Plant Gene and Traits 2024, Vol.15, No.3, 141-151 http://genbreedpublisher.com/index.php/pgt 142 2 Understanding the GS2Gene 2.1 Identification and characterization of the GS2 gene The GS2 gene has been identified as a significant regulator of grain size and weight in rice. In a study involving 204 diverse rice germplasms, GS2 was found to be associated with grain length (GL), grain width (GW), and grain thickness (GT). The gene's role in these traits was confirmed through the use of InDel markers, which successfully identified multiple alleles contributing to these phenotypic variations. Additionally, the GS2 genewas one of the nine major genes studied for its impact on grain size and weight, highlighting its importance in rice breeding programs aimed at improving yield and grain appearance (Gull et al., 2019). 2.2 GS2’s mechanisms of action in rice development The mechanisms by which GS2 influences rice development are multifaceted. GS2 is a positive regulator downstream of GSK2 in response to brassinosteroid (BR) signaling, which is crucial for cell expansion in spikelet hulls (Huang et al., 2022). The interaction between GSK2 and GS2, where GSK2 phosphorylates GS2, enhances the accumulation of GS2 in the nucleus, thereby promoting cell expansion and increasing grain size. This interaction underscores the importance of the BR signaling pathway in regulating grain size through GS2. Furthermore, the GS2 gene’s role in regulating grain size was also supported by its association with other genes like GS3, GS7, andGW8, which collectively influence grain length, width, and thickness. 2.3 Evolutionary perspective of GS2 across rice varieties The evolutionary significance of the GS2 gene across different rice varieties has been explored through genetic and phenotypic analyses. Studies have shown that GS2, along with other grain size-related genes, exhibits considerable genetic variation among different rice germplasms. This variation is crucial for the adaptability and selection of rice varieties with desirable traits. For instance, the GS2 gene was found to be a part of a complex network of genes that regulate grain size, with different alleles contributing to variations in grain length, width, and thickness (Ngangkham et al., 2018). The evolutionary perspective of GS2 is further highlighted by its interaction with other genes like GS3 and GW2, which are also key regulators of grain size and have been studied extensively in various rice landraces. These interactions and variations suggest that GS2 has played a significant role in the domestication and breeding of rice varieties with improved yield and grain quality. 3GS2 and Its Impact on Grain Size and Weight 3.1 Genetic regulation of grain size and weight by GS2 The GS2 gene plays a crucial role in the genetic regulation of grain size and weight in rice. GS2 is part of a complex network of genes that interact to control these traits. For instance, the GS2 gene is known to interact with the brassinosteroid (BR) signaling pathway, which is essential for cell expansion in spikelet hulls, thereby influencing grain size (Lyu et al., 2020). Additionally, GS2 is a downstream component of the GSK2-related BR signaling response, which further underscores its role in grain size regulation. The interaction between GS2 and other genes, such as OsOFP19, also highlights its importance in the genetic regulation of grain size and weight (Huang et al., 2022). 3.2 Phenotypic variations resulting fromGS2 mutations Mutations in the GS2 gene can lead to significant phenotypic variations in rice grain size and weight (Dash, 2020). For example, the SMALL GRAIN2 (SG2) mutant, which harbors a mutation in the GS2 gene, exhibits smaller grains and a semi-dwarf phenotype due to repressed cell expansion in the spikelet hulls. This mutation causes insensitivity to exogenous BR treatment, further affecting grain size. Additionally, the overexpression of GS2 can lead to larger grains, while its loss of function results in smaller grains, demonstrating the gene's critical role in determining grain size and weight (Tian et al., 2019). 3.3 Interaction of GS2 with other yield-related genes GS2 interacts with several other yield-related genes to regulate grain size and weight. For instance, GS2 interacts with OsOFP19, a negative regulator of grain shape, to control gene expression and grain size (Ngangkham et al., 2018). This interaction plays an antagonistic role, with GS2 promoting and OsOFP19 inhibiting grain size. Furthermore, GS2 is part of a broader network involving other genes such as GW5, which also regulates grain
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