Effect of Hybridization on Somatic Mutations and Genomic Rearrangements in Plants.

Hybridization has been routinely practiced in agriculture to enhance the crop yield. Principally, it can cause hybrid vigor where hybrid plants display increased size, biomass, fertility, and resistance to diseases, when compared to their parents. During hybridization, hybrid offspring receive a genomic shock due to mixing of distant parental genomes, which triggers a myriad of genomic rearrangements, e.g., transpositions, genome size changes, chromosomal rearrangements, and other effects on the chromatin. Recently, it has been reported that, besides genomic rearrangements, hybridization can also alter the somatic mutation rates in plants. In this review, we provide in-depth insights about hybridization triggered genomic rearrangements and somatic mutations in plants.

Use of Ultrasonication Technology for the Increased Production of Plant Secondary Metabolites.

Plant secondary metabolites (PSMs) provide taste, color, odor, and resistance to plants, and they are also used to treat cancer and cardiovascular diseases. Synthesis of PSMs in plants is stimulated in response to different forms of external stress. Use of ultrasonication (US) to clean or decontaminate fruits and vegetables leads to physical stress that finally results in the accumulation of PSMs. US can stimulate accumulation of taxol, ginsenoside saponins, shikonin, and resveratrol, e.g., up to 319-fold increase of resveratrol synthesis has been observed in grape due to US. US also increases carotenoids, total phenolics, and isoflavonoids accumulation. Furthermore, US shows synergistic effects in PSMs synthesis-when combined with ultraviolet (UV) irradiation, jasmonic acid (JA) or salicylic acid (SA). It has been observed that US stimulates the production of reactive oxygen species (ROS) which then upregulates expression of phenylalanine ammonia lyase (PAL), resulting in the synthesis of PSMs. In this review, we summarize the effects of US, as a physical stress, to maximize the accumulation of PSMs in crop produce and in cell cultures.

An Overview of LEDs' Effects on the Production of Bioactive Compounds and Crop Quality.

Light-emitting diodes (LEDs) are characterized by their narrow-spectrum, non-thermal photon emission, greater longevity, and energy-saving characteristics, which are better than traditional light sources. LEDs thus hold the potential to revolutionize horticulture lighting technology for crop production, protection, and preservation. Exposure to different LED wavelengths can induce the synthesis of bioactive compounds and antioxidants, which in turn can improve the nutritional quality of horticultural crops. Similarly, LEDs increase the nutrient contents, reduce microbial contamination, and alter the ripening of postharvest fruits and vegetables. LED-treated agronomic products can be beneficial for human health due to their good nutrient value and high antioxidant properties. Besides that, the non-thermal properties of LEDs make them easy to use in closed-canopy or within-canopy lighting systems. Such configurations minimize electricity consumption by maintaining optimal incident photon fluxes. Interestingly, red, blue, and green LEDs can induce systemic acquired resistance in various plant species against fungal pathogens. Hence, when seasonal clouds restrict sunlight, LEDs can provide a controllable, alternative source of selected single or mixed wavelength photon source in greenhouse conditions.

Metabolic engineering of Nicotiana benthamiana for the increased production of taxadiene.

We report the production of taxadiene by transformation of N. benthamiana with a taxadiene synthase gene. The production was significantly increased by an elicitor treatment or metabolic pathway shunting. Paclitaxel (Taxol(®)) was first isolated from the bark of the pacific yew tree as an anticancer agent and has been used extensively to treat various types of cancer. Taxadiene, the first committed product of paclitaxel synthesis is cyclized from geranylgeranyl diphosphate (GGPP), and further complex hydroxylation and acylation processes of the unique taxane core skeleton produce paclitaxel. To accomplish de novo production of taxadiene, we transformed Nicotiana benthamiana with a taxadiene synthase (TS) gene. The introduced TS gene under the transcriptional control of the CaMV 35S promoter was constitutively expressed in N. benthamiana, and the de novo production of taxadiene was confirmed by mass spectroscopy profiling. Transformed N. benthamiana homozygous lines produced 11-27 µg taxadiene/g of dry weight. The highest taxadiene production line TSS-8 was further treated with an elicitor, methyl jasmonate, and metabolic pathway shunting by suppression of the phytoene synthase gene expression which resulted in accumulation of increased taxadiene accumulation by 1.4- or 1.9-fold, respectively. In summary, we report that the production of taxadiene in N. benthamiana was possible by the ectopic expression of the TS gene, and higher accumulation of taxadiene could be achieved by elicitor treatment or metabolic pathway shunting of the terpenoid pathway.

Current Status and De Novo Synthesis of Anti-Tumor Alkaloids in Nicotiana.

Alkaloids are the most diversified nitrogen-containing secondary metabolites, having antioxidant and antimicrobial properties, and are extensively used in pharmaceuticals to treat different types of cancer. Nicotiana serves as a reservoir of anti-cancer alkaloids and is also used as a model plant for the de novo synthesis of various anti-cancer molecules through genetic engineering. Up to 4% of the total dry weight of Nicotiana was found to be composed of alkaloids, where nicotine, nornicotine, anatabine, and anabasine are reported as the dominant alkaloids. Additionally, among the alkaloids present in Nicotiana, ß-carboline (Harmane and Norharmane) and Kynurenines are found to show anti-tumor effects, especially in the cases of colon and breast cancers. Creating new or shunting of existing biosynthesis pathways in different species of Nicotiana resulted in de novo or increased synthesis of different anti-tumor molecules or their derivatives or precursors including Taxadiane (~22.5 µg/g), Artemisinin (~120 µg/g), Parthenolide (~2.05 ng/g), Costunolide (~60 ng/g), Etoposide (~1 mg/g), Crocin (~400 µg/g), Catharanthine (~60 ng/g), Tabersonine (~10 ng/g), Strictosidine (~0.23 mg/g), etc. Enriching the precursor pool, especially Dimethylallyl Diphosphate (DMAPP), down-regulating other bi-product pathways, compartmentalization or metabolic shunting, or organelle-specific reconstitution of the precursor pool, might trigger the enhanced accumulation of the targeted anti-cancer alkaloid in Nicotiana.

Preparation of resveratrol-enriched grape juice from ultrasonication treated grape fruits.

Grape (Vitis spp.) is a major source of resveratrol that can be eaten directly or after making jam, jelly, wine and juice. Resveratrol (3,5,4'-trihydroxystilbene) has a profound positive influence on human health, including anti-carcinogenic, anti-cancer, anti-inflammatory, and anti-ageing effects and the ability to lower blood sugar. During industrial production of grape juice, resveratrol is lost because of the use of clarifying agents and filtration; therefore, commercial grape juice contains very low amounts of resveratrol. In this study, we investigated the accumulation of resveratrol in grape juice prepared from three varieties of grape, viz. Campbell Early, Muscat Bailey A (MBA) and Kyoho, following post-harvest ultrasonication cleaning for 5 min and 6h of incubation in the dark at 25 °C. This process resulted in the amounts of resveratrol increasing by 1.53, 1.15 and 1.24 times in juice prepared from Campbell Early, MBA and Kyoho, respectively, without changing the amounts of total soluble solids. Overall, our results indicate that ultrasonication treatment of post-harvested grape fruits can be an effective method for producing resveratrol-enriched grape juice as well as cleaning grapes thoroughly.