Fig. 1

Illustration of cotton fiber developmental timeline focusing on the first half of development. Cotton fiber development starts with initiation of fiber cells on the ovule seed coat, which begins around the time of flower opening (anthesis) and continues during the first few days of seed development during which the fiber cells taper to reduce cell diameter (by 2 days post anthesis; DPA). The elongation phase, which includes primary wall synthesis, has complex dynamics and persists for about 20 days. At approximately 16 DPA, the transition between elongation and cell wall thickening begins. The mature, cellulose-rich fiber is fully formed at about 50 DPA. Images are placed in their approximate position along the developmental timeline. Cut capsules (“bolls”) and developing fibers are shown to the left and right of the timeline, respectively. Confocal images of developing fibers show the orientation of the cellulose microfibrils, which changes from approximately transverse during elongation to an increasingly steep helix beginning at the transition stage. Images of growing ovules with fiber combed away in two directions are intercalated