Plant Gene and Traits 2024, Vol.15, No.3, 141-151 http://genbreedpublisher.com/index.php/pgt 143 width and weight through the BR signaling pathway (Tian et al., 2019). The interaction between GS2 and these genes highlights the complex genetic network that controls grain size and weight in rice. 4 Case Studies: GS2 Gene Manipulation in Rice 4.1 Detailed analysis of GS2 gene modification experiments The GS2 gene has been identified as a significant regulator of grain size and weight in rice. Various studies have explored the genetic and molecular mechanisms underlying its function. For instance, the study by Huang et al. (2022) demonstrated that the SG2 gene, which encodes a protein with a Ribonuclease H-like domain, is a positive regulator downstream of GSK2 in response to brassinosteroids (BR) signaling. The mutation in SG2 resulted in smaller grain size due to repressed cell expansion in spikelet hulls. This indicates that SG2, and by extension GS2, plays a crucial role in the BR signaling pathway, affecting grain size. Another study Lyu et al. (2020) highlighted the role of the GSK2-OML4 pathway in regulating grain size and weight (Figure 1). The LARGE1 gene, encoding the OML4 protein, is phosphorylated by GSK2 and negatively controls grain size (Lyu et al., 2020). Loss of function of OML4 leads to larger and heavier grains, suggesting that manipulating the GSK2-OML4 pathway, which includes GS2, can significantly impact grain size and weight. Figure 1 Large1 influences grain size and plant morphology (Adopted from Lyu et al., 2020) Image caption: (A) Mature paddy grains of ZHJ and large1-1, (B) Brown rice grains of ZHJ and large1-1, (C) and (D) ZHJ (C) and large1-1, (D) plants at mature stage, (E) ZHJ (left) and large1-1 (right) panicles, (F) and (G) Grain length (F) and width (G) of ZHJ and large1-1, (H) The 1000-grain weight of ZHJ and large1-1, (I) Plant height of ZHJ and large1-1, (J) Panicle length of ZHJ and large1-1, (K) Number of ZHJ and large1-1 primary panicle branches, (L) Number of ZHJ and large1-1 secondary panicle branches, (M) Grain number per panicle of ZHJ and large1-1. Values ( [F] to [H]) are given as mean ± SD (n ≥ 50). Values ( [I] to [M]) are given as means ± SD (n = 20). Asterisks indicate significant differences between ZHJ and large1-1. **, P < 0.01 compared with the wild type (ZHJ) by Student’s t test. Bar in (A) and (B) = 2 mm; bar in (C) to (E) = 10 cm (Adopted from Lyu et al., 2020) Lyu et al. (2020) found that the large1-1 variant of the ZHJ rice strain exhibits significant differences in grain size and plant morphology compared to the wild type. The study measured several parameters and revealed that large1-1 grains are notably longer and wider, and the 1000-grain weight is higher, indicating larger individual grain mass. Additionally, plants with the large1-1 mutation are taller, with increased panicle length and a higher number of both primary and secondary branches on the panicles. Furthermore, large1-1 plants produce more grains per panicle, demonstrating enhanced reproductive capability. These morphological and reproductive enhancements were statistically significant with a p-value of less than 0.01, suggesting that the large1-1 mutation positively influences both grain yield and overall plant structure (Haliru et al., 2020).
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