Napus Cultivars Research Articles

Molecular characterization of Brassica napus stress related transcription factors, BnMYB44 and BnVIP1, selected based on comparative analysis of Arabidopsis thaliana and Eutrema salsugineum transcriptomes

Many studies have been performed to identify regulatory circuit underlying plant stress tolerance. However, the reliability of some findings has been criticized because of exclusive use of stress sensitive plant species such as Arabidopsis thaliana. Sensitive plant species often harbor narrow defensive mechanisms and have relatively low capacity for adaptive responses. Therefore, it is useful to employ tolerant model plants, such as Eutrema salsugineum, to provide comprehensive insights into various mechanisms involved in response to abiotic stresses. In this study, comparative transcriptome and regulatory network analysis of stress-sensitive (A. thaliana) and -tolerant (E. salsugineum) model plants uncovered regulatory hierarchies underlying response to abiotic stresses and suggested the transcription factor genes, MYB44 and VIP1 as the candidate hub genes to perform molecular analyses on their Brassica napus homologs, BnMYB44 and BnVIP1. The full-length coding sequence of BnMYB44 and BnVIP1 with 891 and 969bp long were cloned and sequenced. They shared high similarity with their counterparts in other plants at nucleotide and amino acid levels. The expression patterns of BnMYB44 and BnVIP1 genes of the two B. napus cultivars under drought and salt stress conditions coupled with the data obtained from the physiological measurements as well as analysis of the BnMYB44 and BnVIP1 promoters suggested that BnMYB44 and BnVIP1 genes may contribute to responses to drought and salt stresses in B. napus.

Comparative orchestrating response of four oilseed rape (Brassica napus) cultivars against the selenium stress as revealed by physio-chemical, ultrastructural and molecular profiling

Selenium (Se) is an essential micro-element for human and animals. In higher plants, Se essentiality or phyto-toxicity is less explored. Therefore, we aimed to examine the effects of Se (0, 25, 50, and 100 µM) as sodium selenite on the physio-chemical, cell ultra-structural and genomic alterations in hydroponically grown seedlings of four cultivars of B. napus (cvs. Zheda 619, Zheda 622, ZS 758, and ZY 50). Results showed that excessive (100 µM) Se (IV) exhibited significant reduction in plant growth parameters, declined pigment contents, lower water-soluble protein levels, and overproduction of H2O2 and MDA contents. A significant increase in antioxidant enzyme activities and transcript levels of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), except catalase (CAT) were noticed in the leaves and roots. Non-enzymatic antioxidants including glutathione (GSH) and oxidized glutathione (GSSG), except GSSG in roots were enhanced under higher Se (IV) levels. Transmission electron microscopy analysis revealed the ultrastructural damages in leaf mesophyll and root tip cells induced by excessive Se (IV). Less-significant phytotoxic effects were observed in above-mentioned parameters at 50 µM Se (IV). Overall, Se (IV) supplementation at 25 µM displayed marginal beneficial effect by enhancing plant growth, pigment contents, protein levels and restrict H2O2 and MDA overproduction. A marginal increase/decrease in ROS-detoxifying enzymes (except CAT activity) and elevated GSH and GSSG levels were noticed. The accumulation of Se (IV) was much higher in roots as compared to leaves. This accumulation was maximum in Zheda 622 and minimum in ZS 758, followed by Zheda 619 and ZY 50. Overall findings showed that Zheda 622 was the most sensitive and ZS 758 as most tolerant to Se (IV) phyto-toxicity. In addition, Se (IV) was found beneficial until 25 µM Se (IV) but phytotoxic at higher Se levels especially at 100 µM Se (IV).

Combining R gene and quantitative resistance increases effectiveness of cultivar resistance against Leptosphaeria maculans in Brassica napus in different environments.

Using cultivar resistance against pathogens is one of the most economical and environmentally friendly methods for control of crop diseases. However, cultivar resistance can be easily rendered ineffective due to changes in pathogen populations or environments. To test the hypothesis that combining R gene-mediated resistance and quantitative resistance (QR) in one cultivar can provide more effective resistance than use of either type of resistance on its own, effectiveness of resistance in eight oilseed rape (Brassica napus) cultivars with different R genes and/or QR against Leptosphaeria maculans (phoma stem canker) was investigated in 13 different environments/sites over three growing seasons (2010/2011, 2011/2012 and 2012/2013). Cultivar Drakkar with no R genes and no QR was used as susceptible control and for sampling L. maculans populations. Isolates of L. maculans were obtained from the 13 sites in 2010/2011 to assess frequencies of avirulent alleles of different effector genes (AvrLm1, AvrLm4 or AvrLm7) corresponding to the resistance genes (Rlm1, Rlm4 or Rlm7) used in the field experiments. Results of field experiments showed that cultivars DK Cabernet (Rlm1 + QR) and Adriana (Rlm4 + QR) had significantly less severe phoma stem canker than cultivars Capitol (Rlm1) and Bilbao (Rlm4), respectively. Results of controlled environment experiments confirmed the presence of Rlm genes and/or QR in these four cultivars. Analysis of L. maculans populations from different sites showed that the mean frequencies of AvrLm1 (10%) and AvrLm4 (41%) were less than that of AvrLm7 (100%), suggesting that Rlm1 and Rlm4 gene-mediated resistances were partially rendered ineffective while Rlm7 resistance was still effective. Cultivar Excel (Rlm7 + QR) had less severe canker than cultivar Roxet (Rlm7), but the difference between them was not significant due to influence of the effective resistance gene Rlm7. For the two cultivars with only QR, Es-Astrid (QR) had less severe stem canker than NK Grandia (QR). Analysis of the relationship between severity of stem canker and weather data among the 13 sites in the three growing seasons showed that increased severity of stem canker was associated with increased rainfall during the phoma leaf spot development stage and increased temperature during the stem canker development stage. Further analysis of cultivar response to environmental factors showed that cultivars with both an Rlm gene and QR (e.g. DK Cabernet, Adriana and Excel) were less sensitive to a change in environment than cultivars with only Rlm genes (e.g. Capitol, Bilbao) or only QR (e.g. DK Grandia). These results suggest that combining R gene and QR can provide effective, stable control of phoma stem canker in different environments.

Isolation and identification of rapeseed (Brassica napus) cultivars for potential higher and lower Cd accumulation

AbstractCadmium (Cd) as a non‐essential toxic metal has become one of the seriously environmental problems. Overload of Cd into plant shoots, particularly the addible parts (i.e., grains), jeopardizes crop production and food safety. Isolating and identifying genotypic variations in Cd accumulation of rapeseed (Brassica napus) cultivars is an efficient approach for phytoremediation and developing lower Cd‐accumulating plants. In this study, a trial was conducted under natural condition in Nanjing, China, from 2014 to 2017, and identified 64 rapeseed cultivars collected from the areas of Gui Zhou province. Rapeseed grew under moderate Cd exposure (5 mg kg−1) for 5 months, and shoots were harvested for Cd quantification. A great variation of total Cd concentrations in shoots, ranking from 0.16 to 17.03 mg Cd kg−1, was found. Following the initial examination of all cultivars, two sets of plants with high (#138 and #177) and low (#208 and #244) Cd concentrations were further investigated. Throughout the growth period, cultivars #138 and #177 accumulated more Cd during vegetative (30, 60, and 120 d) and late developmental (180 d) stages than cultivars #208 and #244. The higher Cd concentration in shoots of #138 and #177 was associated with the higher Cd concentration in xylem sap, suggesting the greater capability of Cd translocation from roots to shoots. Compared to #208 and #244, Cd exposure moderately reduced zinc and iron concentrations in some tissues of #138 and #177, whereas the manganese and magnesium concentrations showed no change. Although #138 and #177 cultivars accumulated more Cd in their shoots, no Cd toxicity was detected. Moreover, both #138 and #177 cultivars had a similar biomass to #208 or #244. These results suggest that #138 and #177 rapeseeds are tolerant to Cd stress.

Genome-wide identification of hexokinase gene family in Brassica napus: structure, phylogenetic analysis, expression, and functional characterization.

Genome-wide identification, expression analysis, and functional characterization of previously uncharacterized hexokinase family of oil crop, Brassica napus, underscore the importance of this gene family in plant growth and development. In plants, the multi-gene family of dual-function hexokinases (HXKs) plays important roles in sugar metabolism and sensing that affect growth and development. Rapeseed (Brassica napus L.) is an important oil crop;however, little is known about the B. napus HXK gene family. We identified 19 putative HXKs in B. napus genome. B. rapa and B. oleracea, the two diploid progenitors of B. napus, contributed almost equally to the BnHXK genes. Phylogenetic analysis divided the 19 BnHXKs into four groups. The exon-intron structures of BnHXKs share high similarity to those of HXKs in Arabidopsis and rice. The group III and IV BnHXKs are highly expressed in roots, whereas group I members preferentially express in leaves. Analysis of seed transcriptomes at different developmental stages showed that most of group I and IV HXKs are highly expressed 2-weeks after pollination (2WAP), compared to 4WAP for group III. BnHKXs are differentially expressed in susceptible and tolerant B. napus cultivars after fungal infection, suggesting the possible involvement in defense response. We generated rapeseed RNAi lines for BnHXK9, a member of relatively less characterized group IV, by pollen-mediated gene transformation. The seedlings of BnHXK9-RNAi lines showed delayed growth compared to the wild type. The RNAi plants were dwarf with curly leaves, suggesting the involvement of BnHXK9 in plant development. Collectively, our findings provides a comprehensive account of BnHXK gene family in an important crop and a starting point for further elucidation of their roles in sugar metabolism and sensing, as well as plant growth and development.

Virulence and pathotype classification of Plasmodiophora brassicae populations collected from clubroot resistant canola (Brassica napus) in Canada

Clubroot, caused by Plasmodiophora brassicae Wor., is an important soilborne disease of canola (Brassica napus L.) in Canada that is managed mainly by planting clubroot-resistant (CR) cultivars. Populations of P. brassicae representing 106 fields in Alberta were obtained from galled roots of CR canola plants collected in 2014–2016 and characterized for virulence on seven CR canola cultivars. Sixty-one of these populations could overcome resistance in at least one CR cultivar and were evaluated further by inoculation on 13 Brassica hosts termed the Canadian Clubroot Differential (CCD) Set. The CCD Set included the differentials of Williams and Somé et al., selected hosts of the European Clubroot Differential Set, and the B. napus cultivars ‘Brutor’, ‘Mendel’, ‘Westar’ and ‘45H29’. Each unique virulence pattern on the CCD Set represented a distinct pathotype and was identified with a letter. Five reference isolates, obtained prior to the introduction of CR canola, also were assessed. A total of 17 pathotypes were detected using the CCD Set, compared with five pathotypes using the system of Williams and two with the system of Somé et al., suggesting that the CCD Set has a greater differentiating capacity. Pathotype A, a variant of pathotype 3 (as per Williams) which is able to overcome the resistance in CR B. napus, was predominant. The original pathotype 3, which is avirulent on CR canola, was classified as CCD pathotype H. An integrated strategy, combining other tools in addition to resistance, will be needed for the sustainable management of clubroot.

Major Co-localized QTL for Plant Height, Branch Initiation Height, Stem Diameter, and Flowering Time in an Alien Introgression Derived Brassica napus DH Population.

Plant height (PH), branch initiation height (BIH), and stem diameter (SD) are three stem-related traits that play crucial roles in plant architecture and lodging resistance. Herein, we show one doubled haploid (DH) population obtained from a cross between Y689 (one Capsella bursa-pastoris derived Brassica napus intertribal introgression) and Westar (B. napus cultivar) that these traits were significantly positively correlated with one another and with flowering time (FT). Based on a high-density SNP map, a total of 102 additive quantitative trait loci (QTL) were identified across six environments. Seventy-two consensus QTL and 49 unique QTL were identified using a two-round strategy of QTL meta-analysis. Notably, a total of 19 major QTL, including 11 novel ones, were detected for these traits, which comprised two QTL clusters on chromosomes A02 and A07. Conditional QTL mapping was performed to preliminarily evaluate the genetic basis (pleiotropy or tight linkage) of the co-localized QTL. In addition, QTL by environment interactions (QEI) mapping was performed to verify the additive QTL and estimate the QEI effect. In the genomic regions of all major QTL, orthologs of the genes involved in phytohormone biosynthesis, phytohormone signaling, flower development, and cell differentiation in Arabidopsis were proposed as candidate genes. Of these, BnaA02g02560, an ortholog of Arabidopsis GASA4, was suggested as a candidate gene for PH, SD, and FT; and BnaA02g08490, an ortholog of Arabidopsis GNL, was associated with PH, BIH and FT. These results provide useful information for further genetic studies on stem-related traits and plant growth adaptation.

Genome-Wide Identification and Expression Profiling of Cytokinin Oxidase/Dehydrogenase (CKX) Genes Reveal Likely Roles in Pod Development and Stress Responses in Oilseed Rape (Brassica napus L.).

Cytokinin oxidase/dehydrogenases (CKXs) play a critical role in the irreversible degradation of cytokinins, thereby regulating plant growth and development. Brassica napus is one of the most widely cultivated oilseed crops worldwide. With the completion of whole-genome sequencing of B. napus, genome-wide identification and expression analysis of the BnCKX gene family has become technically feasible. In this study, we identified 23 BnCKX genes and analyzed their phylogenetic relationships, gene structures, conserved motifs, protein subcellular localizations, and other properties. We also analyzed the expression of the 23 BnCKX genes in the B. napus cultivar Zhong Shuang 11 (‘ZS11’) by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), revealing their diverse expression patterns. We selected four BnCKX genes based on the results of RNA-sequencing and qRT-PCR and compared their expression in cultivated varieties with extremely long versus short siliques. The expression levels of BnCKX5-1, 5-2, 6-1, and 7-1 significantly differed between the two lines and changed during pod development, suggesting they might play roles in determining silique length and in pod development. Finally, we investigated the effects of treatment with the synthetic cytokinin 6-benzylaminopurine (6-BA) and the auxin indole-3-acetic acid (IAA) on the expression of the four selected BnCKX genes. Our results suggest that regulating BnCKX expression is a promising way to enhance the harvest index and stress resistance in plants.

The role of calcium, silicon and salicylic acid treatment in protection of canola plants against boron toxicity stress

Boron (B) toxicity often limits crop yield and the quality of production in agricultural areas. Here, we investigated the effects of calcium (Ca), silicon (Si) and salicylic acid (SA) on development of B toxicity, B allocation in canola (Brassica napus cultivar Sarw 4) and its role in non-enzymatic antioxidants in relation to yield of this cultivar under B toxicity. Canola seedlings were subjected to four B levels induced by boric acid in the absence or presence of Ca, Si and SA. The results showed that Ca, Si and SA addition ameliorated the inhibition in canola growth, water content (WC), and improved siliqua number, siliqua weight and seed index. The B content in shoots and roots and total B accumulation in the whole plant were increased in control plants under B-toxicity-stress, and these parameters were significantly decreased by addition of Ca, Si and SA. The shoot ascorbate pool (ascorbate, AsA, and dehydroascorbate, DHA), α-tocopherol and phenolics (free and bound) were increased under B toxicity, and were significantly decreased in most cases by addition of Ca, Si and SA, except α-tocopherol, which increased at low B levels (0, 25 and 50mg kg soil-1). The glutathione content did not obviously change by B stress, while added Ca, Si and SA inhibited its accumulation under B stress. In addition, B toxicity reduced the shoot flavonoids content; however, this reduction was not alleviated by the use of Ca, Si and SA treatments. It could be concluded that growth and yield of canola plants grown under high B concentration improved after external application of Ca, Si or SA.

Ecotoxicological and Interactive Effects of Copper and Chromium on Physiochemical, Ultrastructural, and Molecular Profiling in Brassica napus L.

Heavy metal accumulation causes huge environmental problems, particularly in agricultural ecosystems which have deteriorative effects on the yield and quality of crops. Individual copper (Cu) and chromium (Cr) effects have been investigated extensively in plants; however, co-contamination of Cu and Cr induced stress on Brassica napus L. is still unclear. In the present experiment, the interactive effects of Cu and Cr were studied in two B. napus cultivars (Zheda 622 and ZS 758). Results showed that the application of Cr was more toxic than Cu, and their combined stress had shown a significant adverse effect on plant growth. Biomass and photosynthetic pigment were decreased remarkably under all metal treatments. Individual treatments of Cu and Cr and their combination cause the accumulation of ROS and lipid peroxidation. Moreover, the activities of antioxidant enzymes and their mRNA transcription levels, such as catalase (CAT), ascorbate peroxidase, glutathione reductase, superoxide dismutase, and peroxidase, were increased, especially when treated with Cr alone or under Cu+Cr combined treatment in both cultivars, except for the CAT activity which was decreased in both leaves and roots of sensitive cultivar Zheda 622 as compared with their respective controls. Additionally, nonenzymatic antioxidants like reduced and oxidized glutathione showed a differential activity pattern in roots and leaves of both cultivars. A more pronounced modification in chloroplast ultrastructure was observed in both cultivars under Cu+Cr treatment followed by Cr and Cu alone treatments. Furthermore, synergistic effects of Cu and Cr were prominent; this may be due to the enhanced metals uptake under combined treatment, which suggests that Cr and Cu interaction is not competitive but is rather additive and genotypic-dependent.

The Effect of Cold Stress on the Expression of Several Genes Associated with Cold Signal Transduction System Pathway in Cultivars of Canola (Brassica napus)

The identification of genes that are involved in the adaptation and tolerance to cold stress especially the regulatory genes is essential. In this study the expression patterns of four cold induced-genes was investigated in two Zarfam (Resistant) and Sarigol (Susceptible) Brssica napus cultivars using real-time PCR technique. After RNA extraction and cDNA synthesis, expression of four genes, including, CBF17, Bn115, COR25 and NAC5–11 were studied in the seedling stage of Sarigol and Zarfam cultivars under controlled and cold stress (−4°C) condition for 0, 3, 6, 12 and 24 hours after cold treatments. The results indicated that in Zarfam the cold induced-genes generally had higher expression than Sarigol. Also, the CBF17 and NAC5-11genes which considered as the genes induced at the early stages of plant response to cold, were highly expressed in the early hours of cold stress in the Zarfam (especially when treated for 6 hours) and then the expression levels of these genes gradually decreased, on the other hand the Bn115 and COR25 as genes involved in homeostasis process and improvement resistance to stress effects were induced after transcription factors. It is observed that the Bn115 and COR25 genes had the maximum expression in 24 hours after treatment under cold stress.

Enhancing food security in arid areas of Pakistan through newly developed drought tolerant and short duration mustard (Brassica juncea L.) Canola

Food security is the crucial global issue, especially in developing countries like Pakistan. Since edible oil is an essential food item, its persistent paucity in the country and huge import for meeting domestic requirements, has attained it second largest import item after petroleum products. The aim of present study is qualitative and quantitative evaluation of newly developed short duration and drought tolerant canola quality Brassica juncea lines ZBJ-06012 and ZBJ-08051 to overcome the unfavorable edible oil situation in the country. Thirteen lines were evaluated in randomized complete block design (RCBD) for seed yield, oil quality, maturity period and drought tolerance under different agro-climatic zones both in irrigated and arid areas across the Punjab province at eight locations in Micro Yield Trials during Rabi season 2012-13 and 2013-14. Presently, grown non-canola mustard varieties Khanpur Raya and Anmol Raya were used as check varieties. Brassica napus cultivars Punjab canola and Faisal canola were also included in the trials for comparison study of mustard and rapeseed genotypes. Data for all traits under observation was analyzed through Principle Component Analysis (PCA) to evaluate the best performing lines in irrigated as well as in rain fed areas. Principal Component Analysis showed first 2 PCs having Eigen value >1 explaining 76.4% and 72% of the total variation at irrigated areas and rain fed areas respectively. The mean seed yield was also compared by Least Significant Difference (LSD) test to study the significance at 5% probability level. Canola quality B. juncea lines ZBJ-06012 and ZBJ-08051 have shown good adaptability, early maturity, non-shattering, disease and drought tolerance traits with high yield potential in comparison with presently grown Brassica napus cultivars ?Punjab Canola? and ?Faisal Canola?. Due to these prominent features, these lines have a great scope for motivating farmers to grow canola quality B. juncea when compared with B. napus and non-canola B. juncea. Future challenges demand further development of high yielding, short duration and aphid tolerant mustard cultivars having high oil content and canola quality. There is a great potential of exploiting genetic variability in the existing B. juncea material to achieve the aforesaid goals by using conventional plant breeding techniques.

Cultivar Variation in Hormonal Balance Is a Significant Determinant of Disease Susceptibility to Xanthomonas campestris pv. campestris in Brassica napus.

This study aimed to directly elucidate cultivar variation in disease susceptibility and disease responses in relation to hormonal status in the interaction of Brassica napus cultivars and Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot disease. Fully expanded leaves of six B. napus cultivars (cvs. Capitol, Youngsan, Saturnin, Colosse, Tamra, and Mosa) were inoculated with Xcc. At 14 days post-inoculation with Xcc, cultivar variation in susceptibility or resistance was interpreted with defense responses as estimated by redox status, defensive metabolites, and expression of phenylpropanoid synthesis-related genes in relation to endogenous hormonal status. Disease susceptibility of six cultivars was distinguished by necrotic lesions in the Xcc-inoculated leaves and characterized concurrently based on the higher increase in reactive oxygen species and lipid peroxidation. Among these cultivars, as the susceptibility was higher, the ratios of abscisic acid (ABA)/jasmonic acid (JA) and salicylic acid (SA)/JA tended to increase with enhanced expression of SA signaling regulatory gene NPR1 and transcriptional factor TGA1 and antagonistic suppression of JA-regulated gene PDF 1.2. In the resistant cultivar (cv. Capitol), accumulation of defensive metabolites with enhanced expression of genes involved in flavonoids (chalcone synthase), proanthocyanidins (anthocyanidin reductase), and hydroxycinnamic acids (ferulate-5-hydroxylase) biosynthesis and higher redox status were observed, whereas the opposite results were obtained for susceptible cultivars (cvs. Mosa and Tamra). These results clearly indicate that cultivar variation in susceptibility to infection by Xcc was determined by enhanced alteration of the SA/JA ratio, as a negative regulator of redox status and phenylpropanoid synthesis in the Brasica napus–Xcc pathosystem.

Earliness traits in rapeseed (Brassica napus): SNP loci and candidate genes identified by genome-wide association analysis.

Life cycle timing is critical for yield and productivity of Brassica napus (rapeseed) cultivars grown in different environments. To facilitate breeding for earliness traits in rapeseed, SNP loci and underlying candidate genes associated with the timing of initial flowering, maturity and final flowering, as well as flowering period (FP) were investigated in two environments in a diversity panel comprising 300 B. napus inbred lines. Genome-wide association studies (GWAS) using 201,817 SNP markers previously developed from SLAF-seq (specific locus amplified fragment sequencing) revealed a total of 131 SNPs strongly linked (P < 4.96E-07) to the investigated traits. Of these 131 SNPs, 40 fell into confidence intervals or were physically adjacent to previously published flowering time QTL or SNPs. Phenotypic effect analysis detected 35 elite allelic variants for early maturing, and 90 for long FP. Candidate genes present in the same linkage disequilibrium blocks (r2>0.6) or in 100 kb regions around significant trait-associated SNPs were screened, revealing 57 B. napus genes (33 SNPs) orthologous to 39 Arabidopsis thaliana flowering time genes. These results support the practical and scientific value of novel large-scale SNP data generation in uncovering the genetic control of agronomic traits in B. napus, and also provide a theoretical basis for molecular marker-assisted selection of earliness breeding in rapeseed.

Differential cobalt-induced effects on plant growth, ultrastructural modifications, and antioxidative response among four Brassica napus (L.) cultivars

Despite the increasing environmental threat of cobalt in the modern era, less is known as its phytotoxicity behavior. Therefore, the present study was undertaken to assess the toxicity effects of cobalt and to understand the associated physio-biochemical response in Brassica napus, an economically important plant crop species. Five-day-old seedlings of four cultivars (Zheda 619, Zheda 622, ZS 758, and ZY 50) were exposed to five different levels of cobalt under hydroponic conditions. Results showed a concentration-dependent inhibition of plant growth, accompanied by notable chlorophyll loss, protein degradation, and accumulation of reactive oxygen species and malondialdehyde. Further, Co contents in different plants parts were found to be higher in Zheda 622 than all other cultivars. In all cultivars, the contents of enzymatic activities (SOD, POD, GR, and GSH) were markedly increased following cobalt exposure; by contrast, catalase and ascorbate peroxidase activities declined with increased cobalt concentration in medium, which was also, echoed by the pattern of enzymes-related mRNA levels. Morphological observations, supported by ultrastructural analysis revealed clear differences in cobalt sensitivity among cultivars, with ZS 758 identified as less sensitive cultivar, and Zheda 622 the most sensitive one. In addition to revealing genotypic differences in cobalt sensitivity in B. napus, findings suggest the mechanisms of cobalt tolerance in this specie could, at least partially, in relation with the ability of plant to sustain the activity of superoxide dismutase and guaicol peroxidase and to maintain glutathione reduced pool through the action of glutathione reductase.

Molecular genetics and functional genomics of abiotic stress-responsive genes in oilseed rape (Brassica napus L.): a review of recent advances and future

Abiotic stresses are the key factors which negatively influence plant development and productivity and are the main cause of extensive agricultural production losses worldwide. Brassica napus is an oilseed crop of global economic significance and major contributor to the total oilseed production, quite often encounters abiotic stresses, resulting in reduced agricultural productivity. Hence, there is an immediate need being felt to raise B. napus cultivars which would be more suitable for various abiotic stress conditions presently and in the years to come. Biotechnology and molecular plant breeding has emerged as an important tool for molecular understanding of plant response to various abiotic stresses. Currently, various stress-responsive genes and mechanisms have been identified and functionally characterized in model plant Arabidopsis and other major crop plants such as Oryza sativa and Zea mays. However, very inadequate success has been achieved in this direction in a major oilseed crop such as B. napus. In this review, we present the latest methods and approaches of studying abiotic stress in B. napus. In this review, we describe the genes functioning as markers for crop breeding and discuss the recent progress and advances in genome editing by break through CRISPR/Cas9 multigene–multiplex approaches for developing multiple abiotic stress tolerance with our on-going research as a scheme. We also throw some light on molecular genetics, plant breeding and abiotic stress biotechnology of B. napus which offer a new prospective on the research directions for the practical plant breeding and functional genomics of B. napus in response to different abiotic stress conditions.

The high-quality genome of Brassica napus cultivar 'ZS11' reveals the introgression history in semi-winter morphotype.

Allotetraploid oilseed rape (Brassica napus L.) is an agriculturally important crop. Cultivation and breeding of B. napus by humans has resulted in numerous genetically diverse morphotypes with optimized agronomic traits and ecophysiological adaptation. To further understand the genetic basis of diversification and adaptation, we report a draft genome of an Asian semi-winter oilseed rape cultivar 'ZS11' and its comprehensive genomic comparison with the genomes of the winter-type cultivar 'Darmor-bzh' as well as two progenitors. The integrated BAC-to-BAC and whole-genome shotgun sequencing strategies were effective in the assembly of repetitive regions (especially young long terminal repeats) and resulted in a high-quality genome assembly of B. napus 'ZS11'. Within a short evolutionary period (~6700years ago), semi-winter-type 'ZS11' and the winter-type 'Darmor-bzh' maintained highly genomic collinearity. Even so, certain genetic differences were also detected in two morphotypes. Relative to 'Darmor-bzh', both two subgenomes of 'ZS11' are closely related to its progenitors, and the 'ZS11' genome harbored several specific segmental homoeologous exchanges (HEs). Furthermore, the semi-winter-type 'ZS11' underwent potential genomic introgressions with B. rapa (Ar ). Some of these genetic differences were associated with key agronomic traits. A key gene of A03.FLC3 regulating vernalization-responsive flowering time in 'ZS11' was first experienced HE, and then underwent genomic introgression event with Ar , which potentially has led to genetic differences in controlling vernalization in the semi-winter types. Our observations improved our understanding of the genetic diversity of different B. napus morphotypes and the cultivation history of semi-winter oilseed rape in Asia.

Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures &gt;30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.

Genome-Wide Association Mapping of Seed Coat Color in Brassica napus.

Seed coat color is an extremely important breeding characteristic of Brassica napus. To elucidate the factors affecting the genetic architecture of seed coat color, a genome-wide association study (GWAS) of seed coat color was conducted with a diversity panel comprising 520 B. napus cultivars and inbred lines. In total, 22 single-nucleotide polymorphisms (SNPs) distributed on 7 chromosomes were found to be associated with seed coat color. The most significant SNPs were found in 2014 near Bn-scaff_15763_1-p233999, only 43.42 kb away from BnaC06g17050D, which is orthologous to Arabidopsis thaliana TRANSPARENT TESTA 12 (TT12), an important gene involved in the transportation of proanthocyanidin precursors into the vacuole. Two of eight repeatedly detected SNPs can be identified and digested by restriction enzymes. Candidate gene mining revealed that the relevant regions of significant SNP loci on the A09 and C08 chromosomes are highly homologous. Moreover, a comparison of the GWAS results to those of previous quantitative trait locus (QTL) studies showed that 11 SNPs were located in the confidence intervals of the QTLs identified in previous studies based on linkage analyses or association mapping. Our results provide insights into the genetic basis of seed coat color in B. napus, and the beneficial allele, SNP information, and candidate genes should be useful for selecting yellow seeds in B. napus breeding.

Carbohydrate microarrays and their use for the identification of molecular markers for plant cell wall composition

Genetic improvement of the plant cell wall has enormous potential to increase the quality of food, fibers, and fuels. However, the identification and characterization of genes involved in plant cell wall synthesis is far from complete. Association mapping is one of the few techniques that can help identify candidate genes without relying on our currently incomplete knowledge of cell wall synthesis. However, few cell wall phenotyping methodologies have proven sufficiently precise, robust, or scalable for association mapping to be conducted for specific cell wall polymers. Here, we created high-density carbohydrate microarrays containing chemically extracted cell wall polysaccharides collected from 331 genetically diverse Brassica napus cultivars and used them to obtain detailed, quantitative information describing the relative abundance of selected noncellulosic polysaccharide linkages and primary structures. We undertook genome-wide association analysis of data collected from 57 carbohydrate microarrays and identified molecular markers reflecting a diversity of specific xylan, xyloglucan, pectin, and arabinogalactan moieties. These datasets provide a detailed insight into the natural variations in cell wall carbohydrate moieties between B. napus genotypes and identify associated markers that could be exploited by marker-assisted breeding. The identified markers also have value beyond B. napus for functional genomics, facilitated by the close genetic relatedness to the model plant Arabidopsis Together, our findings provide a unique dissection of the genetic architecture that underpins plant cell wall biosynthesis and restructuring.