EASI Transformation: An Efficient Transient Expression Method for Analyzing Gene Function in Catharanthus roseus Seedlings

A rapid and efficient Agrobacterium-mediated transient transformation system in grape berries

Transient transformation is extremely useful for rapid in vivo assessment of gene function, especially for fruit-related genes. Grape berry, while an important fruit crop, is recalcitrant to transient transformation, due to the high turgor pressure in its mesocarp cells that limits the ability of Agrobacterium to penetrate into the tissue. It is urgent to establish a simple transient transformation system for rapid analysis of gene function. In this study, different injection methods, grape genotypes, and developmental stages were tested in order to develop a rapid and efficient Agrobacterium-mediated transient transformation methodology for grape berries. Two injection methods, namely punch injection and direct injection, were evaluated using the β-glucuronidase (GUS) gene and by x-gluc tissue staining and 4-methylumbelliferyl-β-D-glucuronide fluorescence analysis. The results indicated that there were no significant differences on transformation effects between the two methods, but the latter was more suitable because of its simplicity and convenience. Six grape cultivars ('Hanxiangmi', 'Moldova', 'Zijixin', 'Jumeigui', 'Shine-Muscat', and 'A17') were tested for transient transformation. 'Hanxiangmi', 'Moldova', and 'Zijixin' grape berries were not suitable for agroinfiltration due to frequently fruit cracking, browning, and formation of scar skin. The fruit integrity rates of 'Jumeigui', 'Shine-Muscat', and 'A17' berries were all above 80%, and GUS activity was detected in the berries of the three cultivars 3-14 days after injection with the Agrobacterium culture, while higher GUS activities were observed in the 'Jumeigui' berries. The levels of GUS activity in injected berries at 7-8 weeks after full blooming (WAFB) were more than twice at 6 WAFB. In subsequent assays, the over-expression of MYB transcription factor VvMYB44 via transient transformation accelerated the anthocyanin accumulation and fruit coloring through raising the expression levels of VvLAR1, VvUFGT, VvLDOX, VvANS, and VvDFR, which verified the effectiveness of this transformation system. These experiments finally identified the reliable grape cultivars and suitable operational approach for transient transformation and further indicated that this Agrobacterium-mediated transient transformation system was efficient and suitable for the elucidation of gene function in grape berries.

Critical parameters for robust Agrobacterium-mediated transient transformation and quantitative promoter assays in Catharanthus roseus seedlings

Agrobacterium-mediated transient expression methods are widely used to study gene function in both model and non-model plants. Using a dual-luciferase assay, we quantified the effect of Agrobacterium-infiltration parameters on the transient transformation efficiency of Catharanthus roseus seedlings. We showed that transformation efficiency is highly sensitive to seedling developmental state and a pre- and post-infiltration dark incubation and is less sensitive to the Agrobacterium growth stage. For example, 5 versus 6 days of germination in the dark increased seedling transformation efficiency by seven- to eight-fold while a dark incubation pre- and post-infiltration increased transformation efficiency by five- to 13-fold. Agrobacterium in exponential compared with stationary phase increased transformation efficiency by two-fold. Finally, we quantified the variation in our Agrobacterium-infiltration method in replicate infiltrations and experiments. Within a given experiment, significant differences of up to 2.6-fold in raw firefly luciferase (FLUC) and raw Renilla luciferase (RLUC) luminescence occurred in replicate infiltrations. These differences were significantly reduced when FLUC was normalized to RLUC values, highlighting the utility of including a reference reporter to minimize false positives. Including a second experimental replicate further reduced the potential for false positives. This optimization and quantitative validation of Agrobacterium infiltration in C. roseus seedlings will facilitate the study of this important medicinal plant and will expand the application of Agrobacterium-mediated transformation methods in other plant species.

The role of the Golden2-like (GLK) transcription factor in regulating terpenoid indole alkaloid biosynthesis in Catharanthus roseus

KEY MESSAGE

A GLK homologue was identified and functionally characterized in Catharanthus roseus. Silencing CrGLK with VIGS or the chloroplast retrograde signaling inducer lincomycin increased terpenoid indole alkaloid biosynthesis. Catharanthus roseus is the sole source of the chemotherapeutic terpenoid indole alkaloids (TIAs) vinblastine and vincristine. TIA pathway genes, particularly genes in the vindoline pathway, are expressed at higher levels in immature versus mature leaves, but the molecular mechanisms responsible for this developmental regulation are unknown. We investigated the role of GOLDEN2-LIKE (GLK) transcription factors in contributing to this ontogenetic regulation since GLKs are active in seedlings upon light exposure and in the leaf's early development, but their activity is repressed as leaves age and senesce. We identified a GLK homologue in C. roseus and functionally characterized its role in regulating TIA biosynthesis, with a focus on the vindoline pathway, by transiently reducing its expression through two separate methods: virus-induced gene silencing (VIGS) and application of chloroplast retrograde signaling inducers, norflurazon and lincomycin. Reducing CrGLK levels with each method reduced chlorophyll accumulation and the expression of the light harvesting complex subunit (LHCB2.2), confirming its functional homology with GLKs in other plant species. In contrast, reducing CrGLK via VIGS or lincomycin increased TIA accumulation and TIA pathway gene expression, suggesting that CrGLK may repress TIA biosynthesis. However, norflurazon had no effect on TIA gene expression, indicating that reducing CrGLK alone is not sufficient to induce TIA biosynthesis. Future work is needed to clarify the specific molecular mechanisms leading to increased TIA biosynthesis with CrGLK silencing. This is the first identification and characterization of GLK in C. roseus and the first investigation of how chloroplast retrograde signaling might regulate TIA biosynthesis.

The "Duckweed Dip": Aquatic Spirodela polyrhiza Plants Can Efficiently Uptake Dissolved, DNA-Wrapped Carbon Nanotubes from Their Environment for Transient Gene Expression

Duckweeds (Lemnaceae) are aquatic nongrass monocots that are the smallest and fastest-growing flowering plants in the world. While having simplified morphologies, relatively small genomes, and many other ideal traits for emerging applications in plant biotechnology, duckweeds have been largely overlooked in this era of synthetic biology. Here, we report that Greater Duckweed (Spirodela polyrhiza), when simply incubated in a solution containing plasmid-wrapped carbon nanotubes (DNA-CNTs), can directly uptake the DNA-CNTs from their growth media with high efficiency and that transgenes encoded within the plasmids are expressed by the plants─without the usual need for large doses of nanomaterials or agrobacterium to be directly infiltrated into plant tissue. This process, called the "duckweed dip", represents a streamlined, "hands-off" tool for transgene delivery to a higher plant that we expect will enhance the throughput of duckweed engineering and help to realize duckweed's potential as a powerhouse for plant synthetic biology.

A Cotyledon-based Virus-Induced Gene Silencing (Cotyledon-VIGS) approach to study specialized metabolism in medicinal plants

BACKGROUND

Virus-induced gene silencing (VIGS) is widely used in plant functional genomics. However, the efficiency of VIGS in young plantlets varies across plant species. Additionally, VIGS is not optimized for many plant species, especially medicinal plants that produce valuable specialized metabolites.

RESULTS

We evaluated the efficacy of five-day-old, etiolated seedlings of Catharanthus roseus (periwinkle) for VIGS. The seedlings were vacuum-infiltrated with Agrobacterium tumefaciens GV3101 cells carrying the tobacco rattle virus (TRV) vectors. The protoporphyrin IX magnesium chelatase subunit H (ChlH) gene, a key gene in chlorophyll biosynthesis, was used as the target for VIGS, and we observed yellow cotyledons 6 days after infiltration. As expected, the expression of CrChlH and the chlorophyll contents of the cotyledons were significantly decreased after VIGS. To validate the cotyledon based-VIGS method, we silenced the genes encoding several transcriptional regulators of the terpenoid indole alkaloid (TIA) biosynthesis in C. roseus, including two activators (CrGATA1 and CrMYC2) and two repressors (CrGBF1 and CrGBF2). Silencing CrGATA1 led to downregulation of the vindoline pathway genes (T3O, T3R, and DAT) and decreased vindoline contents in cotyledons. Silencing CrMYC2, followed by elicitation with methyl jasmonate (MeJA), resulted in the downregulation of ORCA2 and ORCA3. We also co-infiltrated C. roseus seedlings with TRV vectors that silence both CrGBF1 and CrGBF2 and overexpress CrMYC2, aiming to simultaneous silencing two repressors while overexpressing an activator. The simultaneous manipulation of repressors and activator resulted in significant upregulation of the TIA pathway genes. To demonstrate the broad application of the cotyledon-based VIGS method, we optimized the method for two other valuable medicinal plants, Glycyrrhiza inflata (licorice) and Artemisia annua (sweet wormwood). When TRV vectors carrying the fragments of the ChlH genes were infiltrated into the seedlings of these plants, we observed yellow cotyledons with decreased chlorophyll contents.

CONCLUSIONS

The widely applicable cotyledon-based VIGS method is faster, more efficient, and easily accessible to additional treatments than the traditional VIGS method. It can be combined with transient gene overexpression to achieve simultaneous up- and down-regulation of desired genes in non-model plants. This method provides a powerful tool for functional genomics of medicinal plants, facilitating the discovery and production of valuable therapeutic compounds.

The "Duckweed Dip": Aquatic Spirodela polyrhiza Plants Can Efficiently Uptake Dissolved, DNA-Wrapped Carbon Nanotubes from Their Environment for Transient Gene Expression

Duckweeds (Lemnaceae) are aquatic non-grass monocots that are the smallest and fastest-growing flowering plants in the world. While having simplified morphologies, relatively small genomes, and many other ideal traits for emerging applications in plant biotechnology, duckweeds have been largely overlooked in this era of synthetic biology. Here, we report that Greater Duckweed (Spirodela polyrhiza), when simply incubated in a solution containing plasmid-wrapped carbon nanotubes (DNA-CNTs), can directly up-take the DNA-CNTs from their growth media with high efficiency and that transgenes encoded within the plasmids are expressed by the plants-without the usual need for large doses of nanomaterials or agrobacterium to be directly infiltrated into plant tissue. This process, called the "duckweed dip", represents a streamlined, 'hands-off' tool for transgene delivery to a higher plant that we expect will enhance the throughput of duckweed engineering and help to realize duckweed's potential as a powerhouse for plant synthetic biology. (148 words).

An Agrobacterium-Mediated Transient Expression Method for Functional Assay of Genes Promoting Disease in Monocots

Agrobacterium-mediated transient expression (AMTE) has been widely used for high-throughput assays of gene function in diverse plant species. However, its application in monocots is still limited due to low expression efficiency. Here, by using histochemical staining and a quantitative fluorescence assay of β-glucuronidase (GUS) gene expression, we investigated factors affecting the efficiency of AMTE on intact barley plants. We found prominent variation in GUS expression levels across diverse vectors commonly used for stable transformation and that the vector pCBEP produced the highest expression. Additionally, concurrent treatments of plants with one day of high humidity and two days of darkness following agro-infiltration also significantly increased GUS expression efficiency. We thus established an optimized method for efficient AMTE on barley and further demonstrated its efficiency on wheat and rice plants. We showed that this approach could produce enough proteins suitable for split-luciferase assays of protein-protein interactions on barley leaves. Moreover, we incorporated the AMTE protocol into the functional dissection of a complex biological process such as plant disease. Based on our previous research, we used the pCBEP vector to construct a full-length cDNA library of genes upregulated during the early stage of rice blast disease. A subsequent screen of the library by AMTE identified 15 candidate genes (out of ~2000 clones) promoting blast disease on barley plants. Four identified genes encode chloroplast-related proteins: OsNYC3, OsNUDX21, OsMRS2-9, and OsAk2. These genes were induced during rice blast disease; however, constitutive overexpression of these genes conferred enhanced disease susceptibility to Colletotrichum higginsianum in Arabidopsis. These observations highlight the power of the optimized AMTE approach on monocots as an effective tool for facilitating functional assays of genes mediating complex processes such as plant-microbe interactions.

Ethyl Methane Sulfonate and Sodium Azide-Mediated Chemical and X-ray-Mediated Physical Mutagenesis Positively Regulate Peroxidase 1 Gene Activity and Biosynthesis of Antineoplastic Vinblastine in Catharanthus roseus

Catharanthus roseus synthesizes bioactive therapeutic metabolites, known as monoterpenoid indole alkaloids (MIAs), including antineoplastic vinblastine and vincristine, which have high global demand, and antihypertensive ajmalicine, a serpentine. However, the in planta biosynthesis and accumulation of these phytopharmaceuticals are very low, attributed to their high cytotoxicity in the plant. Considering the low in planta concentration and over-harvesting of plant resources, biotechnological interventions have been undertaken to enhance the production of MIAs in plant systems. The present study was carried out to mutation through chemical and physical mutagenesis with sodium azide, ethyl methane sulfonate and X-rays, respectively, on C. roseus to determine their possible effects on the transcriptional modulation of MIA biosynthetic pathways in planta. The chemical mutagenesis resulted in delayed seed pod development in mutated C. roseus plants, with distinct leaf morphology and flower color. However, X-ray mutagenesis resulted in pollen-less sterile flowers. An HPLC analysis confirmed the higher catharanthine, vindoline and vinblastine content in sodium azide and X-ray mutants, and was further supported by higher PRX1 transcript levels estimated through real-time PCR analysis. The transcription factors WRKY1 and ORCA2 were found negatively regulated along with major MIA pathway genes in chemical mutants and their M₁ generation, but showed positive regulation in X-ray M₀ mutants. The induced mutagenesis of C. roseus provides a prospective strategy to modulate plant transcriptomes and enhance the biosynthesis of pharmaceutically important antineoplastic vinblastine in the plant.

Metabolic engineering to enhance the accumulation of bioactive flavonoids licochalcone A and echinatin in Glycyrrhiza inflata (Licorice) hairy roots

Echinatin and licochalcone A (LCA) are valuable chalcones preferentially accumulated in roots and rhizomes of licorice (Glycyrrhiza inflata). The licorice chalcones (licochalcones) are valued for their anti-inflammatory, antimicrobial, and antioxidant properties and have been widely used in cosmetic, pharmaceutical, and food industries. However, echinatin and LCA are accumulated in low quantities, and the biosynthesis and regulation of licochalcones have not been fully elucidated. In this study, we explored the potential of a R2R3-MYB transcription factor (TF) AtMYB12, a known regulator of flavonoid biosynthesis in Arabidopsis, for metabolic engineering of the bioactive flavonoids in G. inflata hairy roots. Overexpression of AtMYB12 in the hairy roots greatly enhanced the production of total flavonoids (threefold), echinatin (twofold), and LCA (fivefold). RNA-seq analysis of AtMYB12-overexpressing hairy roots revealed that expression of phenylpropanoid/flavonoid pathway genes, such as phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and flavanone 3'-hydroxylase (F3'H), is significantly induced compared to the control. Transient promoter activity assay indicated that AtMYB12 activates the GiCHS1 promoter in plant cells, and mutation to the MYB-binding motif in the GiCHS1 promoter abolished activation. In addition, transcriptomic analysis revealed that AtMYB12 overexpression reprograms carbohydrate metabolism likely to increase carbon flux into flavonoid biosynthesis. Further, AtMYB12 activated the biotic defense pathways possibly by activating the salicylic acid and jasmonic acid signaling, as well as by upregulating WRKY TFs. The transcriptome of AtMYB12-overexpressing hairy roots serves as a valuable source in the identification of potential candidate genes involved in LCA biosynthesis. Taken together, our findings suggest that AtMYB12 is an effective gene for metabolic engineering of valuable bioactive flavonoids in plants.

An Efficient Root Transformation System for Recalcitrant Vicia sativa

Common vetch (Vicia sativa) is a multi-purpose legume widely used in pasture and crop rotation systems. Vetch seeds have desirable nutritional characteristics and are often used to feed ruminant animals. Although transcriptomes are available for vetch, problems with genetic transformation and plant regeneration hinder functional gene studies in this legume species. Therefore, the aim of this study was to develop a simple, efficient and rapid hairy root transformation system for common vetch to facilitate functional gene analysis. At first, we infected the hypocotyls of 5-day-old in vitro or in vivo, soil-grown seedlings with Rhizobium rhizogenes K599 using a stabbing method and produced transgenic hairy roots after 24 days at 19 and 50% efficiency, respectively. We later improved the hairy root transformation in vitro by infecting different explants (seedling, hypocotyl-epicotyl, and shoot) with R. rhizogenes. We observed hairy root formation at the highest efficiency in shoot and hypocotyl-epicotyl explants with 100 and 93% efficiency, respectively. In both cases, an average of four hairy roots per explant were obtained, and about 73 and 91% of hairy roots from shoot and hypocotyl-epicotyl, respectively, showed stable expression of a co-transformed marker β-glucuronidase (GUS). In summary, we developed a rapid, highly efficient, hairy root transformation method by using R. rhizogenes on vetch explants, which could facilitate functional gene analysis in common vetch.

EASI Transformation Protocol: An Agrobacterium-Mediated Transient Transformation Protocol for Catharanthus roseus Seedlings

Catharanthus roseus produces medicinal terpenoid indole alkaloids, including the critical anti-cancer compounds vinblastine and vincristine in its leaves. Recently, we developed a highly efficient transient expression method relying on Agrobacterium-mediated transformation of seedlings to facilitate rapid and high-throughput studies on the regulation of terpenoid indole alkaloid biosynthesis in C. roseus . We detail our optimized protocol known as efficient Agrobacterium-mediated seedling infiltration method (EASI), including the development of constructs used in EASI and an example experimental design that includes appropriate controls. We applied our EASI method to rapidly screen and evaluate transcriptional activators and repressors and promoter activity. Our EASI method can be used for promoter transactivation studies or transgene overexpression paired with downstream analyses like quantitative PCR or metabolite analysis. Our protocol takes about 16 days from sowing seeds to obtaining the results of the experiment.

A Rapid and Efficient Vacuum-Based Agroinfiltration Protocol for Transient Gene Overexpression in Leaves of Catharanthus roseus

Functional genomics analyses in planta can be hampered in non-model plants that are recalcitrant to the genetic transformation such as the medicinal plant Catharanthus roseus (Apocynaceae). No stable transformation and regeneration of plantlets have been achieved with a high efficiency in this plant to date. In addition, while virus-mediated transient gene silencing has been reported a decade ago in C. roseus, tools for transient overexpression remain scarce. Here, we describe an efficient and reliable methodology for transiently overexpressing any gene of interest in C. roseus leaves. This protocol combines a vacuum-based Agroinfiltration approach and the high translational efficiency of a deconstructed virus-based binary vector (pEAQ-HT). The described methodology is robust, easy to perform, and results in high amount of transient expression in C. roseus. This protocol is expected to serve as valuable tool to enhance the in planta characterization of gene functions or even transiently knock-in novel enzymatic activities.

Generation of Stable Catharanthus roseus Hairy Root Lines with Agrobacterium rhizogenes

Agrobacterium rhizogenes is the bacterial agent that causes hairy root disease in dicots and is purposefully engineered for the development of transgenic hairy root cultures. Due to their genetic and metabolic stability, hairy root cultures offer advantages as a tissue culture system for investigating the function of transgenes and as a production platform for specialized metabolites or proteins. The process for generating hairy root cultures involves first infecting the explant with A. rhizogenes, excising and eliminating A. rhizogenes from the emerging hairy roots, selecting for transgenic hairy roots on plates containing the selective agent, confirming genomic integration of transgenes by PCR, and finally adapting the hairy roots in liquid media. Here we provide a detailed protocol for developing and maintaining transgenic hairy root cultures of our medicinal plant of interest, Catharanthus roseus.

Terpenoid indole alkaloid biosynthesis in Catharanthus roseus: effects and prospects of environmental factors in metabolic engineering

Plants synthesize a vast array of specialized metabolites that primarily contribute to their defense and survival under adverse conditions. Many of the specialized metabolites have therapeutic values as drugs. Biosynthesis of specialized metabolites is affected by environmental factors including light, temperature, drought, salinity, and nutrients, as well as pathogens and insects. These environmental factors trigger a myriad of changes in gene expression at the transcriptional and posttranscriptional levels. The dynamic changes in gene expression are mediated by several regulatory proteins that perceive and transduce the signals, leading to up- or down-regulation of the metabolic pathways. Exploring the environmental effects and related signal cascades is a strategy in metabolic engineering to produce valuable specialized metabolites. However, mechanistic studies on environmental factors affecting specialized metabolism are limited. The medicinal plant Catharanthus roseus (Madagascar periwinkle) is an important source of bioactive terpenoid indole alkaloids (TIAs), including the anticancer therapeutics vinblastine and vincristine. The emerging picture shows that various environmental factors significantly alter TIA accumulation by affecting the expression of regulatory and enzyme-encoding genes in the pathway. Compared to our understanding of the TIA pathway in response to the phytohormone jasmonate, the impacts of environmental factors on TIA biosynthesis are insufficiently studied and discussed. This review thus focuses on these aspects and discusses possible strategies for metabolic engineering of TIA biosynthesis. PURPOSE OF WORK: Catharanthus roseus is a rich source of bioactive terpenoid indole alkaloids (TIAs). The objective of this work is to present a comprehensive account of the influence of various biotic and abiotic factors on TIA biosynthesis and to discuss possible strategies to enhance TIA production through metabolic engineering.

ptxD/Phi as alternative selectable marker system for genetic transformation for bio-safety concerns: a review

Antibiotic and herbicide resistance genes are the most common marker genes for plant transformation to improve crop yield and food quality. However, there is public concern about the use of resistance marker genes in food crops due to the risk of potential gene flow from transgenic plants to compatible weedy relatives, leading to the possible development of “superweeds” and antibiotic resistance. Several selectable marker genes such as aph, nptII, aaC3, aadA, pat, bar, epsp and gat, which have been synthesized to generate transgenic plants by genetic transformation, have shown some limitations. These marker genes, which confer antibiotic or herbicide resistance and are introduced into crops along with economically valuable genes, have three main problems: selective agents have negative effects on plant cell proliferation and differentiation, uncertainty about the environmental effects of many selectable marker genes, and difficulty in performing recurrent transformations with the same selectable marker to pyramid desired genes. Recently, a simple, novel, and affordable method was presented for plant cells to convert non-metabolizable phosphite (Phi) to an important phosphate (Pi) for developing cells by gene expression encoding a phosphite oxidoreductase (PTXD) enzyme. The ptxD gene, in combination with a selection medium containing Phi as the sole phosphorus (P) source, can serve as an effective and efficient system for selecting transformed cells. The selection system adds nutrients to transgenic plants without potential risks to the environment. The ptxD/Phi system has been shown to be a promising transgenic selection system with several advantages in cost and safety compared to other antibiotic-based selection systems. In this review, we have summarized the development of selection markers for genetic transformation and the potential use of the ptxD/Phi scheme as an alternative selection marker system to minimize the future use of antibiotic and herbicide marker genes.

Repression of ZCT1, ZCT2 and ZCT3 affects expression of terpenoid indole alkaloid biosynthetic and regulatory genes

Terpenoid indole alkaloids (TIAs) include several valuable pharmaceuticals. As Catharanthus roseus remains the primary source of these TIA pharmaceuticals, several research groups have devoted substantial efforts to increase production of these compounds by C. roseus. Efforts to increase TIA production by overexpressing positive regulators of TIA biosynthetic genes have met with limited success. This limited success might be due to the fact that overexpression of several positive TIA regulators turns on expression of negative regulators of TIA biosynthetic genes. Consequently, a more effective approach for increasing expression of TIA biosynthetic genes might be to decrease expression of negative regulators of TIA biosynthetic genes. Towards this end, an RNAi construct was generated that expresses a hairpin RNA carrying nucleotide fragments from three negative transcriptional regulators of TIA genes, ZCT1, ZCT2 and ZCT3, under the control of a beta-estradiol inducible promoter. Transgenic C. roseus hairy root lines carrying this ZCT RNAi construct exhibit significant reductions in transcript levels of all three ZCT genes. Surprisingly, out of eight TIA biosynthetic genes analyzed, seven (CPR, LAMT, TDC, STR, 16OMT, D4H and DAT) exhibited decreased rather than increased transcript levels in response to reductions in ZCT transcript levels. The lone exception was T19H, which exhibited the expected negative correlation in transcript levels with transcript levels of all three ZCT genes. A possible explanation for the T19H expression pattern being the opposite of the expression patterns of the other TIA biosynthetic genes tested is that T19H shunts metabolites away from vindoline production whereas the products of the other genes tested shunt metabolites towards vindoline metabolism. Consequently, both increased expression of T19H and decreased expression of one or more of the other seven genes tested would be expected to have similar effects on flux through the TIA pathway. As T19H expression is lower in the ZCT RNAi hairy root lines than in the control hairy root line, the ZCTs could act directly to inhibit expression of T19H. In contrast, ZCT regulation of the other seven TIA biosynthetic genes tested is likely to occur indirectly, possibly by the ZCTs turning off expression of a negative transcriptional regulator of some TIA genes. In fact, transcript levels of a negative TIA transcriptional regulator, GBF1, exhibited a strong, and statistically significant, negative correlation with transcript levels of ZCT1, ZCT2 and ZCT3. Together, these findings suggest that the ZCTs repress expression of some TIA biosynthetic genes, but increase expression of other TIA biosynthetic genes, possibly by turning down expression of GBF1.

A simple and efficient Agrobacterium-mediated in planta transformation protocol for horse gram (Macrotyloma uniflorum Lam. Verdc.)

BACKGROUND

Recalcitrant nature is a major constraint for the in vitro regeneration and genetic transformation of leguminous species members. Therefore, an improved genetic transformation in horse gram has been developed via in planta method, in which Agrobacterium strain harboring binary vector pCAMBIA2301 was used for the transformation. Several factors affecting in planta transformations were put forth viz. Agrobacterium cell density, co-cultivation, and sonication combined with vacuum infiltration duration which were optimized.

RESULTS

Germinated seeds were sonicated and vacuum infiltrated with different densities of Agrobacterium culture and co-cultivated in half-strength MS medium with 100 μM of acetosyringone for 48 h. Seedlings were washed with cefotaxime and sowed in vermiculite soil for maturation. T1 plants were subjected to histochemical and molecular analysis to ensure transformation efficiency. Among various combinations analyzed, maximum transformation efficiency (20.8%) was attained with seeds of 5 min sonication combined with vacuum infiltration with 0.6 optical density of Agrobacterium culture.

CONCLUSIONS

It concludes that a different Agrobacterium cell density with sonication combined with vacuum infiltration has improved transgenic efficiency in horse gram plants. This simple and efficient method is feasible for the stable expression of foreign genes that could be beneficial for future food security.

Catharanthus roseus Combined with Ursolic Acid Attenuates Streptozotocin-Induced Diabetes through Insulin Secretion and Glycogen Storage

Catharanthus roseus (C. roseus) and ursolic acid (UA) are ayurvedic medicines with multiple pharmacological activities including antidiabetic activity, but till date, no study is available on their combination. This study documented the antidiabetic efficacy of the combination of C. roseus and UA in rats. Rats were divided into six groups. All groups were given a single dose of Streptozotocin (STZ) at a dose of 50 mg/kg by intraperitoneal route for induction of diabetes, except the normal control group. Group 1 was treated as a normal control (NC) group and fed with saline water, Group 2 as a Diabetes Control group, Group 3 as a STZ+C. roseus ethanolic extract (CREE) group at 50 mg/kg p.o., Group 4 as a STZ+UA group orally at 50 mg/kg, Group 5 as a STZ+CREE (25 mg/kg p.o.)+UA (25 mg/kg p.o.) group, and Group 6 as a STZ+Glimepiride (0.1 mg/kg) group. Diabetes was confirmed after 72 hours by estimation of blood glucose level, and then treatment was given for the next 28 days. During the course of treatment, plasma insulin and blood glucose were measured regularly at the interval of 7 days. At the end of the protocol, blood was collected and animals were sacrificed. The glucose level, insulin level, liver glycogen storage level, and antioxidant enzymes (LPO, CAT, SOD, GPx, GST) were measured. The blood glucose level in Group 5 significantly (P < 0.001) reduced to 98.35 ± 2.45 mg/dl in comparison with that in Group 2 (321.75 ± 5.46 mg/dl). The level of plasma insulin in Group 5 increased (13.65 ± 0.10 μU/ml) significantly (P < 0.01) as compared with that in Group 2 (05.93 ± 0.31 μU/ml). In Group 5, the level of glycogen in liver was significantly (P < 0.01) increased as compared with that in Group 2 rats. The level of antioxidant enzymes in Group 5 restored toward normal values significantly (P < 0.01; P < 0.001) as compared with that in Group 2 animals. These findings suggest that low-dose combination of CREE and UA is effective in the treatment of diabetes.

The regulation of ZCT1, a transcriptional repressor of monoterpenoid indole alkaloid biosynthetic genes in Catharanthus roseus

Cys2/His2-type (C2H2) zinc finger proteins, such as ZCT1, are an important class of transcription factors involved in growth, development, and stress responses in plants. In the medicinal plant Catharanthus roseus, the zinc finger Catharanthus transcription factor (ZCT) family represses monoterpenoid indole alkaloid (MIA) biosynthetic gene expression. Here, we report the analysis of the ZCT1 promoter, which contains several hormone-responsive elements. ZCT1 is responsive to not only jasmonate, as was previously known, but is also induced by the synthetic auxin, 1-naphthalene acetic acid (1-NAA). Through promoter deletion analysis, we show that an activation sequence-1-like (as-1-like)-motif and other motifs contribute significantly to ZCT1 expression in seedlings. We also show that the activator ORCA3 does not transactivate the expression of ZCT1 in seedlings, but ZCT1 represses its own promoter, suggesting a feedback mechanism by which the expression of ZCT1 can be limited.