Abstract
Radish (Raphanus sativus L.) is an important root vegetable worldwide. The development of F1 hybrids, which are extensively used for commercial radish production, relies on cytoplasmic male sterility (CMS). To identify candidate genes responsible for CMS in NWB cytoplasm, we sequenced the normal and NWB CMS radish mitochondrial genomes via next-generation sequencing. A comparative analysis revealed 18 syntenic blocks and 11 unique regions in the NWB CMS mitogenome. A detailed examination indicated that orf463a was the most likely causal factor for male sterility in NWB cytoplasm. Interestingly, orf463a was identical to orf463, which is responsible for CMS in Dongbu cytoplasmic and genic male sterility (DCGMS) radish. Moreover, only structural variations were detected between the NWB CMS and DCGMS mitochondrial genomes, with no nucleotide polymorphisms (SNPs) or meaningful indels. Further analyses revealed these two mitochondrial genomes are coexisting isomeric forms belonging to the same mitotype. orf463a was more highly expressed in flower buds than in vegetative organs and its expression was differentially regulated in the presence of restorer of fertility (Rf) genes. orf463a was confirmed to originate from Raphanus raphanistrum. In this study, we identified a candidate gene responsible for the CMS in NWB cytoplasm and clarified the relationship between NWB CMS and DCGMS.
Highlights
Radish (Raphanus sativus L.), which is a Brassicaceae crop, is mainly used as a root vegetable and is widely cultivated in East Asia, especially in China, Japan, and South Korea [1]
The NWB cytoplasmic male sterility (CMS) and normal radish mitochondrial genomes were sequenced with the Illumina
An examination of 12 natural populations indicated that orf463a is specific to the mitochondrial genomes of radish lines with the NWB-type cytoplasm, making it the most likely candidate gene inducing the CMS in NWB CMS lines (Figure 3)
Summary
Radish (Raphanus sativus L.), which is a Brassicaceae crop, is mainly used as a root vegetable and is widely cultivated in East Asia, especially in China, Japan, and South Korea [1]. As a cross-pollinated plant, radish exhibits high hybrid vigor, which is beneficial for the commercial production of hybrid seeds. Self-incompatibility and cytoplasmic male sterility (CMS) are two major traits associated with radish hybrid seed production. Because of their vulnerability to environmental factors, self-incompatible lines are unstable, which results in the production of impure hybrid seeds. Male sterility may be useful for developing an efficient and cost-effective method for applying heterosis to hybrid production. Cytoplasmic male sterility is a maternally inherited trait in which plants develop normally, but fail to produce functional pollen, and is often associated with the rearrangement of genes in the mitochondrial genome [2,3]. Plant mitochondrial genomes, which differ considerably from animal mitochondrial genomes, are large (200–2400 kb), complex, and comprise multipartite structures because
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