Cotton Genomics and Genetics 2025, Vol.16, No.4, 192-201 http://cropscipublisher.com/index.php/cgg 197 used for cell wall modification, which can make the cell wall looser and softer, which is conducive to stretching. In this way, the cell wall can be more easily stretched, which is important for the rapid growth of cotton fibers. If XTH is acetylated, its activity will change, thereby affecting the structure of the cell wall. The whole process can help the fiber grow longer and stronger (Cao et al., 2020; Zhang et al., 2018). Figure 2 Silencing GhWRKY16 by RNA interference in cotton hinders fiber initiation and elongation. A, RT-qPCR analysis of GhWRKY16 (Gh_D06G0175) expression in 9 DPA fibers of the wild-type and GhWRKY16-RNAi lines. The cotton polyubiquitin gene GhUBI1 (EU604080) was used as reference; GhWRKY16 transcript levels in the wild-type were set to 1. B, Comparison of mature fiber length and seed phenotype with or without fuzz between GhWRKY16-RNAi lines (T2 generation) and the wild-type. C, Mean mature fiber length in GhWRKY16-RNAi lines and the wild-type. D, Fiber length and relative GhWRKY16 expression is positively correlated in the RNAi lines. E, In vitro cotton ovule culture. 1 DPA ovules of GhWRKY16-RNAi lines and the wild-type were cultured in liquid Beasley-Ting medium for 12 days. F, Mean fiber length of the cultured ovules (12-18 days) from GhWRKY16-RNAi lines and the wild-type (n > 30 ovules per line). Fiber length of wild-type ovules was set to 1. G, Mean number of fiber initials counted from the middle of 0 DPA ovules. H, Scanning electronic micrographs of ovule surface from GhWRKY16-RNAi lines and the wild-type. Error bars represent standard deviation (sd) of three biological replicates. **P<0.01 by Dunnett t test between the wild-type and GhWRKY16-RNAi lines. WT, wild-type; L1-L10, GhWRKY16-RNAi cotton lines. Scale bars: 1 cm (B, E), 100 µm (H) (Adopted from Wang et al., 2021) 7.3 Correlation between E2 ubiquitin ligases and fiber length Studies have found that some E3 ubiquitin ligases, such as GhMAX2 and GhATL68b, play a big role in cotton fiber development. GhMAX2 will "tag" a protein called GhS1FA, so that the protein will be degraded. GhS1FA is an inhibitory protein that affects fatty acid synthesis. If it is gone, fatty acids can be synthesized normally, which helps fiber growth (Sun et al., 2025). GhATL68b is also related to fatty acid metabolism. Experiments have found that without GhATL68b, cotton fibers will become shorter and the quality will deteriorate. But if some specific fatty acids are added to it, the situation will improve (Li et al., 2024). This shows that the ubiquitination process is critical. It allows some unnecessary proteins to be removed in time, ensuring that the fibers can grow smoothly, become longer and stronger.
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