Rice Genomics and Genetics 2025, Vol.16, No.1, 1-13 http://cropscipublisher.com/index.php/rgg 2 markers and restorer genes (Li et al., 2007; Zhu et al., 2009; Tan and Chen, 2015; Zhu, 2016; Hu and Qian, 2022; Zang, et al., 2024). Environment-sensitive genic male sterility (EGMS) can be further divided into photoperiod-sensitive (PGMS), temperature-sensitive (TGMS) and humidity-sensitive (HGMS) types, which are regulated by specific genetic loci (Li et al., 2007; Sun et al., 2021; Xue et al., 2018; Chen et al., 2020). The primary objective of this paper is to provide a comprehensive overview of the current status and future prospects of MS genes in hybrid rice. This includes the identification and functional analysis of key genes involved in MS, as well as the molecular mechanisms underlying this trait. By synthesizing recent advancements in genomics, proteomics, and biotechnology, this review aims to highlight the potential applications of MS genes in improving hybrid rice breeding programs. Additionally, we discuss the challenges and opportunities associated with the development of novel MS systems and their implications for global food security. Through this review, we seek to provide valuable insights for researchers, breeders, and policymakers involved in the advancement of hybrid rice technology. 2 Overview of MS in Rice MS in rice is a crucial trait for hybrid rice breeding, enabling the production of high-yielding hybrid varieties. MS can be classified into three main types like CMS, GMS, and EGMS. Each type has distinct genetic and molecular mechanisms that contribute to their utility in hybrid rice breeding programs. 2.1CMS CMS is a maternally inherited trait caused by the interaction between mitochondrial and nuclear genomes. CMS results in the dysfunction of pollen and anther development, leading to MS. The CMS trait is controlled by specific mitochondrial genes, which can be counteracted by nuclear-encoded restorer of fertility (Rf) genes that restore male fertility (Chen and Liu, 2014; Li et al., 2007; Song et al., 2020; Tang et al., 2016; Sun et al., 2021). For instance, the WA352 gene in the WA type of CMS interacts with the mitochondrial copper chaperone COX11, leading to the production of reactive oxygen species and resulting in MS (Wang et al., 2018). The CMS system has been widely utilized in hybrid rice breeding due to its stable inheritance and the ability to produce high-yielding hybrids. 2.2GMS GMS is controlled by nuclear genes and does not involve the cytoplasmic genome. GMS can be induced by mutations in specific nuclear genes that are essential for pollen development. The GMS system is advantageous because it allows for the easy manipulation of MS through traditional breeding methods. Recent advancements have utilized CRISPR/Cas9 technology to create GMS mutants, such as the CYP703A3-deficient male-sterile mutant, which can be used in hybrid rice production (Song et al., 2020). GMS systems are characterized by their stable sterility and the ability to combine freely with other genetic backgrounds, making them valuable for hybrid breeding. 2.3EGMS EGMS includes PGMS, TGMS and HGMS. EGMS lines exhibit MS under specific environmental conditions, such as changes in day length or temperature or humidity, and revert to fertility under different conditions. This reversible sterility is controlled by nuclear genes and can involve epigenetic regulation by noncoding RNAs (Li et al., 2007; Chen and Liu, 2014; Tang et al., 2016; Toriyama, 2021). For example, the P/TGMS line Peiai64S (PA64S) shows MS under high temperatures and long daylight conditions, with miRNAs such as miR156, miR5488, and miR399 playing roles in regulating this sterility (Sun et al., 2021). The TGMS trait of AnS-1 was found to be caused by C-to-A mutation in TMS5, resulting in a premature stop codon in the RNase Z protein (Zhou et al., 2014; Yan et al., 2024). HGMS is a new type of EGMS discovered in rice recent year, it has defects in the structure of the pollen wall, and the pollen is prone to dehydration and inactivation in low humidity environments, but remains viable in high humidity environments (Xue et al., 2018; Chen et al., 2020) (Figure 1). EGMS systems are particularly useful for hybrid seed production as they allow for the easy multiplication of MS lines under appropriate environmental conditions.
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