Comparative Transcriptomics Uncovers Upstream Factors Regulating BnFAD3 Expression and Affecting Linolenic Acid Biosynthesis in Yellow-Seeded Rapeseed (Brassica napus L.).

α-Linolenic acid (ALA) is an important nutrient component in rapeseed oil, and rapeseed breeders want to either restrain or enhance the function of fatty acid desaturases (FADs) in the ALA biosynthesis pathway. To determine the reason for the upregulation of rapeseed BnFAD genes in two high-ALA accessions, R8Q10 and YH25005, we compared their transcriptome profiles in the seed at 24 days after pollination (DAP) with those of two low-ALA lines, A28 and SW. The expression levels of twenty-eight important genes in the seed samples at 20, 27, and 34 DAP were also investigated using an RT-qPCR. The expression levels of genes involved in flavonoid and proanthocyanidin synthesis, including BnCHS, BnCHI, BnDFR, BnFLS1, BnLDOX, BnBAN, BnTT10, and BnTT12 and genes encoding the transcription factors BnTT1, BnTT2, BnTT8, and BnTT16 were lower in R8Q10 and YH25005 than in A28 and SW. The expression levels of genes encoding master transcription factors in embryo development, such as BnLEC1, BnABI3, BnFUS3, BnL1L, BnAREB3, and BnbZIP67, were elevated significantly in the two high-ALA accessions. Combined with previous results in the Arabidopsis and rapeseed literature, we speculated that the yellow-seededness genes could elevate the activity of BnLEC1, BnABI3, BnFUS3, and BnbZIP67, etc., by reducing the expression levels of several transparent testa homologs, resulting in BnFAD3 and BnFAD7 upregulation and the acceleration of ALA synthesis. Yellow-seededness is a favorable factor to promote ALA synthesis in the two high-ALA accessions with the yellow-seeded trait. These findings provide initial insights into the transcriptomic differences between high-/low-ALA germplasms and a theoretic basis for seed quality breeding.

Microscopic and Transcriptomic Comparison of Powdery Mildew Resistance in the Progenies of Brassica carinata × B. napus.

Powdery mildew is a widespread disease in rapeseed due to a lack of resistant germplasm. We compared the foliar epidermal features and transcriptomic responses between the resistant (R) and susceptible (S) plants among the two parents and progenies of Brassica carinata × B. napus. The amount of cuticular wax and callose deposition on the R plants was much lower than that on the S plants; hence, these chemicals are not all essential to pre-penetration resistance, although the cuticular wax on the R plants had more needle-like crystals. A total of 1049 genes involved in various defense responses were expressed differentially among the R/S plants. The expression levels of two well-known susceptibility genes, MLO6 and MLO12, were much lower in the R plant, indicating an important role in PM resistance. A set of genes related to wax biosynthesis (KCS6, LACS2, CER and MAH1), cell wall modification (PMR5, PMEI9, RWA2, PDCB1 and C/VIF2), chloroplast function (Chlorophyllase-1, OEP161, PSBO1, CP29B and CSP41b), receptor kinase activity (ERECTA, BAK1, BAM2, LYM1, LYM3, RLK902, RLP11, ERL1 and ERL2), IPCS2, GF14 lambda, RPS4 and RPS6 were highly expressed in the R plants. In the S plants, most highly expressed genes were involved in later defense responses, including CERK1, LYK4, LIK1, NIMIN-1, CHITINASE 10, PECTINESTERASE, CYP81F2 and RBOHF and the genes involved in salicylic acid-dependent systemic acquired resistance and hypersensitive responses, indicating the occurrence of severe fungal infection. The results indicate that some uncertain pre-penetration defenses are pivotal for high resistance, while post-penetration defenses are more important for the S plant survival.