Analysis of BnGPAT9 Gene Expression Patterns in Brassica napus and Its Impact on Seed Oil Content

Glycerol-3-phosphate acyltransferase (GPAT) genes encode enzymes involved in the biosynthesis of plant oils. Rapeseed has four BnGPAT9 genes, but the expression patterns and functions of these four homologous copies in rapeseed for seed oil accumulation are not well understood. In this study, we cloned the four BnGPAT9 genes and their promoters from Brassica napus and found significant differences in the expression of BnGPAT9 genes among different rapeseed varieties. We confirmed that BnGPAT9-A01/C01 are highly conserved in rapeseed, with high expression levels in various tissues, especially during the late stages of silique development and seed maturation. All four BnGPAT9 genes (BnGPAT9-A01/C01/A10/C09) can promote seed oil accumulation, but BnGPAT9-A01/C01 have a greater effect. Overexpression in Arabidopsis and rapeseed increased seed oil content and altered fatty acid composition, significantly increasing linolenic acid content. Transcriptome analysis revealed that BnGPAT9 genes promote the upregulation of genes related to oil synthesis, particularly those in the Plant–pathogen interaction, alpha-Linolenic acid metabolism, MAPK signaling pathway—plant, and Glutathione metabolism pathways. In summary, these results indicate that the four BnGPAT9 genes in rapeseed have different expression patterns and roles in regulating seed oil accumulation, with BnGPAT9-A01/C01 contributing the most to promoting oil accumulation.