Phosphorus Regulates Cotton Fiber Development Through GhPHR1-GhGCS1 Module

Cotton is an important cash crop globally. Cotton fiber is the main economic product of cotton plants. Phosphorus, as one of the essential nutrients, plays an important role in plant growth and development. However, few studies focus on phosphorus regulating fiber elongation. In this study, we used the cotton ovule culture system in vitro to explore the effects of various phosphorus levels on fiber and ovule growth, and screened for phosphorus-responsive factor, as well as revealed its action mechanism. The results indicated that fiber elongation was more sensitive than ovule growth to phosphorus deficiency. GhPHR1, a homolog of phosphate starvation response 1 (PHR1) in upland cotton, was significantly upregulated in fibers and ovules under phosphorus-deficient conditions. GhPHR1 directly binds to the promoter of the glucosylceramide synthase gene in cotton (GhGCS1) and positively regulates its expression. Overexpressing GhGCS1 enhanced phosphorus uptake and transport in cotton, increased phosphorus content in fiber cells, and promoted fiber cell elongation. Conversely, downregulating GhGCS1 reduced phosphorus content in fiber cells and suppressed fiber elongation. These findings demonstrate the importance of the GhPHR1-GhGCS1 molecular module in regulating fiber cell elongation and elucidate the molecular mechanism by which phosphorus influences fiber elongation.