Rice Genomics and Genetics 2025, Vol.16, No.1, 1-13 http://cropscipublisher.com/index.php/rgg 5 SaM genes in indica-japonica hybrids restores pollen viability, demonstrating their direct involvement in pollen abortion (Xie et al., 2017). Environmental factors, particularly temperature, significantly impact the expression and function of MS genes. The TGMS system in rice, governed by genes like TMS5, is highly sensitive to temperature changes, with specific mutations leading to sterility at higher temperatures and fertility at lower temperatures (Zhou et al., 2016; Xu et al., 2020; Fang et al., 2022). This temperature-dependent regulation is crucial for the practical application of TGMS lines in hybrid rice breeding, allowing for controlled fertility based on environmental conditions. The functional analysis of MS genes in hybrid rice involves a combination of advanced genomic tools, detailed expression studies, and an understanding of the physiological and biochemical mechanisms underlying MS. These insights are essential for developing efficient hybrid breeding strategies and overcoming reproductive barriers in rice and other crops. 5 Case Studies of Key MS Genes in Rice 5.1 osnp1-1 mutant gene To uncover new rice genes that regulate MS, Chang et al. (2016) generated an ethyl methanesulfonate-induced mutant library in Huanghuazhan (HHZ), a prominent indica cultivar in China, and screened for MS mutants. Among these, a mutant named osnp1-1 exhibited complete MS but maintained normal vegetative growth, inflorescence, and flower morphology (Figure 2A). The osnp1-1 mutant had small, whitish anthers (Figure 2B) devoid of pollen grains (Figure 2C). This MS phenotype was stable under varying day lengths (10 h~16 h) and temperature ranges (20 °C~38 °C). Additionally, approximately 87%~92% of spikelets displayed the extrusion of one or both stigmas (Figure 3D). Cross-pollination with wild-type (WT) HHZ under natural field conditions resulted in a seed set of 40% or higher. These characteristics suggested that osnp1-1 could be a valuable MS line for hybrid rice production. Back-crossing with WT HHZ produced fertile F1 progeny, and the F2 population showed a 3:1 segregation ratio of fertile to sterile plants (216:68), indicating that osnp1-1 is a single recessive mutation (Chang et al., 2016). Figure 2 Phenotypes of osnp1-1 and molecular identification of OsNP1 (Adopted from Chang et al., 2016) Image caption: This image shows in detail the changes in the osnp1-1 mutant at the morphological and molecular levels, and provides important information about the role of the OsNP1 gene in rice flower organ development (Adopted from Chang et al., 2016)
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