Transcriptome de novo assembly and analysis of differentially expressed genes related to cytoplasmic male sterility in onion.

Onion (Allium cepa L.) is one of the major vegetables in China and accounts for a large proportion of China's vegetable exports. Onion cytoplasmic male sterility, which is often used in onion breeding, is caused by the interaction between the nuclear genes and the cytoplasm. However, the underlying molecular mechanism of onion cytoplasmic male sterility remains unclear. In this study, we analysed the anther microstructure of the onion cytoplasmic male sterile line SA2 and the onion maintainer line SB2. We found that the pollen abortion in SA2 occurred at the tetrad stage during the microspore development, which was very different from that in SB2. We used the Illumina HiSeq platform to sequence RNA from anthers at the tetrad stage collected from the SA2 and SB2 lines. The RNA sequencing and transcriptome assembly produced 146,413 All-Unigenes. Based on an analysis of the differentially expressed genes, we identified two cytoplasmic control genes, atp9 and cox1, and three nuclear-related genes, SERK1, AG and AMS. These transcriptomic results were also verified by fluorescence quantitative PCR. Our study provides important information about genes related to onion cytoplasmic male sterility, and it will help improve the understanding of the molecular mechanism of onion cytoplasmic male sterility.