Multiomics reveal pivotal roles of sodium translocation and compartmentation in regulating salinity resistance in allotetraploid rapeseed

Progress on Salt Tolerance in Brassica napus

In China, saline-alkali lands constitute 5.01% of the total land area, having a significant impact on both domestic and international food production. Rapeseed (Brassica napus L.), as one of the most important oilseed crops in China, has garnered considerable attention due to its potential adaptability to saline conditions. Breeding and improving salt-tolerant varieties is a key strategy for the effective utilization of saline lands. Hence, it is important to conduct comprehensive research into the adaptability and salt tolerance mechanisms of Brassica napus in saline environments as well as to breed novel salt-tolerant varieties. This review summarizes the molecular mechanism of salt tolerance, physiological and phenotypic indexes, research strategies for the screening of salt-tolerant germplasm resources, and genetic engineering tools for salt stress in Brassica napus. It also introduces various agronomic strategies for applying exogenous substances to alleviate salt stress and provide technological tools and research directions for future research on salt tolerance in Brassica napus.

Pectin demethylation-mediated cell wall Na+ retention positively regulates salt stress tolerance in oilseed rape

KEY MESSAGE

Integrated phenomics, ionomics, genomics, transcriptomics, and functional analyses present novel insights into the role of pectin demethylation-mediated cell wall Na+ retention in positively regulating salt tolerance in oilseed rape. Genetic variations in salt stress tolerance identified in rapeseed genotypes highlight the complicated regulatory mechanisms. Westar is ubiquitously used as a transgenic receptor cultivar, while ZS11 is widely grown as a high-production and good-quality cultivar. In this study, Westar was found to outperform ZS11 under salt stress. Through cell component isolation, non-invasive micro-test, X-ray energy spectrum analysis, and ionomic profile characterization, pectin demethylation-mediated cell wall Na+ retention was proposed to be a major regulator responsible for differential salt tolerance between Westar and ZS11. Integrated analyses of genome-wide DNA variations, differential expression profiling, and gene co-expression networks identified BnaC9.PME47, encoding a pectin methylesterase, as a positive regulator conferring salt tolerance in rapeseed. BnaC9.PME47, located in two reported QTL regions for salt tolerance, was strongly induced by salt stress and localized on the cell wall. Natural variation of the promoter regions conferred higher expression of BnaC9.PME47 in Westar than in several salt-sensitive rapeseed genotypes. Loss of function of AtPME47 resulted in the hypersensitivity of Arabidopsis plants to salt stress. The integrated multiomics analyses revealed novel insights into pectin demethylation-mediated cell wall Na+ retention in regulating differential salt tolerance in allotetraploid rapeseed genotypes. Furthermore, these analyses have provided key information regarding the rapid dissection of quantitative trait genes responsible for nutrient stress tolerance in plant species with complex genomes.

Morpho-physiological, Genomic, and Transcriptional Diversities in Response to Potassium Deficiency in Rapeseed (Brassica napus L.) Genotypes

Variations in the resistance to potassium (K) deficiency among rapeseed genotypes emphasize complicated regulatory mechanisms. In this study, a low-K-sensitivity accession (L49) responded to K deficiency with smaller biomasses, severe leaf chlorosis, weaker photosynthesis ability, and deformed stomata morphology compared to a low-K resistant accession (H280). H280 accumulated more K+ than L49 under low K. Whole-genome resequencing (WGS) revealed a total of 5,538,622 single nucleotide polymorphisms (SNPs) and 859,184 insertions/deletions (InDels) between H280 and L49. RNA-seq identified more differentially expressed K+ transporter genes with higher expression in H280 than in L49 under K deficiency. Based on the K+ profiles, differential expression profiling, weighted gene coexpression network analysis, and WGS data between H280 and L49, BnaC4.AKT1 was proposed to be mainly responsible for root K absorption-mediated low K resistance. BnaC4.AKT1 was expressed preferentially in the roots and localized on the plasma membrane. An SNP and an InDel found in the promoter region of BnaC4.AKT1 were proposed to be responsible for its differential expression between rapeseed genotypes. This study identified a gene resource for improving low-K resistance. It also facilitates an integrated knowledge of the differential physiological and transcriptional responses to K deficiency in rapeseed genotypes.

Multiomics reveals an essential role of long-distance translocation in regulating plant cadmium resistance and grain accumulation in allohexaploid wheat (Triticum aestivum)

Cadmium (Cd) is a highly toxic heavy metal that readily enters cereals, such as wheat, via the roots and is translocated to the shoots and grains, thereby posing high risks to human health. However, the vast and complex genome of allohexaploid wheat makes it challenging to understand Cd resistance and accumulation. In this study, a Cd-resistant cultivar of wheat, 'ZM1860', and a Cd-sensitive cultivar, 'ZM32', selected from a panel of 442 accessions, exhibited significantly different plant resistance and grain accumulation. We performed an integrated comparative analysis of the morpho-physiological traits, ionomic and phytohormone profiles, genomic variations, transcriptomic landscapes, and gene functionality in order to identify the mechanisms underlying these differences. Under Cd toxicity, 'ZM1860' outperformed 'ZM32', which showed more severe leaf chlorosis, poorer root architecture, higher accumulation of reactive oxygen species, and disordered phytohormone homeostasis. Ionomics showed that 'ZM32' had a higher root-to-shoot translocation coefficient of Cd and accumulated more Cd in the grains than 'ZM1860'. Whole-genome re-sequencing (WGS) and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in abiotic stress responses and ion transport between the two genotypes. Combined ionomics, transcriptomics, and functional gene analysis identified the plasma membrane-localized heavy metal ATPase TaHMA2b-7A as a crucial Cd exporter regulating long-distance Cd translocation in wheat. WGS- and PCR-based analysis of sequence polymorphisms revealed a 25-bp InDel site in the promoter region of TaHMA2b-7A, and this was probably responsible for the differential expression. Our multiomics approach thus enabled the identification of a core transporter involved in long-distance Cd translocation in wheat, and it may provide an elite genetic resource for improving plant Cd resistance and reducing grain Cd accumulation in wheat and other cereal crops.

Genome-Wide Identification and Functional Characterization Reveals the Pivotal Roles of BnaA8.ATG8F in Salt Stress Tolerance and Nitrogen Limitation Adaptation in Allotetraploid Rapeseed

Autophagy is a common physiological process in organisms, including higher plants. The ATG8 subfamily, the core member of the autophagy-related gene (ATG) family, plays a key role in plant growth and development and nutrient stress responses. However, the core ATG8 homologs and their roles in stress resistance remain elusive in allotetraploid rapeseed (AACC, Brassica napus L.). In this study, we identified 29 ATG8 subgroup members, consisting of three phylogenetic clades, based on the analysis of genomic annotation and conserved motifs. Differential transcriptional responses of BnaATG8s to salt stress, nitrogen limitation, and other nutrient stresses were investigated, and we identified BnaA8.ATG8F as the core ATG8 member through gene co-expression network analysis. Decreased BnaA8.ATG8F expression repressed the salt tolerance of transgenic rapeseed plants by significantly reducing the root Na⁺ retention under salt stress. Moreover, downregulation of BnaA8.ATG8F increased nitrogen (N) limitation sensitivity of transgenic rapeseed plants through decreasing N uptake, translocation, and enhancing N remobilization under nitrogen starvation. In summary, we identified the core ATG8 homologs and characterized their physiological and molecular mechanisms underlying salt stress tolerance and nitrogen limitation adaptation. Our results may provide elite genetic resources for the genetic improvement of nutrient stress tolerance in rapeseed.

Comparative physiological and transcriptomic analyses reveal ascorbate and glutathione coregulation of cadmium toxicity resistance in wheat genotypes

BACKGROUND

Cadmium (Cd) is a heavy metal with high toxicity that severely inhibits wheat growth and development. Cd easily accumulates in wheat kernels and enters the human food chain. Genetic variation in the resistance to Cd toxicity found in wheat genotypes emphasizes the complex response architecture. Understanding the Cd resistance mechanisms is crucial for combating Cd phytotoxicity and meeting the increasing daily food demand.

RESULTS

Using two wheat genotypes (Cd resistant and sensitive genotypes T207 and S276, respectively) with differing root growth responses to Cd, we conducted comparative physiological and transcriptomic analyses and exogenous application tests to evaluate Cd detoxification mechanisms. S276 accumulated more H₂O₂, O₂^-, and MDA than T207 under Cd toxicity. Catalase activity and levels of ascorbic acid (AsA) and glutathione (GSH) were greater, whereas superoxide dismutase (SOD) and peroxidase (POD) activities were lower in T207 than in S276. Transcriptomic analysis showed that the expression of RBOHA, RBOHC, and RBOHE was significantly increased under Cd toxicity, and two-thirds (22 genes) of the differentially expressed RBOH genes had higher expression levels in S276 than inT207. Cd toxicity reshaped the transcriptional profiling of the genes involving the AsA-GSH cycle, and a larger proportion (74.25%) of the corresponding differentially expressed genes showed higher expression in T207 than S276. The combined exogenous application of AsA and GSH alleviated Cd toxicity by scavenging excess ROS and coordinately promoting root length and branching, especially in S276.

CONCLUSIONS

The results indicated that the ROS homeostasis plays a key role in differential Cd resistance in wheat genotypes, and the AsA-GSH cycle fundamentally and vigorously influences wheat defense against Cd toxicity, providing insight into the physiological and transcriptional mechanisms underlying Cd detoxification.