Traits In Rapeseed Research Articles

Discovery of Pod Shatter-Resistant Associated SNPs by Deep Sequencing of a Representative Library Followed by Bulk Segregant Analysis in Rapeseed

BackgroundSingle nucleotide polymorphisms (SNPs) are an important class of genetic marker for target gene mapping. As of yet, there is no rapid and effective method to identify SNPs linked with agronomic traits in rapeseed and other crop species.Methodology/Principal FindingsWe demonstrate a novel method for identifying SNP markers in rapeseed by deep sequencing a representative library and performing bulk segregant analysis. With this method, SNPs associated with rapeseed pod shatter-resistance were discovered. Firstly, a reduced representation of the rapeseed genome was used. Genomic fragments ranging from 450–550 bp were prepared from the susceptible bulk (ten F2 plants with the silique shattering resistance index, SSRI <0.10) and the resistance bulk (ten F2 plants with SSRI >0.90), and also Solexa sequencing-produced 90 bp reads. Approximately 50 million of these sequence reads were assembled into contigs to a depth of 20-fold coverage. Secondly, 60,396 ‘simple SNPs’ were identified, and the statistical significance was evaluated using Fisher's exact test. There were 70 associated SNPs whose –log10 p value over 16 were selected to be further analyzed. The distribution of these SNPs appeared a tight cluster, which consisted of 14 associated SNPs within a 396 kb region on chromosome A09. Our evidence indicates that this region contains a major quantitative trait locus (QTL). Finally, two associated SNPs from this region were mapped on a major QTL region.Conclusions/Significance70 associated SNPs were discovered and a major QTL for rapeseed pod shatter-resistance was found on chromosome A09 using our novel method. The associated SNP markers were used for mapping of the QTL, and may be useful for improving pod shatter-resistance in rapeseed through marker-assisted selection and map-based cloning. This approach will accelerate the discovery of major QTLs and the cloning of functional genes for important agronomic traits in rapeseed and other crop species.

Genetic structure and linkage disequilibrium pattern of a rapeseed (Brassica napus L.) association mapping panel revealed by microsatellites

Understanding the population structure and linkage disequilibrium (LD) is a prerequisite for association mapping of complex traits in a target population. In this study, we assessed the genetic diversity, population structure and the extent of LD in a panel of 192 inbred lines of Brassica napus from all over the world using 451 single-locus microsatellite markers. The inbred lines could be divided into P1 and P2 groups by a model-based population structure analysis. Out of the 142 inbred lines in the P1 group, 126 lines were from China and Japan, and the remaining 16 lines were from Europe, Canada and Australia. In the P2 group, 33 out of the 50 lines were from Europe, Canada, and Australia, and the remaining 17 lines were from China. Structure analysis further divided each group into two subgroups. AMOVA, pairwise F (ST) and neutrality analyses confirmed the differentiation between groups and subgroups. More than 80 % of the pairwise kinship estimates between inbred lines were <0.05, indicating that relative kinship is weak in our panel. Only 6 % linked marker pairs showed LD, suggesting the low level of LD in this association panel. The LD decayed within 0.5-1 cM at the genome level, and varied considerably across each group and subgroup, due to the population size, genetic background and genetic drift. The characterization of the population structure and LD patterns would be useful for performing association studies for complex agronomic traits in rapeseed.

Interrelationship between grain yield and related traits in rapeseed (Brassica napus L.)

Interrelationship between grain yield and related traits in rapeseed (Brassica napus L.)

Maternal control of seed oil content in Brassica napus: the role of silique wall photosynthesis

Seed oil content is an important agronomic trait in rapeseed. However, our understanding of the regulatory processes controlling oil accumulation is still limited. Using two rapeseed lines (zy036 and 51070) with contrasting oil content, we found that maternal genotype greatly affects seed oil content. Genetic and physiological evidence indicated that difference in the local and tissue-specific photosynthetic activity in the silique wall (a maternal tissue) was responsible for the different seed oil contents. This effect was mimicked by in planta manipulation of silique wall photosynthesis. Furthermore, the starch content and expression of the important lipid synthesis regulatory gene WRINKLED1 in developing seeds were linked with silique wall photosynthetic activity. 454 pyrosequencing was performed to explore the possible molecular mechanism for the difference in silique wall photosynthesis between zy036 and 51070. Interestingly, the results suggested that photosynthesis-related genes were over-represented in both total silique wall expressed genes and genes that were differentially expressed between genotypes. A potential regulatory mechanism for elevated photosynthesis in the zy036 silique wall is proposed on the basis of knowledge from Arabidopsis. Differentially expressed ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)-related genes were used for further investigations. Oil content correlated closely with BnRBCS1A expression levels and Rubisco activities in the silique wall, but not in the leaf. Taken together, our results highlight an important role of silique wall photosynthesis in the regulation of seed oil content in terms of maternal effects.

Analysis of Genetic Effects for Heterosis of ErucicAcid and Glucosinolate Contents in Rapeseed (Brassica napus L.)

Abstract The embryo, cytoplasmic, and maternal heterosis for erucic acid content (EAC) and glucosinolate content (GLS) of rapeseed ( Brassica napus L.) were studied by using the genetic models for quantitative traits of seeds in diploid crops. Eight parents were included in a diallel mating design in two years. It was found that the heterosis of EAC and GLS was simultaneously controlled by genetic main effects and genotypexenvironment (GE) interaction effects. The general heterosis of most crosses for EAC was significantly positive, while it was not for GLS. The general heterosis was more important for two quality traits of rapeseed because of the low GE interaction heterosis in both years, especially for GLS. Among different genetic systems, significant positive embryo general heterosis and the negative maternal general heterosis were found for EAC and GLS in most hybrid crosses. Some hybrids with significant negative interaction heterosis were detected for either of EAC or GLS. In general, maternal general and interaction heterosis was more important for reducing EAC and GLS of rapeseed.

A Dynamic and Complex Network Regulates the Heterosis of Yield-Correlated Traits in Rapeseed (Brassica napus L.)

Although much research has been conducted, the genetic architecture of heterosis remains ambiguous. To unravel the genetic architecture of heterosis, a reconstructed F2 population was produced by random intercross among 202 lines of a double haploid population in rapeseed (Brassica napus L.). Both populations were planted in three environments and 15 yield-correlated traits were measured, and only seed yield and eight yield-correlated traits showed significant mid-parent heterosis, with the mean ranging from 8.7% (branch number) to 31.4% (seed yield). Hundreds of QTL and epistatic interactions were identified for the 15 yield-correlated traits, involving numerous variable loci with moderate effect, genome-wide distribution and obvious hotspots. All kinds of mode-of-inheritance of QTL (additive, A; partial-dominant, PD; full-dominant, D; over-dominant, OD) and epistatic interactions (additive × additive, AA; additive × dominant/dominant × additive, AD/DA; dominant × dominant, DD) were observed and epistasis, especially AA epistasis, seemed to be the major genetic basis of heterosis in rapeseed. Consistent with the low correlation between marker heterozygosity and mid-parent heterosis/hybrid performance, a considerable proportion of dominant and DD epistatic effects were negative, indicating heterozygosity was not always advantageous for heterosis/hybrid performance. The implications of our results on evolution and crop breeding are discussed.

Analysis on genetic contribution of some traits to seed yield in rapeseed by additive-dominance genetic method of mixed model

Analysis on genetic contribution of some traits to seed yield in rapeseed by additive-dominance genetic method of mixed modelA genetic model is developed with additive, dominance and genotype x environment interaction effects for the progeny from a diallel mating design. To uncover the genetic contributions of some traits of rapeseed to seed yield and find indicator traits for indirect selection, multivariable conditional analysis was conducted based on this method. Therefore, an experiment was conducted to estimate genetic parameters using a half diallel of nine international rapeseed cultivars. The 36 Fl hybrids, the parents and four additional cultivars were planted in the breeding nurseries in 2008 and 2009. Several traits including number of pods per plant (NPP), pod length (LP), height of the first pod (HFP), height of the first lateral branch (HFB), stem diameter (SD), days of flowering period (FP), days to physiological maturity (DPM) and seed yield were recorded. The genetic variance component (VDxY) was significant for all the studied traits but the genetic variance component (VA) was significant for NPP, HFB, HFP, DPM and SY traits and the genetic variance component (VD) was significant for HFB, HFP, LP and FP traits. There was significant positive phenotypic correlation (rA) between seed yield with NPP and HFP and there was significant positive dominance x year interaction correlation (rDxY) between seed yield with NPP and DPM while there was significant negative dominance x year interaction correlation (rDxY) between seed yield with HFB, LP and FP. There were significantly positive additive effects of SY for two parents Orient and Talaye. Finally according to additive-dominance genetic model and conditional genetic effects, the genotypes Talaye proved good general combiner for seed yield improvement and crosses 4 × 8 (Orient × Talaye), 7 × 8 (Opera × Talaye) were found the best specific combiner for all the studied traits.

Changes in yield and seed quality traits in rapeseed genotypes by sulphur fertilization

Sulphur is considered more as a soil amendment to remedy alkaline soils rather than a fertilizer in crop production. However, as one of the macronutrients, just as N–P–K, it is able to have a direct and significant effect on yield and quality in some crops. There might be a sound potential of increasing seed yield and quality of rapeseed, the second important oil crop around the world, with the use of sulphur as a fertilizer in cultural practices. Our objective in this study is to determine the effects of sulphur fertilization on seed yield and several seed and oil quality traits in rapeseed. Five rapeseed genotypes were grown for two consecutive growing seasons in Canakkale, in a RCB design with three replications. The experimental plots were given 0, 100 or 200 kg ha−1 sulphur along with a fixed amount of 240 kg ha−1 N. Results indicated that sulphur fertilization had positive effects on seed yield and some of the seed and oil quality components. On the other hand, excessive sulphur fertilization, or naturally occurring high levels in the soil, may have adverse effects in elevating some undesired compounds, such as glucosinolates.

Zero erucic acid trait of rapeseed (Brassica napus L.) results from a deletion of four base pairs in the fatty acid elongase 1 gene

The fatty acid elongase 1 (FAE1) gene is a key gene in the erucic acid biosynthesis in rapeseed. The complete coding sequences of the FAE1 gene were isolated separately from eight high and zero erucic acid rapeseed cultivars (Brassica napus L.). A four base pair deletion between T1366 and G1369 in the FAE1 gene was found in a number of the cultivars, which leads to a frameshift mutation and a premature stop of the translation after the 466th amino acid residue. This deletion was predominantly found in the C-genome and rarely in the A-genome of B. napus. Expression of the gene isoforms with the four base pair deletion in a yeast system generated truncated proteins with no enzymatic activity and could not produce very long chain fatty acids as the control with an intact FAE1 gene did in yeast cells. In the developing rape seeds the FAE1 gene isoforms with the four base pair deletion were transcribed normally but failed to translate proteins to form a functional complex. The four base pair deletion proved to be a mutation responsible for the low erucic acid trait in rapeseed and independent from the point mutation reported by Han et al. (Plant Mol Biol 46:229-239, 2001).

Detection of QTL for six yield-related traits in oilseed rape (Brassica napus) using DH and immortalized F2 populations

The inheritance of yield-related traits in rapeseed (Brassica napus) is poorly understood, and the investigations on mapping of quantitative trait loci (QTL) for such traits are only few. QTL related to six traits were mapped which include plant height (PH), height of lowest primary effective branch (HPB), length of main inflorescence (LMI), silique length (SL), number of primary branches (FB) and silique density (SD). A set of 258 doubled haploid (DH) lines derivatives of a cross between a canola variety Quantum and a resynthesized B. napus line No.2127-17, and a fixed immortalized F(2) (designated as IF(2)) population generated by randomly permutated intermating of these DHs were investigated. A genetic linkage map was constructed using 208 SSR and 189 SRAP markers for the DH population. Phenotypic data were collected from three environments for the two populations. Using composite interval mapping analyses, 30 and 22 significant QTL were repeatedly detected across environments for the six traits in the DH and IF(2) populations, respectively. Twenty-nine QTL were common between the two populations. The directions of parental contribution for all common QTL were the same, showing a great potential for marker-assisted selection in improving these traits. Some chromosomal regions harbor QTL for multiple traits, which were consistent with significant phenotypic correlations observed among traits. The results provided a better understanding of the genetic factors controlling yield-related traits in rapeseed.

Analysis of embryo, cytoplasmic and maternal correlations for quality traits of rapeseed (Brassica napus L.) across environments

Analysis of embryo, cytoplasmic and maternal correlations for quality traits of rapeseed (Brassica napus L.) across environments

Manipulation of plant oil composition for the production of valuable chemicals. Progress, problems, and prospects.

The first transgenic crop with a modified seed oil composition was released for commercial use in 1995. Many additional transgenic rapeseed varieties expressing novel seed oils or proteins are now under development. Recent research advances in Arabidopsis molecular genetics and the emerging relatedness between the Arabidopsis and Brassica genomes will enable more radical manipulation of many key agronomic traits in rapeseed. These will range from greatly improved seed oil yield to the production of seed oils with defined fatty acid contents ranging from C8 to C24 chain lengths and including many desirable functionalities including double bonds, triple bonds, hydroxy and epoxide groups. Much of the technology currently being development in rapeseed and soybean oil modification will be directly applicable to other oil crops including high yield tropical perennials such as oil palm.

Rapeseed Mutants with Reduced Levels of Polyunsaturated Fatty Acids and Increased Levels of Oleic Acid

Development of cultivars of both tetraploid (Brassica napus L.) and diploid (B. rapa L.) rapeseed with reduced levels of polyunsaturated fatty acids and increased levels of oleic acid could increase both the utility and value of the oil. The objective of this experiment was to use chemcical mutagenesis to induce mutations for these traits in rapeseed. Imbibed seed of ‘R‐500’ (B. rapa) and ‘Cascade’ (B. napus) were treated with 5% v/v of ethyl methanesulfonate. The M2 generations of these populations were screened to identify mutants with low levels of polyunsaturated fatty acids (PUFA) using a modified thiobarbituric acid procedure. Putative mutants and their derived progeny were increased in the greenhouse and the seed analyzed for fatty acid composition using gas chromatography. The most promising mutant identified from 4 734 M2 seeds of B. rapa, was M‐30, which had 2.1% linoleic acid and 3.0% linolenic acid, vs. 11.9% linoleic and 8.6% linolenic acid in the original cultivar. This mutant was crossed with ‘Tobin’ to derive F4 lines having &lt;6% total PUFA and oleic acid concentrations &gt;87%. The most promising mutant identified from 39 504 M2 seeds of B. napus was X‐82, which had 6.6% PUFA, vs. 27.4% PUFA in Cascade. Several M3 and M4 lines derived from X‐82 had &lt;6% total PUFA and &gt;88% oleic acid. The development of commercial cultivars with reduced levels of polunsaturated fatty acid in both B. rapa and B. napus could develop new markets for both industrial rapeseed and edible canola oil.