Cotton Genomics and Genetics 2025, Vol.16, No.1, 1-11 http://cropscipublisher.com/index.php/cgg 8 biochemical analyses further demonstrated how this gene controls cell wall relaxation, allowing fibers to elongate (Shan et al., 2014). In addition, a regulatory module called miR396b-GRF5 was also found to be important for fiber development. After inhibiting miR396b through virus-induced gene silencing (VIGS), cotton fibers became longer, indicating that this module can also be used to improve fiber quality (Zhang et al., 2022a). 9.3 Integrative omics for hormonal regulation insights Researchers are now also using a combination of "multi-omics" methods to fully understand how hormones affect cotton fiber growth. For example, a study used GWAS, RNA-seq, and DAP-seq together to find seven genes related to fiber elongation. These genes are all regulated by GhBES1.4 in the BR pathway (Liu et al., 2022). Another study comparing phosphorylated proteomes found the role of GhSK13 in the BR signaling pathway. This gene is related to the organization of the microtubule skeleton, energy metabolism, etc., and has a great influence. This study found a total of 900 protein substrates that may be regulated, deepening our understanding of BR signaling (Wang et al., 2020). Another gene, GhLTP4, is also very important. It can increase the content of ceramide and activate auxin signaling. These two effects combined can make cotton fiber cells grow faster (Duan et al., 2023). 10 Conclusions and Future Perspectives Research on how hormones regulate cotton fiber elongation has led to a number of important discoveries. For example, GhMYB212 is a key transcription factor that regulates the GhSWEET12 gene, thereby controlling the entry of sucrose into the elongating fiber cells. In this way, it can affect the length and quality of cotton fibers. Studies have also found that a variety of hormones are involved in regulating fiber development. Some hormones have a promoting effect, such as auxin, gibberellins, brassinolide, ethylene, jasmonic acid and estrolactone; there are also hormones that inhibit fiber growth, such as cytokinins and abscisic acid. In addition, two transcription factors called GhFP2 and GhACE1, one promoting growth and the other inhibiting growth, play an "antagonistic" regulatory role. There is also GhHOX3, which is a homeodomain protein that can work with other proteins and gibberellins signals to control the fiber elongation process. Glucose is not just a nutrient, it can also act as a signaling substance, synergistically with brassinolide to regulate fiber lengthening. The study also found that the peptide hormone GhPSK can promote fiber growth and improve quality. The Ca2+-dependent protein kinases GhCPK84 and GhCPK93 phosphorylate GhSUS2 (sucrose synthase). Phosphorylated GhSUS2 inhibits fiber elongation. Finally, there is a gene called GhLTP4, which regulates lipid metabolism, increases ceramide content, and activates auxin signaling, thereby promoting continued elongation of fiber cells. Although we have made many discoveries, there are still many unresolved problems in this field. For example, the relationship between hormones is very complex, and they will affect each other and even interfere with each other. Although we know which hormones are involved in regulation, it is not clear how they "cooperate" or "fight" specifically. In addition, transcription factors with opposite functions such as GhFP2 and GhACE1 also make research more difficult to analyze. Another problem is that it is not easy to turn discoveries in the laboratory into technologies that can be used in the field. Genes like GhPSK, which seem to have potential, work well in experiments, but will they have side effects in real field environments? We don't know yet. In addition, external environments such as weather, soil, and climate can also affect the effects of hormones, which adds another layer of difficulty to the research. However, the research also brings a lot of hope. It provides us with many new directions for improving cotton in the future. For example, regulating GhMYB212 and GhSWEET12 can improve the transport of sucrose and make the fibers longer. We can also adjust the hormone pathway: while strengthening the effects of "good hormones" such as auxin and gibberellin, while reducing the negative effects of cytokinin and abscisic acid, it is more likely that cotton will grow high-quality fibers. Peptide hormones such as GhPSK also provide new ideas for us to try biotechnology intervention.
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