Rice Genomics and Genetics 2025, Vol.16, No.1, 1-13 http://cropscipublisher.com/index.php/rgg 3 Figure 1 Phenotypes of humidity-sensitive genic male sterility 1 (hms1) mutants in different humidity conditions (Adopted from Xue et al., 2018) Image caption: (a) Whole-plant morphology of rice (Oryza sativa) Zhonghua11 (ZH11) and the hms1 mutant grown in a paddy field in Guangzhou, China (50%~90% relative humidity (RH)). (b) Seed setting of the ZH11 and hms1 plants grown in the paddy field. (c) Whole-plant morphology of ZH11 and hms1 plants grown in an artificial climate chamber (75% RH). (d) Seed setting of ZH11 and hms1 plants grown in an artificial climate chamber. (e) Seed setting of ZH11. (f-i) Seed setting of hms1 plants at 45% (f), 55% (g), 60% (h) and 75% RH (i). (j) Seed-setting rates of ZH11 and hms1 plants at different humidity percentages. Bars: (a, c) 20 cm; (b, d-i) 5 cm. Error bars indicate SD (n=5) (two-tailed Student’s t-test; **, P< 0.01) (Adopted from Xue et al., 2018) 2.4 Importance of MS in hybrid rice breeding MS is a cornerstone of hybrid rice breeding, enabling the production of high-yielding hybrid varieties through the exploitation of heterosis or hybrid vigor. The use of CMS, GMS, and EGMS systems has significantly contributed to the success of hybrid rice breeding programs worldwide. CMS systems, such as the WA, HL, BT, DT types, have been extensively used for over 40 years, leading to substantial increases in rice productivity (Chen and Tan, 2015; Toriyama, 2021). GMS and EGMS systems offer additional flexibility and ease of use in breeding programs, allowing for the development of diverse hybrid combinations (Tang et al., 2016; Chen et al., 2020; Song et al., 2020). The integration of molecular and genetic insights into MS mechanisms continues to enhance the efficiency and effectiveness of hybrid rice breeding, ensuring food security and agricultural sustainability (Li et al., 2007; Chen and Liu, 2014; Sun et al., 2021; Jiang et al., 2022). 3 Identification of MS Genes 3.1 Traditional genetic approaches Mutagenesis and phenotypic screening have been fundamental in identifying MS genes in rice. For instance, a GMS gene, ms-h (t), was induced by chemical mutagenesis and mapped to chromosome 9. This gene was found to have a pleiotropic effect on chalky endosperm, making it a valuable resource for understanding the biochemical mechanisms underlying MS and its related traits (Koh et al., 1999). Genetic mapping and QTL analysis have been extensively used to locate MS genes. The TGMS gene tms3(t) was mapped using bulked segregant analysis (BSA), identifying several RAPD markers linked to the gene on chromosome 6 (Subudhi et al., 1997). Similarly, two fertility restorer loci for the WA-CMS system were mapped to chromosomes 1 and 10, providing crucial markers for marker-assisted selection in hybrid rice breeding programs (Suresh et al., 2012). Additionally, qCTR5 and qCTR12 for cold tolerance and anther length affecting MS were identified on chromosomes 5 and 12 respectively, with specific candidate genes linked to these QTLs (Shimono et al., 2016).
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