Optimization of Mature Embryo-Based Tissue Culture and Agrobacterium-Mediated Transformation in Model Grass Brachypodium distachyon

Opportunities and Challenges of In Vitro Tissue Culture Systems in the Era of Crop Genome Editing

Currently, the development of genome editing (GE) tools has provided a wide platform for targeted modification of plant genomes. However, the lack of versatile DNA delivery systems for a large variety of crop species has been the main bottleneck for improving crops with beneficial traits. Currently, the generation of plants with heritable mutations induced by GE tools mostly goes through tissue culture. Unfortunately, current tissue culture systems restrict successful results to only a limited number of plant species and genotypes. In order to release the full potential of the GE tools, procedures need to be species and genotype independent. This review provides an in-depth summary and insights into the various in vitro tissue culture systems used for GE in the economically important crops barley, wheat, rice, sorghum, soybean, maize, potatoes, cassava, and millet and uncovers new opportunities and challenges of already-established tissue culture platforms for GE in the crops.

Establishment of an efficient regeneration and Agrobacterium transformation system in mature embryos of calla lily (Zantedeschia spp.)

Calla lily (Zantedeschia spp.) have great aesthetic value due to their spathe-like appearance and richness of coloration. However, embryonic callus regeneration is absent from its current regeneration mechanism. As a result, constructing an adequate and stable genetic transformation system is hampered, severely hindering breeding efforts. In this research, the callus induction effectiveness of calla lily seed embryos of various maturities was evaluated. The findings indicated that mature seed embryos were more suitable for in vitro regeneration. Using orthogonal design experiments, the primary elements influencing in vitro regeneration, such as plant growth regulators, genotypes, and nanoscale materials, which was emergent uses for in vitro regeneration, were investigated. The findings indicated that MS supplemented with 6-BA 2 mg/L and NAA 0.1 mg/L was the optimal medium for callus induction (CIM); the germination medium (GM) was MS supplemented with 6-BA 2 mg/L NAA 0.2 mg/L and 1 mg/L CNTs, and the rooting medium (RM) was MS supplemented with 6-BA 2 mg/L NAA 0.7 mg/L and 2 mg/L CNTs. This allowed us to verify, in principle, that the Agrobacterium tumefaciens-mediated genetic transformation system operates under optimal circumstances using the GUS reporter gene. Here, we developed a seed embryo-based genetic transformation regeneration system, which set the stage for future attempts to create new calla lily varieties.

Establishment of an efficient transformation method of garden stock (Matthiola incana) using a callus formation chemical inducer

Matthiola incana is an important floricultural plant that blooms from winter to spring, and had been desired to be established a transformation system. This study successfully obtained stable transgenic plants from M. incana. We used Agrobacterium tumefaciens harboring a binary vector containing the β-glucuronidase gene (GUS) under the control of cauliflower mosaic virus 35S promoter to evaluate the transformation frequency of M. incana. We observed that cocultivation with the A. tumefaciens strain GV3101 for 5 days effectively enhanced the infection frequency, assessed through a transient GUS expression area in the seedling. Furthermore, the addition of 100 µM acetosyringone was necessary for Agrobacterium infection. However, we could not obtain transgenic plants on a shoot formation medium supplemented with 1 mg l^-1 6-benzyladenine (BA). For callus formation from the leaf sections, a medium supplemented with 1-50 µM fipexide (FPX), a novel callus induction chemical, was employed. Then, the callus formation was observed after 2 weeks, and an earlier response was detected than that in the BA medium (4-6 weeks). Results also showed that cultivation in a selection medium supplemented with 12.5 µM FPX obtained hygromycin-resistant calli. Thus, this protocol achieved a 0.7% transformation frequency. Similarly, progenies from one transgenic line were observed on the basis of GUS stains on their leaves, revealing that the transgenes were also inherited stably. Hence, FPX is considered a breakthrough for establishing the transformation protocol of M. incana, and its use is proposed in recalcitrant plants.

Ectopic expression of Vigna radiata's vacuolar Na+/H+ antiporter gene (VrNHX1) in indica rice (Oryza sativa L.)

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Successful Agrobacterium-mediated transformation of indica Dhan28 and BRRI Dhan29

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Ectopic expression of the Na+/H+ exchanger 1 (VrNHX1) from Vigna radiata L. Wilczek in indica rice improves salinity tolerance.

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Under 150 mM NaCl salinity stress, transgenic lines performed significantly better than wild type.

It is essential to develop high salt-tolerant rice varieties in order to cultivate the salt-affected lands. In this study, Na⁺/H⁺ exchanger 1 (NHX1) gene isolated from Vigna radiata L. Wilczek was transferred in Bangladesh Rice Research Institute (BRRI) developed two indica rice genotypes BRRI Dhan28 and BRRI Dhan29 using in-planta approach for improvement of salinity tolerance. Embryonic axes of matured dehusked rice seeds were injured and co-cultivated with Agrobacterium strain harboring VrNHX1 gene and finally regenerated. GUS histochemical assay and PCR amplification of GUS-a and VrNHX1 were performed to confirm the transformation. Expression confirmation was done by semi-quantitative RT-PCR. Under salinity stress, transgenic lines showed higher chlorophyll, relative water content and decreased electrolyte leakage, proline content, lipid peroxidation level, and catalase enzyme activity which represent the better physiology than control plants. Moreover, under salinity stress (150 mM), transgenic lines exhibited superior growth and salt tolerant than non-transgenic plants.

Plant Cell and Organism Development

Plants represent a unique and fascinating group of living organisms [...].

In Vitro Tissue Culture in Brachypodium: Applications and Challenges

Brachypodium distachyon has become an excellent model for plant breeding and bioenergy grasses that permits many fundamental questions in grass biology to be addressed. One of the constraints to performing research in many grasses has been the difficulty with which they can be genetically transformed and the generally low frequency of such transformations. In this review, we discuss the contribution that transformation techniques have made in Brachypodium biology as well as how Brachypodium could be used to determine the factors that might contribute to transformation efficiency. In particular, we highlight the latest research on the mechanisms that govern the gradual loss of embryogenic potential in a tissue culture and propose using B. distachyon as a model for other recalcitrant monocots.