Cotton Genomics and Genetics 2025, Vol.16, No.6, 290-299 http://cropscipublisher.com/index.php/cgg 291 complicate experiments, technological breakthroughs are gradually overcoming these obstacles. The latest research shows that this technology has demonstrated great potential in revealing the molecular regulation of key biological processes such as cotton fiber elongation, opening a new window for future crop improvement and basic research (Chen et al., 2023). 2 Cotton Fiber Elongation: Developmental and Molecular Features 2.1 Cellular mechanisms of fiber elongation: turgor-driven expansion and cytoskeletal dynamics Cotton fibers are actually cells that can grow by themselves. It can be continuously elongated, even reaching several centimeters in length, and this ability is quite impressive. Its driving force comes from inflationary pressure, but inflationary pressure does not emerge out of thin air. Sucrose and potassium ions play a crucial role here. Transport proteins carry them into the cells, and water enters along with them, thereby maintaining internal pressure. Meanwhile, the intercellular filaments act like "gates" that can open and close to regulate these flow processes. However, inflation pressure alone is not enough. The directionality and shape maintenance of fibers rely on the cytoskeleton, especially actin filaments and microtubules. In vivo imaging shows that these structures are not static but are constantly rearranged. The growth of fibers is not uniform and advancing from the top, but rather follows a slightly topical and somewhat diffused stretching pattern (Figure 1). It is precisely this flexible and dynamic skeletal organization that enables individual cells to complete elongation at an extremely high speed. Figure 1 Cotton fiber development. (A) Progression of cotton flower and boll development. Fiber developments are classified into five stages, including initiation, elongation, transition, secondary cell wall (SCW) biosynthesis, and maturation. DPA, days post-anthesis. (B) Images of fibers at progressive developmental stages: SEM of fiber initials (bar = 10 µm) and fibers during early elongation (bar = 100 µm); TEM of the first stage of fiber thickening during the transition stage (three adjacent fibers are shown; bar = 300 nm) and near the end of secondary cell wall synthesis (bar = 1 µm); and light micrograph of cross-sectioned mature, dried, fibers (Adapted from Bai and Scheffler, 2024) 2.2 Key hormonal regulators and gene networks involved in fiber cell elongation There is not just one "behind-the-scenes commander" regulating the elongation of cotton fibers. Plant hormones are like several commanders with distinct personalities. Auxin, gibberellin (GA), brassinosterol (BRs), and ethylene drive cells to continue growing, while abscisic acid (ABA) and cytokinin often hit the brakes.
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