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.

Bamboo Salt and Triple Therapy Synergistically Inhibit Helicobacter pylori-Induced Gastritis In Vivo: A Preliminary Study.

Helicobacter pylori infections are a major cause of gastrointestinal disorders, including gastric ulcers, gastritis, and gastric cancer. Triple therapy, using two antibiotics and a proton pump inhibitor, is recommended for the treatment of H. pylori infections. However, antibiotic resistance in H. pylori is an emerging issue. Bamboo salt, a traditional Korean salt made by baking solar sea salt in bamboo barrels, can ameliorate the symptoms of various gastrointestinal diseases. Herein, we compared the anti-H. pylori activity of triple therapy (clarithromycin, metronidazole, and omeprazole), solar salt, and bamboo salt in vivo as a preliminary study. Four-week-old C57BL/6 male mice were inoculated for eight weeks with the H. pylori Sydney Strain 1 (SS-1) and orally administered triple therapy drugs and salts for five days. The transcript levels of the H. pylori-expressed gene CagA and inflammatory cytokines Tnfα and Il-1ß significantly decreased in the bamboo salt treated mice than those in the H. pylori-infected control group. This effect was further enhanced by using triple therapy and bamboo salt together. Solar salt caused modest inhibition of H. pylori-induced inflammation. We also demonstrated the synergistic effects of bamboo salt and triple therapy against H. pylori. Thus, bamboo salt may be a potential candidate agent against the treatment of H. pylori-associated gastritis.

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.

δ-Catenin Participates in EGF/AKT/p21Waf Signaling and Induces Prostate Cancer Cell Proliferation and Invasion.

Prostate cancer (PCa) is the second most leading cause of death in males. Our previous studies have demonstrated that δ-catenin plays an important role in prostate cancer progression. However, the molecular mechanism underlying the regulation of δ-catenin has not been fully explored yet. In the present study, we found that δ-catenin could induce phosphorylation of p21Waf and stabilize p21 in the cytoplasm, thus blocking its nuclear accumulation for the first time. We also found that δ-catenin could regulate the interaction between AKT and p21, leading to phosphorylation of p21 at Thr-145 residue. Finally, EGF was found to be a key factor upstream of AKT/δ-catenin/p21 for promoting proliferation and metastasis in prostate cancer. Our findings provide new insights into molecular controls of EGF and the development of potential therapeutics targeting δ-catenin to control prostate cancer progression.

Identification of α-Tomatine 23-Hydroxylase Involved in the Detoxification of a Bitter Glycoalkaloid.

Tomato plants (Solanum lycopersicum) contain steroidal glycoalkaloid α-tomatine, which functions as a chemical barrier to pathogens and predators. α-Tomatine accumulates in all tissues and at particularly high levels in leaves and immature green fruits. The compound is toxic and causes a bitter taste, but its presence decreases through metabolic conversion to nontoxic esculeoside A during fruit ripening. This study identifies the gene encoding a 23-hydroxylase of α-tomatine, which is a key to this process. Some 2-oxoglutarate-dependent dioxygenases were selected as candidates for the metabolic enzyme, and Solyc02g062460, designated Sl23DOX, was found to encode α-tomatine 23-hydroxylase. Biochemical analysis of the recombinant Sl23DOX protein demonstrated that it catalyzes the 23-hydroxylation of α-tomatine and the product spontaneously isomerizes to neorickiioside B, which is an intermediate in α-tomatine metabolism that appears during ripening. Leaves of transgenic tomato plants overexpressing Sl23DOX accumulated not only neorickiioside B but also another intermediate, lycoperoside C (23-O-acetylated neorickiioside B). Furthermore, the ripe fruits of Sl23DOX-silenced transgenic tomato plants contained lower levels of esculeoside A but substantially accumulated α-tomatine. Thus, Sl23DOX functions as α-tomatine 23-hydroxylase during the metabolic processing of toxic α-tomatine in tomato fruit ripening and is a key enzyme in the domestication of cultivated tomatoes.

Identification of a 3ß-Hydroxysteroid Dehydrogenase/ 3-Ketosteroid Reductase Involved in α-Tomatine Biosynthesis in Tomato.

α-Tomatine and dehydrotomatine are major steroidal glycoalkaloids (SGAs) that accumulate in the mature green fruits, leaves and flowers of tomato (Solanum lycopersicum), and function as defensive compounds against bacteria, fungi, insects and animals. The aglycone of dehydrotomatine is dehydrotomatidine (5,6-dehydrogenated tomatidine, having the Δ5,6 double bond; the dehydro-type). The aglycone of α-tomatine is tomatidine (having a single bond between C5 and C6; the dihydro-type), which is believed to be derived from dehydrotomatidine via four reaction steps: C3 oxidation, isomerization, C5 reduction and C3 reduction; however, these conversion processes remain uncharacterized. In the present study, we demonstrate that a short-chain alcohol dehydrogenase/reductase designated Sl3ßHSD is involved in the conversion of dehydrotomatidine to tomatidine in tomato. Sl3ßHSD1 expression was observed to be high in the flowers, leaves and mature green fruits of tomato, in which high amounts of α-tomatine are accumulated. Biochemical analysis of the recombinant Sl3ßHSD1 protein revealed that Sl3ßHSD1 catalyzes the C3 oxidation of dehydrotomatidine to form tomatid-4-en-3-one and also catalyzes the NADH-dependent C3 reduction of a 3-ketosteroid (tomatid-3-one) to form tomatidine. Furthermore, during co-incubation of Sl3ßHSD1 with SlS5αR1 (steroid 5α-reductase) the four reaction steps converting dehydrotomatidine to tomatidine were completed. Sl3ßHSD1-silenced transgenic tomato plants accumulated dehydrotomatine, with corresponding decreases in α-tomatine content. Furthermore, the constitutive expression of Sl3ßHSD1 in potato hairy roots resulted in the conversion of potato SGAs to the dihydro-type SGAs. These results demonstrate that Sl3ßHSD1 is a key enzyme involved in the conversion processes from dehydrotomatidine to tomatidine in α-tomatine biosynthesis.

A Dioxygenase Catalyzes Steroid 16α-Hydroxylation in Steroidal Glycoalkaloid Biosynthesis.

Steroidal glycoalkaloids (SGAs) are toxic specialized metabolites that are found in the Solanaceae. Potato (Solanum tuberosum) contains the SGAs α-solanine and α-chaconine, while tomato (Solanum lycopersicum) contains α-tomatine, all of which are biosynthesized from cholesterol. However, although two cytochrome P450 monooxygenases that catalyze the 22- and 26-hydroxylation of cholesterol have been identified, the 16-hydroxylase remains unknown. Feeding with deuterium-labeled cholesterol indicated that the 16α- and 16ß-hydrogen atoms of cholesterol were eliminated to form α-solanine and α-chaconine in potato, while only the 16α-hydrogen atom was eliminated in α-tomatine biosynthesis, suggesting that a single oxidation at C-16 takes place during tomato SGA biosynthesis while a two-step oxidation occurs in potato. Here, we show that a 2-oxoglutarate-dependent dioxygenase, designated as 16DOX, is involved in SGA biosynthesis. We found that the transcript of potato 16DOX (St16DOX) was expressed at high levels in the tuber sprouts, where large amounts of SGAs are accumulated. Biochemical analysis of the recombinant St16DOX protein revealed that St16DOX catalyzes the 16α-hydroxylation of hydroxycholesterols and that (22S)-22,26-dihydroxycholesterol was the best substrate among the nine compounds tested. St16DOX-silenced potato plants contained significantly lower levels of SGAs, and a detailed metabolite analysis revealed that they accumulated the glycosides of (22S)-22,26-dihydroxycholesterol. Analysis of the tomato 16DOX (Sl16DOX) gene gave essentially the same results. These findings clearly indicate that 16DOX is a steroid 16α-hydroxylase that functions in the SGA biosynthetic pathway. Furthermore, St16DOX silencing did not affect potato tuber yield, indicating that 16DOX may be a suitable target for controlling toxic SGA levels in potato.

Novel steroidal saponins from Dioscorea esculenta (Togedokoro).

Fifteen steroidal saponins 1-15, which include 4 furostanol glycosides 1-3 and 15, and 11 spirostanol glycosides 4-14, were isolated from the tubers and leaves of lesser yam (Dioscorea esculenta, Togedokoro). Their structures were identified by nuclear magnetic resonance and liquid chromatography mass spectroscopy. Four steroidal saponins 9, 11, 14, and 15 were found to be novel compounds.

Four New Dicaffeoylquinic Acid Derivatives from Glasswort (Salicornia herbacea L.) and Their Antioxidative Activity.

Four new dicaffeoylquinic acid derivatives and two known 3-caffeoylquinic acid derivatives were isolated from methanol extracts using the aerial parts of Salicornia herbacea. The four new dicaffeoylquinic acid derivatives were established as 3-caffeoyl-5-dihydrocaffeoylquinic acid, 3-caffeoyl-5-dihydrocaffeoylquinic acid methyl ester, 3-caffeoyl-4-dihydrocaffeoylquinic acid methyl ester, and 3,5-di-dihydrocaffeoylquinic acid methyl ester. Their chemical structures were determined by nuclear magnetic resonance and electrospray ionization-mass spectroscopy (LC-ESI-MS). In addition, the presence of dicaffeoylquinic acid derivatives in this plant was reconfirmed by LC-ESI-MS/MS analysis. The isolated compounds strongly scavenged 1,1-diphenyl-2-picrylhydrazyl radicals and inhibited cholesteryl ester hydroperoxide formation during rat blood plasma oxidation induced by copper ions. These results indicate that the caffeoylquinic acid derivatives may partially contribute to the antioxidative effect of S. herbacea.

Integrated gene-free potato genome editing using transient transcription activator-like effector nucleases and regeneration-promoting gene expression by Agrobacterium infection.

Genome editing is highly useful for crop improvement. The method of expressing genome-editing enzymes using a transient expression system in Agrobacterium, called agrobacterial mutagenesis, is a shortcut used in genome-editing technology to improve elite varieties of vegetatively propagated crops, including potato. However, with this method, edited individuals cannot be selected. The transient expression of regeneration-promoting genes can result in shoot regeneration from plantlets, while the constitutive expression of most regeneration-promoting genes does not result in normally regenerated shoots. Here, we report that we could obtain genome-edited potatoes by positive selection. These regenerated shoots were obtained via a method that combined a regeneration-promoting gene with the transient expression of a genome-editing enzyme gene. Moreover, we confirmed that the genome-edited potatoes obtained using this method did not contain the sequence of the binary vector used in Agrobacterium. Our data have been submitted to the Japanese regulatory authority, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and we are in the process of conducting field tests for further research on these potatoes. Our work presents a powerful method for regarding regeneration and acquisition of genome-edited crops through transient expression of regeneration-promoting gene.

δ-Catenin promotes cell migration and invasion via Bcl-2-regulated suppression of autophagy in prostate cancer cells.

As a member of the catenin family, δ-catenin is overexpressed in many cancers, including prostate cancer, and the role of δ-catenin in prostate tumor growth has been reported. However, the involvement of δ-catenin in the migration and invasion of prostate cancer has rarely been studied. In this study, we innovatively proposed that δ-catenin would enhance the migration and invasion ability of prostate cancer cells. It is worth noting that the molecular mechanism underlying the effect involved the downregulation of autophagy. We demonstrated that δ-catenin could suppress autophagy by Bcl-2-regulated disruption of the Beclin1-Vps34 autophagosome complex. Furthermore, the effect of δ-catenin on promoting cell migration and invasion was dependent upon ß-catenin-mediated Bcl-2 transcription. Finally, using rapamycin and bafilomycin, we largely confirmed that the degradation of Snails by autolysosomes may be related to δ-catenin regulated migration and invasion. Overall, our results indicated that δ-catenin promoted cell migration and invasion of prostate cancer cells via Bcl-2-regulated autophagy suppression.

Controlled Drug Release Using Chitosan-Alginate-Gentamicin Multi-Component Beads.

This study aimed to develop improved multi-component beads with controlled, sustained delivery of antibiotics, such as gentamicin (GM). Antibiotic-loaded beads with rapid-release and the sustained-release system can be used for bone restoration. Single and multi-component beads were prepared by gelation using various combinations of chitosan and calcium chloride as cationic components and alginate and citric acid as anions. GM release was also controlled by crosslinking using citric acid. The optimum beads were obtained using 5% or 2% sodium alginate, 3% chitosan, and 0.1 mol/L citric acid. The beads were characterized by FTIR, TG-DTG, swelling behavior, and SEM. All GM-loaded beads revealed good antimicrobial activity. The rate and kinetics of release in the phosphate buffer solution were controlled by changing the amount of chitosan in the calcium chloride solution and using citric acid as the crosslinking agent. Crosslinked beads were prepared for the release of about 80% of the loaded drug within 24 h. The study concluded that the chitosan-alginate beads provided faster GM release but crosslinking with citric acid was efficient for sustained-release beads containing gentamicin.

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

Potato (Solanum tuberosum), a worldwide major food crop, produces the toxic, bitter tasting solanidane glycoalkaloids α-solanine and α-chaconine. Controlling levels of glycoalkaloids is an important focus on potato breeding. Tomato (Solanum lycopersicum) contains a bitter spirosolane glycoalkaloid, α-tomatine. These glycoalkaloids are biosynthesized from cholesterol via a partly common pathway, although the mechanisms giving rise to the structural differences between solanidane and spirosolane remained elusive. Here we identify a 2-oxoglutarate dependent dioxygenase, designated as DPS (Dioxygenase for Potato Solanidane synthesis), that is a key enzyme for solanidane glycoalkaloid biosynthesis in potato. DPS catalyzes the ring-rearrangement from spirosolane to solanidane via C-16 hydroxylation. Evolutionary divergence of spirosolane-metabolizing dioxygenases contributes to the emergence of toxic solanidane glycoalkaloids in potato and the chemical diversity in Solanaceae.

bFGF-mediated phosphorylation of δ-catenin increases its protein stability and the ability to induce the nuclear redistribution of ß-catenin.

Recently, we have shown that δ-catenin strengthened the epidermal growth factor receptor (EGFR)/Erk1/2 signaling pathway through the association between EGFR and δ-catenin. Now, we further analyzed the correlation between basic fibroblast growth factor (bFGF)/fibroblast growth factor receptor 1 (FGFR1) and δ-catenin in prostate cancer and investigated the molecular mechanism underlying the role of bFGF/FGFR1 modulation in CWR22Rv-1 (Rv-1) cells. Here, we demonstrated that bFGF phosphorylated the tyrosine residues of δ-catenin in Rv-1 cells and further proved that the bFGF mediated FGFR1/δ-catenin tyrosine phosphorylation was time dependent. Furthermore, we demonstrated that bFGF stabilized the expression of δ-catenin through weakening its association with GSK3ß and enhancing its stability to induce ß-catenin into the nuclear by strengthening the processing of E-cadherin. In a word, these results indicated that bFGF/FGFR1 signaling pathway could enhance the tumor progression of prostate cancer via δ-catenin.

Does 3-pentadecylcatechol, an urushiol derivative, get absorbed in the body? A rat oral administration experiment.

Urushiols are important active compounds found in the sap of the lacquer tree (Rhus verniciflua Stokes). Recently, various biological effects of urushiols, such as antioxidant, antimicrobial, and anticancer activities, have been reported. However, urushiols can also induce skin allergies. Nevertheless, the lacquer tree has traditionally been used in Korea as a folk medicine. In this study, we evaluated the absorption and metabolism of 3-pentadecylcatechol (PDC), a natural urushiol. PDC (48.0 mg/kg body wt.) in 1 mL propylene glycol was orally administered to rats (Sprague-Dawley, male, 6 weeks old). Blood plasma, urine, and feces were collected, separately. PDC was not detected in the extracts from rat blood plasma and urine. However, 89.4 ± 5.2% of the orally administered PDC was detected in the feces extracts, indicating that PDC was predominantly excreted and not absorbed.

Targeted genome editing in tetraploid potato through transient TALEN expression by Agrobacterium infection.

Genome editing using site-specific nucleases, such as transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeat-CRISPR-associated protein 9 (CRISPR-Cas9), is a powerful technology for crop breeding. For plant genome editing, the genome-editing reagents are usually expressed in plant cells from stably integrated transgenes within the genome. This requires crossing processes to remove foreign nucleotides from the genome to generate null segregants. However, in highly heterozygous plants such as potato, the progeny lines have different agronomic traits from the parent cultivar and do not necessarily become elite lines. Agrobacteria can transfer exogenous genes on T-DNA into plant cells. This has been used both to transform plants stably and to express the genes transiently in plant cells. Here, we infected potato, with Agrobacterium tumefaciens harboring TALEN-expression vector targeting sterol side chain reductase 2 (SSR2) gene and regenerated shoots without selection. We obtained regenerated lines with disrupted-SSR2 gene and without transgene of the TALEN gene, revealing that their disruption should be caused by transient gene expression. The strategy using transient gene expression by Agrobacterium that we call Agrobacterial mutagenesis, developed here should accelerate the use of genome-editing technology to modify heterozygous plant genomes.

New caryophyllene-type sesquiterpene and flavonol tetraglycoside with sixteen known compounds from sword bean (Canavalia gladiata).

Eighteen compounds including new caryophyllene-type sesquiterpene and flavonol tetraglycoside were purified and isolated from sword beans (Canavalia gladiata). Two new compounds, (Z,1R,7S,9S)-7-hydroxy-11,11-dimethyl-8-methylenebicyclo[7.2.0]undec-4-ene-4-carboxylic acid (2) and kaempferol-7-O-α-l-dirhamnopyranosyl(1 → 2;1 → 6)-O-ß-d-glucopyranosyl(1 → 2)-O-α-l-rhamnopyranoside (9), were identified. Other known compounds including methyl gallate (1), (2S,3S,4E,8E)-2-aminooctadeca-4,8-diene-1,3-diol 1-O-ß-d-glucopyranoside (3), (2S,3S,4E,8Z)-2-aminooctadeca-4,8-diene-1,3-diol 1-O-ß-d-glucopyranoside (4), lupeol (5), trilinolein (6), 1,6-di-O-galloyl ß-d-glucopyranoside (7), N-(2-methoxybenzoyl)homoserine (8), dihydrophaseic acid (10), dillenetin (11), kaempferol-7-O-[2-O-ß-d-glucopyranosyl-6-O-α-l-rhamnopyranosyl]-α-l-rhamnopyranoside (12), canavalioside (13), kaempferol-3-O-[2-O-ß-d-glucopyranosyl-6-O-α-l-rhamnopyranosyl]-ß-d-glucopyranoside (14), kaempferol-3-O-(2,6-O-α-l-dirhamnopyranosyl)-ß-d-glucopyranoside (15), kaempferol-3-O-rutinoside (16), gladiatoside A1 (17), and gladiatoside B1 (18) were identified. The chemical structures of these compounds were determined by ESI-MS and NMR analyses.

Ionization Neutralizes the Allergy-Inducing Property of 3-Pentadecylcatechol: A Urushiol Derivative.

Urushiols are amphipathic compounds found in Rhus verniciflua Stokes that exhibit various biological activities. However, their practical use is very restricted due to their contact dermatitis-inducing property. Therefore, we applied the ionization method to remove the allergenic properties of the urushiols and to increase their usability. One of the natural urushiols, 3-pentadecylcatechol (PDC), was heated for 30 min with a solution of H2O and sodium carbonate (Na2CO3). The reaction product was analyzed by electrospray ionization mass spectrometry (ESI-MS). Ionized PDC with an m/z value of 316.9 and complexed PDCs with Na+ of 1 - 3 atoms with m/z values of 340.8, 365.2, and 380.8 were detected. PDC and ionized PDC (3 µmol/3 mg of Vaseline) treatments were applied on the rear of left ear of Sprague-Dawley rats once daily for 10 days. Erythema and swelling were observed on the ear skin treated with PDC, but not in case of ionized PDC. Compared with control, contact hypersensitivity-related biomarkers (neutrophils, eosinophils, immunoglobulin E, and histamine) in the blood were significantly higher only in the PDC-treated group. In addition, Il-1b, Il-6, Tnfα, and Cox-2 mRNA expression levels were dramatically increased in the ear tissue of PDC-treated rats, but in the ionized PDC-treated group, they were similar to those in the control group. Overall, it was confirmed that the allergenic property of the urushiol PDC was removed by ionization. This method is expected to be useful for preventing allergy induction in cooking and food processing using R. verniciflua Stokes.

Hatching stimulation activity of steroidal glycoalkaloids toward the potato cyst nematode, Globodera rostochiensis.

Cyst nematodes (Globodera spp. and Heterodera spp.) are highly evolved sedentary endoparasites that are considered as harmful pests worldwide. The hatching of the dormant eggs of cyst nematodes occurs in response to hatching factors (HFs), which are compounds that are secreted from the roots of host plants. Solanoeclepin A (SEA), a triterpene compound, has been isolated as HF for potato cyst nematode (PCN) eggs, whereas other compounds, such as steroidal glycoalkaloids (SGAs), are also known to show weak hatching stimulation (HS) activity. However, the structures of both compounds are different and the HF-mediated hatching mechanism is still largely unknown. In the present study, we observed specific hatching of PCN eggs stimulated by the hairy root culture media of potato and tomato, revealing the biosynthesis and secretion of HFs. SGAs, such as α-solanine, α-chaconine, and α-tomatine, showed significant HS activity, despite being remarkably less activities than that of SEA. Then, we evaluated the contribution of SGAs on the HS activities of the hairy root culture media. The estimated SGAs content in the hairy root culture media were low and nonconcordant with the HS activity of those, suggesting that the HS activity of SGAs did not contribute much. The analysis of structure-activity relationship revealed that the structural requirements of the HS activity of SGAs are dependent on the sugar moieties attached at the C3-hydoroxyl group and the alkaloid property of their aglycones. The stereochemistry in the EF rings of their aglycone also affected the strength of the HS activity.

Efficient genome engineering using Platinum TALEN in potato.

Potato (Solanum tuberosum) is one of the most important crops in the world. However, it is generally difficult to breed a new variety of potato crops because they are highly heterozygous tetraploid. Steroidal glycoalkaloids (SGAs) such as α-solanine and α-chaconine found in potato are antinutritional specialized metabolites. Because of their toxicity following intake, controlling the SGA levels in potato varieties is critical in breeding programs. Recently, genome-editing technologies using artificial site-specific nucleases such as TALEN and CRISPR-Cas9 have been developed and used in plant sciences. In the present study, we developed a highly active Platinum TALEN expression vector construction system, and applied to reduce the SGA contents in potato. Using Agrobacterium-mediated transformation, we obtained three independent transgenic potatoes harboring the TALEN expression cassette targeting SSR2 gene, which encodes a key enzyme for SGA biosynthesis. Sequencing analysis of the target sequence indicated that all the transformants could be SSR2-knockout mutants. Reduced SGA phenotype in the mutants was confirmed by metabolic analysis using LC-MS. In vitro grown SSR2-knockout mutants exhibited no differences in morphological phenotype or yields when compared with control plants, indicating that the genome editing of SGA biosynthetic genes such as SSR2 could be a suitable strategy for controlling the levels of toxic metabolites in potato. Our simple and powerful plant genome-editing system, developed in the present study, provides an important step for future study in plant science.