Cotton Genomics and Genetics 2025, Vol.16, No.6, 269-277 http://cropscipublisher.com/index.php/cgg 274 Figure 2 Drought-induced cellular and molecular signaling pathways to enhance drought tolerance in plants (Adopted from Mahmood et al., 2019) 7 Applications of Promoter Variants in Cotton Improvement 7.1 Using promoter variants to enhance cotton stress tolerance Not all resilience improvement measures rely on radical gene editing. Sometimes, the details of the "regulatory layer" such as promoter variations are even more crucial. Especially under drought, high temperature or saline-alkali stress, some naturally occurring promoter variants or variations modified through engineering means can more flexibly regulate gene expression. Some only function in specific tissues, while others are activated only when stress occurs. A certain insertion/deletion site of the GhHSP70-26 promoter is linked to improving the drought and heat tolerance of cotton and is regarded as a target worthy of close attention in breeding (Guo et al., 2023). Another example is the GhNAC2 promoter, which can "respond" to various hormones and adverse signals. Using it to drive the expression of downstream beneficial genes is a feasible path to enhance overall adaptability (Naresh et al., 2024). Although these regulatory changes may seem like mere "patchwork", when combined with marker-assisted selection and molecular breeding techniques, their effects are no worse than those of gene knockout. 7.2 Promoter engineering in genetically modified cotton The core of transgenic technology is not merely about "what genes to add", but rather "how to regulate their expression". In cotton breeding, some naturally derived or designed inducible promoters are being used to precisely regulate the expression timing and position of target genes. The advantage of doing so is that it can reduce some common side effects and also enhance the resistance of cotton to adverse environments (Shan et al., 2019). A representative case is that the expression of the IPT gene was controlled by the aging-inducing promoter SAG12. As a result, not only did the salt tolerance of cotton increase, but the antioxidant capacity was also significantly enhanced, and even the ion balance was more stable (Shan et al., 2019). In addition, tools like
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