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The Moore Lab
Understanding the make-up of the Ph1 complex and its role in chromosome pairing

Chemical modification of chromosome pairing

The 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 chemicals

The Ph1 locus contains a cluster of genes related to the human cell cycle checkpoint kinase Cdk2 (Al-Kaff et al, 2007).  Certain chemicals affect the activity of Cdk proteins.  The protein phosphatase inhibitor okadaic acid, for example, indirectly activates some Cdk complexes. By injecting wheat plants with chemicals such as these, 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.

Injection of wheat x rye hybrids with chemicals

  1. The chemical is injected into the stems of embryo-rescued F1 plants from a wheat x rye intercross.


  2. The chemical is introduced into the stem below the developing spike before chromosome pairing takes place.

 

Leaves and stem cut away to
show developing spike

Increased chromosome pairing

  1. Wheat and rye chromosomes do not normally pair, but following injection with certain chemicals, formation of bivalents and other chromosome associations was observed.

Injection of Beaver x Soissons lines with specific chemicals

The 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 specific chemicals, 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 breeding

If 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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