Cotton Genomics and Genetics 2025, Vol.16, No.1, 1-11 http://cropscipublisher.com/index.php/cgg 7 8 Case Study: Hormonal Interventions in Elite Cotton Varieties 8.1 Overview of selected case study This case study focuses on how hormones can be used to improve the fiber quality of high-quality cotton. Cotton fiber develops from the epidermis of the ovule and is a very important raw material for the global textile industry. Recently, studies have found that many plant hormones are related to the development of cotton fiber, especially in the process of fiber lengthening and improvement (Shan et al., 2014; Xiao et al., 2019; Jan et al., 2022). 8.2 Hormonal manipulations to improve fiber quality Researchers have tried several hormone intervention methods to improve cotton fiber quality: Auxin and gibberellin can make fibers longer. Auxin can loosen the cell wall, thereby allowing the cell to elongate. Gibberellin cooperates with some transcription factors to promote fiber elongation (Shan et al., 2014; Xiao et al., 2019). Brassinolide (BR) is very important for cotton fiber elongation. It can regulate the synthesis of a kind of VLCFA (very long chain fatty acid). VLCFAs are critical for cell membrane stability and cell elongation. Studies have found that if the BR-related gene GhBES1.4 is expressed more, the fibers can become longer (Liu et al., 2022; Yang et al., 2023). The peptide hormone (GhPSK) can promote fiber growth by regulating potassium ion efflux and the cell respiratory chain. Overexpression of GhPSK makes cotton fibers thin and long (Han et al., 2014). Glucose is not only a nutrient, it can also be used as a "signal". It interacts with BR and promotes fiber elongation together. Studies have found that when the glucose concentration is low, the fiber grows better; too high a concentration will inhibit growth. This shows that glucose signaling is also important in fiber development (Li et al., 2021). 8.3 Lessons learned and implications for breeding programs Through these hormone intervention methods, researchers have summarized some experiences that can help future breeding work: Precisely target hormone pathways: Figuring out which hormone pathways control fiber quality and how they affect each other is the key to improvement strategies. For example, the coordination between glucose and BR indicates that hormones should be used in “appropriate amounts” and not one-sidedly (Li et al., 2021). Use genetic engineering to regulate key genes: Some genes, such as GhBES1.4 and GhPSK, are directly involved in hormone synthesis or signal transduction. If the expression of these genes is increased or decreased, the length and fineness of the fiber can be affected. Experimental results show that this regulation method is effective (Han et al., 2014; Liu et al., 2022). Use a combination hormone strategy: Different hormones sometimes cooperate with each other, and sometimes "fight" with each other. For example, auxin, gibberellin and BR have positive effects; but cytokinin and ABA have negative effects. Therefore, when using these hormones together, it is necessary to consider the ratio and balance to best promote fiber development (Xiao et al., 2019; Jan et al., 2022). 9 Technological Advances in Hormonal Studies 9.1 Transcriptomic approaches to decipher hormonal pathways Now we have more advanced transcriptomics technology, which allows us to understand the role of hormones in cotton fiber growth more clearly. For example, a study found that if GhBES1.4, a transcription factor related to brassinolide (BR), is expressed more, the fiber will become longer; if it is "turned off", the fiber will become shorter. This was analyzed by combining DAP-seq and RNA-seq technologies. Scientists have found 1531 target genes regulated by this gene, which also allows us to better understand how it regulates cotton fiber development (Liu et al., 2022). In addition, scientists used digital gene expression analysis to compare the fiber transcriptomes of different cotton varieties and found that some genes related to sugars, fatty acids and secondary metabolism are more expressed in varieties with longer fibers. These genes are also likely to be related to fiber elongation (Fang et al., 2014). 9.2 CRISPR/Cas9 and functional genomics in cotton CRISPR/Cas9 and other genomic tools are now being used to study the functions of key genes in cotton. For example, GhHOX3 is a transcription factor involved in fiber elongation. If we reduce its expression, the fibers will become shorter; but if we increase its expression, the fibers will become longer. Transcriptome and
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