Cotton Genomics and Genetics 2025, Vol.16, No.6, 290-299 http://cropscipublisher.com/index.php/cgg 295 5.3 Interpretation: implications for targeted breeding and molecular interventions in elongation control These spatially resolved data are not merely "academic refinances"; they actually provide available targets for breeding. Those genes that are highly expressed at the tips or elongation regions of fibers, such as GhEXPA1, GhRDL1 and GhMYB25-like genes, are precisely the most worthy of attention in molecular improvement. They can provide direct references for genetic engineering or molecular marker-assisted selection, thereby enhancing fiber length and quality. More importantly, understanding the regulatory networks and spatial dynamics of these genes means that researchers can intervene more specifically (Ma et al., 2024). Whether by adjusting the expression intensity or optimizing the signal pathway, these findings have paved the way for creating higher-quality and more economically valuable cotton varieties. 6 Functional Insights from Spatial Gene Expression Data 6.1 Discovery of region-specific transcriptional modules regulating elongation In the growth of cotton fibers, control is not concentrated in a few genes but is dispersed in multiple region-specific regulatory modules. Through the reconstruction and analysis of large-scale spatial transcriptomes, researchers have depicted a complex map of gene regulatory networks. The roles of some modules are particularly prominent. For example, the GhWRKY28-GhTOL9 module and its related ESCRT pathway are considered to play a key role in the initiation and elongation of fibers (Yang et al., 2024). Interestingly, such modules are often closely associated with expression quantitative trait loci (EQtls) between subgenomes, such as "regulatory hotspot 456", which can indirectly affect the expression of genes like KCS1, and KCS1 happens to be a key node that determines whether cells can elongate normally. This also indicates that the development of fibers is not dominated by a single regulatory mechanism. Different regions and different developmental time Windows may each activate independent regulatory modules, like an orderly yet decentralized collaboration rather than a centralized command system. 6.2 Spatial distribution of oxidative stress genes and ros scavenging pathways Rapidly growing fibers are a high-energy-consuming activity, and oxidative stress is inevitable. To maintain balance, plants seem to have "zoned out" their antioxidant systems. Studies have found that genes involved in the ascorbic acid-glutathione cycle, especially members of the MDHAR family, are expressed most strongly in the region with the fastest elongation (Zhou et al., 2021; Hou et al., 2022). These regions simultaneously exhibit higher ascorbic acid content and antioxidant activity, suggesting that the cells here must respond more actively to the stress brought by reactive oxygen species. What's more interesting is that when some key elongation regulatory factors are silenced, the expression of genes related to oxidoreductases also decreases accordingly. In other words, the oxidation equilibrium is not maintained independently but is intertwined with the mechanism of fiber elongation. Through such spatial distribution regulation, plants not only elongate their fibers but also quietly prevent "self-oxidation". 6.3 Functional roles of sugar transporters and energy metabolism genes in elongation zones For fibers to be elongated, they must first have "energy". The transport efficiency of sugar almost determines whether cells can expand smoothly. Studies have shown that the transcription factor GhMYB212 can directly activate the sucrose transporter gene GhSWEET12, helping sucrose continuously enter elongated cells (Liu et al., 2022; Duan et al., 2024). Once the functions of GhMYB212 or GhSWEET12 are lost, the accumulation of sucrose is significantly reduced, and the length of the fibers also decreases significantly. Conversely, GhMYB4 can also inhibit GhSWEET12, but this inhibition is not absolute. bHLH and other MYB factors will intervene in the opposite direction, thereby forming a delicate balance between sugar and lipid metabolism.
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