The biosynthetic pathway of potato solanidanes diverged from that of spirosolanes due to evolution of a dioxygenase

Steroidal scaffold decorations in Solanum alkaloid biosynthesis

Steroidal glycoalkaloids (SGAs) are specialized metabolites produced by hundreds of Solanum species, including important vegetable crops such as tomato, potato, and eggplant. Although it has been known that SGAs play important roles in defense in plants and "anti-nutritional" effects (e.g., toxicity and bitterness) to humans, many of these molecules have documented anti-cancer, anti-microbial, anti-inflammatory, anti-viral, and anti-pyretic activities. Among these, α-solasonine and α-solamargine isolated from black nightshade (Solanum nigrum) are reported to have potent anti-tumor, anti-proliferative, and anti-inflammatory activities. Notably, α-solasonine and α-solamargine, along with the core steroidal aglycone solasodine, are the most widespread SGAs produced among the Solanum plants. However, it is still unknown how plants synthesize these bioactive steroidal molecules. Through comparative metabolomic-transcriptome-guided approach, biosynthetic logic, combinatorial expression in Nicotiana benthamiana, and functional recombinant enzyme assays, here we report the discovery of 12 enzymes from S. nigrum that converts the starting cholesterol precursor to solasodine aglycone, and the downstream α-solasonine, α-solamargine, and malonyl-solamargine SGA products. We further identified six enzymes from cultivated eggplant that catalyze the production of α-solasonine, α-solamargine, and malonyl-solamargine SGAs from solasodine aglycone via glycosylation and atypical malonylation decorations. Our work provides the gene tool box and platform for engineering the production of high-value, steroidal bioactive molecules in heterologous hosts using synthetic biology.

Potato Berries as a Valuable Source of Compounds Potentially Applicable in Crop Protection and Pharmaceutical Sectors: A Review

Potato (Solanum tuberosum) is a major agricultural crop cultivated worldwide. To meet market demand, breeding programs focus on enhancing important agricultural traits such as disease resistance and improvement of tuber palatability. However, while potato tubers get a lot of attention from research, potato berries are mostly overlooked due to their level of toxicity and lack of usefulness for the food production sector. Generally, they remain unused in the production fields after harvesting the tuber. These berries are toxic due to high levels of glycoalkaloids, which might confer some interesting bioactivities. Berries of various solanaceous species contain bioactive secondary metabolites, suggesting that potato berries might contain similarly valuable metabolites. Therefore, possible applications of potato berries, e.g., in the protection of plants against pests and pathogens, as well as the medical exploitation of their anti-inflammatory, anticarcinogenic, and antifungal properties, are plausible. The presence of valuable compounds in potato berries could also contribute to the bioeconomy by providing a novel use for otherwise discarded agricultural side streams. Here we review the potential use of these berries for the extraction of compounds that can be exploited to produce pharmaceuticals and plant protection products.

Recent developments in the enzymatic modifications of steroid scaffolds

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.

Exploring the Evolvability of Plant Specialized Metabolism: Uniqueness Out Of Uniformity and Uniqueness Behind Uniformity

The huge structural diversity exhibited by plant specialized metabolites has primarily been considered to result from the catalytic specificity of their biosynthetic enzymes. Accordingly, enzyme gene multiplication and functional differentiation through spontaneous mutations have been established as the molecular mechanisms that drive metabolic evolution. Nevertheless, how plants have assembled and maintained such metabolic enzyme genes and the typical clusters that are observed in plant genomes, as well as why identical specialized metabolites often exist in phylogenetically remote lineages, is currently only poorly explained by a concept known as convergent evolution. Here, we compile recent knowledge on the co-presence of metabolic modules that are common in the plant kingdom but have evolved under specific historical and contextual constraints defined by the physicochemical properties of each plant specialized metabolite and the genetic presets of the biosynthetic genes. Furthermore, we discuss a common manner to generate uncommon metabolites (uniqueness out of uniformity) and an uncommon manner to generate common metabolites (uniqueness behind uniformity). This review describes the emerging aspects of the evolvability of plant specialized metabolism that underlie the vast structural diversity of plant specialized metabolites in nature.

Anthriscus sylvestris Deoxypodophyllotoxin Synthase Involved in the Podophyllotoxin Biosynthesis

Tetrahydrofuran ring formation from dibenzylbutyrolactone lignans is a key step in the biosynthesis of aryltetralin lignans including deoxypodophyllotoxin and podophyllotoxin. Previously, Fe(II)- and 2-oxoglutarate-dependent dioxygenase (2-ODD) from Podophyllum hexandrum (Himalayan mayapple, Berberidaceae) was found to catalyze the cyclization of a dibenzylbutyrolactone lignan, yatein, to give deoxypodophyllotoxin and designated as deoxypodophyllotoxin synthase (DPS). Recently, we reported that the biosynthesis of deoxypodophyllotoxin and podophyllotoxin evolved in a lineage-specific manner in phylogenetically unrelated plant species such as P. hexandrum and Anthriscus sylvestris (cow parsley, Apiaceae). Therefore, a comprehensive understanding of the characteristics of DPSs that catalyze the cyclization of yatein to deoxypodophyllotoxin in various plant species is important. However, for plant species other than P. hexandrum, the isolation of the DPS enzyme gene and the type of the enzyme, e.g. whether it is 2-ODD or another type of enzyme such as cytochrome P-450, have not been reported. In this study, we report the identification and characterization of A. sylvestris DPS (AsDPS). Phylogenetic analysis showed that AsDPS belonged to the 2-ODD superfamily and shared moderate amino acid sequence identity (40.8%) with P. hexandrum deoxypodophyllotoxin synthase (PhDPS). Recombinant protein assay indicated that AsDPS and PhDPS differ in terms of the selectivity of substrate enantiomers. Protein modeling using AlphaFold2 and site-directed mutagenesis indicated that the Tyr305 residue of AsDPS probably contributes to substrate recognition. This study advances our understanding of the podophyllotoxin biosynthetic pathway in A. sylvestris and provides new insight into 2-ODD involved in plant secondary (specialized) metabolism.

Characterization of the horse chestnut genome reveals the evolution of aescin and aesculin biosynthesis

Horse chestnut (Aesculus chinensis) is an important medicinal tree that contains various bioactive compounds, such as aescin, barrigenol-type triterpenoid saponins (BAT), and aesculin, a glycosylated coumarin. Herein, we report a 470.02 Mb genome assembly and characterize an Aesculus-specific whole-genome duplication event, which leads to the formation and duplication of two triterpenoid biosynthesis-related gene clusters (BGCs). We also show that AcOCS6, AcCYP716A278, AcCYP716A275, and AcCSL1 genes within these two BGCs along with a seed-specific expressed AcBAHD6 are responsible for the formation of aescin. Furthermore, we identify seven Aesculus-originated coumarin glycoside biosynthetic genes and achieve the de novo synthesis of aesculin in E. coli. Collinearity analysis shows that the collinear BGC segments can be traced back to early-diverging angiosperms, and the essential gene-encoding enzymes necessary for BAT biosynthesis are recruited before the splitting of Aesculus, Acer, and Xanthoceras. These findings provide insight on the evolution of gene clusters associated with medicinal tree metabolites.

Recent advances in steroidal glycoalkaloid biosynthesis in the genus Solanum

Steroidal glycoalkaloids (SGAs) are specialized metabolites found in members of Solanum species, and are also known as toxic substances in Solanum food crops such as tomato (Solanum lycopersicum), potato (Solanum tuberosum), and eggplant (Solanum melongena). SGA biosynthesis can be divided into two main parts: formation of steroidal aglycones, which are derived from cholesterol, and glycosylation at the C-3 hydroxy group. This review focuses on recent studies that shed light on the complete process of the aglycone formation in SGA biosynthesis and structural diversification of SGAs by duplicated dioxygenases, as well as the development of non-toxic potatoes through genome editing using these findings.

Effect of Potato Vine and Leaf Mixed Silage Compared to Whole Corn Crops on Growth Performance, Apparent Digestibility, and Serum Biochemical Characteristics of Fattening Angus Bull

This study aims to explore the different growth performances of the Angus bull on potato vine and leaf mixed silage in the early fattening period and to provide a reference animal production trial. Thirty-six 13-month-old Angus bulls were divided into three groups with 403.22 ± 38.97 kg initial body weight and fed with three different silage diets: (1) control: whole-plant corn silage as control (CS); (2) treatment 1: 50% whole-plant corn +50% potato vine and leaf silage (PVS1); and (3) treatment 2: 75% potato vine and leaf +15% rice straw +10% cornmeal silage (PVS2). After the 14 days pre-feeding, the formal experiment was carried out for 89 days. The result showed that the ash content of the potato vine and leaf mixed silage (PVS) in the treatment groups was higher than that in control group, and the ash content of PVS1 and PVS2 even reached 10.42% and 18.48% (DM%), respectively, which was much higher than that of the CS group at 4.94%. The crude protein content in silage also increased with the additional amount of potato vine and leaf. The apparent crude protein digestibility of the PVS groups was also significantly higher than that of the CS group (p < 0.05). In terms of serum biochemical indexes, blood urea nitrogen (BUN) in the experimental groups was significantly higher than in the control group (p < 0.05). Compared with PVS2, cholesterol (CHO) was significantly lower in the CS and PVS1 groups (p < 0.05). Moreover, the high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) of PVS2 were significantly higher than those of the CS and PVS1 group (p < 0.05), and daily gain (ADG) as a key production index had a significantly negative correlation with the CHO (r = -0.38, p < 0.05) and HDL-C (r = -0.40, p < 0.05) of cattle. In conclusion, PVS had higher crude protein content and ash but less starch than whole-corn silage. The PVS could replace whole-plant corn silage at the same dry matter status and did not affect the weight gain in this trial.

The Therapeutic Value of Solanum Steroidal (Glyco)Alkaloids: A 10-Year Comprehensive Review

Steroidal (glycol)alkaloids S(G)As are secondary metabolites made of a nitrogen-containing steroidal skeleton linked to a (poly)saccharide, naturally occurring in the members of the Solanaceae and Liliaceae plant families. The genus Solanum is familiar to all of us as a food source (tomato, potato, eggplant), but a few populations have also made it part of their ethnobotany for their medicinal properties. The recent development of the isolation, purification and analysis techniques have shed light on the structural diversity among the SGAs family, thus attracting scientists to investigate their various pharmacological properties. This review aims to overview the recent literature (2012-2022) on the pharmacological benefits displayed by the SGAs family. Over 17 different potential therapeutic applications (antibiotic, antiviral, anti-inflammatory, etc.) were reported over the past ten years, and this unique review analyzes each pharmacological effect independently without discrimination of either the SGA's chemical identity or their sources. A strong emphasis is placed on the discovery of their biological targets and the subsequent cellular mechanisms, discussing in vitro to in vivo biological data. The therapeutic value and the challenges of the solanum steroidal glycoalkaloid family is debated to provide new insights for future research towards clinical development.

Solanoeclepin B, a hatching factor for potato cyst nematode

The potato cyst nematode (PCN) causes extensive crop losses worldwide. Because the hatching of PCN requires host-derived molecules known as hatching factors (HFs), regulating HF production in host plants may help to control this harmful pest. Solanoeclepin A (SEA), isolated from potato, is the most active HF for PCN; however, its biosynthesis is completely unknown. We discovered a HF called solanoeclepin B (SEB) from potato and tomato root exudates and showed that SEB was biosynthesized in the plant and converted to SEA outside the plant by biotic agents. Moreover, we identified five SEB biosynthetic genes encoding three 2-oxoglutarate-dependent dioxygenases and two cytochrome P450 monooxygenases in tomato. Exudates from tomato hairy roots in which each of the genes was disrupted contained no SEB and had low hatch-stimulating activity for PCN. These findings will help to breed crops with a lower risk of PCN infection.

Deciphering the network of cholesterol biosynthesis in Paris polyphylla laid a base for efficient diosgenin production in plant chassis

Cholesterol serves as a key precursor for many high-value chemicals such as plant-derived steroidal saponins and steroidal alkaloids, but a plant chassis for effective biosynthesis of high levels of cholesterol has not been established. Plant chassis have significant advantages over microbial chassis in terms of membrane protein expression, precursor supply, product tolerance, and regionalization synthesis. Here, using Agrobacterium tumefaciens-mediated transient expression technology, Nicotiana benthamiana, and a step-by-step screening approach, we identified nine enzymes (SSR1-3, SMO1-3, CPI-5, CYP51G, SMO2-2, C14-R-2, 8,7SI-4, C5-SD1, and 7-DR1-1) from the medicinal plant Paris polyphylla and established detailed biosynthetic routes from cycloartenol to cholesterol. Specfically, we optimized HMGR, a key gene of the mevalonate pathway, and co-expressed it with the PpOSC1 gene to achieve a high level of cycloartenol (28.79 mg/g dry weight, which is a sufficient amount of precursor for cholesterol biosynthesis) synthesis in the leaves of N. benthamiana. Subsequently, using a one-by-one elimination method we found that six of these enzymes (SSR1-3, SMO1-3, CPI-5, CYP51G, SMO2-2, and C5-SD1) were crucial for cholesterol production in N. benthamiana, and we establihed a high-efficiency cholesterol synthesis system with a yield of 5.63 mg/g dry weight. Using this strategy, we also discovered the biosynthetic metabolic network responsible for the synthesis of a common aglycon of steroidal saponin, diosgenin, using cholesterol as a substrate, obtaining a yield of 2.12 mg/g dry weight in N. benthamiana. Our study provides an effective strategy to characterize the metabolic pathways of medicinal plants that lack a system for in vivo functional verification, and also lays a foundation for the synthesis of active steroid saponins in plant chassis.

Fruity, sticky, stinky, spicy, bitter, addictive, and deadly: evolutionary signatures of metabolic complexity in the Solanaceae

Covering: 2000-2022Plants collectively synthesize a huge repertoire of metabolites. General metabolites, also referred to as primary metabolites, are conserved across the plant kingdom and are required for processes essential to growth and development. These include amino acids, sugars, lipids, and organic acids. In contrast, specialized metabolites, historically termed secondary metabolites, are structurally diverse, exhibit lineage-specific distribution and provide selective advantage to host species to facilitate reproduction and environmental adaptation. Due to their potent bioactivities, plant specialized metabolites attract considerable attention for use as flavorings, fragrances, pharmaceuticals, and bio-pesticides. The Solanaceae (Nightshade family) consists of approximately 2700 species and includes crops of significant economic, cultural, and scientific importance: these include potato, tomato, pepper, eggplant, tobacco, and petunia. The Solanaceae has emerged as a model family for studying the biochemical evolution of plant specialized metabolism and multiple examples exist of lineage-specific metabolites that influence the senses and physiology of commensal and harmful organisms, including humans. These include, alcohols, phenylpropanoids, and carotenoids that contribute to fruit aroma and color in tomato (fruity), glandular trichome-derived terpenoids and acylsugars that contribute to plant defense (stinky & sticky, respectively), capsaicinoids in chilli-peppers that influence seed dispersal (spicy), and steroidal glycoalkaloids (bitter) from Solanum, nicotine (addictive) from tobacco, as well as tropane alkaloids (deadly) from Deadly Nightshade that deter herbivory. Advances in genomics and metabolomics, coupled with the adoption of comparative phylogenetic approaches, resulted in deeper knowledge of the biosynthesis and evolution of these metabolites. This review highlights recent progress in this area and outlines opportunities for - and challenges of-developing a more comprehensive understanding of Solanaceae metabolism.

Tandem Gene Duplication of Dioxygenases Drives the Structural Diversity of Steroidal Glycoalkaloids in the Tomato Clade

Cultivated tomato (Solanum lycopersicum) contains α-tomatine, a steroidal glycoalkaloid (SGA), which functions as a defense compound to protect against pathogens and herbivores; interestingly, wild species in the tomato clade biosynthesize a variety of SGAs. In cultivated tomato, the metabolic detoxification of α-tomatine during tomato fruit ripening is an important trait that aided in its domestication, and two distinct 2-oxoglutarate-dependent dioxygenases (DOXs), a C-23 hydroxylase of α-tomatine (Sl23DOX) and a C-27 hydroxylase of lycoperoside C (Sl27DOX), are key to this process. There are tandemly duplicated DOX genes on tomato chromosome 1, with high levels of similarity to Sl23DOX. While these DOX genes are rarely expressed in cultivated tomato tissues, the recombinant enzymes of Solyc01g006580 and Solyc01g006610 metabolized α-tomatine to habrochaitoside A and (20R)-20-hydroxytomatine and were therefore named as habrochaitoside A synthase (HAS) and α-tomatine 20-hydroxylase (20DOX), respectively. Furthermore, 20DOX and HAS exist in the genome of wild tomato S. habrochaites accession LA1777, which accumulates habrochaitoside A in its fruits, and their expression patterns were in agreement with the SGA profiles in LA1777. These results indicate that the functional divergence of α-tomatine-metabolizing DOX enzymes results from gene duplication and the neofunctionalization of catalytic activity and gene expression, and this contributes to the structural diversity of SGAs in the tomato clade.

2-oxoglutarate-dependent dioxygenases drive expansion of steroidal alkaloid structural diversity in the genus Solanum

Solanum steroidal glycoalkaloids (SGAs) are renowned defence metabolites exhibiting spectacular structural diversity. Genes and enzymes generating the SGA precursor pathway, SGA scaffold and glycosylated forms have been largely identified. Yet, the majority of downstream metabolic steps creating the vast repertoire of SGAs remain untapped. Here, we discovered that members of the 2-OXOGLUTARATE-DEPENDENT DIOXYGENASE (2-ODD) family play a prominent role in SGA metabolism, carrying out three distinct backbone-modifying oxidative steps in addition to the three formerly reported pathway reactions. The GLYCOALKALOID METABOLISM34 (GAME34) enzyme catalyses the conversion of core SGAs to habrochaitosides in wild tomato S. habrochaites. Cultivated tomato plants overexpressing GAME34 ectopically accumulate habrochaitosides. These habrochaitoside enriched plants extracts potently inhibit Puccinia spp. spore germination, a significant Solanaceae crops fungal pathogen. Another 2-ODD enzyme, GAME33, acts as a desaturase (via hydroxylation and E/F ring rearrangement) forming unique, yet unreported SGAs. Conversion of bitter α-tomatine to ripe fruit, nonbitter SGAs (e.g. esculeoside A) requires two hydroxylations; while the known GAME31 2-ODD enzyme catalyses hydroxytomatine formation, we find that GAME40 catalyses the penultimate step in the pathway and generates acetoxy-hydroxytomatine towards esculeosides accumulation. Our results highlight the significant contribution of 2-ODD enzymes to the remarkable structural diversity found in plant steroidal specialized metabolism.

The steroidal alkaloids α-tomatine and tomatidine: Panorama of their mode of action and pharmacological properties

The steroidal glycoalkaloid α-tomatine (αTM) and its aglycone tomatidine (TD) are abundant in the skin of unripe green tomato and present in tomato leaves and flowers. They mainly serve as defensive agents to protect the plant against infections by insects, bacteria, parasites, viruses, and fungi. In addition, the two products display a range of pharmacological properties potentially useful to treat various human diseases. We have analyzed all known pharmacological activities of αTM and TD, and the corresponding molecular targets and pathways impacted by these two steroidal alkaloids. In experimental models, αTM displays anticancer effects, particularly strong against androgen-independent prostate cancer, as well as robust antifungal effects. αTM is a potent cholesterol binder, useful as a vaccine adjuvant to improve delivery of protein antigens or therapeutic oligonucleotides. TD is a much less cytotoxic compound, able to restrict the spread of certain viruses (such as dengue, chikungunya and porcine epidemic diarrhea viruses) and to provide cardio and neuro-protective effects toward human cells. Both αTM and TD exhibit marked anti-inflammatory activities. They proceed through multiple signaling pathways and protein targets, including the sterol C24 methyltransferase Erg6 and vitamin D receptor, both directly targeted by TD. αTM is a powerful regulator of the NFkB/ERK signaling pathway implicated in various diseases. Collectively, the analysis shed light on the multitargeted action of αTM/TD and their usefulness as chemo-preventive or chemotherapeutic agents. A novel medicinal application for αTM is proposed.

Employing CRISPR/Cas Technology for the Improvement of Potato and Other Tuber Crops

New breeding technologies have not only revolutionized biological science, but have also been employed to generate transgene-free products. Genome editing is a powerful technology that has been used to modify genomes of several important crops. This review describes the basic mechanisms, advantages and disadvantages of genome editing systems, such as ZFNs, TALENs, and CRISPR/Cas. Secondly, we summarize in detail all studies of the CRISPR/Cas system applied to potato and other tuber crops, such as sweet potato, cassava, yam, and carrot. Genes associated with self-incompatibility, abiotic-biotic resistance, nutrient-antinutrient content, and post-harvest factors targeted utilizing the CRISPR/Cas system are analyzed in this review. We hope that this review provides fundamental information that will be useful for future breeding of tuber crops to develop novel cultivars.

Biotechnological development of plants for space agriculture

The ideal plant for cultivation in space would provide as many nutrients from as few inputs as possible. Here, we discuss how biotechnology could be used to produce a potato cultivar suitable for humans in space.

The logistical and practical challenges of supplying food for long-term space missions are substantial. In this comment, the authors discuss potential biotechnological approaches that could be used to aid the production of food crops in space.

Tomato E8 Encodes a C-27 Hydroxylase in Metabolic Detoxification of α-Tomatine during Fruit Ripening

Tomato (Solanum lycopersicum) contains α-tomatine, a steroidal glycoalkaloid that contributes to the plant defense against pathogens and herbivores through its bitter taste and toxicity. It accumulates at high levels in all the plant tissues, especially in leaves and immature green fruits, whereas it decreases during fruit ripening through metabolic conversion to the nontoxic esculeoside A, which accumulates in the mature red fruit. This study aimed to identify the gene encoding a C-27 hydroxylase that is a key enzyme in the metabolic conversion of α-tomatine to esculeoside A. The E8 gene, encoding a 2-oxoglutalate-dependent dioxygenase, is well known as an inducible gene in response to ethylene during fruit ripening. The recombinant E8 was found to catalyze the C-27 hydroxylation of lycoperoside C to produce prosapogenin A and is designated as Sl27DOX. The ripe fruit of E8/Sl27DOX-silenced transgenic tomato plants accumulated lycoperoside C and exhibited decreased esculeoside A levels compared with the wild-type (WT) plants. Furthermore, E8/Sl27DOX deletion in tomato accessions resulted in higher lycoperoside C levels in ripe fruits than in WT plants. Thus, E8/Sl27DOX functions as a C-27 hydroxylase of lycoperoside C in the metabolic detoxification of α-tomatine during tomato fruit ripening, and the efficient detoxification by E8/27DOX may provide an advantage in the domestication of cultivated tomatoes.

Characterization of C-26 aminotransferase, indispensable for steroidal glycoalkaloid biosynthesis

Steroidal glycoalkaloids (SGAs) are toxic specialized metabolites found in members of the Solanaceae, such as Solanum tuberosum (potato) and Solanum lycopersicum (tomato). The major potato SGAs are α-solanine and α-chaconine, which are biosynthesized from cholesterol. Previously, we have characterized two cytochrome P450 monooxygenases and a 2-oxoglutarate-dependent dioxygenase that function in hydroxylation at the C-22, C-26 and C-16α positions, but the aminotransferase responsible for the introduction of a nitrogen moiety into the steroidal skeleton remains uncharacterized. Here, we show that PGA4 encoding a putative γ-aminobutyrate aminotransferase is involved in SGA biosynthesis in potatoes. The PGA4 transcript was expressed at high levels in tuber sprouts, in which SGAs are abundant. Silencing the PGA4 gene decreased potato SGA levels and instead caused the accumulation of furostanol saponins. Analysis of the tomato PGA4 ortholog, GAME12, essentially provided the same results. Recombinant PGA4 protein exhibited catalysis of transamination at the C-26 position of 22-hydroxy-26-oxocholesterol using γ-aminobutyric acid as an amino donor. Solanum stipuloideum (PI 498120), a tuber-bearing wild potato species lacking SGA, was found to have a defective PGA4 gene expressing the truncated transcripts, and transformation of PI 498120 with functional PGA4 resulted in the complementation of SGA production. These findings indicate that PGA4 is a key enzyme for transamination in SGA biosynthesis. The disruption of PGA4 function by genome editing will be a viable approach for accumulating valuable steroidal saponins in SGA-free potatoes.

Flavonoids and saponins in plant rhizospheres: roles, dynamics, and the potential for agriculture

Plants are in constant interaction with a myriad of soil microorganisms in the rhizosphere, an area of soil in close contact with plant roots. Recent research has highlighted the importance of plant-specialized metabolites (PSMs) in shaping and modulating the rhizosphere microbiota; however, the molecular mechanisms underlying the establishment and function of the microbiota mostly remain unaddressed. Flavonoids and saponins are a group of PSMs whose biosynthetic pathways have largely been revealed. Although these PSMs are abundantly secreted into the rhizosphere and exert various functions, the secretion mechanisms have not been clarified. This review summarizes the roles of flavonoids and saponins in the rhizosphere with a special focus on interactions between plants and the rhizosphere microbiota. Furthermore, this review introduces recent advancements in the dynamics of these metabolites in the rhizosphere and indicates potential applications of PSMs for crop production and discusses perspectives in this emerging research field.

Antioxidants in Potatoes: A Functional View on One of the Major Food Crops Worldwide

With a growing world population, accelerating climate changes, and limited arable land, it is critical to focus on plant-based resources for sustainable food production. In addition, plants are a cornucopia for secondary metabolites, of which many have robust antioxidative capacities and are beneficial for human health. Potato is one of the major food crops worldwide, and is recognized by the United Nations as an excellent food source for an increasing world population. Potato tubers are rich in a plethora of antioxidants with an array of health-promoting effects. This review article provides a detailed overview about the biosynthesis, chemical and health-promoting properties of the most abundant antioxidants in potato tubers, including several vitamins, carotenoids and phenylpropanoids. The dietary contribution of diverse commercial and primitive cultivars are detailed and document that potato contributes much more than just complex carbohydrates to the diet. Finally, the review provides insights into the current and future potential of potato-based systems as tools and resources for healthy and sustainable food production.