Cotton Genomics and Genetics 2025, Vol.16, No.1, 12-20 http://cropscipublisher.com/index.php/cgg 14 2.2 Salinity stress: ion imbalance and osmotic challenges Salt stress is also an important issue affecting cotton cultivation, especially in areas with high irrigation water or severe drought. Too much salt in the soil can cause ion poisoning and osmotic pressure, affecting the normal ion balance and water absorption of cells. This will make it difficult for seeds to germinate, the plants will grow slowly, turn yellow, and the fiber will decrease. Cotton can cope with these problems by regulating ion transport proteins and accumulating some small molecules. However, if it is in a high-salt environment for a long time, these countermeasures will not be enough, and it will eventually lead to serious yield reductions (Wang et al., 2017; Kilwake et al., 2023). 2.3 Temperature extremes: heat and cold sensitivity in cotton Cotton is afraid of both heat and cold, and climate change is making such extreme weather more and more common. Too hot weather will damage photosynthesis, cause rapid evaporation of water, and accelerate the production of reactive oxygen species (ROS), causing cell damage and reduced yields. Too cold weather will affect membrane stability, enzyme activity and other metabolic processes, thereby affecting the normal growth of plants. When faced with these temperature changes, cotton will activate some specific gene expressions and metabolic adjustments to protect itself, but if the time is too long or the degree is too severe, the plant may suffer irreparable damage, ultimately leading to a significant reduction in yield (Guo et al., 2022). 3 Gene Editing Technologies Applicable to Cotton Improvement After all, traditional breeding is sometimes too slow, but the environmental problems facing cotton cannot wait. In recent years, gene editing technology has become more and more practical, and many researchers have begun to use it to "hands-on" adjust the genes of cotton. It's not for the pursuit of some cool new methods, but because it can really help solve real problems. It is difficult to improve resistance to environmental stresses such as drought and salinity by conventional means. But now, with these editing tools, target genes can be adjusted more accurately. Interestingly, this technology can not only improve stress resistance, but sometimes also increase yields, and can even fine-tune the specific traits of cotton according to the agricultural needs of different regions (Thangaraj et al., 2024). 3.1 CRISPR/Cas systems: advancements and specific tools The CRISPR/Cas system, especially CRISPR/Cas9, has become the main method for editing cotton genes because of its simple operation, high efficiency and strong adaptability. It can not only accurately modify the target gene, but also modify multiple genes at a time, and even find similar homologous genes in the complex tetraploid cotton genome for manipulation (Gao et al., 2017). There are now updated versions of CRISPR/Cas12a (also called Cpf1) and CRISPR/Cas13, which can recognize more target sequences and are more specific and less likely to accidentally damage genes (Li et al., 2019). Scientists have also improved the design method of guide RNA and promoter selection, which can increase the success rate of editing (Long et al., 2018). This system has been used to improve many important traits of cotton, such as stress resistance, fiber quality and yield. 3.2 TALENs and ZFNs: earlier platforms and their limitations Transcription activator-like effector nucleases (TALENs) and zinc finger nucleases (ZFNs) are the earliest tools used for genetic modification of plants (including cotton). These two tools can indeed achieve site-specific gene modification, but because the operation requires complex protein design, low efficiency and high cost, they are now used less and less (Khan et al., 2023). These problems have led researchers to choose CRISPR systems more for cotton improvement (Kumar et al., 2024). 3.3 Base editing and prime editing: precision in nucleotide modification If conventional CRISPR is like "cutting" the gene, then base editing and Prime editing are much more meticulous. They do not need to cut the DNA, but can directly make "micro-modifications" to the nucleotides in situ. These two methods are actually upgraded versions of CRISPR technology, but they are played in different ways. Sometimes you just want to replace one base with another, and don't want to make a big fuss - then use base editing. Prime editing has more "means", not only can it replace, but also can add, delete, and even accurately change a specific sequence. However, having said that, although these technologies are new, they have already
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