Abstract
GPAT, the rate-limiting enzyme in triacylglycerol (TAG) synthesis, plays an important role in seed oil accumulation. In this study, two AhGPAT9 genes were individually cloned from the A- and B- genomes of peanut, which shared a similarity of 95.65%, with 165 site differences. The overexpression of AhGPAT9 or the knock-down of its gene expression increased or decreased the seed oil content, respectively. Allelic polymorphism analysis was conducted in 171 peanut germplasm, and 118 polymorphic sites in AhGPAT9A formed 64 haplotypes (a1 to a64), while 94 polymorphic sites in AhGPAT9B formed 75 haplotypes (b1 to b75). The haplotype analysis showed that a5, b57, b30 and b35 were elite haplotypes related to high oil content, whereas a7, a14, a48, b51 and b54 were low oil content types. Additionally, haplotype combinations a62/b10, a38/b31 and a43/b36 were associated with high oil content, but a9/b42 was a low oil content haplotype combination. The results will provide valuable clues for breeding new lines with higher seed oil content using hybrid polymerization of high-oil alleles of AhGPAT9A and AhGPAT9B genes.
Highlights
Plant lipids, including glycerolipids, membrane lipids, signaling molecules, photosynthetic pigments, plant hormones and plant surface protective substances, play important roles in plant growth, development and stress responses
Secondary structure prediction showed that AhGPAT9A consisted of 46.01% α helices, 15.96% extended strands, 3.72% β turns and 34.31% random coils, while AhGPAT9B consisted of 43.35% α helices, 17.82% extended strands, 3.46% β turns and 35.37% random coils
Four conserved acyltransferase domains were identified in AhGPAT9, which are important for acyltransferase activity (Fig. 1B)
Summary
Plant lipids, including glycerolipids, membrane lipids, signaling molecules, photosynthetic pigments, plant hormones and plant surface protective substances, play important roles in plant growth, development and stress responses. GPAT9 is responsible for the first step of TAG synthesis, in which a fatty acid is transferred from acyl-CoA to the sn-1 site of glycerol-3-phosphate (G3P), forming lysophosphatidic acids (LPA)[8,9,10,11,12,13]. Studies have shown that GPAT9 exhibits no phosphatase activity and that the majority of the acylation reactions catalyzed by this enzyme take place at the sn-1 position rather than the sn-2 position (5.3:1 ratio)[21]. GPAT9 is a membrane binding protein located in the ER; that exhibits sn-1 acyltransferase activity with a preference for acyl-CoA as its substrate, shares high homology with mGPAT3 and mGPAT4, which are related to animal fat synthesis, and it plays an important role in the synthesis of plant membrane lipids and storage lipids[21,22]. GPAT9 is responsible for the biosynthesis of TAG and plant membrane lipids in plants
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