Developing multifunctional crops by engineering Brassicaceae glucosinolate pathways

Complexity Meets Risk-The Next Generation of Genome-Edited Plants Challenges Established Concepts for Environmental Risk Assessment in the EU

For 20 years, the environmental risk assessment (ERA) of genetically modified plants (GMPs) has used a comparative assessment approach, comparing the GMP to presumably safe and familiar non-modified plant varieties. With new genomic techniques, it is now possible to design complex GMP applications with systemic metabolic changes, resulting in novel plant phenotypes. These plant phenotypes can exhibit profoundly altered morphological, physiological, or compositional characteristics, intentionally lacking equivalence with parental plants and non-modified comparators. Through the analysis of case studies involving GMPs with modifications of complex metabolic pathways, we evaluate the current practice of the comparative safety assessment approach applied in ERA in the European Union and its ability to inform ERA, particularly regarding environmental risks. Our findings show that the existing approach has notable weaknesses when applied to complex GMP applications. We suggest complementing ERA with a hypothesis-driven assessment approach that considers various protection goals and relies on whole-plant experimental assessments to draw risk conclusions. As plant modifications become increasingly complex, such as the development of synthetic biology plants, conducting ecologically realistic assessments will be crucial for future ERA.

Deciphering the heterogeneous glucosinolates composition in leaves and seeds: strategies for developing Brassica napus genotypes with low seed glucosinolates content but high leaf glucosinolates content

Rapeseed cakes with low glucosinolates content (GC) possess high feeding value. However, the pursuit of low-GC seeds has inadvertently resulted in a reduction of GC in leaves, making plants more susceptible to stress and lowering their nutritional quality. Therefore, it is imperative to disrupt the tight association between GC in these two tissues and ultimately develop genotypes with low-GC seeds but high-GC leaves. The distinct mechanisms underlying glucosinolate (GSL) synthesis in these two tissues remain unclear. Here, we discovered that aliphatic and aromatic GSLs, rather than indole GSLs, contribute to the positive correlation between GC in seeds and leaves. We performed selective-sweep analyses and identified the genomic footprints left after decades of intense selection for low-GC seeds. By conducting genome-wide association studies and analyzing differentially expressed genes in high- and low-GC seeds and leaves, we compiled lists of distinct genes involved in GSL synthesis in leaves and seeds separately. In particular, BnMYB28 plays a key role in regulating GC in both seeds and leaves. Selection and manipulation of BnaC09.MYB28 would affect GC in both tissues. However, downregulation of BnaA02.MYB28 and/or BnaC02.MYB28 would likely reduce GC in seeds without causing a concurrent reduction in GC in leaves.

Phenotypic advantages and improved genomic stability following selection in advanced selfing-generations of Brassica allohexaploids

Allopolyploids often exhibit advantages in vigor and adaptability compared to diploids. A long-term goal in the economically important Brassica genus has been to develop a new allohexaploid crop type (AABBCC) by combining different diploid and allotetraploid crop species. However, early-generation allohexaploids often face challenges like unstable meiosis and low fertility, and the phenotypic performance of these synthetic lines has rarely been assessed. This study analyzes agronomic traits, fertility, and genome stability in ArArBcBcCcCc lines derived from four crosses between B. carinata and B. rapa after 9-11 selfing generations. Our results demonstrate polyploid advantage in vigor and seed traits, considerable phenotypic variation, and high fertility and genome stability. Meanwhile, parental genotypes significantly influence outcomes in advanced allohexaploids. Structural variants, largely resulting from A-C homoeologous exchanges, contribute to genomic variation and influence hexaploid genome stability, with the A sub-genome showing the highest variability. Both positive and negative impacts of SVs on fertility and seed weight are observed. Pseudo-euploids, frequently appearing, do not significantly affect fertility or other agronomic traits compared to euploids, indicating a potential pathway toward a stable allohexaploid species. These findings provide insights into the challenge and potential for developing an adaptable and stable Brassica hexaploid through selection.

Glucosinolates in Human Health: Metabolic Pathways, Bioavailability, and Potential in Chronic Disease Prevention

Glucosinolates (GSLs) are sulfur-containing compounds predominantly found in cruciferous vegetables such as broccoli, kale, and Brussels sprouts, and are recognized for their health-promoting properties. Upon consumption, GSLs undergo hydrolysis by the enzyme myrosinase, resulting in bioactive compounds like isothiocyanates and specific indole glucosinolate degradation products, such as indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM), which contribute to a range of health benefits, including anti-cancer, anti-inflammatory, and cardioprotective effects. This review explores the structure, metabolism, and bioavailability of GSLs. Recent evidence supports the protective role of GSLs in chronic diseases, with mechanisms including the modulation of oxidative stress, inflammation, and detoxification pathways. Furthermore, the innovative strategies to enhance GSL bioactivity, such as biofortification, genetic introgression, and optimized food processing methods, have been examined. These approaches seek to increase GSL content in edible plants, thereby maximizing their health benefits. This comprehensive review provides insights into dietary recommendations, the impact of food preparation, and recent advances in GSL bioavailability enhancement, highlighting the significant potential of these bioactive compounds in promoting human health and preventing chronic diseases.

Catalysts for sulfur: understanding the intricacies of enzymes orchestrating plant sulfur anabolism

MAIN CONCLUSION

This review highlights the sulfur transporters, key enzymes and their encoding genes involved in plant sulfur anabolism, focusing on their occurrence, chemistry, location, function, and regulation within sulfur assimilation pathways. Sulfur, a vital element for plant life, plays diverse roles in metabolism and stress response. This review provides a comprehensive overview of the sulfur assimilation pathway in plants, highlighting the intricate network of enzymes and their regulatory mechanisms. The primary focus is on the key enzymes involved: ATP sulfurylase (ATPS), APS reductase (APR), sulfite reductase (SiR), serine acetyltransferase (SAT), and O-acetylserine(thiol)lyase (OAS-TL). ATPS initiates the process by activating sulfate to form APS, which is then reduced to sulfite by APR. SiR further reduces sulfite to sulfide, a crucial step that requires significant energy. The cysteine synthase complex (CSC), formed by SAT and OAS-TL, facilitates the synthesis of cysteine, thereby integrating serine metabolism with sulfur assimilation. The alternative sulfation pathway, catalyzed by APS kinase and sulfotransferases, is explored for its role in synthesizing essential secondary metabolites. This review also delves into the regulatory mechanism of these enzymes such as environmental stresses, sulfate availability, phytohormones, as well as translational and post-translational regulations. Understanding the key transporters and enzymes in sulfur assimilation pathways and their corresponding regulation mechanisms can help researchers grasp the importance of sulfur anabolism for the life cycle of plants, clarify how these enzymes and their regulatory processes are integrated to balance plant life systems in response to changes in both external conditions and intrinsic signals.

Metabolomic and Transcriptomic Profiles in Diverse Brassica oleracea Crops Provide Insights into the Genetic Regulation of Glucosinolate Profiles

Glucosinolates (GSLs) are plant secondary metabolites commonly found in the cruciferous vegetables of the Brassicaceae family, offering health benefits to humans and defense against pathogens and pests to plants. In this study, we investigated 23 GSL compounds' relative abundance in four tissues of five different Brassica oleracea morphotypes. Using the five corresponding high-quality B. oleracea genome assemblies, we identified 183 GSL-related genes and analyzed their expression with mRNA-Seq data. GSL abundance and composition varied strongly, among both tissues and morphotypes, accompanied by different gene expression patterns. Interestingly, broccoli exhibited a nonfunctional AOP2 gene due to a conserved 2OG-FeII_Oxy domain loss, explaining the unique accumulation of two health-promoting GSLs. Additionally, transposable element (TE) insertions were found to affect the gene structure of MAM3 genes. Our findings deepen the understanding of GSL variation and genetic regulation in B. oleracea morphotypes, providing valuable insights for breeding with tailored GSL profiles in these crops.

Recent advances in the contribution of glucosinolates degradation products to cruciferous foods odor: factors that influence degradation pathways and odor attributes

As one of the most important vegetables and oils consumed globally, cruciferous foods are appreciated for their high nutritional value. However, there is no comprehensive knowledge to sufficiently unravel the "flavor mystery" of cruciferous foods. The present review provides a comprehensive literature on the recent advances regarding the contribution of glucosinolates (GSL) degradation products to cruciferous foods odor, which focuses on key GSL degradation products contributing to distinct odor of cruciferous foods (Brassica oleracea, Brassica rapa, Brassica napus, Brassica juncea, Raphanus sativus), and key factors affecting GSL degradation pathways (i.e., enzyme-induced degradation, thermal-induced degradation, chemical-induced degradation, microwave-induced degradation) during different processing and cooking. A total of 93 volatile GSL degradation products (i.e., 36 nitriles, 33 isothiocyanates, 3 thiocyanates, 5 epithionitriles, and 16 sulfides) and 29 GSL (i.e., 20 aliphatic, 5 aromatic, and 4 indolic) were found in generalized cruciferous foods. Remarkably, cruciferous foods have a distinctive pungent, spicy, pickled, sulfur, and vegetable odor. In general, isothiocyanates are mostly present in enzyme-induced degradation of GSL and are therefore often enriched in fresh-cut or low-temperature, short-time cooked cruciferous foods. In contrast, nitriles are mainly derived from thermal-induced degradation of GSL, and are thus often enriched in high-temperature, long-time cooked cruciferous foods.

Metabolome and transcriptome analyses reveal changes of rapeseed in response to ABA signal during early seedling development

Seed germination is an important development process in plant growth. The phytohormone abscisic acid (ABA) plays a critical role during seed germination. However, the mechanism of rapeseed in response to ABA is still elusive. In order to understand changes of rapeseed under exogenous ABA treatment, we explored differentially expressed metabolites (DEMs) and the differentially expressed genes (DEGs) between mock- and ABA-treated seedlings. A widely targeted LC-MS/MS based metabolomics were used to identify and quantify metabolic changes in response to ABA during seed germination, and a total of 186 significantly DEMs were identified. There are many compounds which are involved in ABA stimuli, especially some specific ABA transportation-related metabolites such as starches and lipids were screened out. Meanwhile, a total of 4440 significantly DEGs were identified by transcriptomic analyses. There was a significant enrichment of DEGs related to phenylpropanoid and cell wall organization. It suggests that exogenous ABA mainly affects seed germination by regulating cell wall loosening. Finally, the correlation analysis of the key DEMs and DEGs indicates that many DEGs play a direct or indirect regulatory role in DEMs metabolism. The integrative analysis between DEGs and DEMs suggests that the starch and sucrose pathways were the key pathway in ABA responses. The two metabolites from starch and sucrose pathways, levan and cellobiose, both were found significantly down-regulated in ABA-treated seedlings. These comprehensive metabolic and transcript analyses provide useful information for the subsequent post-transcriptional modification and post germination growth of rapeseed in response to ABA signals and stresses.

Application of Tryptophan and Methionine in Broccoli Seedlings Enhances Formation of Anticancer Compounds Sulforaphane and Indole-3-Carbinol and Promotes Growth

Broccoli is a popular cruciferous vegetable that is well known for its abundant health-promoting biochemicals. The most important of these beneficial biochemicals are glucosinolates, including glucoraphanin and glucobrassicin. Glucoraphanin and glucobrassicin can be broken down by myrosinases into sulforaphane and indole-3-carbinol, which have been demonstrated to have potent cancer-preventive properties. Efforts to increase glucoraphanin in broccoli seedlings have long been a focus; however, increasing glucoraphanin and glucobrassicin simultaneously, as well as enhancing myrosinase activity to release more sulforaphane and indole-3-carbinol, have yet to be investigated. This study aims to investigate the impact of the combined application of tryptophan and methionine on the accumulation of sulforaphane and indole-3-carbinol, as well as their precursors. Furthermore, we also examined whether this application has any effects on seedling growth and the presence of other beneficial compounds. We found that the application of methionine and tryptophan not only increased the glucoraphanin content by 2.37 times and the glucobrassicin content by 3.01 times, but that it also caused a higher myrosinase activity, resulting in a1.99 times increase in sulforaphane and a 3.05 times increase in indole-3-carbinol. In addition, better plant growth and an increase in amino acids and flavonoids were observed in broccoli seedlings with this application. In conclusion, the simultaneous application of tryptophan and methionine to broccoli seedlings can effectively enhance their health-promoting value and growth. Our study provides a cost-effective and multi-benefit strategy for improving the health value and yield of broccoli seedlings, benefiting both consumers and farmers.

Light regulation of the biosynthesis of phenolics, terpenoids, and alkaloids in plants

Biosynthesis of specialized metabolites (SM), including phenolics, terpenoids, and alkaloids, is stimulated by many environmental factors including light. In recent years, significant progress has been made in understanding the regulatory mechanisms involved in light-stimulated SM biosynthesis at the transcriptional, posttranscriptional, and posttranslational levels of regulation. While several excellent recent reviews have primarily focused on the impacts of general environmental factors, including light, on biosynthesis of an individual class of SM, here we highlight the regulation of three major SM biosynthesis pathways by light-responsive gene expression, microRNA regulation, and posttranslational modification of regulatory proteins. In addition, we present our future perspectives on this topic.

Dynamic profiling of intact glucosinolates in radish by combining UHPLC-HRMS/MS and UHPLC-QqQ-MS/MS

Glucosinolates (GSLs) and their degradation products in radish confer plant defense, promote human health, and generate pungent flavor. However, the intact GSLs in radish have not been investigated comprehensively yet. Here, an accurate qualitative and quantitative analyses of 15 intact GSLs from radish, including four major GSLs of glucoraphasatin (GRH), glucoerucin (GER), glucoraphenin (GRE), and 4-methoxyglucobrassicin (4MGBS), were conducted using UHPLC-HRMS/MS in combination with UHPLC-QqQ-MS/MS. Simultaneously, three isomers of hexyl GSL, 3-methylpentyl GSL, and 4-methylpentyl GSL were identified in radish. The highest content of GSLs was up to 232.46 μmol/g DW at the 42 DAG stage in the 'SQY' taproot, with an approximately 184.49-fold increase compared to the lowest content in another sample. That the GSLs content in the taproots of two radishes fluctuated in a similar pattern throughout the five vegetative growth stages according to the metabolic profiling, whereas the GSLs content in the '55' leaf steadily decreased over the same period. Additionally, the proposed biosynthetic pathways of radish-specific GSLs were elucidated in this study. Our findings will provide an abundance of qualitative and quantitative data on intact GSLs, as well as a method for detecting GSLs, thus providing direction for the scientific progress and practical utilization of GSLs in radish.