International Journal of Horticulture, 2025, Vol.15, No.5, 218-233 http://hortherbpublisher.com/index.php/ijh 224 This pattern of increase and decrease means that plants switch metabolic priorities at different growth stages: more carbon is allocated to building structures (cellulose, lignin) in the early stage, while more is used to store energy (sucrose) in the later stage. Perlo et al. (2022) used weighted gene co-expression network analysis (WGCNA) to reveal for the first time the changing pattern of sugarcane gene expression with developmental stage and variety, and identified two gene co-expression modules associated with high sugar content and high fiber content, respectively. Among them, the high sugar module is enriched with genes in pathways such as sucrose synthesis and transport, while the high fiber module is enriched with genes related to cell wall biosynthesis and defense, and the expression of the two modules is significantly negatively correlated. This result indicates that there is a genetic network in sugarcane that coordinates sweetness and fiber formation, and the spatiotemporal expression of different gene clusters jointly shapes the final quality traits. By analyzing the expression patterns of these key genes, researchers can further understand when and where regulation can achieve the optimization of sugarcane quality. For example, if sugar accumulation genes can be specifically upregulated and some lignin synthesis genes can be downregulated in the late stage of sugarcane stalk development, the dual purpose of increasing sweetness and reducing fiber content may be achieved. This fine regulation needs to be based on a full grasp of the spatiotemporal expression patterns of genes. 4.2 Transcription factors involved in trait coordination: NAC, MYB, bZIP Transcription factors (TFs) are upstream molecular switches that regulate gene expression and play a pivotal role in plant secondary metabolism and cell wall development. Some key TFs can simultaneously affect sugar metabolism and cell wall synthesis pathways, and are therefore regarded as molecular targets for the coordinated improvement of sweetness and texture traits (Khan et al., 2023). In crops such as sugarcane, transcription factors of the NAC and MYB families have been shown to be involved in the regulation of secondary cell walls. NAC transcription factors are a large class of regulators unique to plants, among which the master switch genes for secondary wall thickness regulation often belong to the NST subfamily. The sugarcane genome contains a large number of NAC genes. Wang et al. (2023) identified NAC genes of the ATAF subfamily in Saccharum spontaneum and functionally analyzed the homologous ScNAC2 of cultivated sugarcane, suggesting that it plays an important role in biological stress response and other aspects. Although there is insufficient evidence that NAC directly regulates sugarcane cell wall synthesis, given that Arabidopsis NST1/2 can initiate the transcription of cellulose and lignin synthesis genes, it can be speculated that some NACs in sugarcane may play a similar "master switch" role in the process of stem lignification. When these NACs are highly expressed, they may promote cell wall reinforcement and make the stems harder; conversely, inhibiting the activity of some NACs may help reduce lignin deposition and thus soften the texture. This provides ideas for future molecular breeding. MYB transcription factors are also widely involved in metabolic regulation, especially phenolic and lignin pathways. Studies have shown that AtMYB58/63 and others can directly activate the expression of lignin synthase genes, thereby controlling the degree of fiber lignification. The corresponding MYB regulatory network in sugarcane has not yet been clearly identified, but some MYB gene expression changes have been observed in sugarcane with genetic engineering to reduce lignin, suggesting that MYB may be involved in the feedback regulation of lignin synthesis. The bZIP family transcription factors play a special role in the connection between sugar signals and sugar metabolism genes. Mehdi et al. (2024b) reported that a bZIP transcription factor ScbZIP44 in sugarcane is controlled by sucrose levels: there is a sucrose-responsive upstream open reading frame (SC-uORF) on the 5'UTR of the gene, and the uORF is activated to inhibit the translation of the main ORF when sucrose is high. When the sweetness is high, the protein level of ScbZIP44 decreases, resulting in the release of its inhibitory effect on downstream sucrose metabolism genes, thereby promoting more sucrose accumulation. Conversely, under low sugar conditions, the increase in bZIP44 protein will inhibit sucrose synthesis-related genes, forming a negative feedback. This discovery reveals the ingenious self-regulatory mechanism in the sugar metabolism pathway, and also shows that it is possible to improve the sweetness of sugarcane through transcription factors (such as modifying the uORF element of ScbZIP44 so that it is no longer inhibited by sucrose). Transcription factors such as AP2/ERF,
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