Genome shock in a synthetic allotetraploid wheat invokes subgenome-partitioned gene regulation, meiotic instability, and karyotype variation.

This article focuses on the immediate genomic, phenotypic, and meiotic consequences of synthetic allopolyploidization between the diploid progenitors of bread wheat, Triticum urartu (AA) and Aegilops tauschii (DD). By generating reciprocal diploid F1 hybrids (AD and DA) and corresponding synthetic allotetraploids (AADD and DDAA), the study disentangles the effects of hybridization alone from those combined with whole-genome duplication (allopolyploidization). The allotetraploids exhibited greater vigor, fertility, and phenotypic novelty compared to sterile F1 hybrids, with distinct subgenome expression biases—D subgenome dominating vegetative traits and A subgenome influencing reproductive traits. Extensive karyotype variation and meiotic instability were observed in the allotetraploids, primarily due to homoeologous chromosome pairing, but these chromosomal changes did not directly correlate with meiotic irregularities, suggesting that subgenome- and chromosome-biased gene expression and functional constraints also shape genome stability. These findings provide insights into the evolutionary dynamics of allopolyploid genomes and have implications for crop improvement strategies using synthetic polyploids.