Arginine decarboxylase (ADC), a rate-limiting enzyme in the polyamine biosynthesis pathway, plays a critical role in plant growth and development. Our previous study revealed that cotton GhADC2 has potential to regulate fiber initiation. In this study, we further elucidate the molecular mechanism by which GhADC2 regulates fiber development. Overexpression of GhADC2 significantly enhanced fiber elongation, whereas RNAi-mediated suppression of GhADC2 resulted in shorter fibers. Further analysis demonstrated that the promoter of GhADC2 is transcriptionally regulated by transcription factor GhMYB2. Subcellular localization assays using Arabidopsis protoplasts and tobacco leaves revealed that GhADC2 localizes to the cell nucleus, differing from the usual chloroplast localization of ADCs. Yeast library screening identified GhBCCP1, a nuclear-targeted protein in cotton fibers, as an interacting partner of GhADC2. GhBCCP1 directly regulates plant physiological processes by catalyzing the conversion of acetyl-CoA to malonyl-CoA. Metabolomic sequencing of GhADC2 overexpression and RNAi plants highlighted significant enrichment in the tryptophan metabolism and flavonoid biosynthesis pathways. Collectively, our data demonstrate that GhADC2 is a positive regulator of cotton fiber development, and that it is transcriptionally activated by GhMYB2 and physically interacts with GhBCCP1, suggesting that these three components form a regulatory module associated with fiber growth. These findings provide valuable information for improving cotton fiber quality.

Cotton (Gossypium spp.) is the most important natural textile fiber crop in the world. The ideal plant architecture of cotton is suitable for mechanical harvesting and productivity in modern agricultural production. However, cotton genes regulating plant development and architecture have not been fully identified. We identified a basic helix-loop-helix (bHLH) transcription factor, GhPAS1 (PAGODA1 SUPPRESSOR 1) in G. hirsutum (Upland cotton). GhPAS1 was located in the nucleus and showed a strong transcription activation effect. Tissue-specific expression patterns showed that GhPAS1 was highly expressed in floral organs, followed by high expression in early stages of ovule development and rapid fiber elongation. GhPAS1 overexpression in Arabidopsis and BRZ (brassinazole, BR biosynthesis inhibitor) treatment indicated that GhPAS1 positively regulates and responds to the BR (brassinosteroid) signaling pathway and promotes cell elongation. GhPAS1 overexpression in Arabidopsis mediated plant development in addition to increasing plant biomass. Virus-induced gene silencing of GhPAS1 indicated that down-regulation of GhPAS1 inhibited cotton growth and development, as plant height, fruit branch length, and boll size of silenced plants were lower than in control plants. Fiber length and seed yield were also lower in silenced plants. We conclude that GhPAS1, a bHLH transcription factor, regulates plant development and architecture in cotton. These findings may help breeders and researchers develop cotton cultivars with desirable agronomic characteristics.