The functional divergence of homologous GPAT9 genes contributes to the erucic acid content of Brassica napus seeds

Abstract

Abstract Background The early allopolyploid Brassica napus was a hybrid of two Brassica species, that had undergone a whole genome duplication event followed by genome restructuring, including deletions and small scale duplications. A large number of homologous genes appeared functional divergence during species domestication. Due to the high conservation of de novo glycerolipid biosynthesis, multiple homologues of glycerol-3-phosphate acyltransferases (GPATs) have been found in B. napus. Moreover, the functional variances among these homologous GPAT-encoding genes are unclear. Results In this study, four B. napus homologous genes encoding glycerol-3-phosphate acyltransferase 9 (BnaGPAT9) were characterized. Although a bioinformatics analysis indicated high protein sequence similarity, the homologues demonstrated tissue-specific expression patterns and functional divergence. Yeast genetic complementation assays revealed that BnaGPAT9-A1/C1 homologues but not BnaGPAT9-A10/C9 homologues encoded functional GPAT enzymes. Furthermore, a single nucleotide polymorphism of BnaGPAT9-C1 that occurred during the domestication process was associated with enzyme activity and contributed to the fatty acid composition. The seed-specific expression of BnGPAT9-C1 1124A increased the erucic acid content in the transformant seeds. Conclusions This study revealed that BnaGPAT9 gene homologues evolved into functionally divergent forms with important roles in erucic acid biosynthesis.

Keywords

• Brassica napus
• Glycerol 3-phosphate acyltransferase 9
• Yeast genetic complementation
• Haplotype
• Erucic acid