Field Crop 2025, Vol.8, No.1, 32-40 http://cropscipublisher.com/index.php/fc 36 5 Molecular Mechanisms Regulating Tuber Size and Yield 5.1 Hormone regulation mechanism: the role of gibberellins and cytokinins in tuber growth Tuber development is affected by the combined effects of multiple hormones, not just one hormone. For example, gibberellins (especially GA₃) have a prominent effect on tuber dormancy and germination. Studies have shown that the transcription factor StTCP15 can regulate the ratio between ABA and GA₃. When this ratio is lower, tubers will germinate earlier; conversely, if the expression of StTCP15 decreases, germination will be delayed (Wang et al., 2022). However, the role of cytokinins and auxins cannot be ignored. Auxin is often considered to be the "starting signal" for the formation of initial tubers, but it also needs to cooperate with other hormones, such as the interaction with gibberellins and strigolactones in runners, which will directly affect the final yield. In addition, some experiments have artificially increased the expression level of GA oxidase (such as what Kolachevskaya et al., 2019 did), and found that it does bring significant changes to tuber formation and productivity. 5.2 Regulatory function of transcription factor network in tuber development If hormones are the source of signals, then transcription factors may be more like "conductors". They do not directly produce hormones, but determine the specific effects of hormone signals. For example, R2R3-MYB members in the MYB family often appear in studies related to tuber development, especially those processes related to hormone response or environmental stress (Sun et al., 2019). StTCP15 is also an example. As mentioned earlier, it affects the pathways of ABA and GA₃, thereby affecting tuber dormancy. In addition, growth regulators such as GRF also have their own "division of labor": StGRF1, 2, and 5 are more likely to participate in tuber germination, while StGRF4 and 9 are more active during dormancy (Cui et al., 2024). The regulation of these factors is not linear or isolated. They often cross and cooperate with each other, allowing tubers to "self-regulate" size and yield in a complex environment. 5.3 Application of key gene editing technologies (such as CRISPR-Cas9) In the past, the regulation of tuber development mainly relied on natural variation and traditional breeding, but now the situation is different. Tools such as CRISPR-Cas9 allow researchers to precisely "move" a gene, such as StGA3ox3, which controls GA biosynthesis. If this gene is regulated, the rhythm of tuber formation will also change (Malankar et al., 2023). Other studies have found that phasiRNA siRD29(-) can affect the expression of StGA3ox3 in the early stage of tuber formation, which actually provides the possibility of RNA-level regulation. In addition to gibberellin synthesis genes, researchers have also tried to increase the expression of some auxin synthesis genes driven by tuber-specific promoters, and found that it can increase tuber yield (Zhang, 2024). In general, gene editing makes regulation more "specific", rather than relying on guesswork and screening as before. 6 Breeding Strategies for Potato Tuber Size and Yield 6.1 Traditional breeding: long-lasting, but also with many limitations In the past, potato breeding was basically based on experience and eyes-whoever has a large tuber, high yield, and disease resistance is selected. Seed selection, hybridization, and then screening generation after generation, the process is not complicated, but slow. Moreover, the most reliable thing about this method is the intuitively visible "phenotype", such as the size of the tuber or the growth of the plant. But there are also many problems. Potatoes themselves are polyploids, and the genome is complex. In addition, the traits are easily affected by the environment. Sometimes the same variety grows differently in different plots (Schönhals et al., 2017; Tessema et al., 2022). This makes phenotypic breeding time-consuming and unreliable. Especially for "invisible" traits such as drought tolerance and tuber shape, it is easy to be missed, but they are linked to processing and sales and cannot be ignored (Aliche et al., 2019). 6.2 Molecular breeding: accurate and efficient, but the threshold is not low In contrast, molecular breeding today is like installing navigation. The marker-assisted selection (MAS) method can "calculate" whether the plant will produce good tubers in the future when it is still young. For example, the size, shape, and density of the tubers have clear QTL regions and DNA markers, and breeders can screen seedlings in advance based on these "fingerprints" (Park et al., 2024). Genomic selection (GS) goes a step further and predicts the "potential value" of the plant before it grows out, so that strains with strong stress resistance can be
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