The Ph1 locus is needed to ensure specific somatic and meiotic centromere association

The correct pairing and segregation of chromosomes during meiosis is essent ial for genetic stability and subsequent fertility. This is more difficult to achieve in polyploid species, such as wheat, because they possess more t han one diploid set of similar chromosomes. In wheat, the Ph1 locus ensures correct homologue pairing and recombination(1). Although clustering of tel omeres into a bouquet early in meiosis has been suggested to facilitate hom ologue pairing(2,3), centromeres associate in pairs in polyploid cereals ea rly during floral development(4). We can now extend this observation to roo t development. Here we show that the Ph1 locus acts both meiotically and so matically by reducing non-homologous centromere associations. This has the effect of promoting true homologous association when centromeres are induce d to associate. In fact, non-homologously associated centromeres separate a t the beginning of meiosis in the presence, but not the absence, of Ph1. Th is permits the correction of homologue association during the telomere-bouq uet stage in meiosis. We conclude that the Ph1 locus is not responsible for the induction of centromere association, but rather for its specificity.