Genetic transformation of date palm (Phoenix dactylifera L. cv. ‘Estamaran’) via particle bombardment

The establishment of transient expression systems and their application for gene function analysis of flavonoid biosynthesis in Carthamus tinctorius L

BACKGROUND

Safflower (Carthamus tinctorius L.) is an important economic crop and a traditional medicinal material rich in flavonoids, which can alleviate cardiovascular and cerebrovascular pathologies. Thus, many candidate genes involved in safflower flavonoid biosynthesis have been cloned. However, owing to the lack of a homologous gene expression system, research on gene function is limited to model plants. Therefore, a gene function identification protocol for safflower must be established.

RESULTS

In the present study, using safflower callus as the experimental material, Agrobacterium and biolistic transient expression systems were established. In the Agrobacterium transient expression system, the highest transformation rate was obtained at the original Agrobacterium concentration of OD600 0.4, infiltration concentration of OD600 0.6, infection for 20 min, co-culture for 3 days, and acetosyringone concentration of 100 μmol·L-1. In the biolistic transient expression system, the highest transformation efficiency was observed at helium pressure of 1,350 psi, vacuum degree of -0.8 bar, flight distance of 6.5 cm, one round of bombardment, plasmid concentration of 3 μg·shot-1, and gold particle concentration of 100 μg·shot-1. Further, these two transient expression systems were used for the functional analysis of CtCHS1 as an example. After overexpression, relative CtCHS1 expression increased, particularly in Agrobacterium-transformed calli. Additionally, the contents of some flavonoids were altered; for instance, naringenin and genistein levels were significantly increased in Agrobacterium-transformed calli, whereas luteolin, luteolin-7-O-rutinoside, and apigenin derivative levels were significantly decreased in biolistic-transformed calli.

CONCLUSION

Using safflower callus as the experimental material, highly efficient Agrobacterium and biolistic transient expression systems were successfully established, and the utility of both systems for investigating gene function was demonstrated. The proposed safflower callus transient expression systems will be useful for further functional analyses of flavonoid biosynthetic genes in safflower.

Is CRISPR/Cas9 a way forward to fast-track genetic improvement in commercial palms? Prospects and limits

Commercially important palms (oil palm, coconut, and date palm) are widely grown perennial trees with tremendous commercial significance due to food, edible oil, and industrial applications. The mounting pressure on the human population further reinforces palms' importance, as they are essential crops to meet vegetable oil needs around the globe. Various conventional breeding methods are used for the genetic improvement of palms. However, adopting new technologies is crucial to accelerate breeding and satisfy the expanding population's demands. CRISPR/Cas9 is an efficient genome editing tool that can incorporate desired traits into the existing DNA of the plant without losing common traits. Recent progress in genome editing in oil palm, coconut and date palm are preliminarily introduced to potential readers. Furthermore, detailed information on available CRISPR-based genome editing and genetic transformation methods are summarized for researchers. We shed light on the possibilities of genome editing in palm crops, especially on the modification of fatty acid biosynthesis in oil palm. Moreover, the limitations in genome editing, including inadequate target gene screening due to genome complexities and low efficiency of genetic transformation, are also highlighted. The prospects of CRISPR/Cas9-based gene editing in commercial palms to improve sustainable production are also addressed in this review paper.

Advances and Perspectives of Transgenic Technology and Biotechnological Application in Forest Trees

Transgenic technology is increasingly used in forest-tree breeding to overcome the disadvantages of traditional breeding methods, such as a long breeding cycle, complex cultivation environment, and complicated procedures. By introducing exogenous DNA, genes tightly related or contributed to ideal traits-including insect, disease, and herbicide resistance-were transferred into diverse forest trees, and genetically modified (GM) trees including poplars were cultivated. It is beneficial to develop new varieties of GM trees of high quality and promote the genetic improvement of forests. However, the low transformation efficiency has hampered the cultivation of GM trees and the identification of the molecular genetic mechanism in forest trees compared to annual herbaceous plants such as Oryza sativa. In this study, we reviewed advances in transgenic technology of forest trees, including the principles, advantages and disadvantages of diverse genetic transformation methods, and their application for trait improvement. The review provides insight into the establishment and improvement of genetic transformation systems for forest tree species. Challenges and perspectives pertaining to the genetic transformation of forest trees are also discussed.

The retrospect and prospect of the applications of biotechnology in Phoenix dactylifera L

Date palm (Phoenix dactylifera L.) is one of the most important fruit trees that contribute a major part to the economy of Middle East and North African countries. It is quintessentially called "tree of life" owing to its resilience to adverse climatic conditions, along with manifold nutritional-cum-medicinal attributes that comes from its fruits and other plant parts. Being a tree with such immense utility, it has gained substantial attention of tree breeders for its genetic advancement via in vitro biotechnological interventions. Herein, an extensive review of biotechnological research advances in date palm has been consolidated as one of the major research achievements during the past two decades. This article compares the different biotechnological techniques used in this species such as: tissue and organ culture, bioreactor-mediated large-scale propagation, cell suspension culture, embryogenic culture, protoplast culture, conservation (for short- and long-term) of germplasms, in vitro mutagenesis, in vitro selection against biotic and abiotic stresses, secondary metabolite production in vitro, and genetic transformation. This review provides an insight on crop improvement and breeding programs for improved yield and quality fruits; besides, it would undeniably facilitate the tissue culture-based research on date palm for accelerated propagation and enhanced production of quality planting materials, along with conservation and exchange of germplasms, and genetic engineering. In addition, the unexplored research methodologies and major bottlenecks identified in this review should be contemplated on in near future.

Genetic Transformation System for Woody Plant Tripterygium wilfordii and Its Application to Product Natural Celastrol

Tripterygium wilfordii is a perennial woody liana medicinal plant with several crucial biological activities. Although studies on tissue culture have previously been conducted, research on genetic transformation is much more challenging and therefore results in slower progress. In the present study, a highly efficient transformation system involving the particle bombardment of T. wilfordii with the reporter egfp gene using the PDS-1000/He system was established. A total of seven parameters affecting the genetic transformation were investigated using an L18 (6 × 36)-type orthogonal array. The result indicated that DNA delivery conditions of 3-cm target distance, 1100 psi helium pressure, 28 mmHg chamber vacuum pressure, three times number of bombardment, CaCl2 as precipitation agent, 2 μg plasmid DNA concentration and 48 h post-bombardment incubation time were optimal for T. wilfordii cell suspensions transformation. The average transformation efficiency was 19.17%. Based on this transformation system, the overexpression of two T. wilfordii farnesyl pyrophosphate synthase genes (TwFPSs) was performed in cell suspensions. Integration of the TwFPSs in the genome was verified by PCR analysis and also by Southern blotting using hygromycin gene as a probe. Real-time quantitative PCR analysis showed that the expression of TwFPS1&2 was highly up regulated in transgenic cell suspensions compared with control cells. The detection of metabolites showed that TwFPS1&2 could highly increase the celastrol content (973.60 μg/g) in transgenic cells. These results indicated that this transformation system is an effective protocol for characterizing the function of genes in the terpenoid biosynthetic pathway.

CRISPR/Cas9: A Practical Approach in Date Palm Genome Editing

The genetic modifications through breeding of crop plants have long been used to improve the yield and quality. However, precise genome editing (GE) could be a very useful supplementary tool for improvement of crop plants by targeted genome modifications. Various GE techniques including ZFNs (zinc finger nucleases), TALENs (transcription activator-like effector nucleases), and most recently clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 (CRISPR-associated protein 9)-based approaches have been successfully employed for various crop plants including fruit trees. CRISPR/Cas9-based approaches hold great potential in GE due to their simplicity, competency, and versatility over other GE techniques. However, to the best of our knowledge no such genetic improvement has ever been developed in date palm-an important fruit crop in Oasis agriculture. The applications of CRISPR/Cas9 can be a challenging task in date palm GE due to its large and complex genome, high rate of heterozygosity and outcrossing, in vitro regeneration and screening of mutants, high frequency of single-nucleotide polymorphism in the genome and ultimately genetic instability. In this review, we addressed the potential application of CRISPR/Cas9-based approaches in date palm GE to improve the sustainable date palm production. The availability of the date palm whole genome sequence has made it feasible to use CRISPR/Cas9 GE approach for genetic improvement in this species. Moreover, the future prospects of GE application in date palm are also addressed in this review.

Transient GUS Gene Expression in Date Palm Fruit Using Agroinjection Transformation Technique

Transient expression of foreign genes in plant tissue is a valuable tool for testing the efficacy of transformation methods. In this work, we present, for the first time, the utilization of agroinjection as an efficient transformation system for gene delivery in date palm fruit. The research utilized Agrobacterium tumefaciens strain LBA4404 harboring the binary vector pRI201-AN-GUS carrying the beta-glucuronidase (GUS) gene, under the control of a CaMV 35S and kanamycin (NPTII) as an antibiotic gene under the control of a NOS promoter. Based on histochemical assay of agroinjected fruit for the GUS gene expressions, this protocol has proved to be an efficient and reliable tool for transgene expression in date palm. PCR for plasmid DNA, extracted from the transformed Agrobacterium, demonstrated the generation of the expected amplicon, corresponding to the GUS gene using GUS primers.

Microprojectile Bombardment Transformation of Date Palm Using the Insecticidal Cholesterol Oxidase (ChoA) Gene

The overall objective of this work is to optimize the transformation system for date palm as a first step toward production of date palm clones resistant to noxious pests. A construct harboring the cholesterol oxidase (ChoA) gene, which renders plant resistance against insect attack, is introduced into embryogenic date palm callus using the PDS-1000/He particle bombardment system. The process involves the establishment of embryogenic callus cultures as well as immature embryo-derived microcalli that are used as target tissues for shooting and optimization of transformation conditions. This chapter in addition explains molecular and histochemical assays conducted to confirm gene integration and expression.

Genetic Transformation of Date Palm Via Microprojectile Bombardment

Efficient protocols for date palm embryogenic callus and somatic embryo transformation with uidA gene are described in this chapter. The embryogenic callus transformation procedure is 1.6 μm gold particle size coated with 2.5 μg DNA (pAct1-D plasmid), 1100 psi helium pressure, 9 cm target distance, 26 inHg vacuum pressure, 3 mm distance between the rupture disk and macrocarrier, and osmotic pretreatment with 0.4 M mannitol followed by 60 min air desiccation. The somatic embryo transformation procedure is 0.6 μm gold particle size coated with 2.5 μg DNA (pAct1-D plasmid), 1350 psi helium pressure, 6 cm target distance, 28 inHg vacuum pressure, 3 mm distance between the rupture disk and macrocarrier, and osmotic pretreatment with 0.4 M mannitol followed by 60 min air desiccation. Protocols for analysis of the transgenic plantlets have also been described.

Vectorization of Nucleic Acids for Therapeutic Approach: Tutorial Review

Oligonucleotides present a high therapeutic potential for a wide variety of diseases. However, their clinical development is limited by their degradation by nucleases and their poor blood circulation time. Depending on the administration mode and the cellular target, these macromolecules will have to cross the vascular endothelium, to diffuse through the extracellular matrix, to be transported through the cell membrane, and finally to reach the cytoplasm. To overcome these physiological barriers, many strategies have been developed. Here, we review different methods of DNA vectorization, discuss limitations and advantages of the various vectors, and provide new perspectives for future development.

ATDOF5.8 protein is the upstream regulator of ANAC069 and is responsive to abiotic stress

ANAC069 encodes a plasma membrane-bound NAC protein that integrates auxin and salt signals to regulate Arabidopsis thaliana seed germination. However, the regulatory network of ANAC069 has not been revealed. Here, we report that ANAC069 is a direct target gene of the ATDOF5.8 transcription factor. There are seven DOF motifs in the promoter of ANAC069, which is highly enriched in the promoter. Yeast one-hybrid (Y1H) assays showed that a Dof protein, ATDOF5.8, binds to the DOF motifs. The interaction between ATDOF5.8 and the promoter of ANAC069 was further confirmed by transient expression assays in tobacco leaves. Chromatin Immunoprecipitation (ChIP) results suggested that the binding of ATDOF5.8 to DOF motifs in the promoter of ANAC069 occurs in vivo in Arabidopsis to regulate the expression of ANAC069. Moreover, ATDOF5.8 and ANAC069 share similar expression patterns in response to salt, drought and ABA treatment. Taken together, the results suggested a regulatory network model mediated by ANAC069, under abiotic stress conditions, ATDOF5.8 regulates the expression of ANAC069, and the activated ANAC069 binds to NAC recognition sequences or other motifs to regulate the expression of genes containing these motifs in their promoters.

Salt tolerance research in date palm tree (Phoenix dactylifera L.), past, present, and future perspectives

The date palm can adapt to extreme drought, to heat, and to relatively high levels of soil salinity. However, excessive amounts of salt due to irrigation with brackish water lead to a significant reduction in the productivity of the fruits as well as marked decrease in the viable numbers of the date palm trees. It is imperative that the nature of the existing salt-adaptation mechanism be understood in order to develop future date palm varieties that can tolerate excessive soil salinity. In this perspective article, several research strategies, obstacles, and precautions are discussed in light of recent advancements accomplished in this field and the properties of this species. In addition to a physiological characterization, we propose the use of a full range of OMICS technologies, coupled with reverse genetics approaches, aimed toward understanding the salt-adaption mechanism in the date palm. Information generated by these analyses should highlight transcriptional and posttranscriptional modifications controlling the salt-adaptation mechanisms. As an extremophile with a natural tolerance for a wide range of abiotic stresses, the date palm may represent a treasure trove of novel genetic resources for salinity tolerance.