Drought is one of the most adverse abiotic stresses that hinder growth and development of Brassica napus L., threatening its yield and quality. In this study, we identified the candidate genes that influence oil and protein content changes according to the results of the genome wide association mapping (GWAS) and differentially expressed genes (DEGs) under drought stress in B. napus.

A natural population comprising 183 B. napus lines under drought stress across two years was genotyped with a Brassica 60K Illumina Infinium SNP array to perform GWAS. Combined with drought stressed seed transcriptome data from different treatment periods, the candidate genes related to the changes in oil and protein contents under drought stress were identified.

The analysis showed that the best model for phenotypic data analysis in 2 years was mainly the Q or naïve model, and a total of 38 significant associated loci were detected (P<1/31597 or P<1/31278). By integrating GWAS and transcriptome results, 256 common genes were selected, and by comparing the database information of B. napus and Arabidopsis thaliana, 25 related candidate genes were identified. These genes, including transcription factors (e.g., bZIP transcription factor GBF6, TALE transcription factor ATH1, MYB-like Domain transcription factor MYBD, NAC transcription factor ANAC029, ERF transcription factor ERF111), related kinases (e.g., PIP5K1, PFK7), related proteins (e.g., seed stores protein CRU3, chloroplast protein DG238 and CP12, stress-responsive proteins HUP26 and M10), are involved in multiple biological processes such as photosynthetic reaction, substance transport, and stress response. For instance, oil-related protein kinase CIPK9, ABCA9 transporter, storage-related protein CRU3, may provide basis for explaining the changes in oil and protein contents of B. napus under drought stress.

The 25 identified candidate genes may affect the accumulation of protein and oil contents under drought stress during the seed development in B. napus.