Homoeologous exchanges contribute to branch angle variations in rapeseed: Insights from transcriptome, QTL-seq and gene functional analysis.

Branch angle (BA) is a critical morphological trait that significantly influences planting density, light interception and ultimately yield in plants. Despite its importance, the regulatory mechanism governing BA in rapeseed remains poorly understood. In this study, we generated 109 transcriptome data sets for 37 rapeseed accessions with divergent BA phenotypes. Relative to adaxial branch segments, abaxial segments accumulated higher levels of auxin and exhibited lower expression of six TCP1 homologues and one GA20ox3. A co-expression network analysis identified two modules highly correlated with BA. The modules contained homologues to known BA control genes, such as FUL, YUCCA6, TCP1 and SGR3. Notably, a homoeologous exchange (HE), occurring at the telomeres of A09, was prevalent in large BA accessions, while an A02-C02 HE was common in small BA accessions. In their corresponding regions, these HEs explained the formation of hub gene hotspots in the two modules. QTL-seq analysis confirmed that the presence of a large A07-C06 HE (~8.1 Mb) was also associated with a small BA phenotype, and BnaA07.WRKY40.b within it was predicted as candidate gene. Overexpressing BnaA07.WRKY40.b in rapeseed increased BA by up to 20°, while RNAi- and CRISPR-mediated mutants (BnaA07.WRKY40.b and BnaC06.WRKY40.b) exhibited decreased BA by up to 11.4°. BnaA07.WRKY40.b was exclusively localized to the nucleus and exhibited strong expression correlations with many genes related to gravitropism and plant architecture. Taken together, our study highlights the influence of HEs on rapeseed plant architecture and confirms the role of WRKY40 homologues as novel regulators of BA.

Comparative genome-wide analysis of circular RNAs in Brassica napus L.: target-site versus non-target-site resistance to herbicide stress.

Circular RNAs (circRNAs), a class of non-coding RNA molecules, are recognized for their unique functions; however, their responses to herbicide stress in Brassica napus remain unclear. In this study, the role of circRNAs in response to herbicide treatment was investigated in two rapeseed cultivars: MH33, which confers non-target-site resistance (NTSR), and EM28, which exhibits target-site resistance (TSR). The genome-wide circRNA profiles of herbicide-stressed and non-stressed seedlings were analyzed. The findings indicate that NTSR seedlings exhibited a greater abundance of circRNAs, shorter lengths of circRNAs and their parent genes, and more diverse functions of parent genes compared with TSR seedlings. Compared to normal-growth plants, the herbicide-stressed group exhibited similar trends in the number of circRNAs, functions of parent genes, and differentially expressed circRNAs as observed in NTSR seedlings. In addition, a greater number of circRNAs that function as competing microRNA (miRNA) sponges were identified in the herbicide stress and NTSR groups compared to the normal-growth and TSR groups, respectively. The differentially expressed circRNAs were validated by qPCR. The differntially expressed circRNA-miRNA networks were predicted, and the mRNAs targeted by these miRNAs were annotated. Our results suggest that circRNAs play a crucial role in responding to herbicide stress, exhibiting distinct responses between NTSR and TSR in rapeseed. These findings offer valuable insights into the mechanisms underlying herbicide resistance in rapeseed.

Pathogen-Derived Extracellular Vesicles: Emerging Mediators of Plant-Microbe Interactions.

Extracellular vesicles (EVs) are lipid bilayer-enclosed nanoparticles that deliver bioactive proteins, nucleic acids, lipids, and other small molecules from donor to recipient cells. They have attracted significant interest recently due to their important roles in regulating plant-microbe interaction. During microbial infection, plant EVs play a prominent role in defense by delivering small regulatory RNA into pathogens, resulting in the silencing of pathogen virulence genes. Pathogens also deliver small RNAs into plant cells to silence host immunity genes. Recent evidence indicates that microbial EVs may be involved in pathogenesis and host immunity modulation by transporting RNAs and other biomolecules. However, the biogenesis and function of microbial EVs in plant-microbe interaction remain ill-defined. In this review, we discuss various aspects of microbial EVs, with a particular focus on current methods for EV isolation, composition, biogenesis, and their roles in plant-microbe interaction. We also discussed the potential role of microbial EVs in cross-kingdom RNA trafficking from pathogens to plants, as it is a highly likely possibility to explore in the future. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Comparative proteomic and physiological analyses reveal tribenuron-methyl phytotoxicity and nontarget-site resistance mechanisms in Brassica napus.

The application of herbicides is the most effective strategy for weed control and the development of herbicide-resistant crops will facilitate the weed management. The acetolactate synthase-inhibiting herbicide, tribenuron-methyl (TBM), is broadly used for weed control. However, its application in rapeseed field is restricted since rapeseed is sensitive to TBM. Herein, an integrated study of cytological, physiological and proteomic analysis of the TBM-resistant rapeseed mutant M342 and its wild-type (WT) plants was conducted. After TBM spraying, M342 showed improved tolerance to TBM, and proteins implicated in non-target-site resistance (NTSR) to herbicides had a significantly higher level in M342 as compared with the WT. Differentially accumulated proteins (DAPs) between these two genotypes were enriched in glutathione metabolism and oxidoreduction coenzyme metabolic process, which protected the mutant from oxidative stress triggered by TBM. Important DAPs related to stress or defence response were up-accumulated in M342 regardless of the TBM treatment, which might serve as the constitutive part of NTSR to TBM. These results provide new clues for further exploration of the NTSR mechanism in plants and establish a theoretical basis for the development of herbicide-resistant crops.

Ammonia borane positively regulates cold tolerance in Brassica napus via hydrogen sulfide signaling.

BACKGROUND: Cold stress adversely influences rapeseeds (Brassica napus L.) growth and yield during winter and spring seasons. Hydrogen (H2) is a potential gasotransmitter that is used to enhance tolerance against abiotic stress, including cold stress. However, convenience and stability are two crucial limiting factors upon the application of H2 in field agriculture. To explore the application of H2 in field, here we evaluated the role of ammonia borane (AB), a new candidate for a H2 donor produced by industrial chemical production, in plant cold tolerance. RESULTS: The application with AB could obviously alleviate the inhibition of rapeseed seedling growth and reduce the oxidative damage caused by cold stress. The above physiological process was closely related to the increased antioxidant enzyme system and reestablished redox homeostasis. Importantly, cold stress-triggered endogenous H2S biosynthesis was further stimulated by AB addition. The removal or inhibition of H2S synthesis significantly abolished plant tolerance against cold stress elicited by AB. Further field experiments demonstrated that the phenotypic and physiological performances of rapeseed plants after challenged with cold stress in the winter and early spring seasons were significantly improved by administration with AB. Particularly, the most studied cold-stress response pathway, the ICE1-CBF-COR transcriptional cascade, was significantly up-regulated either. CONCLUSION: Overall, this study clearly observed the evidence that AB-increased tolerance against cold stress could be suitable for using in field agriculture by stimulation of H2S signaling.

Synergistic mutations of two rapeseed AHAS genes confer high resistance to sulfonylurea herbicides for weed control.

KEY MESSAGE: A double mutant 5N of rapeseed was obtained with a synergistic effect of high resistance to sulfonylurea herbicide. Excellent weed control was observed in Ning R201 created by 5N resources. Sulfonylurea herbicides, which inhibit acetohydroxyacid synthase (AHAS), have become the most widely used herbicides worldwide. However, weed control in rapeseed crop production remains challenging in China due to the shortage of available herbicide-resistant cultivars. In this study, we developed a rapeseed line (PN19) with sulfonylurea herbicide resistance through seed mutagenesis. Molecular analysis revealed a Trp-574-Leu mutation in BnAHAS1-2R of PN19 according to the sequence of Arabidopsis thaliana, and an allele-specific cleaved amplified polymorphic sequence marker was developed to target the point mutation. A double mutant (5N) with very high sulfonylurea resistance was then created through pyramiding two mutant genes of PN19 and M342 by molecular marker-assisted selection. Herbicide resistance identification, toxicology testing, and an in vitro enzyme activity assay of AHAS in 5N indicated that each mutant was four and eight times more resistant to sulfonylurea than M342 and PN19, respectively. Protein structure analysis of AHAS1 demonstrated that the leucine of mutant Trp-574-Leu destroyed the original π-plane stacking effect of the local region for tribenuron-methyl binding, leading to herbicide tolerance. Isobole graph analysis showed a significant synergistic effect of the combination of two mutant genes in 5N for improved tolerance to sulfonylurea herbicides. Finally, we bred rapeseed variety Ning R201 using 5N herbicide resistance resources, and observed excellent weed control performance. Together, these results demonstrate the practical value of 5N application for optimizing and simplifying rapeseed cultivation in China.

Three BnaIAA7 homologs are involved in auxin/brassinosteroid-mediated plant morphogenesis in rapeseed (Brassica napus L.).

KEY MESSAGE: BnaIAA7 crosstalk with BR signaling is mediated by the interaction between BnaARF8 and BnaBZR1 to regulate rapeseed plant morphogenesis. Auxin (indole-3-acetic acid, IAA) and brassinosteroids (BRs) are essential regulators of plant morphogenesis. However, their roles in rapeseed have not been reported. Here, we identified an extremely dwarf1 (ed1) mutant of rapeseed that displays reduced stature, short hypocotyls, as well as wavy and curled leaves. We isolated ED1 by map-based cloning, and found that it encodes a protein homologous to AtIAA7. ED1 acts as a repressor of IAA signaling, and IAA induces its degradation through its degron motif. A genomic-synteny analysis revealed that ED1 has four homologs in rapeseed, but two were not expressed. Analyses of transcriptomes and of various mutant BnaIAA7s in transgenic plants revealed that the three expressed BnaIAA7 homologs had diverse expression patterns. ED1/BnaC05.IAA7 predominantly functioned in stem elongation, BnaA05.IAA7 was essential for reproduction, while BnaA03.IAA7 had the potential to reduce plant height. Physical interaction assays revealed that the three BnaIAA7 homologs interacted in different ways with BnaTIRs/AFBs and BnaARFs, which may regulate the development of specific organs. Furthermore, BnaARF8 could directly interact with the BnaIAA7s and BnaBZR1. We propose that BnaIAA7s interact with BR signaling via BnaARF8 and BnaBZR1 to regulate stem elongation in rapeseed.

Identification and application of markers closely linked to the restorer gene (Rfm) in rapeseed (Brassica napus L.).

The Mutsu-Isuzu cytoplasmic male sterility (MI CMS) system is one of the three-line hybrid systems used in China. As we know, the hybrid system is tightly associated with the yield variation in F1 heterosis, while the restorer gene for the MI CMS (Rfm) has not been finely mapped for further application in marker-assisted selection (MAS). In this study, the sets of near-isogenic lines (NILs) of Rfm in two different genetic backgrounds were hybridized with the genome-wide 60 K single-nucleotide polymorphism (SNP) chip of Brassica for screening the possible associated genomic region of Rfm. Through screening genotypes with SNP loci and sequencing the candidate loci, one 2.5 Mb physical region (covering three scaffolds) on chrA09 was identified as the candidate for the Rfm region. Then, the SSR markers for the target scaffolds were used to detect the recombination in an F2 population and narrowed the Rfm gene within the genetic distance of 0.52 cM, equivalent to a 350 kb physical segment. Moreover, the markers were tested to improve new elite restoration lines and to assess the percentage of hybrid seeds. Our results could potentially accelerate the map-based cloning of the Rfm gene to benefit rapeseed breeding.

Selective modes determine evolutionary rates, gene compactness and expression patterns in Brassica.

It has been well documented that most nuclear protein-coding genes in organisms can be classified into two categories: positively selected genes (PSGs) and negatively selected genes (NSGs). The characteristics and evolutionary fates of different types of genes, however, have been poorly understood. In this study, the rates of nonsynonymous substitution (Ka ) and the rates of synonymous substitution (Ks ) were investigated by comparing the orthologs between the two sequenced Brassica species, Brassica rapa and Brassica oleracea, and the evolutionary rates, gene structures, expression patterns, and codon bias were compared between PSGs and NSGs. The resulting data show that PSGs have higher protein evolutionary rates, lower synonymous substitution rates, shorter gene length, fewer exons, higher functional specificity, lower expression level, higher tissue-specific expression and stronger codon bias than NSGs. Although the quantities and values are different, the relative features of PSGs and NSGs have been largely verified in the model species Arabidopsis. These data suggest that PSGs and NSGs differ not only under selective pressure (Ka /Ks ), but also in their evolutionary, structural and functional properties, indicating that selective modes may serve as a determinant factor for measuring evolutionary rates, gene compactness and expression patterns in Brassica.

Unconditional and conditional QTL analyses of seed fatty acid composition in Brassica napus L.

BACKGROUND: The fatty acid composition of B. napus' seeds determines the oil's nutritional and industrial values, and affects seed germination. Many studies have reported correlations among C16:0, C18:0, C18:1, C18:2 and C18:3 based on phenotypic data; however, the genetic basis of the fatty acid composition in B. napus is still not well understood. RESULTS: In this study, unconditional and conditional quantitative trail locus (QTL) mapping analyses were conducted using a recombinant inbred line in six environments. In total, 21 consensus QTLs each for C16:0, C18:0 and C18:2, 16 for C18:1 and 22 for C18:3 were detected by unconditional mapping. The QTLs with overlapping confidence intervals were integrated into 71 pleiotropically unique QTLs by meta-analysis. Two major QTLs, uuqA5-6 and uuqA5-7, simultaneously affected the fatty acids, except C18:0, in most of environments, with the homologous genes fatty acid desaturase 2 (FAD2) and glycerol-3-phosphate sn-2-acyltransferase 5 (GPAT5) occurring in the confidence interval of uuqA5-6, while phosphatidic acid phosphohydrolase 1 (PAH1) was assigned to uuqA5-7. Moreover, 49, 30, 48, 60 and 45 consensus QTLs were detected for C16:0, C18:0, C18:1, C18:2 and C18:3, respectively, by the conditional mapping analysis. In total, 128 unique QTLs were subsequently integrated from the 232 conditional consensus QTLs. A comparative analysis revealed that 63 unique QTLs could be identified by both mapping methodologies, and 65 additional unique QTLs were only identified in conditional mapping. CONCLUSIONS: Thus, conditional QTL mapping for fatty acids may uncover numerous additional QTLs that were inhibited by the effects of other traits. These findings provide useful information for better understanding the genetic relationships among fatty acids at the QTL level.

Transcriptome Analysis of Sclerotinia sclerotiorum at Different Infection Stages on Brassica napus.

Sclerotinia sclerotiorum is one of the most important plant pathogens, causing enormous losses in a variety of economically important crops including Brassica napus. The interaction of S. sclerotiorum with its hosts is more complex than initially thought, and still poorly understood. In this study, transcriptome analysis was conducted using S. sclerotiorum RNA from the leaf of B. napus. We mapped 11,074,508 and 11,495,788 paired-end reads. A total of 13,313 genes were obtained and classified according to their functional categories. At 6 h post inoculation (hpi) and 24 hpi, the majority of the upregulated differentially expressed genes (DEGs) were focused on DNA binding and ATP binding. However, the genes under the category of ion binding and oxidoreductase activity were also activated at 24 hpi. Most of the upregulated DEGs at 48 hpi were classified in the category of hydrolase activity. The expression levels of these genes related to hydrolase function were analyzed. The results showed that different genes were activated at different stages. The relative expression level of parts of interesting genes which were activated during the infection process was evaluated by quantitative real-time PCR (qRT-PCR). Our results provide new insight into the infection mechanism of S. sclerotiorum.

Genome-Wide Association Study Reveals the Genetic Basis of Crude Fiber Components in Brassica napus L. Shoots at Stem Elongation Stage.

Brassica napus is currently the principal field crop for producing materials for primary, secondary and tertiary industries. B. napus shoots at stem elongation stage are rich in anthocyanins, vitamin C and mineral elements such as selenium, calcium and zinc, and represent a new type of green vegetable. However, the high crude fiber (CF) content of B. napus shoots affects their taste, and few studies have focused on the quality traits of these vegetables. In this study, we investigated five traits related to the CF components, including neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose (Hem) and cellulose (Cel), of B. napus shoots. Whole-genome resequencing at a depth of ∼20× was utilized to genotype an association panel of 202 diverse accessions, which resulted in the identification of 6,093,649 single nucleotide polymorphisms (SNPs) and 996,252 indels, respectively. A genome-wide association study (GWAS) was performed for the five CF-related traits based on the phenotypic data observed in four environments. A total of 1,285 significant SNPs were detected at the threshold of -log10 (p) = 5.16, and 97 significant association regions were obtained. In addition, seven candidate genes located on chromosomes A2 (one gene), A8 (three genes), A9 (two genes) and C9 (one gene) related to CF traits were identified, and ten lines containing low CF contents were selected as excellent germplasm resources for breeding. Our results contributed new insights into the genetic basis of CF traits and suggested germplasm resources for the quality improvement of B. napus shoots.

Optimal Energy Shaping Control for a Backdrivable Hip Exoskeleton.

Task-dependent controllers widely used in exoskeletons track predefined trajectories, which overly constrain the volitional motion of individuals with remnant voluntary mobility. Energy shaping, on the other hand, provides task-invariant assistance by altering the human body's dynamic characteristics in the closed loop. While human-exoskeleton systems are often modeled using Euler-Lagrange equations, in our previous work we modeled the system as a port-controlled-Hamiltonian system, and a task-invariant controller was designed for a knee-ankle exoskeleton using interconnection-damping assignment passivity-based control. In this paper, we extend this framework to design a controller for a backdrivable hip exoskeleton to assist multiple tasks. A set of basis functions that contains information of kinematics is selected and corresponding coefficients are optimized, which allows the controller to provide torque that fits normative human torque for different activities of daily life. Human-subject experiments with two able-bodied subjects demonstrated the controller's capability to reduce muscle effort across different tasks.

Comparative Transcriptome Analysis Reveals the Molecular Basis of Brassica napus in Response to Aphid Stress.

Rapeseed is a globally important economic crop that can be severely impacted by aphids. However, our understanding of rapeseed resistance to aphid stress is very limited. In this study, we analyzed the resistance characteristics of the low aphid-susceptible variety APL01 and the highly aphid-susceptible variety Holly in response to aphid stress. APL01 had a more significant inhibitory effect on aphid proliferation compared with Holly during the early stage of inoculation, whereas Holly showed stronger tolerance to aphid stress compared with APL01 during the later stage of inoculation. Through transcriptome, physiological, and gene expression analyses, it was revealed that chitinase activity, catalase activity, calcium signal transduction, and activation of systemic acquired resistance might be involved in aphid resistance in B. napus. The degree of inhibition of photosynthesis in plants under aphid stress directly determines the tolerance of B. napus to aphid stress. Furthermore, four promising candidate genes were screened from eight genes related to rapeseed response to biotic stress through RT-qPCR analysis of gene expression levels. These research findings represent an important step forward in understanding the resistance of rapeseed to aphid stress and provide a solid foundation for the cloning of genes responsible for this resistance.

Genetic Dissection and Germplasm Selection of the Low Crude Fiber Component in Brassica napus L. Shoots.

BACKGROUND: Brassica napus is one of the most important oil crops in the world, and B. napus shoots are nutrient-rich fresh vegetables. The crude fiber (CF) component is one of the most important factors affecting the taste quality of B. napus shoots, but the factors underlying the desirable low-CF trait remain poorly understood. METHODS: In this study, a high-density single-nucleotide polymorphism (SNP) map was used to map quantitative trait loci (QTLs) for five CF-related traits in a recombinant inbred population. RESULTS: A total of 49 QTLs were obtained in four environments, including eleven, twelve, eight, twelve and six QTLs for content of neutral detergent fiber, acid detergent fiber, acid detergent lignin, hemicellulose and cellulose, respectively. The phenotypic variation explained by single QTL ranged from 4.62% to 14.76%. Eight of these QTLs were further integrated into four unique QTLs, which controlled two different traits simultaneously. Five CF-component-related candidate genes were identified, among which BnaC03g07110D and BnaC07g21271D were considered to be the most likely candidate genes. In addition, five lines with low CF content were selected, which can be used as excellent germplasm resources in breeding. CONCLUSIONS: The QTLs identified in this study will contribute to our understanding of the genetic mechanism of CF and can be used as targets for reducing CF content in B. napus shoots. In addition, this study also provided excellent germplasm resources for low CF content breeding.

Genetic Diversity Analysis of Brassica Yellows Virus Causing Aberrant Color Symptoms in Oilseed Rape.

The emergence of brassica yellow virus (BrYV) has increasingly damaged crucifer crops in China in recent years. In 2020, a large number of oilseed rape in Jiangsu showed aberrant leaf color. A combined RNA-seq and RT-PCR analysis identified BrYV as the major viral pathogen. A subsequent field survey showed that the average incidence of BrYV was 32.04%. In addition to BrYV, turnip mosaic virus (TuMV) was also frequently detected. As a result, two near full-length BrYV isolates, BrYV-814NJLH and BrYV-NJ13, were cloned. Based on the newly obtained sequences and the reported BrYV and turnip yellow virus (TuYV) isolates, a phylogenetic analysis was performed, and it was found that all BrYV isolates share a common root with TuYV. Pairwise amino acid identity analysis revealed that both P2 and P3 were conserved in BrYV. Additionally, recombination analysis revealed seven recombinant events in BrYV as TuYV. We also attempted to determine BrYV infection by quantitative leaf color index, but no significant correlation was found between the two. Systemic observations indicated that BrYV-infected plants had different symptoms, such as no symptom, purple stem base and red old leaves. Overall, our work proves that BrYV is closely related to TuYV and could be considered as an epidemic strain for oilseed rape in Jiangsu.

Tailoring the Dispersion of Metals on ZnO with Preadsorbed Water.

The dispersity of metal particles over oxide surfaces is generally critical for the applications of the metal/oxide hybridized systems. In this work, we have experimentally investigated the hydration effect of preadsorbed water species over the Cu and Pd particles deposited on the ZnO(10-10) surface. Using scanning tunneling microscopy (STM), we clearly saw that both Cu and Pd grow as three-dimensional particles on the clean ZnO(10-10) surface but disperse into single atoms and few-atom clusters on the water-covered surfaces. Moreover, X-ray photoelectron spectroscopy (XPS) measurements revealed that Cu is readily oxidized by interacting with the molecular water while Pd tends to bind the surface hydroxyls and keep neutral status. Our work has demonstrated the effective role of the surface water in tuning the morphologies as well as electronic states of the supported metals, which may bring new insights to a number of important surface processes with water in presence.

Unveiling the Atomic Structure and Growth Dynamics of One-Dimensional Water on ZnO(10-10).

The adsorption and organization state of water on the metal oxide surface is of critical importance for wide fields where interface chemistry dominates. On the technically important ZnO(10-10) surface, we found water assembles into an one-dimensional (1D) chain structure at submonolayer coverage instead of the well-known half-dissociated two-dimensional (2D) island. With a combination of high resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we clearly distinguished the single and double water chains, which are composed of dissociated monomers and half-dissociated dimers, respectively. Moreover, we unambiguously determined that single water molecules dissociate spontaneously before agglomerating into ordered phase, which is contrary to the proposition of previous studies. These results have deepened our understandings of the adsorbed water species on the ZnO surface, which may bring new insights into the mechanisms of water-stimulated surface reactions.

Fine Mapping and Characterization of a Major Gene Responsible for Chlorophyll Biosynthesis in Brassica napus L.

Rapeseed (Brassica napus L.) is mainly used for oil production and industrial purposes. A high photosynthetic efficiency is the premise of a high yield capable of meeting people's various demands. Chlorophyll-deficient mutants are ideal materials for studying chlorophyll biosynthesis and photosynthesis. In a previous study, we obtained the mutant yl1 for leaf yellowing throughout the growth period by ethyl methanesulfonate mutagenesis of B. napus. A genetic analysis showed that the yl1 chlorophyll-deficient phenotype was controlled by one incompletely dominant gene, which was mapped on chromosome A03 by a quantitative trait loci sequencing analysis and designated as BnA03.Chd in this study. We constructed an F2 population containing 5256 individuals to clone BnA03.Chd. Finally, BnA03.Chd was fine-mapped to a 304.7 kb interval of the B. napus 'ZS11' genome containing 58 annotated genes. Functional annotation, transcriptome, and sequence variation analyses confirmed that BnaA03g0054400ZS, a homolog of AT5G13630, was the most likely candidate gene. BnaA03g0054400ZS encodes the H subunit of Mg-chelatase. A sequence analysis revealed a single-nucleotide polymorphism (SNP), causing an amino-acid substitution from glutamic acid to lysine (Glu1349Lys). In addition, the molecular marker BnaYL1 was developed based on the SNP of BnA03.Chd, which perfectly cosegregated with the chlorophyll-deficient phenotype in two different F2 populations. Our results provide insight into the molecular mechanism underlying chlorophyll synthesis in B. napus.

Fine Mapping and Candidate Gene Analysis of BnC08.cds, a Recessive Gene Responsible for Sepal-Specific Chlorophyll-Deficiency in Brassica napus L.

Chloroplast development is crucial for photosynthesis and plant growth and many factors are involved in its regulation. The regulatory mechanism differs in different green tissues, and previous studies have focused on chloroplasts in leaves. In this study, a mutant with sepal-specific chlorophyll-deficiency was observed in Brassica napus and named as df74. Genetic analysis indicated that the phenotype was controlled by a single recessive nuclear gene. The gene was located on chromosome C08 by bulked-segregant analysis with whole-genome sequencing, which was designated as BnC08.cds. To fine-map the BnC08.cds, a F2 population was created from the cross of df74 and Zhongshuang11 (ZS11). Finally, the BnC08.cds was fine-mapped in the region between the single-nucleotide polymorphism (SNP) markers M5 and M6, corresponding to a 228.72 kb interval of the B. napus "ZS11" genome. Eighteen genes were predicted in the target region, and it was speculated that BnaC08G0442100ZS was the most likely candidate gene based on the results of transcriptome analyses and sequence variation analyses. These results provide a foundation to explore the regulation of chloroplast development in sepals.