The Brassica Napus Fatty Acid Exporter FAX1-1 Contributes to Biological Yield, Seed Oil Production, and Oil Quality

Abstract Background: In the oilseed crop Brassica napus (rapeseed), various metabolic processes influence seed oil production, oil quality, and biological yield. However, the role of plastid membrane proteins in these traits has not been explored. Results: Our genome-wide association study (GWAS) of 520 B. napus accessions identified the chloroplast membrane protein-localized FATTY ACID EXPORTER 1-1 (FAX1-1) as a candidate associated with biological yield. Seed transcript levels of BnaFAX1-1 were higher in a cultivar with high seed oil content relative to a low-oil cultivar. BnaFAX1-1 localized to the plastid envelope. When expressed in Arabidopsis thaliana, BnaFAX1-1 enhanced biological yield (total plant dry matter), seed yield and seed oil content per plant. Likewise, in the field, B. napus BnaFAX1-1 overexpression lines (BnaFAX1-1-OE) displayed significantly enhanced biological yield, seed yield, and seed oil content compared with the wild type. BnaFAX1-1 overexpression also up-regulated gibberellic acid 4 (GA4) biosynthesis, which may contribute to biological yield improvement. Furthermore, oleic acid (C18:1) significantly increased in BnaFAX1-1 overexpression seeds. Conclusion: Our results indicated that the putative fatty acid exporter BnaFAX1-1 simultaneously improved seed oil production, oil quality and biological yield in B. napus, providing new approaches for future molecular breeding.