Rice Genomics and Genetics 2025, Vol.16, No.1, 1-13 http://cropscipublisher.com/index.php/rgg 8 6 Application of MS Genes in Rice Breeding 6.1 Development of MS lines The development of MS lines is a critical step in hybrid rice breeding. MS can be induced through various genetic and cytoplasmic mechanisms. For instance, the FA-CMS system, controlled by the mitochondrial gene FA182, has shown stable MS, which can be restored by a single nuclear gene, OsRf19. This system simplifies the breeding process and has demonstrated promising results in developing high-performing hybrids (Figure 4) (Jiang et al., 2022). Additionally, the CRISPR/Cas9-mediated editing of the TMS5 gene has accelerated the development of TGMS lines, which are crucial for hybrid seed production (Zhou et al., 2016). Figure 4 Functional analysis of the CMS gene FA182and the restorer gene OsRf19(Adopted from Jiang et al., 2022) Image caption: The image provided contains five panels labeled A to E, each showing different aspects of the functional analysis of the CMS gene FA182 and the restorer gene OsRf19in rice (Adopted from Jiang et al., 2022) 6.2 Hybrid seed production systems The two-line system involves the use of EGMS lines that are sensitive to environmental conditions such as temperature or photoperiod or humidity. For example, the CRISPR/Cas9 system has been used to create GMS lines by editing the OsOPR7 gene, which can be restored to fertility by exogenous methyl jasmonate, thus establishing a two-line system for hybrid rice production (Pak et al., 2020). This system offers flexibility and efficiency in hybrid seed production. In addition, a third-generation hybrid rice system has succeeded in propagating and utilizing recessive nuclear MS lines using a transgenic construct-driven nongenetically modified (GM) system called seed production technology (Chang et al., 2016; Wu et al., 2016). Such a genetically engineered MS system has the ability to propagate nontransgenic MS seeds for hybrid rice seed (HRS) production and to overcome the intrinsic problems of the first two generations of hybrid rice systems (Wu et al., 2016; Zhang et al., 2018). The three-line system utilizes CMS lines, maintainer lines, and restorer lines. The CMS/Rf system, such as the WA-, HL-, BT-, DT-CMS, is widely used, with fertility restoration controlled by specific nuclear genes. For instance, the mapping of fertility restorer loci on chromosomes 1 and 10 has provided valuable markers for MAS in hybrid rice breeding programs (Yao et al., 2004; Tan and Chen, 2015; Zhu, 2016). The integration of both cytoplasmic and nuclear genome variations has further informed the breeding strategies for hybrid rice (Wan et al., 2019).
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