Cotton Genomics and Genetics 2025, Vol.16, No.5, 241-248 243 For instance, GhAPX10A, GhAPX10D, GhAPX12A and GhAPX12D become active only at the mature stage. They mainly regulate H₂O₂ levels to prevent oxidative damage from disrupting cell wall synthesis (Zhu and Luo, 2024). Experimentally, when APX activity is high, the levels of H₂O₂ are usually relatively low, which indicates that these enzymes do indeed play a protective role. In addition, energy metabolism enzymes such as ATP-dependent phosphofructokinase and glucose-6-phosphate dehydrogenase are also indispensable. They ensure that metabolism does not break down during the high-energy demand stage of fiber construction. 3.3 Hormonal and signal transduction-related enzymes: enzymes involved in ABA and JA pathways It is no longer news that fiber maturation is regulated by hormones, but the enzymes involved are far more complex than we imagine. Take ethylene as an example. There is an E3 ubiquitin ligase (GhXB38D) that affects the entire pathway by regulating the stability of ethylene synthases (GhACS4, GhACO1). The result is that when GhXB38D is inhibited, ethylene is synthesized and the fibers grow better (Figure 1) (Song et al., 2023). Another key player, GhLCBK1, which is related to auxin synthesis, has also been proven to affect fiber elongation. In addition to ethylene and auxin, "established" signaling hormones such as ABA and JA were also present. Some related enzymes were involved, helping plants adjust their maturation rhythms in the face of environmental fluctuations (Tao et al., 2018; Zhang et al., 2024). Figure 1 Suppression of GhXB38Dexpression in cotton promotes fibre elongation (Adopted from Song et al., 2023) Image caption: (a) Relative expression level of GhXB38Din null plants andGhXB38DRNAi lines (GhXB38Di-17, 19and 20) during fibre development (from 0 to 12 DPA). Error bars represent ± SE of three biological replicates (*P < 0.05; **P < 0.01, by Student's t-test). (b) Scanning electron microscope (SEM) images show the ovule surfaces of null plants and GhXB38Di lines at 0 and 3 DPA. SEM images show the epidermal cells in the centre of the ovule. Bars = 100 μm. (c) Average fibre length of null plants andGhXB38D RNAi lines (GhXB38Di-17, 19 and 20). More than 100 seeds per line were used for statistical analysis. Error bars represent ±SE of three biological replicates (*P < 0.05; **P < 0.01, by Student's t-test). (d) Comparison of cotton bolls from null plants and GhXB38Di lines (GhXB38Di-17, 19 and 20) during fibre development (from 0 DPA to 12 DPA and at maturity). Bars = 1 cm (Adopted from Song et al., 2023)
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