Pod shattering causes severe yield loss in rapeseed (Brassica napus L.) under modern agricultural practice. Identification of highly shatter-resistant germplasm is desirable for the development of rapeseed cultivars for mechanical harvesting. In the present study, an elite line OR88 with strong shatter resistance and a lignified-layer bridge (LLB) structure was identified. The LLB structure was unique to OR88 and co-segregated with high pod-shatter resistance. The LLB structure is differentiated at stage 12 of gynoecium development without any gynoecium defects. Genetic analysis showed that LLB is controlled by a single recessive gene. By BSA-Seq and map-based cloning, the resistance gene location was delimited to a 0.688 Mb region on chromosome C09. Transcriptome analysis suggested BnTCP8.C09 as the gene responsible for LLB. The expression of BnTCP.C09 was strongly downregulated in OR88, suppressing cell proliferation in the pod valve margin. KASP markers linked to the candidate gene were developed. This pod shatter-resistant line could be used in rapeseed breeding programs by direct transfer of the gene with the assistance of the DNA markers.

The Nsa cytoplasmic male sterility (CMS) system confers stable male sterility and offers great potential for production of hybrid seeds in oilseed rape. However, genes responsible for male sterility in Nsa CMS have not been identified. By mitochondrial genome sequencing of Nsa CMS and its maintainer line, we identified in an Nsa CMS line several chimeric genes encoding hypothetical proteins harboring transmembrane domains. One novel chimeric gene orf346 showed high identity with cox1 at the 5′ terminal region and was co-transcribed with nad3 and rps12 genes. Transgenic plants of orf346 fused with or without mitochondrial targeting peptide conferred complete male sterility in Arabidopsis. ORF346 was mitochondrion-localized. Expression of orf346 in Escherichia coli inhibited bacterial growth, with excessive accumulation of reactive oxygen species and decreased ATP content. These results reveal a link between the newly identified mitochondrial gene orf346 and the abortion of Nsa CMS. Inadequate energy supply and excessive accumulation of reactive oxygen species may account for pollen abortion in Nsa CMS plants.

Sinapis arvensis, belonging to the genus Sinapis of the family Brassicaceae, has good agronomic characters that make it a valuable genetic resource for crop improvement and is a cytoplasmic source of heterologous cytoplasmic male sterility (CMS). In addition, S. arvensis has played an important role in the evolution of the six major cultivated Brassica species involved in the triangle of U. Using next-generation sequencing, we assembled and revealed the gene composition of S. arvensis cytoplasmic genome. The chloroplast genome comprises 153,590 bp, with 112 individual genes, including 4 rRNA, 29 tRNA, and 79 protein-coding genes. The mitochondrial genome comprises 240,024 bp, with 54 genes, including 18 tRNA, three rRNA and 33 protein-coding genes. Genome structure and evolutionary analysis indicated that the sequences of the S. arvensis organellar genomes were more similar to those of Brassica nigra and B. carinata than to those of other Brassicaceae species. Four mitochondrial open reading frames displaying chimeric structural features and encoding hypothetical proteins with transmembrane domains may account for the infertility of Nsa CMS previously derived from somatic cell hybridization between B. napus and S. arvensis. These results will not only contribute to utilize the germplasm resource of S. arvensis, and comprehend the evolution of organelle genomes within the Brassicaceae family, but also help to identify genes conditioning the alloplasmic male sterility of Nsa CMS in B. napus.

Sequence-specific nucleases (SSN) that generate double-stranded DNA breaks (DSBs) in genes of interest are the key to site-specific genome editing in plants. Genome editing has developed into one method of reducing undesirable traits in crops by the induction of knockout mutations. Different SSN-mediated genome-editing systems, including LAGLIDADG homing endonucleases or meganucleases, zinc-finger nucleases, transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats, are emerging as robust tools for introducing functional mutations in polyploid crops including citrus, wheat, cotton, soybean, rapeseed, potato, grapes, Camelina sativa, dandelion, and tobacco. The approach utilizes knowledge of biological mechanisms for targeted induction of DSBs and their error-prone repair, allowing highly specific changes at designated genome loci. In this review, we briefly describe genome-editing technologies and their application to genetic improvement of polyploid crops.