Plant Cell, Tissue and Organ Culture

Diterpenoids are important compounds for plant survival and have beneficial properties for humans. Bioactive abietanic diterpenes are synthesized in roots of Salvia sclarea (e.g. aethiopinone, 1-oxoaethiopinone, salvipisone, and ferruginol), but at a very low level (about 1 % of root dry weight). To enhance the biosynthesis of this interesting class of compounds, heterologous AtDXS (d-xylulose 5-phosphate synthase) or AtDXR (1-deoxy-d-xylulose 5 phosphate reductoisomerase) genes, encoding the up-stream enzymes of the plastidial 2-C-methyl-D-erythritol 4-phosphate (MEP)-dependent terpenoid pathway, were ectopically expressed in S. sclarea hairy roots. Quantitative targeted metabolic analysis (HPLC–DAD) revealed that three independent root lines, expressing different levels of DXS or DXR transcripts and proteins, synthesized a significant higher content of abietanic diterpenes, compared to the control hairy root line transformed with the empty vector. The increase was gene-dependent, since the overexpression of the AtDXR triggered a 4.4-fold increase in aethiopinone, an abietane quinone-type tricyclic diterpene. In addition, aethiopinone was proved to be cytotoxic to different solid tumor cell lines, with the highest effect on human melanoma A375 cell line (IC50 11.4 µM). Overall these results show that it is possible to boost the metabolic flow towards the synthesis of abietanic diterpenes in S. sclarea hairy roots by overexpressing genes involved in the first steps of the MEP-pathway and provide new insights for the large-scale production of this class of compounds, with potential application in cancer treatment.

Genetic transformation of an elite white poplar genotype (Populus alba L., cv. ‘Villafranca’) was performed with MAT vectors carrying the ipt and rol genes from Agrobacterium spp. as morphological markers. The effects associated with the use of different gene promoters and distinct in vitro regeneration protocols were evaluated. Poplar plantlets showing abnormal ipt and rol phenotypes were produced only in the presence of exogenous growth regulators. The occurrence of abnormal ipt and rol phenotypes allowed the visual selection of transformants. The ipt-type MAT vector pEXM2 was used to monitor the activity of the yeast site-specific recombination R/RS system in the transformed white poplar cells. Results from these experiments demonstrated that recombinase-mediated excision events occurred during the early stages of in vitro culture, thus causing the direct production of ipt marker-free transgenic plants with normal phenotype at an estimated frequency of 36.4%. Beside this unexpected finding, transgenic ipt-shooty plants were obtained at a frequency of 63.6% and normal shoots were subsequently recovered after a prolonged period of in vitro culture. Although the transformation efficiency observed in this study, using both ipt and nptII genes as selection markers, was similar to that previously reported with standard vectors carrying only the nptII gene, the easy identification of ipt transformants, the early recombinase-mediated excision events and finally the relatively short time period required to produce ipt marker-free transgenic plants support for the choice of MAT vectors as a reliable strategy for the future production of marker-free GM poplars.

Adventitious buds of Cupressus sempervirens L., were formed on excised mature embryos cultured for 10 days on half-strength Quoirin and Lepoivre medium (1/2QP) with 10 μM N6-benzyladenine. For shoot development, embryos were transferred to 1/2QP without growth regulators. Axillary shoot formation and rooting occurred spontaneously as adventitious shoots aged and transfer intervals were increased. Embryogenic tissue was obtained from immature embryos on induction media consisting of von Arnold and Eriksson (AE) or Gupta and Durzan (DCR) salts with 10 or 20 μM 2,4-dichlorophenoxyacetic acid. Cultures were maintained on DCR with 5 μM α-naphthaleneacetic acid and 5 μM BA.

Infection of rice with Rice stripe virus (RSV) and Rice black streaked dwarf virus (RBSDV) causes a significant loss of grain production. Due to the lack of natural resistance resources against these viruses, it is imperative to discover a biotechnological approach that will provide effective and safe immunity to RSV and RBSDV. In this study, we constructed three dimeric artificial microRNA (amiRNA) precursor expression vectors (pamiR-M, pamiR-3 and pamiR-U) that simultaneously target the CP genes of RSV and RBSDV based on the structure of the rice (Oryza sativa L.) osa-MIR528 precursor. The transgenic plants were obtained by Agrobacterium tumefaciens-mediated transformation and were shown to express amiRNAs successfully. Viral challenge assays revealed that these transgenic plants demonstrated different resistance (26.66–54.17 %) against RSV and RBSDV infection simultaneously. The amiRNA-targeting 3′-UTR region of CP gene (pamiR-U) induced higher virus resistance: 54.17 % against RSV and 45.83 % against RBSDV. A northern blot assay indicated that there was a good correlation between the resistance level and amiRNAs accumulation. The RNA silencing induced by the original amiRNAs could be bilaterally extended by the siRNA pathway. The amiRNAs, together with the secondary siRNAs, mediated the degradation of viral RNAs. A genetic stability assay showed that transgenes and amiRNA-mediated virus resistance could be stably inherited in the transgenic plants.

Somatic embryogenesis is a complex developmental process that offers great potential for plant propagation. Although many studies have shown that the generation of embryonic cells from somatic cells is accompanied by the synthesis of RNA and DNA and by elevated enzymatic activity, the mechanism of the onset of somatic embryogenesis is not well understood. cDNA-amplified fragment length polymorphism analysis was used to evaluate the gene expression pattern in embryogenic and non-embryogenic of the inbred maize line H99 during the process of embryogenesis. We identified a total of 101 candidate genes associated with the formation of maize embryonic calli. Based on the sequence analysis, these genes included 53 functionally-annotated TDFs involved in such processes as energy production and conversion, cell division and signal transduction, suggesting that somatic embryogenesis undergoes a complex process. Two full-length cDNA sequences, encoding KHCP (kinesin heavy chain like protein) and TypA (tyrosine phosphorylation protein A), and partial sequences, encoding ARF-GEP (guanine nucleotide-exchange protein of ADP ribosylation factor) homologs, were isolated from embryonic calli of maize and named ZmKHCP, ZmTypA and ZmARF-GEP, respectively. Finally, the real-time qRT-PCR results showed that the expression levels of the three genes were significantly higher in the embryonic calli than the non-embryonic calli. Thus, this study provides important clues to understanding the induction of somatic embryogenesis in maize. The candidate genes associated with the formation of embryonic calli may offer additional insights into the mechanism of somatic embryogenesis, and further research on the three candidate genes may determine their role in increasing the rate of induction of embryonic calli, which may aid in the development of cultivars through transgenic breeding.

An in vitro propagation protocol has been developed for Hagenia abyssinica using original material from both juvenile and mature trees. Juvenile explants were obtained from seedlings, as well as shoots and meristems from 5 to 7-month-old greenhouse grown plants. Shoots collected from stem bases of five genotypes were used to establish cultures from mature trees. Explants of seedling origin were used to optimize the multiplication medium and growth regulators concentration. The best result was obtained from shoots subcultured on either MS or WPM medium supplemented with 4.4 μM BAP and 0.49 μM IBA. The initiated shoots from all the different explants were multiplied on these media. Rooting of shoots was achieved using MS medium containing macronutrients at one-third strength supplemented with 4.9 μM IBA. The shoots were kept in the dark for 4 days and transferred to medium of the same composition but containing 0.3% activated charcoal without growth regulators. Up to 100% rooting was achieved depending on genotype. Shoots multiplied on MS medium rooted better than those multiplied on WPM. Plantlets were transferred to pots containing a mixture of soil and perlite in a 2:1 ratio, respectively, and were maintained in the greenhouse. Increased irradiance reduced stem and leaf lengths and increased branch number of micropropagated plants.

Being the crucial step for rice transgenic manipulation, callus culture from mature seeds is severely restricted by browning of induced calli, especially in the case of indica (Oryza Sativa L.) rice. Once this browning occurs, the callus will die and no embryonic calli can be obtained for regeneration. Here we report an induction procedure that overcomes callus browning was found. To clarify the inheritance pattern of callus browning, two reciprocal crosses F2 and two backcrosses BC1 were made between indica cultivar inbred lines 93-11 and YueTaiB (YTB) which produced normal and browning respectively in the same induction medium. The ratio of browning to normal in the reciprocal F2 and backcross (BC1) populations tested was approximately 1:3 and 1:1, respectively, these results indicate that callus browning is controlled by one single chromosomal locus which is tentatively named Ic1 (Induced callus 1). The genetic mapping of this locus was carried out using microsatellite markers (SSR) in a 216 extremely browning F2 seed callus. The analysis of genetic linkage indicated that one single locus that mapped to chromosome 1 was correlated to callus browning, and the closest marker in this study was mapped within 1.9 cM from the target locus.

Betaine aldehyde dehydrogenase (BADH) is a major oxidative enzyme that converts betaine aldehyde to glycine betaine (GB), an osmoprotectant compound in plants. Japonica rice (salt-sensitive) was genetically engineered to enhance salt tolerance by introducing the OsBADH1 gene from Indica rice (salt-tolerant), which is a GB accumulator. We produced transgenic rice plants overexpressing the modified OsBADH1 gene under the control of the maize ubiquitin promoter. The transgenic rice showed increased OsBADH1 gene expression and OsBADH1 enzyme production, resulting in the accumulation of GB. It also exhibited enhanced salt tolerance in immature and mature transgenic rice seedlings. The adverse effect of salt stress on seed germination, the growth of immature and mature seedlings, water status, and photosynthetic pigments was alleviated in transgenic seedlings.

In plant biotechnology, protoplasts are a versatile tool since they are very helpful for both fundamental biology studies and for genetic improvement and genome editing studies. In many plant species, however, reproducible regeneration from protoplasts continues to be a bottleneck. In the present study, we report the development of an efficient method for protoplast isolation, and plant regeneration in Angelica gigas via indirect somatic embryogenesis. Protoplasts were isolated from embryogenic callus using an enzyme mixture of 1.0% Viscozyme® L + 1% Celluclast® 1.5 L + 0.5% Pectinex® XXL with 7 h treatments. Initially, protoplasts were cultured in MS, modified MS (NH4NO3-free medium), and KM media, and viability and cell division data showed the MS medium was suitable for protoplast culture. Subsequently, the thin alginate layer method was applied to the protoplast culture at an optimal density of 1 × 106 cells per mL− 1 and verified the effect of 2,4-D (0.1, 0.5, and 1.0 mg L− 1) alone, and 2,4-D (0.5, and 1.0 mg L− 1) in combination with BA (0.1 and 0.5 mg L− 1) or KN (0.1 and 0.5 mg L− 1) on cell division, micro-callus formation. MS medium supplemented with 1.0 mg L− 1 2,4-D and 0.1 mg L− 1 KN induced optimal cell division, callus formation, and subsequent induction of somatic embryogenesis from the callus. The somatic embryos germinated and converted into plantlets upon transferring to the MS basal medium. This method of Angelica gigas protoplast regeneration can be used for the genetic improvement of this plant. The primary goal of the current study was to develop plant regeneration in Angelica gigas using protoplast culture, which could be valuable for the genetic improvement of this significant medicinal plant.