It is an important breeding strategy to improve Brassica napus by crossing with its parental species, B. oleracea and B. rapa. Interspecific hybridization between B. napus and B. rapa is compatible with high rate of survival embryo, while the hybridization between B. napus and B. oleracea is incompatible with high occurrence of embryo abortion. To understand the diverse embryo fate in the two interspecific hybridizations, here the siliques of B. napus pollinated with B. oleracea (AE) and B. rapa (NE) were employed for transcriptome sequencing at 8 and 16 days after pollination. Compared with NE and female, there were 1274 and 1698 differentially expressed genes (DEGs) in AE at 8 and 16 days after pollination (AE8 and AE16), which were significantly enriched into 67 and 72 GO terms, respectively. Of which 9 and 15 GO terms in cell growth, cell wall formation harbored high ratio of down-regulated expression DEGs (96/131 in AE8, 174/235 in AE16), while 12 and 17 GO terms in the processes of photosynthesis, photorespiration, peroxisome, oxidative stress and systemic acquired resistance harbored high ratio of up-regulated expression DEGs (222/304 in AE8, 214/287 in AE16). A high level of O2−, H2O2 content and antioxidation activity (SOD, CAT) was tested in the siliques of B. napus pollinated with B. oleracea. Our data suggest that disorder of plant hormone metabolism, retardation of cell morphogenesis and the accumulation of reactive oxygen species (ROS) may associate with hybridization incompatibility between B. napus and B. oleracea.

Improving Brassica napus via introgression of the genome components from its parental species, B. oleracea and B. rapa, is an important breeding strategy. Interspecific hybridization between B. napus and B. rapa is compatible with high rate of survival ovules, while the hybridization between B. napus and B. oleracea is incompatible with the high occurrence of embryo abortion. To understand the diverse embryo fate in the two interspecific hybridizations, here, the siliques of B. napus pollinated with B. oleracea (AE) and B. rapa (NE) were employed for transcriptome sequencing at 8 and 16 days after pollination. Compared to NE and the parental line of B. napus, more specific differentially expressed genes (DEGs) (1274 and 1698) were obtained in AE and the parental line of B. napus at 8 and 16 days after pollination (DAP). These numbers were 51 and 5.8 times higher than the number of specific DEGs in NE and parental line of B. napus at 8 and 16 DAP, respectively, suggesting more complex transcriptional changes in AE. Most of DEGs in the terms of cell growth and cell wall formation exhibited down-regulated expression patterns (96(down)/131(all) in AE8, 174(down)/235(all) in AE16), while most of DEGs in the processes of photosynthesis, photorespiration, peroxisome, oxidative stress, and systemic acquired resistance exhibited up-regulated expression patterns (222(up)/304(all) in AE8, 214(up)/287(all) in AE16). This is in accordance with a high level of reactive oxygen species (ROS) in the siliques of B. napus pollinated with B. oleracea. Our data suggest that the disorder of plant hormone metabolism, retardation of cell morphogenesis, and the accumulation of ROS may be associated with hybrid incompatibility between B. napus and B. oleracea.

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