Expression profiles of GhFD homoeologous genes. (A) Heatmap of the expression levels of GhFD genes in 15 tissues. The fiber-bearing ovules at 0, 1, 3 and 5 DPA and fibers at 10, 15, 20 and 25 DPA were sampled. (B–K) Histochemical activity analyses of the cotton FD promoters. Seven-day-old seedlings of GhFDpros:GUS (B–F) and 14-day-old seedlings of GhFDpros:GUS (G–K) are displayed. The ∼2.0 kb sequence upstream from the start codon of each GhFD-D gene was amplified by PCR and independently fused to the GUS to construct GhFDpros:GUS.