3D genome structural variations play important roles in regulating seed oil content of Brassica napus.

Dissecting the complex regulatory mechanism of seed oil content (SOC) is one of the main research goals in Brassica napus. Increasing evidence suggests that genome architecture is linked to multiple biological functions. However, the effect of genome architecture on SOC regulation remains unclear. Here, we used high-throughput chromatin conformation capture to characterize differences in the three-dimensional (3D) landscape of genome architecture of seeds from two B. napus lines, N53-2 (with high SOC) and Ken-C8 (with low SOC). Bioinformatics analysis demonstrated that differentially accessible regions and differentially expressed genes between N53-2 and Ken-C8 were preferentially enriched in regions with quantitative trait loci (QTLs)/associated genomic regions (AGRs) for SOC. A multi-omics analysis demonstrated that expression of SOC-related genes was tightly correlated with genome structural variations in QTLs/AGRs of B. napus. The candidate gene BnaA09g48250D, which showed structural variation in a QTL/AGR on chrA09, was identified by fine-mapping of a KN double-haploid population derived from hybridization of N53-2 and Ken-C8. Overexpression and knockout of BnaA09g48250D led to significant increases and decreases in SOC, respectively, in the transgenic lines. Taken together, our results reveal the 3D genome architecture of B. napus seeds and the roles of genome structural variations in SOC regulation, enriching our understanding of the molecular mechanisms of SOC regulation from the perspective of spatial chromatin structure.

Class A lysophosphatidic acid acyltransferase 2 from Camelina sativa promotes very long-chain fatty acids accumulation in phospholipid and triacylglycerol.

Very long-chain fatty acids (VLCFAs) are important industrial raw materials and can be produced by genetically modified oil plants. For a long time, class A lysophosphatidic acid acyltransferase (LPAT) was considered unable to promote the accumulation of VLCFA in oil crops. The bottlenecks that the transgenic high VLCFA lines have an oil content penalty and the low amount of VLCFA in phosphatidylcholine remains intractable. In the present study, a class A LPAT2 from Camelina sativa (CsaLPAT2) promoting VLCFAs accumulation in phospholipid was found. Overexpression of CsaLPAT2 alone in Arabidopsis seeds significantly increased the VLCFA content in triacylglycerol, including C20:0, C20:2, C20:3, C22:0, and C22:1. The proportion of phosphatidic acid molecules containing VLCFAs in transgenic seeds reached up to 45%, which was 2.8-fold greater than that in wild type. The proportion of phosphatidylcholine and diacylglycerol molecules containing VLCFAs also increased significantly. Seed size in CsaLPAT2 transgenic lines showed a slight increase without an oil content penalty. The total phospholipid content in the seed of the CsaLPAT2 transgenic line was significantly increased. Furthermore, the function of class A LPAT in promoting the accumulation of VLCFAs is conserved in the representative oil crops of Brassicaceae, such as C. sativa, Arabidopsis thaliana, Brassica napus, Brassica rapa, and Brassica oleracea. The findings of this study provide a promising gene resource for the production of VLCFAs.

In Silico Analysis of Fatty Acid Desaturases Structures in Camelina sativa, and Functional Evaluation of Csafad7 and Csafad8 on Seed Oil Formation and Seed Morphology.

Fatty acid desaturases add a second bond into a single bond of carbon atoms in fatty acid chains, resulting in an unsaturated bond between the two carbons. They are classified into soluble and membrane-bound desaturases, according to their structure, subcellular location, and function. The orthologous genes in Camelina sativa were identified and analyzed, and a total of 62 desaturase genes were identified. It was revealed that they had the common fatty acid desaturase domain, which has evolved separately, and the proteins of the same family also originated from the same ancestry. A mix of conserved, gained, or lost intron structure was obvious. Besides, conserved histidine motifs were found in each family, and transmembrane domains were exclusively revealed in the membrane-bound desaturases. The expression profile analysis of C. sativa desaturases revealed an increase in young leaves, seeds, and flowers. C. sativa ω3-fatty acid desaturases CsaFAD7 and CsaDAF8 were cloned and the subcellular localization analysis showed their location in the chloroplast. They were transferred into Arabidopsis thaliana to obtain transgenic lines. It was revealed that the ω3-fatty acid desaturase could increase the C18:3 level at the expense of C18:2, but decreases in oil content and seed weight, and wrinkled phenotypes were observed in transgenic CsaFAD7 lines, while no significant change was observed in transgenic CsaFAD8 lines in comparison to the wild-type. These findings gave insights into the characteristics of desaturase genes, which could provide an excellent basis for further investigation for C. sativa improvement, and overexpression of ω3-fatty acid desaturases in seeds could be useful in genetic engineering strategies, which are aimed at modifying the fatty acid composition of seed oil.