GhSBP1 promotes cotton fiber initiation and elongation by activating GhNRT1.5, GhEzrA, and GhSH3P2.

GhSBP1 positively regulates cotton fiber initiation and elongation. GhSBP1 directly binds to GTAC motifs in the promoters of GhNRT1 . 5, GhEzrA , and GhSH3P2 . A novel regulatory module GhSBP1- GhNRT1 . 5 / GhEzrA / GhSH3P2 controls fiber development. The SQUAMOSA-PROMOTER BINDING PROTEIN (SBP) transcription factor is plant-specific and plays a critical role in developmental processes across many plant species. SBP transcription factors are essential for plant growth, development, and cell elongation. However, the mechanism by which SBP proteins regulate fiber development remains poorly understood in Gossypium hirsutum L. (cotton). In this study, we identified an SBP family transcription factor, designated GhSBP1, in cotton. Overexpression of GhSBP1 increased both fiber cell length and fiber initiation frequency, whereas knockout of GhSBP1 resulted in shorter fibers and reduced fiber initiation, demonstrating that GhSBP1 positively regulates both fiber elongation and initiation. DNA Affinity Purification Sequencing (DAP-seq) enrichment analysis using cotton fibers revealed that GhSBP1 directly binds to the GTAC motif, a key cis -regulatory element. We selected three genes— GhNRT1 . 5, GhEzrA , and GhSH3P2 —that exhibit high expression during the rapid fiber elongation phase. Yeast one-hybrid, luciferase reporter, and electrophoretic mobility shift assays confirmed that GhSBP1 directly interacts with the promoters of these genes. Furthermore, overexpression of GhSBP1 upregulated the expression of these downstream genes, while knockout of GhSBP1 led to their downregulation. Collectively, these findings indicate that GhSBP1 promotes cotton fiber development by modulating the transcription of GhNRT1.5, GhEzrA, and GhSH3P2. This study not only enhances our understanding of GhSBP1 function in cotton fiber development but also identifies potential genetic targets for improving cotton lint production through manipulation of GhSBP1 and its associated regulatory network.