The Moore Lab |
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Chemical modification of chromosome pairingChemical modification of chromosome pairingThe Ph1 locus prevents pairing of wheat chromosomes with those of related species, which restricts the introduction of useful agronomic traits into commercial varieties. If Ph1 is absent, wheat chromosomes can pair with related chromosomes from other species, but the resultant hybrids are unstable. Removing the Ph1 control mechanism using chemicalsThe Ph1 locus contains a cluster of genes related to the human cell cycle checkpoint kinase Cdk2 (Al-Kaff et al., 2007). Ph1 suppresses the activity of Cdk2 genes on the A and D genomes. If Ph1 is absent, these genes are activated. Cdk2 genes can also be activated by the protein phosphatase inhibitor, Okadaic acid. By injecting wheat plants with Okadaic acid, we aim to temporarily turn off Ph1, allowing wheat and related chromosomes to pair so that novel variation can be introduced into wheat. Ph1 will be allowed to turn back on in subsequent generations to stabilize the hybrids. The effect of okadaic acid on chromosome pairingWe assessed the effect of Okadaic acid on the pairing of chromosomes in wheat x rye interspecific hybrids using a detached tiller method. Tillers containing immature pre-meiotic spikes were detached and placed into sucrose solution with or without Okadaic acid. It is vital that the tillers are exposed to the Okadaic acid during pre-meiotic S-phase, some 24 hours prior to the onset of metaphase I.
The tillers were incubated in solution until the immature spike reached meiosis. Then the immature anthers were excised and chromosome pairing examined microscopically. Wheat and rye chromosomes do not normally pair, so at metaphase I, in sucrose alone, 28 individual chromosomes were observed; 21 from wheat and 7 from rye.
However, when the detached tillers were incubated with Okadaic acid, pairing was induced between the wheat and rye chromosomes even in the presence of Ph1.
Okadaic acid produced a similar effect on chromosome pairing to that observed in the absence of Ph1, including an increase in rod bivalent formation and other chromosome associations.
Injection of Beaver x Soissons lines with Okadaic acidThe wheat variety Beaver carries a rye substitution (1BL/1RS); the variety Soissons does not. When these varieties are crossed, Ph1 prevents recombination between them within the rye substitution region. F1 plants from the cross were injected with Okadaic acid, and the plants self-fertilized. Preliminary mapping of DNA from the F2 plants suggests that the drug treatment may be having an effect on recombination within the substituted segment.
Implications for plant breedingIf recombination is successful within the rye substitution regions, the resulting hybrids will be released for breeding. This method should allow introgression of a large number of new traits, and has the advantages that the drug treatment is temporary and it is achieved through a non-GM route. The method is not restricted to wheat, so other crops such as rice, lolium, etc. could benefit too
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