Genome-wide characterization of LEA gene family reveals a positive role of BnaA.LEA6.a in freezing tolerance in rapeseed (Brassica napus L.).

BACKGROUND: Freezing stress is one of the major abiotic stresses that causes extensive damage to plants. LEA (Late embryogenesis abundant) proteins play a crucial role in plant growth, development, and abiotic stress. However, there is limited research on the function of LEA genes in low-temperature stress in Brassica napus (rapeseed). RESULTS: Total 306 potential LEA genes were identified in B. rapa (79), B. oleracea (79) and B. napus (148) and divided into eight subgroups. LEA genes of the same subgroup had similar gene structures and predicted subcellular locations. Cis-regulatory elements analysis showed that the promoters of BnaLEA genes rich in cis-regulatory elements related to various abiotic stresses. Additionally, RNA-seq and real-time PCR results indicated that the majority of BnaLEA family members were highly expressed in senescent tissues of rapeseed, especially during late stages of seed maturation, and most BnaLEA genes can be induced by salt and osmotic stress. Interestingly, the BnaA.LEA6.a and BnaC.LEA6.a genes were highly expressed across different vegetative and reproductive organs during different development stages, and showed strong responses to salt, osmotic, and cold stress, particularly freezing stress. Further analysis showed that overexpression of BnaA.LEA6.a increased the freezing tolerance in rapeseed, as evidenced by lower relative electrical leakage and higher survival rates compared to the wild-type (WT) under freezing treatment. CONCLUSION: This study is of great significance for understanding the functions of BnaLEA genes in freezing tolerance in rapeseed and offers an ideal candidate gene (BnaA.LEA6.a) for molecular breeding of freezing-tolerant rapeseed cultivars.

Identification of environment-insensitive genes for oil content by combination of transcriptome and genome-wide association analysis in rapeseed.

BACKGROUND: The primary objective of rapeseed breeding is to enhance oil content, which is predominantly influenced by environmental factors. However, the molecular mechanisms underlying the impact of these environmental factors on oil accumulation remain inadequately elucidated. In this study, we used transcriptome data from two higher (HOC) and two lower oil content (LOC) inbred lines at 35 days after pollination (DAP) to investigate genes exhibiting stable expression across three different environments. Meanwhile, a genome-wide association study (GWAS) was utilized to detect candidate genes exhibiting significant associations with seed oil content across three distinct environments. RESULTS: The study found a total of 405 stable differentially expressed genes (DEGs), including 25 involved in lipid/fatty acid metabolism and 14 classified as transcription factors. Among these genes, BnBZIP10-A09, BnMYB61-A06, BnAPA1-A08, BnPAS2-A10, BnLCAT3-C05 and BnKASIII-C09 were also found to exhibit significant associations with oil content across multiple different environments based on GWAS of 50 re-sequenced semi-winter rapeseed inbred lines and previously reported intervals. Otherwise, we revealed the presence of additive effects among BnBZIP10-A09, BnKASIII-C09, BnPAS2-A10 and BnAPA1-A08, resulting in a significant increase in seed oil content. Meanwhile, the majority of these stable DEGs are interconnected either directly or indirectly through co-expression network analysis, thereby giving rise to an elaborate molecular network implicated in the potential regulation of seed oil accumulation and stability. CONCLUSIONS: The combination of transcription and GWAS revealed that natural variation in six environment-insensitive gene regions exhibited significant correlations with seed oil content phenotypes. These results provide important molecular marker information for us to further improve oil content accumulation and stability in rapeseed.

Transcriptome and Regional Association Analyses Reveal the Effects of Oleosin Genes on the Accumulation of Oil Content in Brassica napus.

Rapeseed stores lipids in the form of oil bodies. Oil bodies in the seeds of higher plants are surrounded by oleosins. Adjusting oleosin protein levels can prevent the fusion of oil bodies and maintain oil body size during seed development. However, oil contents are affected by many factors, and studies on the complex molecular regulatory mechanisms underlying the variations in seed oil contents of B. napus are limited. In this study, a total of 53 BnOLEO (B. napus oleosin) genes were identified in the genome of B. napus through a genome-wide analysis. The promoter sequences of oleosin genes consisted of various light-, hormone-, and stress-related cis-acting elements, along with transcription factor (TF) binding sites, for 25 TF families in 53 BnOLEO genes. The differentially expressed oleosin genes between two high- and two low-oil-content accessions were explored. BnOLEO3-C09, BnOLEO4-A02, BnOLEO4-A09, BnOLEO2-C04, BnOLEO1-C01, and BnOLEO7-A03 showed higher expressions in the high-oil-content accessions than in low-oil-content accessions, at 25, 35, and 45 days after pollination (DAP) in two different environments. A regional association analysis of 50 re-sequenced rapeseed accessions was used to further analyze these six BnOLEO genes, and it revealed that the nucleotide variations in the BnOLEO1-C01 and BnOLEO7-A03 gene regions were related to the phenotypic variations in seed oil content. Moreover, a co-expression network analysis revealed that the BnOLEO genes were directly linked to lipid/fatty acid metabolism, TF, lipid transport, and carbohydrate genes, thus forming a molecular network involved in seed oil accumulation. These favorable haplotypes can be utilized in molecular marker-assisted selection in order to further improve seed oil contents in rapeseed.

Promising Novel Method of Acetylation Modification for Regulating Fatty Acid Metabolism in Brassica napus L.

In this study, lysine acetylation analysis was conducted using two Brassica napus near-isogenic lines, HOCR and LOCR, containing high and low oleic acid contents, respectively, to explore this relationship. Proteins showing differences in quantitative information between the B. napus lines were identified in lysine acetylation analysis, and KEGG pathways were analyzed, yielding 45 enriched proteins, most of which are involved in carbon fixation in photosynthetic organisms, photosynthesis, ascorbate and aldarate metabolism, and glycolysis. Potential key genes related to fatty acid metabolisms were determined. To further explore the effect of acetylation modification on fatty acid metabolisms, the acyl-ACP3 related gene BnaACP363K was cloned, and a base mutation at No.63 was changed via overlapping primer PCR method. This study is the first to demonstrate that acetylation modification can regulate oleic acid metabolisms, which provides a promising approach for the study of the molecular mechanism of oleic acid in rapeseed.

Regional association and transcriptome analysis revealed candidate genes controlling plant height in Brassica napus.

Plant height is a key morphological trait in rapeseed, which not only plays an important role in determining plant architecture, but is also an important characteristic related to yield. Presently, the improvement of plant architecture is a major challenge in rapeseed breeding. This work was carried out to identify genetic loci related to plant height in rapeseed. In this study, a genome-wide association study (GWAS) of plant height was performed using a Brassica 60 K Illumina Infinium SNP array and 203 Brassica napus accessions. Eleven haplotypes containing important candidate genes were detected and significantly associated with plant height on chromosomes A02, A03, A05, A07, A08, C03, C06, and C09. Moreover, regional association analysis of 50 resequenced rapeseed inbred lines was used to further analyze these eleven haplotypes and revealed nucleotide variation in the BnFBR12-A08 and BnCCR1-C03 gene regions related to the phenotypic variation in plant height. Furthermore, coexpression network analysis showed that BnFBR12-A08 and BnCCR1-C03 were directly connected with hormone genes and transcription factors and formed a potential network regulating the plant height of rapeseed. Our results will aid in the development of haplotype functional markers to further improve plant height in rapeseed. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-022-01337-1.

Genomic insights into the origin, domestication and diversification of Brassica juncea.

Despite early domestication around 3000 BC, the evolutionary history of the ancient allotetraploid species Brassica juncea (L.) Czern & Coss remains uncertain. Here, we report a chromosome-scale de novo assembly of a yellow-seeded B. juncea genome by integrating long-read and short-read sequencing, optical mapping and Hi-C technologies. Nuclear and organelle phylogenies of 480 accessions worldwide supported that B. juncea is most likely a single origin in West Asia, 8,000-14,000 years ago, via natural interspecific hybridization. Subsequently, new crop types evolved through spontaneous gene mutations and introgressions along three independent routes of eastward expansion. Selective sweeps, genome-wide trait associations and tissue-specific RNA-sequencing analysis shed light on the domestication history of flowering time and seed weight, and on human selection for morphological diversification in this versatile species. Our data provide a comprehensive insight into the origin and domestication and a foundation for genomics-based breeding of B. juncea.

Integrative analysis of GWAS and transcriptome to reveal novel loci regulation flowering time in semi-winter rapeseed.

Flowering is an important turning point from vegetative growth to reproductive growth, and vernalization is an essential condition for the flowering of annual winter plants. To investigate the genetic architecture of flowering time in rapeseed, we used the 60 K Brassica Infinium SNP array to perform a genome-wide analysis of haplotype blocks associated with flowering time in 203 Chinese semi-winter rapeseed inbred lines. Twenty-one haplotype regions carrying one or more candidate genes showed a significant association with flowering time. Interestingly, we detected a SNP (Bn-scaff_22728_1-p285715) located in exon 3 of the BnVIN3-C03 gene that showed a significant association with flowering time on chromosome C03. Based on the SNP alleles A and G, two groups of accessions with early and late flowering time phenotypes were selected, respectively, and PCR amplification and gene expression analysis were combined to reveal the structural variation of the BnVIN3-C03 gene that affected flowering time. Moreover, we found that BnVIN3-C03 inhibited the expression of BnFLC-A02, BnFLC-A03.1, BnFLC-A10 and BnFLC-C03.1, thus modulating the flowering time of Brassica napus. This result provides insight into the genetic improvement of flowering time in B. napus.

Insights into the mechanism of multi-walled carbon nanotubes phytotoxicity in Arabidopsis through transcriptome and m6A methylome analysis.

With the increasing production and wide application of carbon nanotubes (CNTs), they are inevitably released into the natural environment and ecosystems, where plants are the main primary producers. Hence, it is imperative to understand the toxic effects of CNTs on plants. The molecular mechanisms underlying the toxic effects of CNTs on plants are still unclear. Therefore, in the present study, we investigated the effects of high concentrations of multi-walled CNTs (MWCNTs) on Arabidopsis. Root elongation and leaf development were severely inhibited after MWCNT exposure. Excess production of H2O2, O2-, and malondialdehyde was observed, indicating that MWCNTs induced oxidative stress. The antioxidant system was activated to counter MWCNTs-induced oxidative stress. Combinatorial transcriptome and m6A methylome analysis revealed that MWCNTs suppressed auxin signaling and photosynthesis. Reactive oxygen species metabolism, toxin metabolism, and plant responses to pathogens were enhanced to cope with the phytotoxicity of MWCNTs. Our results provide new insights into the molecular mechanisms of CNT phytotoxicity and plant defense responses to CNTs.

Regional association analysis coupled with transcriptome analyses reveal candidate genes affecting seed oil accumulation in Brassica napus.

KEY MESSAGE: Regional association analysis of 50 re-sequenced Chinese semi-winter rapeseed accessions in combination with co-expression analysis reveal candidate genes affecting oil accumulation in Brassica napus. One of the breeding goals in rapeseed production is to enhance the seed oil content to cater to the increased demand for vegetable oils due to a growing global population. To investigate the genetic basis of variation in seed oil content, we used 60 K Brassica Infinium SNP array along with phenotype data of 203 Chinese semi-winter rapeseed accessions to perform a genome-wide analysis of haplotype blocks associated with the oil content. Nine haplotype regions harbouring lipid synthesis/transport-, carbohydrate metabolism- and photosynthesis-related genes were identified as significantly associated with the oil content and were mapped to chromosomes A02, A04, A05, A07, C03, C04, C05, C08 and C09, respectively. Regional association analysis of 50 re-sequenced Chinese semi-winter rapeseed accessions combined with transcriptome datasets from 13 accessions was further performed on these nine haplotype regions. This revealed natural variation in the BnTGD3-A02 and BnSSE1-A05 gene regions correlated with the phenotypic variation of the oil content within the A02 and A04 chromosome haplotype regions, respectively. Moreover, co-expression network analysis revealed that BnTGD3-A02 and BnSSE1-A05 were directly linked with fatty acid beta-oxidation-related gene BnKAT2-C04, thus forming a molecular network involved in the potential regulation of seed oil accumulation. The results of this study could be used to combine favourable haplotype alleles for further improvement of the seed oil content in rapeseed.