Landscape of Sequence Variations in Homologous Copies of FAD2 and FAD3 in Rapeseed(Brassica napus L.)Germplasm with High/Low Linolenic Acid Trait

Genetic manipulation(either restraint or enhancement)of the biosynthesis pathway ofα-linolenic acid(ALA)in seed oil is an important goal in Brassica napus breeding.B.napus is a tetraploid plant whose genome often har-bors four and six homologous copies,respectively,of the two fatty acid desaturases FAD2 and FAD3,which con-trol the last two steps of ALA biosynthesis during seed oil accumulation.In this study,we compared their promoters,coding sequences,and expression levels in three high-ALA inbred lines 2006L,R8Q10,and YH25005,a low-ALA line A28,a low-ALA/high-oleic-acid accession SW,and the wildtype ZS11.The expression levels of most FAD2 and FAD3 homologs in the three high-ALA accessions were higher than those in ZS11 and much higher than those in A28 and SW.The three high-ALA accessions shared similar sequences with the pro-moters and CDSs of BnFAD3.C4 and BnFAD3.A3.In A28 and SW,substitution of three amino acid residues in BnFAD2.A5 and BnFAD2.C5,an absence of BnFAD2.C1 locus,and a 549 bp long deletion on the BnFAD3.A3 promoter were detected.The profile of BnFAD2 mutation in the two low-ALA accessions A28 and SW is different from that reported in previous studies.The mutations in BnFAD3 in the high-ALA accessions are reported for thefirst time.In identifying the sites of these mutations,we provide detailed information to aid the design of mole-cular markers for accelerated breeding schemes.

BnaC03.BIN2 regulates plant height by affecting the main inflorescence length and first effective branch height in Brassica napus L.

Rapeseed(Brassica napus L.)is one of the main oil crops in the world,and increasing its yield is of great significance for ensuring the safety of edible oil.Presently,improving rapeseed plant architecture is an effective way to increase rapeseed yield with higher planting density.However,the regulatory mechanism of rapeseed plant architecture is poorly understood.In this study,a dwarf rapeseed mutant dwarf08(df08)is obtained by ethyl methane sulfonate(EMS)-mutagenesis.The decrease in plant height of df08 is mainly caused by the reduction in main inflorescence length and first effective branch height and controlled by a single semi-dominant gene.The hybrid plants(F1)show a semi-dwarf phenotype.Through map-based cloning and transgenic assay,we confirm that the nonsynonymous single nucleotide variant(SNV)(C to T)in BnaC03.BIN2,which is homologous with Arabidopsis(Arabidopsis thaliana)BIN2,is responsible for the dwarfism of df08.BnaC03.BIN2 interacts with BnaBZR1/BES1 and involves in brassinosteroids(BRs)signal transduction.Proline to Leucine substitution in 284(P284L)enhances the protein stability of BnaC03.bin2-D,disrupts BRs signal transduction and affects the expression of genes regulating cell division,leading to dwarfism of df08.This study provides a new insight for the mechanism of rapeseed plant height regulation and creates an elite germplasm that can be used for genetic improvement of rapeseed architecture.

Heterogeneous expression of stearoyl-acyl carrier protein desaturase genes SAD1 and SAD2 from Linum usitatissimum enhances seed oleic acid accumulation and seedling cold and drought tolerance in Brassica napus

Flax(Linum usitatissimum L.)is a versatile crop and its seeds are a major source of unsaturated fatty acids.Stearoyl-acyl carrier protein desaturase(SAD)is a dehydrogenase enzyme that plays a key role in oleic acid biosynthesis as well as responses to biotic and abiotic stresses.However,the function of SAD orthologs from L.usitatissimum has not been assessed.Here,we found that two LuSAD genes,LuSAD1 and LuSAD2,are present in the genome of L.usitatissimum cultivar‘Longya 10’.Heterogeneous expression of either LuSAD1 or LuSAD2 in Arabidopsis thaliana resulted in higher contents of total fatty acids and oleic acid in the seeds.Interestingly,ectopic expression of LuSAD2 in A.thaliana caused altered plant architecture.Similarly,the overexpression of either LuSAD1 or LuSAD2 in Brassica napus also resulted in increased contents of total fatty acids and oleic acid in the seeds.Furthermore,we demonstrated that either LuSAD1 or LuSAD2 enhances seedling resistance to cold and drought stresses by improving antioxidant enzyme activity and nonenzymatic antioxidant levels,as well as reducing membrane damage.These findings not only broaden our knowledge of the LuSAD functions in plants,but also offer promising targets for improving the quantity and quality of oil,and the abiotic stress tolerance of oil-producing crops,through molecular manipulation.

BnaWRKY75 positively regulates the resistance against Sclerotinia sclerotiorum in ornamental Brassica napus

With the development of tourism at home and abroad,Rapeseed(Brassica napus)has become an important ornamental plant.However,its ornamental value at the inflorescence stage is greatly reduced by Sclerotinia sclerotiorum.Identification of important genes in the defense responses is critical for molecular breeding,which is an important strategy for controlling the disease.In this study,we isolated a B.napus WRKY transcription factor gene,BnaWRKY75.BnaWRKY75 was found to encode a nucleus-localized protein and exhibited relatively high expression in the stems.Arabidopsis thaliana transgenic plants expressing BnaWRKY75 showed enhanced resistance to S.sclerotiorum,and both ProBnaWRKY75:GUS and gene expression analyses showed that BnaWRKY75 was highly responsive to S.sclerotiorum infection,indicating the involvement of BnaWRKY75 in response to this infection.Furthermore,overexpression(OE)of BnaWRKY75 in B.napus significantly enhanced the resistance to S.sclerotiorum,whereas the resistance was reduced in RNAi transgenic B.napus plants.Moreover,the BnaWRKY75-OE B.napus plants exhibited constitutive activation of salicylic acid-,jasmonic acid-,and ethylene-mediated defense responses and the inhibition of both H_(2)O_(2)and O_(2)·^(-)accumulation in response to this pathogen.By contrast,BnaWRKY75-RNAi plants showed a reverse pattern,suggesting that BnaWRKY75 is involved in hormonal signaling pathways and in the control of reactive oxygen species accumulation.In conclusion,these data indicate that BnaWRKY75,a regulator of multiple defense responses,positively regulates resistance against S.sclerotiorum,which may guide the improvement of resistance in rapeseed.

Knock-out of BnHva22c reduces the susceptibility of Brassica napus to infection with the fungal pathogen Verticillium longisporum

Verticillium longisporum(Vl43)is a soilborne hemibiotrophic fungal pathogen causing stem striping on oilseed rape(OSR)and severe yield losses.Breeding for resistant varieties is the most promising approach to control this disease.Here,we report the identification of Hva22c as a novel susceptibility factor and its potential for improving OSR resistance.Hva22c is a member of the Hva22 gene family,originally described for barley(Hordeum vulgare).Several Hva22 members have been located at the endoplasmic reticulum.Hva22c is up-regulated in response to Vl43 in both Arabidopsis and OSR.We demonstrate that knock-out of Hva22c in OSR by CRISPR/Cas9 and its homolog in Arabidopsis by T-DNA insertion reduced plants’susceptibility to Vl43 infection and impaired the development of disease symptoms.To understand the underlying mechanism,we analysed transcriptomic data from infected and non-infected roots of hva22c knock-out and wild type plants.We identified a homozygous mutant with frame-shifts in all four BnHva22c loci displaying a vastly altered transcriptional landscape at 6 dpi.Significantly,a large set of genes was suppressed under mock conditions including genes related to the endomembrane systems.Among the up-regulated genes we found several defense-related and phytohormone-responsive genes when comparing mutant to the wild type.These results demonstrate that Hva22c is functionally required for a fully compatible plant-fungus interaction.Its loss of function reduces plant susceptibility,most likely due to endoplasmatic reticulum and Golgi dysfunction accompanied by additionally activated defense responses.These findings can help improve OSR resistance to V.longisporum infection.

The influence of Lactobacillus plantarum fermentation in selenium-enriched Brassica napus L.:changes in the nutritional constituents,bioactivities and bioaccessibility

Selenium(Se)-enriched Brassica napus L.is a valuable organic Se supplement.In this study,the fermentation broth enriched with organic Se(FFS)was prepared using Lactobacillus plantarum to ferment the substrate of Se-enriched Brassica napus L.Significant increases were observed after fermentation in total sugars,reducing sugars,soluble proteins,total phenolic content(TPC),and total flavonoid content(TFC).The organic Se was retained at a concentration of 54.75 mg/g in the freeze-dried sample.Principal component analysis and cluster analysis showed good separation between the FFS and unfermented(FS)groups.Fragrant 2-ethyloxetane had the highest content among all volatiles,while sinapine had the highest content among all phenolic compounds.The fermentation process showed remarkable improvement in the abundance and concentration of volatile compounds and phenolic contents,making FFS exhibit strong antioxidant activity and inhibitory capacity againstα-glucosidase activity.The bioaccessibility of phenolic compounds was significantly greater in FFS compared to FS.ADMET analysis revealed that the majority of phenolic compounds contained in FFS did not exhibit mutagenicity toxicity,hepatotoxicity,skin sensitization,or blood-brain barrier penetration,indicating a favorable level of biosafety.Overall,our study provides a new insight into the further utilization of Se-enriched Brassica napus L.in foods.

Genome-wide and transcriptome-wide identification of the APX gene family in rapeseed (Brassica napus L.) and their expression features under low temperature stress

Ascorbate peroxidase(APX)is a crucial H2O2 scavenger that utilizes ascorbic acid as an electron donor and plays a significant role in plant stress resistance.This study aims to identify and characterize the Brassica napus L.APX gene family through genome and transcriptome sequencing,while also revealing their expression profile under low-temperature stress via transcriptome and proteome analysis.The results indicate the presence of 18 genes with three different conserved domains distributed in Brassica napus L.,which can be classified into three major branches based on phylogenetic analysis.Eleven members were predicted to have the low-temperature response component(LTR).Most APX genes exhibit up-regulated transcriptional expression under low temperature stress,particularly APX2,APX4,APX12,and APX18.In terms of proteomics data,only six members(APX2,APX4,APX8,APX12,APX17,and APX18)showed temporal specificity in their expression patterns.Therefore,this study provides valuable insights into the complexity of the APX family in the functional characterization of its genes for future research.

Dissecting the genetic architecture of glucosinolate compounds for quality improvement in flowering stalk tissues of Brassica napus

Glucosinolates(GSLs) and their hydrolytic products contribute to the quality traits of rapeseed flowering stalk tissues, such as taste, flavor and anticarcinogenic properties(Glucoraphanin). However, little is known about the genetic mechanisms of GSL accumulation in rapeseed flowering stalks. In this study, the variation and genetic architecture of GSL metabolites in flowering stalk tissues were investigated for the first time among a panel of 107 accessions. All GSL compounds exhibited continuous and wide variations in the present population. Progoitrin,glucobrassicanapin and gluconapin were the most abundant GSL compounds. Five quantitative trait loci(QTL) significantly associated with three GSL compounds were identified by genome-wide association study. GRA_C04 was under selected during modern breeding, in which the ratio of lower GSL haplotype(HAP2) in the accessions bred before 1990(52.56%) was significantly lower than that after 1990(78.95%). Four candidate genes, BnaA01. SOT16, BnaA06. SOT17, Bna A06. MYB51a, and Bna A06. MYB51b, were identified in the GTL_A01 and 4OH_A06 regions.These findings provide new insights into GSL biosynthesis in flowering stalk tissues and facilitate quality improvement in rapeseed flowering stalks.

耐渍甘蓝型油菜(Brassica napus)种质筛选与评价

长江流域为中国油菜主产区,生产上频发的渍害已成为影响当地直播油菜成苗的主要障碍。为筛选耐渍材料,对26份优质油菜品种及104个自交系进行渍性鉴定。建立稳定的砂培、淹水、排水培养鉴定方法,根据结果将植物材料划分耐渍等级,并选取高抗、敏感材料进行生理特征比较。鉴定结果表明,试验材料活苗率总体在50%以上,主要集中在60%~90%。渍水处理后,材料间反应分化较为明显,表明受试油菜材料普遍具有对渍害的一般耐受性,在耐渍性上存在丰富的遗传变异。‘阳光2009’耐渍性优异,而高油品种‘中双11’‘浙油50’等耐渍性并不十分突出,这对于直播油菜育种而言不是很有利的因素。Ning1038、ZS11carinata、D-yellow、Arm-Z11、FuC、Z18782、11293AF、Arm11等自交系耐渍性较强,对渍害极为敏感的材料有Jade、D615、Z532AF等。生理特征比较结果表明,渍害发生后,材料间的耐渍性差异在一定程度上与根系活力和抗氧化酶SOD、POD、CAT活性有关。结果为后续油菜耐渍定向改良,培育耐渍高产油菜品种提供参考依据。

BnaUBP15s positively regulates seed size and seed weight in Brassica napus

Brassica napus(B.napus)is a globally significant oilseed crop,making a substantial contribution to both human oil and livestock feed production.Enhancing seed weight is crucial for improving rapeseed yield;however,only a limited number of seed weight-related genes have been functionally validated in B.napus thus far.UBIQUITINSPECIFIC PROTEASE 15(UBP15)belongs to the ubiquitin protease pathway and plays a maternal role in prolonging seed development in Arabidopsis.The potential utilization of UBP15 for enhancing seed yield in B.napus has remained unexplored until now.In this study,we identified the orthologs of UBP15 in B.napus and investigated its functionality using the CRISPR-Cas9 system.We generated mutant plants with multiple editing types targeting Bnaubp15s and successfully isolated T-DNA-free homozygous mutant lines that exhibited edits across four homologs of BnaUBP15 in T2 generation plants.Our preliminary data demonstrated that mutation of BnaUBP15s significantly reduced seed size,seed weight,and plant height while noticeably increasing the number of primary branches.These findings not only provide crucial evidence for further elucidating the molecular mechanism underlying the regulation of seed weight and size by BnaUBP15s but also offer promising novel germplasm for enhancing plant architecture.

First report of Leptosphaeria sclerotioides on Brassica napus in Northwestern China

In 2020,diseased seedlings of winter oilseed rape(Brassica napus)with cankered taproots as well as abundant sclerotium-like structures in the soil surrounding the roots were found in Longxi County of Gansu province of northwestern China.A fungus with production of pycnidia was isolated from the diseased roots,and it was identified based on morphological characteristics,molecular phylogeny(ITS,LSU)and PCR detection with the specific primers.The fungus was identified as Leptosphaeria sclerotioides Gruyter,Aveskamp&Verkley[anamorph:Phoma sclerotioides(Preuss)ex Sacc.].Re-inoculation of isolates of P9 and P10 of L.sclerotioides on winter oilseed rape(B.napus cultivar‘Zhongshuang No.9’)in Wuhan caused formation of abundant sclerotium-like structures in soil surrounding the roots,but failed to produce root cankers as those observed in Gansu possibly due to lack of long peroid of low-temperature conditioning in Wuhan.In spite of this,plant height,pod number and seed yield of oilseed rape were significantly reduced in the treatment with L.sclerotioides P9 and P10,compared to the control treatment.To the best of our knowledge,this is the first report of L.sclerotioides on B.napus in China and the finding broadened our understanding about the natural distribution of this psychrophilic fungus.

Physiological and molecular responses to cold stress in rapeseed(Brassica napus L.)

Low temperature is one of the most important abiotic factors inhibiting growth, productivity, and distribution of rapeseed(Brassica napus L.). Therefore, it is important to identify and cultivate cold-tolerant germplasm. The objective of this study was to figure out the mechanism of chilling(4 and 2°C) and freezing(–2 and –4°C) stresses along with a control(22°C) in B. napus cultivars(1801 and C20) under controlled environment(growth chamber). The experiment was arranged in a complete randomized design with three replications. Our results exhibited that under chilling and freezing stresses, the increment of proline accumulation, soluble sugar and protein contents, and antioxidant enzyme activity were enhanced more in 1801 cultivar compared with C20 cultivar. At –2 and –4°C, the seedlings of C20 cultivar died completely compared with 1801 cultivar. Hydrogen peroxide(H2 O2) and malondialdehyde contents(MDA) increased in both cultivars, but when the temperature was decreased up to –2 and –4°C, the MDA and H2 O2 contents continuously dropped in 1801 cultivar. Moreover, we found that leaf abscisic acid(ABA) was enhanced in 1801 cultivar under chilling and freezing stresses. Additionally, the transcriptional regulations of cold-tolerant genes(COLD1, CBF4, COR6.6, COR15, and COR25) were also determined using real-time quantitative PCR(RT-q PCR). RT-q PCR showed that higher expression of these genes were found in 1801 as compared to C20 under cold stress(chilling and freezing stresses). Therefore, it is concluded from this experiment that 1801 cultivar has a higher ability to respond to cold stress(chilling and freezing stresses) by maintaining hormonal, antioxidative, and osmotic activity along with gene transcription process than C20. The result of this study will provide a solid foundation for understanding physiological and molecular mechanisms of cold stress signaling in rapeseed(B. napus).

Abortive Process of a Novel Rapeseed Cytoplasmic Male Sterility Line Derived from Somatic Hybrids Between Brassica napus and Sinapis alba

Somatic hybridization is performed to obtain significant cytoplasmic male sterility （CMS） lines, whose CMS genes are derived either from the transfer of sterile genes from the mitochondrial genome of donor parent to the counterpart of receptor or production of new sterile genes caused by mitochondrial genome recombination of the biparent during protoplast fusion. In this study, a novel male sterile line, SaNa-IA, was obtained from the somatic hybridization between Brassica napus and Sinapis alba. The normal anther development of the maintainer line, SaNa-IB, and the abortive process of SaNa-IA were described through phenotypic observations and microtome sections. The floral organ of the sterile line SaNa-IA was sterile with a shortened filament and deflated anther. No detectable pollen grains were found on the surface of the sterile anthers. Semi-thin sections indicated that SaNa-IA aborted in the pollen mother cell （PMC） stage when vacuolization of the tapetum and PMCs began. The tapetum radically elongated and became highly vacuolated, occupying the entire locule together with the vacuolated microspores. Therefore, SaNa-IA is different from other CMS lines, such as ogu CMS, pol CMS and nap CMS as shown by the abortive process of the anther.

Molecular evidence for blocking erucic acid synthesis in rapeseed(Brassica napus L.) by a two-base-pair deletion in FAE1(fatty acid elongase 1)

DNA sequences of fatty acid elongase 1 genes FAE1.1 （EA） and FAE1.2 （Ec） were isolated and characterized for 30 com- mercialized low erucic acid rapeseed （LEAR） cultivars in China. Four types of independent mutation leading to low erucic acid trait were found, i.e., a single-base transition （eAl）, a two-base deletion （ec2） and four-base deletion （eC4） as well as single-base transition with a four-base deletion （eA.）. Three genotypes, i.e., eA1eA1eC2eC2, eA1eA1eC4eC4 and eA.eA.ec4ec4 were responsible for LEA content in storage Iipids of different rapeseed cultivars. Most of the LEAR cultivars had a genotype of eA1eA1ec2ec2, which were descended from the first LEAR cultivar, Oro. Yeast expression analysis revealed that two-base-pair （AA） deletion （ec2） at the base sites of 1 422-1 423 in the C genome FAE1 gene resulted in the absence of the condensing enzyme and led to the failure to produce erucic acid. Coexpression of FAE1 and ketoacyI-CoA reductase （KCR） or enoyI-CoA reductase （ECR） was found in high erucic acid rapeseed （HEAR） but not in LEAR （eA1eA1ec2ec2oreA1eA1ec4ec4）. Moreover, KCR and ECR were still coordinately regulated in eA1eA1ec2ec2 or eA1eA1ec4ec4 genotypes, suggesting that the expression of two genes was tightly linked. In addition, specific detection methods were developed by high-resolution melting curve analysis in order to detect eA1 and ec4.

Genetic Diversity of Chinese and Swedish Rapeseed (Brassica napus L.) Analyzed by Inter-Simple Sequence Repeats (ISSRs)

We have compared genetic diversity of 24 Chinese weak-winter, Swedish winter and spring B. napus accessions by inter-simple sequence repeats (ISSRs). By cluster analysis (UPGMA) based on 125 polymorphism bands amplified with 20 primers, the 24 accessions were divided into three groups. Six Swedish winter lines and eight Chinese weak-winter lines were in the group I and the groupⅡwere two Chinese weak-winter lines XiangyoulS and Bao81. The third group contained eight Swedish spring lines. Principal co-ordinates analysis (PCO) showed similar groupings to cluster analysis. Results from cluster analysis and PCO analysis showed very clearly that Chinese weak-winter, Swedish spring and winter accessions were distinguished from each other and Chinese weak-winter accessions in this study were genetically closer to Swedish winter accessions than to Swedish spring accessions. The Chinese weak-winter accessions had larger diversity than Swedish spring or winter accessions did. This study indicated that ISSR is a suitable and effective tool to evaluate genetic diversity among rapeseed germplasm.

Exogenous application of a low concentration of melatonin enhances salt tolerance in rapeseed(Brassica napus L.) seedlings

Melatonin is a naturally occurring compound in plants. Here, we tested the effect of exogenous melatonin on rapeseed（Brassica napus L.） grown under salt stress. Application of 30 μmol L^-1 melatonin alleviated salt-induced growth inhibition, and the shoot fresh weight, the shoot dry weight, the root fresh weight, and the root dry weight of seedlings treated with exogenous melatonin increased by 128.2, 142.9, 122.2, and 124.2%, respectively, compared to those under salt stress. In addition, several physiological parameters were evaluated. The activities of antioxidant enzymes including peroxidase（POD）, catalase（CAT） and ascorbate peroxidase（APX） were enhanced by 16.5, 19.3, and 14.2% compared to their activities in plants without exogenous melatonin application under salt stress, while the H2O2 content was decreased by 11.2% by exogenous melatonin. Furthermore, melatonin treatment promoted solute accumulation by increasing the contents of proline（26.8%）, soluble sugars（15.1%） and proteins（58.8%）. The results also suggested that higher concentrations（〉50 μmol L^-1） of melatonin could attenuate or even prevent the beneficial effects on seedling development. In conclusion, application of a low concentration of exogenous melatonin to rapeseed plants under salt stress can improve the H2O2-scavenging capacity by enhancing the activities of antioxidant enzymes such as POD, CAT and APX, and can also alleviate osmotic stress by promoting the accumulation of osmoregulatory substances such as soluble proteins, proline, and water soluble glucan. Ultimately, exogenous melatonin facilitates root development and improves the biomass of rapeseed seedlings grown under salt stress, thereby effectively alleviating the damage of salt stress in rapeseed seedlings.

Relationship Among Yield Components and Selection Criteria for Yield Improvement in Early Rapeseed (Brassica napus L.)

The objective of this study was to determine the relationship between seed yield and other important agronomic traits of early-maturing rapeseed as a rotation crop in a double-cropping rice area using Pearson＇s correlation coefficient as well as to estimate direct and indirect effects of specific yield component traits on seed yield via path analysis. Nineteen rapeseed genotypes were grown at ten environments in South China during 2008-2009 and 12 characters were evaluated. Analysis of variance showed that environment had a significant impact on all characters. For most characters the genotype by environment interaction was weak and not statistically significant. Simple correlation analysis indicated that the number of primary branches （PB）, number of pods on the main raceme （PR）, and number of seeds per pod made significant contributions to seed yield per plant （SYP）, while 1 000-seed weight was negatively correlated with SYP （r=-0.485, P0.05）. Furthermore, number of pods per plant （PP）, PB, and PR had the greatest direct effects on SYP. In addition, PP and PB were the best indicators to predict seed yield in stepwise regression analysis. Finally, yield component differences between early- and medium-maturity varieties were compared; this showed that to improve the seed yield of early varieties, more emphasis should be given to increase PP, PB, and PR, and reduce plant height and shortening of growth duration in breeding practice.

BnbHLH92a negatively regulates anthocyanin and proanthocyanidin biosynthesis in Brassica napus

Yellow seed trait is a desirable characteristic with potential for increasing seed quality and commercial value in rapeseed,and anthocyanin and proanthocyanidins(PAs)are major seed-coat pigments.Few transcription factors involved in the regulation of anthocyanin and PAs biosynthesis have been characterized in rapeseed.In this study,we identified a transcription factor gene BnbHLH92a(BnaA06T0441000ZS)in rapeseed.Overexpressing BnbHLH92a both in Arabidopsis and in rapeseed reduced levels of anthocyanin and PAs.Correspondingly,the expression profiles of anthocyanin and PA biosynthesis genes(TT3,BAN,TT8,TT18,and TTG1)were shown by quantitative real-time PCR to be inhibited in BnbHLH92a-overexpressing Arabidopsis seeds,indicating that BnbHLH92a represses the anthocyanin and PA biosynthesis pathway in Arabidopsis.BnbHLH92a physically interacts with the BnTTG1 protein and represses the biosynthesis of anthocyanins and PAs in rapeseed.BnbHLH92a also binds directly to the BnTT18 promoter and represses its expression.These results suggest that BnbHLH92a is a novel upstream regulator of flavonoid biosynthesis in B.napus.

Heterosis for Seed Yield, Oil Content and Other Characters in Rapeseed (Brassica napus L.)

Nine inbred lines of rapeseed （Brassica napus L.） used as male were crossed to five recessive genetic male sterile （RGMS） lines used as female to produce 45 single crosses. The crosses, their parents and a check hybrid were tested at two locations during 2007 to 2008 for testing the performance and heterosis of hybrids for seed yield and other characters. Results showed that variations for seed yield, oil content, days to flowering and days to maturity were significant. Mean squares for hybrids were significant for all characters. High heterosis （-4.5%-88.3%）, heterobeltiosis （-15.6%-81.1%） and standard heterosis G34.8%-33.1%） were found for the seed yield. The highest heterosis and heterobeltiosis were found in the cross QH303-4A× 1190. The highest standard heterosis was found in the cross Qianyou8A×Q034. Both positive and negative heterosis of single crosses were detected for the oil content. Small heterosis was found for days to flowering and days to maturity. Among parents, Ⅲ 188, Ⅲ224, and Q034 were proved to be the superior for seed yield when used as parents in most of the hybrid combinations. 2365, Ⅲ224, and QH303-4AB were good for high oil content breeding, Ⅲ 176, 2313 and Qianyou3AB were good for the early hybrid breeding. Total 11 hybrids yielded higher than 2 500 kg·hm^-2 and also gave significantly positive heterosis, heterobeltiosis and standard heterosis. Among them, 10 crosses gave higher oil content than that of check. These crosses can be used in the future breeding program for the seed yield and the oil content. Two crosses including Qianyou3A × Ⅲ224 and Qianyou3A×2313 can be used for the early breeding program.

Genome-wide recombination variation in biparental segregating and reciprocal backcross populations provides information for introgression breeding in Brassica napus

Variation in patterns of recombination in plant genomes provides information about species evolution,genetic diversity and crop improvement. We investigated meiotic crossovers generated in biparental segregating and reciprocal backcross populations of the allopolyploid genome of rapeseed(Brassica napus)(AACC, 2n = 38). A structured set of 1445 intercrossed lines was derived from two homozygous de novo genome-assembled parents that represented the major genetic clusters of semi-winter Chinese and winter European rapeseeds, and was used to increase QTL resolution and achieve genomic reciprocal introgression. A high-density genetic map constructed with 6161 genetic bins and anchored centromere regions was used to establish the pattern of recombination variation in each chromosome. Around 93%of the genome contained crossovers at a mean rate of 3.8 c M Mb^(-1), with the remaining 7% attributed to centromeres or low marker density. Recombination hotspots predominated in the A genome, including two-thirds of those associated with breeding introgression from B. rapa. Genetic background might affect recombination variation. Introgression of genetic diversity from European winter to Chinese semi-winter rapeseed showed an increase in crossover rate under the semi-winter environment. Evidence for an elevated recombination rate having historically contributed to selective trait improvement includes accumulation of favorable alleles for seed oil content on hotspots of chromosome A10. Conversely, strong artificial selection may affect recombination rate variation, as appears to be the case with a coldspot resulting from strong selection for glucosinolate alleles on A09. But the cold region would be promptly reactivated by crossing design indicated by the pedigree analysis. Knowledge of recombination hotspots and coldspots associated with QTL for 22 traits can guide selection strategies for introgression breeding between the two gene pools. These results and rich genomic resources broaden our understanding of recombination behavior in allopolyploids and may advance rapeseed genetic improvement.