The Importance of Controlling Chromosome Pairing- Ph1 Gets “Hot” in Wheat

From studies on models much is known about the recombination during meiosis. However little is known about how chromosomes first recognize each other. This is particularly important in plants which are mostly polyploid. For bread (hexaploid) wheat to be highly fertile, only true homologues must pair at meiosis, rather than the highly related chromosomes present. Correct pairing is controlled by single major locus, Ph1. The downside of the presence of Ph1 is that in wheat-wild relatives hybrids used by breeders to introduce traits from wild relatives, Ph1 prevents exchange between the wheat and wild relative chromosomes. Ph1 has been defined to a region containing a cluster of defective Cdk2 type genes which suppress Cdk2-type activity, H1 phosphorylation, and hence alters chromatin structure. This affects how chromosomes initially interact via the telomeres and centromeres, then processes of intimate alignment propagated from these regions, and  hence the level of initial incorrect associations made. It then affects whether these incorrect associations are processed into recombinant events or not by affecting the stability of these incorrect associations during chromosome adjustment or condensation. Interestingly Cdk2 activity is a major control of chromosome pairing in mammals. Temperature is going to be an important issue for many wheat growing areas in the future. Wheat meiosis is more sensitive to temperature than diploid relatives. The effect of temperature on Ph1 control is going to be important to understand.