing with maize, we have produced haploid plants of durum wheat with the ph1b gene from bread wheat. These haploids show much higher pairing in the presence of ph1b than with ph1c. These results may have a bearing on alien gene transfers into durum wheat.
Technical Abstract: Durum or macaroni wheat (Triticum turgidum L., 2n = 4x = 28; AABB genomes) is a disomic tetraploid with two related genomes, AA and BB, each with seven pairs of homoeologous chromosomes. Although the corresponding chromosomes of the two genomes are closely related so much so that they can compensate for each other’s absence, the Ph1 (pairing homoeologous) gene in the long arm of chromosome 5B ensures pairing only between homologous partners. This Ph1-exercised disciplinary control confers on durum wheat and its successor, bread wheat (Triticum aestivum L., 2n = 6x = 42; AABBDD), diploid-like chromosome pairing and hence disomic inheritance. However, the occurrence of homoeologous pairing is imperative for alien gene transfer from donor species into wheat. The Ph mutants in the form of deletions are available in bread wheat (ph1b) and durum wheat (ph1c). Because of the absence of Ph1, the ph1b-haploids of bread wheat and ph1c-haploids of durum wheat show extensive homoeologous pairing. Here we study the effect of ph1b allele of bread wheat on chromosome pairing in durum haploids. In durum wheat, the ph1b-haploids show much higher (49.43% of complement) pairing than the ph1c-haploids (38.57% complement). It is inferred that the absence of Ph1 in the larger ph1b deletion could induce higher homoeologous pairing than in the smaller ph1c deletion.