Rice Genomics and Genetics 2025, Vol.16, No.4, 219-236 http://cropscipublisher.com/index.php/rgg 232 one transformation and one generation, multiple genes can be specifically modified from different parents, and then hybridized and combined to obtain hybrids that simultaneously possess two superior traits. Similarly, a team from Huazhong Agricultural University in China has also explored the quality improvement of a multi-gene editing stack: they simultaneously knocked out the Wx, SSIIb, and SSIIIa genes in a backbone restorative line, endowing it with the characteristics of low linear and high branched long chains. Then, based on this, they introduced aromatic mutations to obtain a new rice variety with a low GI and prominent aroma. It can be imagined that in the future, by flexibly choosing different gene combinations, various characteristic functional rice varieties can be customized and cultivated. For instance, to meet the needs of the diabetic population, a gene package combining weak Wx alleles with highly resistant starch mutations (such as SBEIIb knockout) can be used to lower the GI. To meet the dietary habits of different regions, a set of high straight chain, soft and thick, and fragrant gene can be combined to balance the texture and flavor of dry rice. When improving multi-gene collaboration, it is also necessary to pay attention to the mutual balance of the effects of different genes (Tang et al., 2022). For instance, while enhancing resistant starch, it is also necessary to take into account both yield and taste. When designing the combination, it is essential to retain the necessary enzyme activity to avoid extreme traits. Through reasonable gene "superposition" and genetic engineering methods, we are expected to create "tailor-made" ideal rice varieties, shifting from a single pursuit of yield to a balance between yield and quality, and providing consumers with more diverse and healthier staple food choices. 6.3 Optimizing pathways by integrating metabolic engineering and traditional breeding Improving the quality of rice is a systematic project. Relying solely on molecular-level improvements often needs to be combined with conventional breeding and cultivation measures to achieve the best results. Therefore, when applying the research results of starch synthesis regulation to breeding practice, it is necessary to comprehensively consider the combination of metabolic engineering and traditional breeding. Firstly, after molecular breeding creates high-quality genotypes, traditional breeding methods such as hybridization and backcrossing remain important means to transfer these genotypes to varieties with excellent agronomic traits. For instance, low-linear glutinous rice mutants were obtained through gene editing, but the background might be experimental materials that were susceptible to diseases or had low yields. In such cases, backcrossing was needed to introduce the glutinous rice alleles into the background of the main cultivated variety, and then the agronomic traits were restored through field selection. In this process, traditional breeding experience and field phenotypic selection are extremely crucial, as quality is only a part of the overall traits of a variety. Secondly, quality traits are largely influenced by the environment and cultivation conditions, and the so-called "variety × environment interaction" is significant. Therefore, when applying high-quality genotypes, it is necessary to combine them with appropriate cultivation management. For instance, high-amylose and high-resistant starch varieties can achieve better quality performance in a cooler environment. However, in a high-temperature environment, cultivation improvements (such as watering to cool down and timely harvesting) are needed to prevent chalkiness and texture deterioration. In addition, when promoting nutritionally fortified functional rice (such as varieties rich in resistant starch), it is also necessary to gradually guide consumers' dietary habits. The quality can be gradually transitioned through hybridization of traditional varieties to make them accepted by the general public. Therefore, new varieties produced by metabolic engineering usually need to go through the refinement of traditional breeding steps, including the improvement of agronomic traits, multi-environment test identification, and the matching of cultivation techniques, before they can become truly valuable varieties. Fortunately, with the development of modern breeding theory, the concept of "collaborative improvement of multiple target traits" has been deeply rooted in people's minds. In the overall goal of genetic improvement of rice, yield, resistance and quality are taken into account in a coordinated manner, and various breeding innovation teams are also building comprehensive genetic engineering breeding plans that are "high-yielding, stress-resistant and high-quality". For instance, among the major molecular design breeding projects implemented in China in recent years, there is a plan to cultivate new varieties of ideal plant types that balance both yield and rice quality. By using gene aggregation methods, multiple yield QTLS are crossed and polymerized with quality sites such as Wx and ALK, and then precisely selected and bred with the help of molecular markers. This reflects the deep integration of traditional breeding
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