Genome-wide association study dissects the genetic control of plant height and branch number in response to low-phosphorus stress in Brassica napus

Exploring silique number in Brassica napus L.: Genetic and molecular advances for improving yield

Silique number is a crucial yield-related trait for the genetic enhancement of rapeseed (Brassica napus L.). The intricate molecular process governing the regulation of silique number involves various factors. Despite advancements in understanding the mechanisms regulating silique number in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), the molecular processes involved in controlling silique number in rapeseed remain largely unexplored. In this review, we identify candidate genes and review the roles of genes and environmental factors in regulating rapeseed silique number. We use genetic regulatory networks for silique number in Arabidopsis and grain number in rice to uncover possible regulatory pathways and molecular mechanisms involved in regulating genes associated with rapeseed silique number. A better understanding of the genetic network regulating silique number in rapeseed will provide a theoretical basis for the genetic improvement of this trait and genetic resources for the molecular breeding of high-yielding rapeseed.

Dissection of quantitative trait nucleotides and candidate genes associated with agronomic and yield-related traits under drought stress in rapeseed varieties: integration of genome-wide association study and transcriptomic analysis

Introduction

An important strategy to combat yield loss challenge is the development of varieties with increased tolerance to drought to maintain production. Improvement of crop yield under drought stress is critical to global food security.

Methods

In this study, we performed multiomics analysis in a collection of 119 diverse rapeseed (Brassica napus L.) varieties to dissect the genetic control of agronomic traits in two watering regimes [well-watered (WW) and drought stress (DS)] for 3 years. In the DS treatment, irrigation continued till the 50% pod development stage, whereas in the WW condition, it was performed throughout the whole growing season.

Results

The results of the genome-wide association study (GWAS) using 52,157 single-nucleotide polymorphisms (SNPs) revealed 1,281 SNPs associated with traits. Six stable SNPs showed sequence variation for flowering time between the two irrigation conditions across years. Three novel SNPs on chromosome C04 for plant weight were located within drought tolerance-related gene ABCG16, and their pleiotropically effects on seed weight per plant and seed yield were characterized. We identified the C02 peak as a novel signal for flowering time, harboring 52.77% of the associated SNPs. The 288-kbps LD decay distance analysis revealed 2,232 candidate genes (CGs) associated with traits. The CGs BIG1-D, CAND1, DRG3, PUP10, and PUP21 were involved in phytohormone signaling and pollen development with significant effects on seed number, seed weight, and grain yield in drought conditions. By integrating GWAS and RNA-seq, 215 promising CGs were associated with developmental process, reproductive processes, cell wall organization, and response to stress. GWAS and differentially expressed genes (DEGs) of leaf and seed in the yield contrasting accessions identified BIG1-D, CAND1, and DRG3 genes for yield variation.

Discussion

The results of our study provide insights into the genetic control of drought tolerance and the improvement of marker-assisted selection (MAS) for breeding high-yield and drought-tolerant varieties.

Soybean type-B response regulator GmRR1 mediates phosphorus uptake and yield by modifying root architecture

Phosphorus (P) plays a pivotal role in plant growth and development. Low P stress can greatly hamper plant growth. Here, we identified a QTL (named QPH-9-1), which is associated with P efficiency across multiple environments through linkage analysis and genome-wide association study. Furthermore, we successfully cloned the underlying soybean (Glycine max) gene GmRR1 (a soybean type-B Response Regulator 1) that encodes a type-B response regulator protein. Knockout of GmRR1 resulted in a substantial increase in plant height, biomass, P uptake efficiency, and yield-related traits due to the modification of root structure. In contrast, overexpression of GmRR1 in plants resulted in a decrease in these phenotypes. Further analysis revealed that knockout of GmRR1 substantially increased the levels of auxin and ethylene in roots, thereby promoting root hair formation and growth by promoting the formation of root hair primordium and lengthening the root apical meristem. Yeast two-hybrid, bimolecular fluorescence complementation, and dual-luciferase assays demonstrated an interaction between GmRR1 and Histidine-containing Phosphotransmitter protein 1. Expression analysis suggested that these proteins coparticipated in response to low P stress. Analysis of genomic sequences showed that GmRR1 underwent a selection during soybean domestication. Taken together, this study provides further insights into how plants respond to low P stress by modifying root architecture through phytohormone pathways.

Genome-wide association study reveals candidate genes controlling root system architecture under low phosphorus supply at seedling stage in Brassica napus

Optimal root system architecture (RSA) is essential for vigorous growth and yield in crops. Plants have evolved adaptive mechanisms in response to low phosphorus (LP) stress, and one of those is changes in RSA. Here, more than five million single-nucleotide polymorphisms (SNPs) obtained from whole-genome re-sequencing data (WGR) of an association panel of 370 oilseed rape (Brassica napus L.) were used to conduct a genome-wide association study (GWAS) of RSA traits of the panel at LP in "pouch and wick" system. Fifty-two SNPs were forcefully associated with lateral root length (LRL), total root length (TRL), lateral root density (LRD), lateral root number (LRN), mean lateral root length (MLRL), and root dry weight (RDW) at LP. There were significant correlations between phenotypic variation and the number of favorable alleles of the associated loci on chromosomes A06 (chrA06_20030601), C03 (chrC03_3535483), and C07 (chrC07_42348561), respectively. Three candidate genes (BnaA06g29270D, BnaC03g07130D, and BnaC07g43230D) were detected by combining transcriptome, candidate gene association analysis, and haplotype analysis. Cultivar carrying "CCGC" at BnaA06g29270DHap1, "CAAT" at BnaC03g07130DHap1, and "ATC" at BnaC07g43230DHap1 had greater LRL, LRN, and RDW than lines carrying other haplotypes at LP supply. The RSA of a cultivar harboring the three favorable haplotypes was further confirmed by solution culture experiments. These findings define exquisite insights into genetic architectures underlying B. napus RSA at LP and provide valuable gene resources for root breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01411-2.

Integrating genome-wide association studies with selective sweep reveals genetic loci associated with tolerance to low phosphate availability in Brassica napus

Oilseed rape (Brassica napus L.; B. napus) is an important oil crop worldwide. However, the genetic mechanisms of B. napus adaptations to low phosphate (P) stress are largely unknown. In this study, a genome-wide association study (GWAS) identified 68 SNPs significantly associated with seed yield (SY) under low P (LP) availability, and 7 SNPs significantly associated with phosphorus efficiency coefficient (PEC) in two trials. Among these SNPs, two, chrC07__39807169 and chrC09__14194798, were co-detected in two trials, and BnaC07.ARF9 and BnaC09.PHT1;2 were identified as candidate genes of them, respectively, by combining GWAS with quantitative reverse-transcription PCR (qRT-PCR). There were significant differences in the gene expression level of BnaC07.ARF9 and BnaC09.PHT1;2 between P-efficient and -inefficiency varieties at LP. SY_LP had a significant positive correlation with the gene expression level of both BnaC07.ARF9 and BnaC09.PHT1;2. BnaC07.ARF9 and BnaA01.PHR1 could directly bind the promoters of BnaA01.PHR1 and BnaC09.PHT1;2, respectively. Selective sweep analysis was conducted between ancient and derived B. napus, and detected 1280 putative selective signals. Within the selected region, a large number of genes related to P uptake, transport, and utilization were detected, such as purple acid phosphatase (PAP) family genes and phosphate transporter (PHT) family genes. These findings provide novel insights into the molecular targets for breeding P efficiency varieties in B. napus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01399-9.

BnIR: A multi-omics database with various tools for Brassica napus research and breeding

In the post-genome-wide association study era, multi-omics techniques have shown great power and potential for candidate gene mining and functional genomics research. However, due to the lack of effective data integration and multi-omics analysis platforms, such techniques have not still been applied widely in rapeseed, an important oil crop worldwide. Here, we report a rapeseed multi-omics database (BnIR; http://yanglab.hzau.edu.cn/BnIR), which provides datasets of six omics including genomics, transcriptomics, variomics, epigenetics, phenomics, and metabolomics, as well as numerous "variation-gene expression-phenotype" associations by using multiple statistical methods. In addition, a series of multi-omics search and analysis tools are integrated to facilitate the browsing and application of these datasets. BnIR is the most comprehensive multi-omics database for rapeseed so far, and two case studies demonstrated its power to mine candidate genes associated with specific traits and analyze their potential regulatory mechanisms.

Genetic dissection of branch architecture in oilseed rape (Brassica napus L.) germplasm

Branch architecture is an important factor influencing rapeseed planting density, mechanized harvest, and yield. However, its related genes and regulatory mechanisms remain largely unknown. In this study, branch angle (BA) and branch dispersion degree (BD) were used to evaluate branch architecture. Branch angle exhibited a dynamic change from an increase in the early stage to a gradual decrease until reaching a stable state. Cytological analysis showed that BA variation was mainly due to xylem size differences in the vascular bundle of the branch junction. The phenotypic analysis of 327 natural accessions revealed that BA in six environments ranged from 24.3° to 67.9°, and that BD in three environments varied from 4.20 cm to 21.4 cm, respectively. A total of 115 significant loci were detected through association mapping in three models (MLM, mrMLM, and FarmCPU), which explained 0.53%-19.4% of the phenotypic variations. Of them, 10 loci were repeatedly detected in different environments and models, one of which qBAD.A03-2 was verified as a stable QTL using a secondary segregation population. Totally, 1066 differentially expressed genes (DEGs) were identified between branch adaxial- and abaxial- sides from four extremely large or small BA/BD accessions through RNA sequencing. These DEGs were significantly enriched in the pathways related to auxin biosynthesis and transport as well as cell extension such as indole alkaloid biosynthesis, other glycan degradation, and fatty acid elongation. Four known candidate genes BnaA02g16500D (PIN1), BnaA03g10430D (PIN2), BnaC03g06250D (LAZY1), and BnaC06g20640D (ARF17) were identified by both GWAS and RNA-seq, all of which were involved in regulating the asymmetric distribution of auxins. Our identified association loci and candidate genes provide a theoretical basis for further study of gene cloning and genetic improvement of branch architecture.

Differential alternative splicing genes and isoform co-expression networks of Brassica napus under multiple abiotic stresses

Alternative splicing (AS) is an important regulatory process that affects plant development and stress responses by greatly increasing the complexity of transcriptome and proteome. To understand how the AS landscape of B. napus changes in response to abiotic stresses, we investigated 26 RNA-seq libraries, including control and treatments with cold, dehydration, salt, and abscisic acid (ABA) at two different time points, to perform comparative alternative splicing analysis. Apparently, AS events increased under all stresses except dehydration for 1 h, and intron retention was the most common AS mode. In addition, a total of 357 differential alternative splicing (DAS) genes were identified under four abiotic stresses, among which 81 DAS genes existed in at least two stresses, and 276 DAS genes were presented under only one stress. A weighted gene co-expression network analysis (WGCNA) based on the splicing isoforms, rather than the genes, pinpointed out 23 co-expression modules associated with different abiotic stresses. Among them, a number of significant hub genes were also found to be DAS genes, which encode key isoforms involved in responses to single stress or multiple stresses, including RNA-binding proteins, transcription factors, and other important genes, such as RBP45C, LHY, MYB59, SCL30A, RS40, MAJ23.10, and DWF4. The splicing isoforms of candidate genes identified in this study could be a valuable resource for improving tolerance of B. napus against multiple abiotic stresses.

Genome-wide association study identifies candidate genes and favorable haplotypes for seed yield in Brassica napus

Oilseed rape (Brassica napus L.) is one of the most essential oil crops. Genetic improvement of seed yield (SY) is a major aim of B. napus breeding. Several studies have been reported on the genetic mechanisms of SY of B. napus. Here, a genome-wide association study (GWAS) of SY was conducted using a panel of 403 natural accessions of B. napus, with more than five million high-quality single-nucleotide polymorphisms (SNPs). A total of 1773 significant SNPs were detected associated with SY, and 783 significant SNPs were co-located with previously reported QTLs. The lead SNPs chrA01__8920351 and chrA02__4555979 were jointly detected in Trial 2_2 and Trial 2_mean value, and in Trial 1_2 and Trial 1_mean value, respectively. Subsequently, two candidate genes of BnaA01g17200D and BnaA02g08680D were identified through combining transcriptome, candidate gene association analysis, and haplotype analysis. BnaA09g10430D detected through lead SNP chrA09__5160639 was associated with SY of B. napus. Our results provide valuable information for studying the genetic control of seed yield in B. napus and valuable genes, haplotypes, and cultivars resources for the breeding of high seed yield B. napus cultivars.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01332-6.

Genetic Diversity and Genome-Wide Association Study of Architectural Traits of Spray Cut Chrysanthemum Varieties

The architecture of spray cut chrysanthemum is crucial for the quality and quantity of cut flower production. However, the mechanism underlying plant architecture still needs to be clarified. In this study, we measured nine architecture-related traits of 195 spray cut chrysanthemum varieties during a two-year period. The results showed that the number of upper primary branches, number of lateral flower buds and primary branch length widely varied. Additionally, plant height had a significant positive correlation with number of leaf nodes and total number of lateral buds. Number of upper primary branches had a significant negative correlation with primary branch diameter, primary branch angle and primary branch length. Plant height, total number of lateral buds, number of upper primary branches, stem diameter, primary branch diameter and primary branch length were vulnerable to environmental impacts. All varieties could be divided into five categories according to cluster analysis, and the typical plant architecture of the varieties was summarized. Finally, a genome-wide association study (GWAS) was performed to find potential functional genes.