Effect of the pairing gene Ph1 on centromere misdivision in common wheat.

The cytologically diploid-like meiotic behavior of hexaploid wheat (i.e., exclusive bivalent pairing of homologues) is largely controlled by the pairing homoeologous gene Ph1. This gene suppresses pairing between homoeologous (partially homologous) chromosomes of the three closely related genomes that compose the hexaploid wheat complement. It has been previously proposed that Ph1 regulates meiotic pairing by determining the pattern of premeiotic arrangement of homologous and homoeologous chromosomes. We therefore assume that Ph1 action may be targeted at the interaction of centromeres with spindle microtubules--an interaction that is critical for movement of chromosomes to their specific interphase positions. Using monosomic lines of common wheat, we studied the effect of this gene on types and rates of centromere division of univalents at meiosis. In the presence of the normal two doses of Ph1, the frequency of transverse breakage (misdivision) of the centromere of univalent chromosomes was high in both first and second meiotic divisions; whereas with zero dose of the gene, this frequency was drastically reduced. The results suggest that Ph1 is a trans-acting gene affecting centromere-microtubules interaction. The findings are discussed in the context of the effect of Ph1 on interphase chromosome arrangement.