Rice Genomics and Genetics 2025, Vol.16, No.2, 106-115 http://cropscipublisher.com/index.php/rgg 108 was knocked out by researchers using CRISPR/Cas9 technology, and it was found that the mutant performed better under drought: ABA accumulation increased, antioxidant capacity increased, and yield did not drop (Usman et al., 2020). This is a bit unexpected. But OsPYL9 is just an example. In fact, drought resistance involves more than just the ABA pathway. Many quantitative trait loci (QTLs) have also been found, such as ABI5 and GBF4, which are genes that "show up" in drought response (Selamat and Nadarajah, 2021). These genes themselves may not be so "hot", but they are very active under stress. Of course, not all relevant studies focus on ABA or transcription factors. Lenka et al. (2011) used transcriptome comparison to find that some genes involved in carbon fixation and flavonoid synthesis are also critical in drought-resistant genotypes. Although these genes seem a bit far from the word "drought resistance", they obviously play a role in maintaining basal metabolism and anti-oxidation. Similar situations also occur in salt and heat stress. For example, the OsCDPK7 gene, which encodes a calcium-dependent protein kinase, performs well in regulating salt stress response. After overexpression, it can drive a group of stress-related genes to upregulate (Saijo et al., 2000). In other words, the presence of this gene can help rice maintain its position in harsh environments. GWAS research is also not idle. In the study of salt tolerance at the seedling stage, the QTL qDTS1-2 is considered to be closely related to salt tolerance, and OsMYB48 may be a key regulatory factor, not only in salt tolerance, but also in drought tolerance (Kim and Kim, 2023). As for heat tolerance, meta-QTL analysis found genes such as OsBiP2 and OsWRKY10, which mainly play a role in heat stress of reproductive organs (Raza et al., 2020), which is particularly important for rice during the flowering and fruiting period. 3.2 Genes related to yield improvement The study of stress resistance cannot avoid yield. Like OsPYL9, in addition to being able to withstand drought, it can also increase grain yield-regardless of whether it is adequately watered (Usman et al., 2020). This gene obviously takes care of both ends. What factors affect yield? Grain development, panicle shape, and grain filling process are all considered. QTL analysis has pointed out that some regions contain genes related to starch and sucrose metabolism. These metabolic pathways directly determine whether the grains can be filled and how much they can be filled (Figure 1) (Qin et al., 2021; Selamat and Nadarajah, 2021). This is not only a problem of stress resistance, but also a matter of whether the grain can fill the pockets. In addition to the grain itself, the biomass and tiller number of the whole plant cannot be ignored. Lenka et al. (2011) pointed out that some genes related to carbon fixation and sugar metabolism are quite active in regulating these traits. More interestingly, genes such as OsAAP7Aand OsAMT2;1, which are involved in nutrient absorption and tillering regulation, were screened out through QTL merging analysis (Raza et al., 2020), which can be said to be "behind-the-scenes heroes". 3.3 Genes related to quality Yield is not the only indicator, and quality is also receiving more and more attention. Taste and nutritional content directly affect the commercial value and nutritional value of rice. Lenka et al. (2011) mentioned that some genes involved in flavonoid biosynthesis were identified in comparative transcriptomes. Such substances are usually classified as "secondary metabolites", but they do help improve the nutritional value of grains. There are also many genes involved in the regulation of texture, especially those related to starch and sucrose metabolism. These genes affect the hardness, stickiness and taste of the grains (Selamat and Nadarajah, 2021), and have actually been repeatedly screened in variety improvement. As for aroma and flavor, the "protagonist" genes responsible for this aspect have not yet been clearly found, but many studies believe that pathways such as flavonoid metabolism may "assist" in it and indirectly affect the smell (Buti et al., 2019; Selamat and Nadarajah, 2021). To find out which genes are really responsible for flavor, we have to wait for further positioning research.
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