Cotton Genomics and Genetics 2025, Vol.16, No.4, 192-201 http://cropscipublisher.com/index.php/cgg 194 3.3 Acetylation and methylation Acetylation and methylation are two common modifications on proteins, especially at the lysine and arginine positions of histones or other proteins. They can change the structure of chromatin and affect the function of proteins (Li, 2024). Generally speaking, acetylation makes genes more likely to be expressed. Methylation is more complicated, sometimes promoting expression and sometimes inhibiting it. These two modifications are very critical in epigenetic regulation and can regulate genes related to cotton fiber elongation and maturation. In addition, these modifications often do not work alone. They work together with other modifications (such as phosphorylation or ubiquitination) to form a complex regulatory system that determines whether genes are active or silent during fiber development (Aguilar-Hernández et al., 2020). 4 Roles of PTMs in Cotton Fiber Elongation 4.1 Signal transduction and hormone response regulation Post-translational modifications (PTMs) such as ubiquitination play an important role in cotton fiber elongation. They mainly affect the hormone signaling pathway. For example, the F-box type E3 enzyme GhMAX2 causes the transcriptional repressor GhS1FA to be ubiquitinated and degraded. This process can activate the signal of brassinolide, increase the synthesis of fatty acids, and thus help the fiber grow better (Sun et al., 2025). There is also a hormone called brassinolide, which also works through PTM. It can regulate genes related to the cytoskeleton. Transcription factors such as GhBES1 can activate the β-tubulin gene GhTUB17. This method connects hormone signals and cytoskeleton regulation together (Zhang et al., 2024). 4.2 Regulation of cell wall remodeling proteins PTMs also affect the functions of some important proteins in the cell wall. Especially in the synthesis and remodeling of polysaccharides, they directly affect the elongation of fibers. Some genes, such as GhMDHAR1 and GhDHAR2, regulate the redox state of cells. This regulation can improve antioxidant capacity and increase the supply of cell wall polysaccharides, thereby prolonging the rapid growth period of fibers (Tian et al., 2024). PTMs such as ubiquitination may regulate the number and activity of enzymes in these processes so that the cell wall can remain flexible and stable during rapid growth (Sun et al., 2025; Tian et al., 2024). 4.3 Cytoplasmic skeleton and cell polarity maintenance The skeleton of fiber cells is mainly composed of microtubules and actin filaments. They help cells maintain polarity and support the special elongation of fibers. PTMs regulate the expression of some cytoskeleton-related proteins, such as GhMAP20L5 and GhTUB17. These proteins can control the arrangement of microtubules and affect the deposition mode of cellulose (Song et al., 2022; Wang et al., 2024; Zhang et al., 2024). Live cell imaging experiments have found that the arrangement of actin and microtubules in cotton fibers is very special, showing a diffuse growth pattern that is biased towards the tip. This pattern is finely controlled by PTM, which allows the cell direction to be stable and the fibers to grow forward all the time (Yu et al., 2019). 5 Roles of PTMs in Fiber Maturation 5.1 Regulation of cellulose and lignin accumulation When cotton fibers enter the mature stage, they begin to synthesize cellulose and lignin in large quantities. At this time, post-translational modifications (PTMs) play a big role. It affects some key proteins, such as transcription factors that regulate genes, and enzymes involved in the synthesis process. Some NAC-like proteins work in pairs. They can regulate genes like GhCesA, which is related to cellulose synthesis. If this gene is expressed more, the fiber cell wall will become thicker (Chen et al., 2025). In addition, there is a transcription factor called GhMYB7, which can bind to a region in front of the GhCesA gene, so that it can control the synthesis rate of cellulose. Changes in PTMs will affect the start time and speed of this process (Figure 1) (Huang et al., 2021). Lignin synthesis is also regulated by PTMs. For example, the enzyme GhCAD37 plays a role in regulating lignin synthesis. If lignin increases, the strength and maturity of cotton fibers will also change (Li et al., 2024). However, the amount of lignin cannot be too much, otherwise it will hinder the synthesis of cellulose and ultimately deteriorate the quality of the fiber (Zheng et al., 2024).
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