Cotton, an intriguing plant species shaped by polyploidization, evolution, and domestication, holds particular interest due to the complex mechanisms governing fiber traits across its two subgenomes. However, the regulatory elements or transcriptional networks between subgenomes during fiber elongation remain elusive. Here, we analyzed 1,462 cotton fiber samples to reconstruct gene expression regulatory networks influencing fiber cell elongation. Inter-subgenomic eQTLs largely dictate gene transcription, with a notable tendency for the D subgenome to regulate A subgenome eGenes. This regulation showcases synchronized homoeologous gene expression driven by colocalized eQTLs and divergent patterns that diminish genetic correlations, thus leading to preferential expression in the A and D subgenomes. Hotspot456 emerged as a key regulator of fiber initiation and elongation, and artificial selection of trans-eQTLs in hotspot456 positively regulating KCS1 has facilitated cell elongation. To elucidate the roles of trans-eQTL in improved fiber breeding, experimentation confirmed the inhibition of GhTOL9 by a specific trans-eQTL via GhWRKY28, which negatively impacts fiber elongation. We propose a model where the GhWRKY28-GhTOL9 module, through the Endosomal Sorting Complex Required for Transport pathway, regulates this process. This research significantly advances our understanding of cotton's evolutionary, domestication processes, and the intricate regulatory mechanisms underlying significant plant traits.
