Mechanism of haploidy-dependent unreductional meiotic cell division in polyploid wheat.

Unreductional meiotic cell division (UMCD) generates unreduced gametes and leads to polyploidy. The tetraploid wheat "Langdon" (LDN) undergoes normal meiosis, but its polyhaploid undergoes UMCD. Here, we found that sister kinetochores oriented syntelically at meiosis I in LDN, but amphitelically in LDN polyhaploid and the interspecific hybrid of LDN with Aegilops tauschii. We also observed that sister centromere cohesion persisted until anaphase II in LDN, LDN polyhaploid, and the interspecific hybrid. Meiocytes with all chromosomes oriented amphitelically underwent UMCD in LDN polyhaploid, and the interspecific hybrid, suggesting the tension created by the amphitelic orientation of sister kinetochores and persistence of centromeric cohesion between sister chromatids at meiosis I contribute to the onset of UMCD. Most likely, some ploidy-regulated genes were responsible for kinetochore orientation at meiosis I in LDN and LDN-derived polyhaploids. In addition, we found sister kinetochores of synapsed chromosomes oriented syntelically, whereas asynapsed chromosomes oriented either amphitelically or syntelically. Thus, synapsis probably is another factor for the coordination of kinetochore orientation in LDN.