Schematic diagram illustrating the mechanistic framework of GhAXR2 and GhSHY2 signaling in the regulation of cotton fiber cell growth. When GhAXR2 is present, it binds to the promoter of 2 transcription repressors, GhARF23-2 and GhARF6-1, to remove GhARF23-2- and GhARF6-1-mediated transcription inhibition of GhCTR1 to promote cotton fiber initiation and elongation (A). When GhAXR2 is absent, GhARF23-2 and GhARF6-1 bind to promoter of GhCTR1 to repress its transcription, which leads to less fiber initiation and shorter fiber cells (B). When GhSHY2 is present, it binds to the promoter of 2 transcription activators, GhARF7-1 and GhARF19-1, to remove GhARF7-1- and GhARF19-1-mediated transcription activation of GhXTH9 and GhC4H, which further leads to less fiber initiation and shorter fiber cells (C). When GhSHY2 is absent, GhARF7-1 and GhARF19-1 bind to promoters of GhXTH9 and GhC4H to activate the transcription of these 2 target genes, which further results in increased fiber initiation and longer cotton fibers (D). Plus (+) sign in the circle stands for promoting gene transcription, plus (-) sign in the circle stands for inhibiting gene transcription.