The combination of Chinsurah Boro II (BT)-type cytoplasmic male sterility (CMS) and
Rf1, the main fertility restorer gene (
Rf) for CMS-BT, has been extensively utilized for the production of three-line commercial
japonica hybrid seeds. The identification of new
Rf genes
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The combination of Chinsurah Boro II (BT)-type cytoplasmic male sterility (CMS) and
Rf1, the main fertility restorer gene (
Rf) for CMS-BT, has been extensively utilized for the production of three-line commercial
japonica hybrid seeds. The identification of new
Rf genes holds significance for the breeding of BT-type restorer lines, aiming to enhance the heterosis level of BT-type
japonica hybrids. In the present study, ‘02428’, a wide-compatibility
japonica variety, was observed to partially restore fertility to BT-type CMS lines. Genetic analysis revealed that ‘02428’ carries a dominant
Rf gene,
Rf21(t), responsible for the fertility restoration of BT-type CMS lines. Leveraging bulked segregant analysis (BSA) resequencing technology and molecular markers, the
Rf21(t) locus was identified, and mapped within a candidate interval of 6–12.5 Mb on chromosome 2. Using the iso-cytoplasmic restorer populations,
Rf21(t) was ultimately mapped to an interval of approximately 77 kb, encompassing 12 predicted genes, including
LOC_Os02g17360, encoding a PPR-domain-containing protein and
LOC_Os02g17380 (Rf2), a cloned
Rf for Lead-rice-type CMS. A comparative sequence analysis, gene expression profiling and gene knockout experiments confirmed that
LOC_Os02g17360 and
LOC_Os02g17380 are the most likely candidates of
Rf21(t). Furthermore,
Rf21(t) showed the dosage effect on the fertility restoration of BT-type CMS lines. This newly identified
Rf21(t) represents a valuable genetic resource for the breeding of BT-type
japonica restorer lines. Our findings offer practical insights for breeders interested in advancing BT-type
japonica hybrid development.
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