Transposable elements as modulators of homoeologous gene expression in bread wheat: lessons from the pan-transcriptome era.
Bread wheat (Triticum aestivum L.) is an allohexaploid (AABBDD) whose three ancestral subgenomes generate complex patterns of gene regulation. Most genes exist as homoeologous triads, and the relative expression balance among copies, homoeolog expression bias, is central to polyploid evolution and adaptation. Recent high-quality assemblies, long-read transcriptomics, and pan-transcriptome resources have uncovered extensive cultivar-specific transcriptional diversity. Because transposable elements (TEs) compose over 80% of the wheat genome, they are prime candidates for shaping subgenome asymmetry. We synthesize recent pan-genomic and transcriptomic evidence, including genome-wide associations between TE insertions and genome-specific expression, and propose a unifying framework in which TEs modulate homoeolog expression by donating cis-regulatory sequences, altering chromatin states, producing small RNAs, and driving structural variation. We discuss experimental and computational challenges for establishing causality, and outline future functional and translational strategies to leverage TE-associated regulatory diversity in wheat breeding.