In Vitro Gamma Mutagenesis Techniques in Rice (Oryza sativa L. var. Lazarroz FL)

Gamma radiation (60Co)-induced mutagenesis offers an alternative to develop rice lines by accelerating the spontaneous mutation process and increasing the pool of allelic variants available for breeding. Ionizing radiation works by direct or indirect damage to DNA and subsequent mutations. The technique can take advantage of in vitro protocols to optimize resources and accelerate the development of traits. This is achieved by exposing mutants to a selection agent of interest in controlled conditions and evaluating large numbers of plants in reduced areas. This chapter describes the protocol for establishing gamma radiation dosimetry and in vitro protocols for optimization at the laboratory level using seeds as the starting material, followed by embryogenic cell cultures, somatic embryogenesis, and regeneration. The final product of the protocol is a genetically homogeneous population of Oryza sativa that can be evaluated for breeding against abiotic and biotic stresses.

Effects of plant growth regulators and sucrose on proliferation and quality of embryogenic tissue in Picea pungens

Embryogenic tissue (ET) is important for genetic modification and plant re-generation. The proliferation ability and vigor of ET are crucial for plant propagation via somatic embryogenesis. In this study, ET was induced from mature zygotic embryos in blue spruce (Picea pungens Engelm.). There were significant differences in ET induction between two provenances, i.e. 78.8 ± 12.5% and 62.50 ± 12.8% respectively. Effects of 2,4-Dichlorophenoxy acetic acid (2,4-D), 6-Benzyl amino-purine (6-BA) and/or sucrose on ET proliferation and somatic embryo (SE) maturation were further investigated with four cell lines. The highest ET proliferation rate reached 1473.7 ± 556.0% biweekly. Concentrations of 2,4-D or 6-BA applied at tissue proliferation stage impacted SE maturation among the cell lines, whereas sucrose showed less effects. The highest rate, 408 ± 230 mature SEs/g FW, was achieved in SE maturation cultures. This research demonstrated that the culture conditions, i.e. the specific concentrations of 2,4-D and BA, at ET proliferation stage affected not only ET growth, but also the quality of ET for SE maturation. This study revealed the necessity and benefit in developing both the general and the genotype-specific protocols for efficient production of mature SEs, or somatic plants in blue spruce.

Cellular responses of oil palm genotypes during somatic embryogenesis involve participation of procambial cells, DNA demethylation, and auxin accumulation

Cell markers of somatic embryogenesis initiation from leaf tissues in oil palm involve the participation of procambial cells, DNA demethylation, and auxin accumulation. Low callogenesis and genotype-dependent response have been mentioned in the development of somatic embryogenesis protocols of Elaeis oleifera × E. guineensis elite hybrids, which requires more detailed investigations of the process. Thus, the initial cellular responses of immature leaves of adult genotypes of this hybrid were investigated for the first time, emphasizing histological, epigenetic, and endogenous auxin changes. Leaf segments from two genotypes, one responsive to somatic embryogenesis (B351733) and another non-responsive (B352933), were inoculated in Murashige and Skoog medium with 450 µM of 4-amino-3, 5, 6-trichloropicolinic acid. For anatomical analysis, samples of both genotypes were collected at 0, 20, 90, and 105 days of cultivation. Samples of both genotypes were also taken at different cultivation periods to analyze DNA methylation status (% 5-mC-5 methylcytosine) via ELISA test. Immunolocalization assays were performed with anti-indole-3-acetic acid and anti-5-methyl-deoxycytosine antibodies from samples of hybrid B351733. We distinguished two groups of cells reactive to the induction of embryogenic callogenesis, parenchymatous sheath cells, and procambial cells; however, only the latter are directly involved with the formation of calluses. The data obtained indicate that the formation of calluses in hybrid B351733 is related to DNA hypomethylation, while the non-responsiveness of leaf explants in hybrid B352932 is related to DNA hypermethylation. The in situ immunolocalization enabled the identification of initial markers of the callogenic process, such as IAA accumulation and hypomethylation. Identifying these events brings the possibility of establishing strategies for efficient manipulation of somatic embryogenesis protocols in palm trees.

Somatic embryogenesis from flower tepals of Hippeastrum aiming regeneration of virus-free plants

Hippeastrum hybridum is an important bulbous flower plant in world floriculture, which are propagated conventionally by the technique known as double or twin scales to obtain plants with clonal origin. However, this technique promotes the propagation of systemic diseases, particularly mosaic-inducing viruses. The aim of this paper was to evaluate the somatic embryogenesis (SE) from tepals as an alternative to provide a technique for SE induction and to obtaining virus-free plantlets of Hippeastrum from infected plants. The concentrations of 2,4-Dichlorofenoxiacetic Acid (2,4-D) and thidiazuron (TDZ) was evaluated in SE induction pathway. The monitoring of viruses during the assays with tepals was performed by Reverse Transcription-Polymerase Chain Reaction. SE induction was obtained, for the first time, in tepal segments from flower buds of Hippeastrum. The 2,4-D was the main factor for embryogenic callus induction, and TDZ increased the SE induction rate. However, conversion of somatic embryos into plantlets were only developed in free-2,4-D media, replaced by 1.0 mg L^-1 6-Benziladenine. Out of five virus species monitored during the experiment, Cucumber mosaic virus was detected in tepals and Hippeastrum mosaic virus in leaves of donor plants. The SE-derived plantlets that germinated in vitro were acclimatized and tested negative for all viruses assayed.

Somatic Embryogenesis in Banana (Musa spp.)

Bananas (Musa ssp.) are among the world's most important crops. In terms of gross value of production, they are the fourth most important global food crop and have an important socioeconomic and ecological role. Somatic embryogenesis (SE) is a developmental process, in which somatic cells differentiate into embryos which eventually develop and regenerate into plants. SE is exploited to generate a large quantity of very high economic value, genetically identical and disease-free plantlets. In bananas, the use of shoot apexes of axillary buds to induce SE resulted an alternative for plant regeneration through embryogenic cell suspension (ECS). The protocol has been scaled up to commercial laboratories for tissue culture (biofactories) for production of planting materials. The genetic stability of regenerated plants and high yields obtained under field conditions demonstrate the feasibility of scaling up this biotechnological protocol and adapting it to commercial production of planting materials to mitigate a critical bottleneck in the value chain of this important crop.

Perspectives of Somatic Embryogenesis: Concluding Remarks

One of the main objectives to achieve in plant tissue culture is the multiplication of the available plant material, taking full advantage of the regenerative capacities of plant cells. Somatic embryogenesis leverages cell totipotency to produce new explants from a cell, thus obtaining many propagules for scientific research, industrial, or exploitation purposes. Somatic embryogenesis (ES) characterizes by being one of the most efficient techniques in plant micropropagation. However, developing an efficient plant ES protocol requires several key factors to consider, as demonstrated throughout the chapters of this book. These chapters highlight the major drivers of the success of ES in different plant species: plant growth regulators, concentration of auxins and cytokines, water deficit, photoperiod, and type of culture medium; techniques such as the use of bioreactors and Thin Cell Layer (TCL); and the influence of stress on the formation of somatic embryos. Research has been conducted to address each phase of somatic embryogenesis, either individually or for all phases. The chapters of this book cover in detail the techniques used and provide guidance that will allow readers to successfully develop all the somatic embryogenesis phases in different cultures, from cell dedifferentiation to differentiation.

Overview of Somatic Embryogenesis

Somatic embryogenesis is a natural phenomenon through which somatic embryos are produced from somatic cells although. It is considered the most efficient morphogenic pathways for plant multiplication. One of the key features of somatic embryogenesis is the use of cellular totipotency, where dedifferentiation is induced to foster cell proliferation, followed by the induction of differentiation using plant growth regulators to produce new plants. There is a cell group with the potential to undergo the somatic embryogenesis pathway through adequate stimulation (plant growth regulators, incubation conditions, and supplementation of the culture medium). There are two somatic embryogenesis pathways in plants: direct and indirect embryogenesis. Direct somatic embryogenesis consists of the formation of embryos directly from isolated cells, without the formation of "callous" tissue. Indirect somatic embryogenesis is characterized by the formation of a callus as a stage that precedes the formation of somatic embryos. It should be stressed that not all plant cells have this morphogenic capacity; consequently, determining the type of factors that drive this type of response has been challenging. This book provides the reader with updated available information on the techniques, relevant protocols, and tools to perform somatic embryogenesis in different plant species for economic purposes.

Somatic Embryogenesis in Citrus (Citrus spp.), var. Valencia

Somatic embryogenesis has been obtained in many citrus cultivars; however, the efficiency of the system is genotype dependent and culture synchronization is important to reach more efficient systems. In this chapter we present a detailed protocol of somatic embryogenesis induction from nucellar tissue and the use of an alternative method of callus sieving for culture synchronization and embryo production. This is a simple method which can also be evaluated for other species aiming at better culture efficiency and somatic embryo production.

Use of Thin Cell Layer Technique for Induction of Somatic Embryogenesis of Agave fourcroydes

Agave fourcroydes (henequén) is a plant used for the extraction of hard fiber from its leaves. Due to its long-life cycle, it is very difficult to genetically improve. Somatic embryogenesis (SE) is a very useful micropropagation technique, that can be used for genetic improvement programs and increase the micropropagation of this species. SE is a morphogenic process by which somatic embryos are generated from somatic cells reprogramming. To initiate the regeneration program, the loss of cell-cell communication is suggested to be important. The Thin Cell Layer (TCL) technique allows for the isolation of specific cell or tissue layers, and in conjunction with strictly controlled growth conditions, may lead to the in vitro induction of specific morphogenic programs. Here, we describe a new protocol for the induction of somatic embryogenesis through TCL culture technique, from stem of elite clonal A. fourcroydes vitroplants previously generated through micropropagation of adventitious shoots.

Somatic Embryogenesis in Pines

Among the different in vitro culture techniques, somatic embryogenesis has been one of the most important developments for plant tissue culture; it has enabled mass propagation and the development of biotechnological tools to enhance the productivity and quality of plantation forestry. This propagation technique together with cryopreservation is the base of multivarietal forestry.The development of somatic embryogenesis in forest trees dates from 1985, and in the last years several studies have focused on the development and optimization of the conifer somatic embryogenesis process to make it more efficient in terms of both the quantity and the characteristics of the plants obtained. However, these advances are not sufficiently refined to be implemented commercially for many Pinus spp. due to the high cost of the process derived from hand labor. Nowadays, trying to add value to the plants produced to compensate the high costs of the process, different studies are being developed in order to obtain Pinus somatic plants with better adaptation to environmental stresses prompted by the current situation of climate change.In this chapter, a summary of the recent somatic embryogenesis systems developed to achieve Pinus spp. high quality plants is presented.

Use of Thin Cell Layer (TCL) to Obtain Somatic Embryogenesis

The thin cell layer (TCL) culture system was initially reported in relation to the model plant Nicotiana tabacum, giving rise to 47 years of continuous application and investigation on micropropagation and plant breeding of over 100 plant species or hybrids. The small sizes of the tissue sections (100 μm to 1-2 mm in thickness), its classification into transverse TCL (tTCL) or longitudinal TCL (lTCL) categories, and the interaction between the cultured cells and the culture medium are the main drivers of its efficacy in tens of plants for the induction of somatic embryogenesis, relative to the conventional in-vitro culture system. Furthermore, it promotes higher productivity and reduced time in the proliferation of cultures, which is key for the differentiation of cells and plant tissues. This chapter describes the main characteristics of the TCL sections, and the interaction between cells under in-vitro culture. In addition, it highlights the latest findings reporting the success of TCL in ornamental, herbaceous, woody, and recalcitrant plants. In most cases, studies on the use of TCL in combination with techniques such as bioreactors, histology, genetic transformation, and fidelity analysis, provide indisputable evidence that highlights the importance of this technique in plant biotechnology. Finally, the perspectives on TCL use are described, underlining the advantages and constraints of the technique for its continued use and future application.

Somatic Embryogenesis of Anthurium andraeanum Linden., -A Tropical Florists' Plant

The global floriculture market is expected to reach US$41.1 billion by 2027 at a CAGR of 5% over the analysis period 2020-2027; on the year 2020, the recorded market value in this trade was US$29.2 billion. The florists mainly use Anthurium andraeanum flowers in fashionable bouquets and floral arrangements because of their beautiful, attractive bright colored eye-catching spathe, candle-like spadix, prolonged vase life, etc. The cut flower industry always seeks elite cultivars and new hybrids of A. andraeanum, that in turn depend on the availability of large numbers of clonal planting propagules. In vitro somatic embryogenesis is an important technique for large-scale clonal propagation, development of transgenic plants, creation of new variety by somaclonal variation, mutagenesis on in vitro plants, and germplasm preservation for future use. Here, we describe the protocol of somatic embryogenesis of Anthurium andraeanum cv. Cancan, an important commercial cultivated variety. The protocol has been optimized by using 4 different types of culture media which are used during embryogenic callus induction, multiplication of callus, induction of somatic embryogenesis, and maturation plus conversion of embryos into plantlets. The protocol outlines the detailed methods from mother plant procurement to hardening of micro plants that is ready to transfer in the field and it can be used for large-scale commercial propagation.

Theobroma cacao: Somatic Embryogenesis

A two-step process combining direct and indirect somatic embryogenesis, on solid and liquid medium, respectively is described for Theobroma cacao L. Staminodes and petals from unopened bud flowers are used to induce primary direct embryos. Then, these primary embryos are cut to produce embryogenic calli which will develop secondary embryos. This step of indirect SE allows us to produce large quantities of embryos and to do mass propagation using liquid culture medium. Despite a very strong clone dependency and high batch-to-batch variability, about 80% of T. cacao cultivars respond to somatic embryogenesis and can be propagated by this method.

Citrus Protoplast Isolation and Plant Regeneration Through Somatic Embryogenesis

Protoplasts are an attractive explant source for biotechnological tools widely used on citrus genetic improvement, such as somatic hybridization and direct genetic transformation. These delicate and responsive materials are subjected to cell proliferation induction and differentiation of somatic embryos which further regenerate into entire plants. The isolation of viable protoplasts followed by regeneration of plants through somatic embryogenesis is an important methodology for breeding applications. The methods presented here can also be used as a reference for protoplast work in other species, followed by protocol optimization for different species/genotypes.

Somatic Embryogenesis in Papaya (Carica papaya L.)

High mortality rates of in vitro plants during ex vitro acclimatization, due to low rooting, is one of the main problems of papaya tissue culture. This work was carried out with the objective to obtain 100% hermaphroditic in vitro plants of the papaya cultivar "Maradol Roja" by somatic embryogenesis, which have an adequate rooting system that allows them a higher survival percentage in the ex vitro acclimatization phase. In international scientific literature, there are several protocols; however, not all of them cover the different phases of somatic embryogenesis. This chapter describes a complete and optimized protocol from immature zygotic embryos in this cultivar. It also looks at the morpho-anatomical characterization of somatic embryos in the different stages of ontogenetic development, as well as high survival rates under ex vitro conditions of the plants obtained. It can be used for genetic improvement and propagation of this species.

Embryogenic callus induction from immature zygotic embryos and genetic transformation of Larix kaempferi 3x Larix gmelinii 9

To date, there are few reports of the successful genetic transformation of larch and other conifers, mainly because it is difficult to transform and integrate exogenous genes. In this study, hybrid larch Larix kaempferi 3x Larix gmelinii 9 cones were collected on June 27, July 1, July 4, July 7 and July 16, 2017. Embryogenic callus induction was studied using a combination of different plant growth regulators and concentrations. The results showed that July 1 was the best stage; the highest induction rate was 10.83%, which cultured in BM medium (Button medium, which formula was listed in S1 Table) with 1.0 mg/L 2,4-D (2,4-dichlorophenoxyacetic acid) and 0.2 mg/L KT(kinetin). When cultured on a proliferation medium for 12 days, proliferation was the fastest, reaching 323.08%, which could also maintain the freshness and vitality. The suitable pre-culture medium for somatic embryogenesis was 1/4 BM medium containing 10 g/L inositol and 60 g/L sucrose. The combination of 45 mg/L ABA (abscisic acid) and 75 g/L PEG4000 (Polyethyene glycol 4000) could promote the number of somatic embryos, and reached the maximum, 210 140 per 1 g FW. The genetic transformation was carried out by the Agrobacterium-mediated transformation method with embryogenic callus cultured for 12 days. The results showed the optimal OD600 of the infection solution(suspension of A. tumefaciens) was 0.5, co-culture time was 2 days, and screening concentration of Hyg (hygromycin B) was 4 mg/L. In this study, the transformation rate of resistance callus was 32.1%. It provides a reference for low genetic transformation efficiency of larch at present. This study could be beneficial for the innovation and breeding of larch by genetic engineering and provides a certain basis for rapid propagation of excellent larch germplasm resources and genetic engineering breeding of larch and other conifers.

Anther Culture in Sweet Pepper (Capsicum annuum L.)

Peppers have a prominent role in traditional cuisine of many different countries all around the world. This is why pepper is one of the most important crops worldwide. Production of doubled haploid (DH) pepper plants has been assessed by different approaches, but at present, the most efficient and universal method is by far anther culture, based on the use of the Dumas de Vaulx et al. protocol published in 1981, and adapted to the particularities of each specific pepper background. In this chapter, we present a method to produce pepper DHs by anther culture, based on the Dumas de Vaulx et al. protocol, but including a number of modifications which, in our experience, allow for a more efficient production DH plants in different pepper genotypes.

Leaf transcriptomic signatures for somatic embryogenesis potential of Elaeis guineensis

Potentially embryogenic oil palms can be identified through leaf transcriptomic signatures. Differential expression of genes involved in flowering time, and stress and light responses may associate with somatic embryogenesis potential. Clonal propagation is an attractive approach for the mass propagation of high yielding oil palms. A major issue hampering the effectiveness of oil palm tissue culture is the low somatic embryogenesis rate. Previous studies have identified numerous genes involved in oil palm somatic embryogenesis, but their association with embryogenic potential has not been determined. In this study, differential expression analysis of leaf transcriptomes from embryogenic and non-embryogenic mother palms revealed that transcriptome profiles from non- and poor embryogenic mother palms were more similar than highly embryogenic palms. A total of 171 genes exhibiting differential expression in non- and low embryogenesis groups could also discriminate high from poor embryogenesis groups of another tissue culture agency. Genes related to flowering time or transition such as FTIP, FRIGIDA-LIKE, and NF-YA were up-regulated in embryogenic ortets, suggesting that reproduction timing of the plant may associate with somatic embryogenesis potential. Several light response or photosynthesis-related genes were down-regulated in embryogenic ortets, suggesting a link between photosynthesis activity and embryogenic potential. As expression profiles of the differentially expressed genes are very similar between non- and low embryogenic groups, machine learning approaches with several candidate genes may generate a more sensitive model to better discriminate non-embryogenic from embryogenic ortets.

From Plant Survival Under Severe Stress to Anti-Viral Human Defense - A Perspective That Calls for Common Efforts

Reprogramming of primary virus-infected cells is the critical step that turns viral attacks harmful to humans by initiating super-spreading at cell, organism and population levels. To develop early anti-viral therapies and proactive administration, it is important to understand the very first steps of this process. Plant somatic embryogenesis (SE) is the earliest and most studied model for de novo programming upon severe stress that, in contrast to virus attacks, promotes individual cell and organism survival. We argued that transcript level profiles of target genes established from in vitro SE induction as reference compared to virus-induced profiles can identify differential virus traits that link to harmful reprogramming. To validate this hypothesis, we selected a standard set of genes named 'ReprogVirus'. This approach was recently applied and published. It resulted in identifying 'CoV-MAC-TED', a complex trait that is promising to support combating SARS-CoV-2-induced cell reprogramming in primary infected nose and mouth cells. In this perspective, we aim to explain the rationale of our scientific approach. We are highlighting relevant background knowledge on SE, emphasize the role of alternative oxidase in plant reprogramming and resilience as a learning tool for designing human virus-defense strategies and, present the list of selected genes. As an outlook, we announce wider data collection in a 'ReprogVirus Platform' to support anti-viral strategy design through common efforts.

Somatic embryogenesis is an effective strategy for dissecting chimerism phenomena in Vitis vinifera cv Nebbiolo

The tendency of somatic embryogenesis to regenerate plants only from the L1 layer, associated with the spread of chimerism in grapevine, must be carefully considered in the framework of biotechnological improvement programmes. Grapevine is an important fruit crop with a high economic value linked to traditional genotypes that have been multiplied for centuries by vegetative propagation. In this way, somatic variations that can spontaneously occur within the shoot apical meristem are fixed in the whole plant and represent a source of intra-varietal variability. Previously identified inconsistencies in the allelic calls of single nucleotide variants (SNVs) suggested that the Vitis vinifera 'Nebbiolo' CVT185 clone is a potential periclinal chimera. We adopted the somatic embryogenesis technique to separate the two genotypes putatively associated with the L1 and L2 layers of CVT185 into different somaclones. Despite the recalcitrance of 'Nebbiolo' to the embryogenic process, 58 somaclones were regenerated and SNV genotyping assays attested that the genotype of all them differed from that of the mother plant and was only attributable to L1. The results confirmed that L2 has low or no competence for differentiating somatic embryos. After one year in the greenhouse, the somaclones showed no phenotypic alterations in comparison with the mother plant; however further analyses are needed to identify potential endogenous sources of variation. The tendency of somatic embryogenesis to regenerate plants only from L1 must be carefully considered in the framework of biotechnological improvement programmes in this species.

Anther Culture of Potato: Method and Applications

Anther culture provides a tool to produce haploid lines from cultivated potato (Solanum tuberosum L.), which has a tetraploid (2n = 4x = 48) genome constitution. Shoot regeneration via direct embryogenesis in anther culture procedure is preferred to produce dihaploid (2n = 2x = 24) potato lines, which can be applied in breeding of potato varieties. The anther culture protocol described in the present chapter can be conducted not only in cultivated potato (S. tuberosum) but also in other genetically related potato species.

Global 5-methylcytosine and physiological changes are triggers of indirect somatic embryogenesis in Coffea canephora

Indirect somatic embryogenesis (ISE) establishment for Coffea species started in the 1970s. Since then, intraspecific variations in the morphogenic pathway have been reported, even in the common environmental condition in vitro. Several authors have suggested that these variations are the result of genetic, epigenetic, and/or physiological events, highlighting the need for investigations to know the causes. Along these lines, this study aimed to investigate and describe, for the first time, the global 5-methylcytosine and physiological changes that occur in the cells of the aggregate suspensions of Coffea canephora during proliferation and somatic embryo regeneration steps. The cell proliferation step was characterized by increase in cell mass in all subcultures; relatively low mean values of global 5-methylcytosine (5-mC%), abscisic acid (ABA), and indole-3-acetic acid (IAA); high mean value of 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor); and increase followed by decrease in spermidine (Spd, a polyamine) level. Therefore, these epigenetic and physiologic aspects promoted the cell proliferation, which is fundamental for ISE. In turn, the somatic embryo regeneration was correlated with global 5-mC% and physiological changes. The competence acquisition, determination, and cell differentiation steps were marked by increases in mean values of 5-mC%, IAA and ABA, and decreases in ACC and Spd, evincing that these changes are the triggers for regeneration and maturation of somatic embryos. Therefore, dynamic and coordinated epigenetic and physiologic changes occur in the cells of the aggregate suspensions during the C. canephora ISE in liquid system.

Optimized Protocol for Development of Androgenic Haploids and Doubled Haploids in FCV Tobacco (Nicotiana tabacum)

Haploids are plants with gametophytic chromosome number, which upon chromosome duplication results in production of doubled haploids (DHs). There are several methods to obtain haploids and DHs, of which in vitro anther culture is the most effective and widely used method in tobacco. The production of haploids and DHs through androgenesis allows for a single-step development of complete homozygous lines from heterozygous genotypes, shortening the time required to produce homozygous genotypes in comparison to the conventional breeding scheme. The DH development process comprises two main steps: induction of androgenesis and duplication of the haploid genome. The critical stages of DH protocol in tobacco are determining the bud stage for anther culture, pretreatment, anther culture media, detection and identification of haploids, and chromosome doubling. Here we present an efficient anther culture protocol to get haploids and DHs in flue-cured virginia (FCV) tobacco. This optimized protocol can be used as a potential tool for generation of haploids and DHs for genetic improvement of tobacco.

Genotype and transcriptome effects on somatic embryogenesis in Cryptomeria japonica

Somatic embryogenesis (SE), which is in vitro regeneration of plant bodies from somatic cells, represents a useful means of clonal propagation and genetic engineering of forest trees. While protocols to obtain calluses and induce regeneration in somatic embryos have been reported for many tree species, the knowledge of molecular mechanisms of SE development is still insufficient to achieve an efficient supply of somatic embryos required for the industrial application. Cryptomeria japonica, a conifer species widely used for plantation forestry in Japan, is one of the tree species waiting for a secure SE protocol; the probability of normal embryo development appears to depend on genotype. To discriminate the embryogenic potential of embryonal masses (EMs) and efficiently obtain normal somatic embryos of C. japonica, we investigated the effects of genotype and transcriptome on the variation in embryogenic potential. Using an induction experiment with 12 EMs each from six genotypes, we showed that embryogenic potential differs between/within genotypes. Comparisons of gene expression profiles among EMs with different embryogenic potentials revealed that 742 differently expressed genes were mainly associated with pattern forming and metabolism. Thus, we suggest that not only genotype but also gene expression profiles can determine success in SE development. Consistent with previous findings for other conifer species, genes encoding leafy cotyledon, wuschel, germin-like proteins, and glutathione-S-transferases are likely to be involved in SE development in C. japonica and indeed highly expressed in EMs with high-embryogenic potential; therefore, these proteins represent candidate markers for distinguishing embryogenic potential.

Improvement of a Genetic Transformation System and Preliminary Study on the Function of LpABCB21 and LpPILS7 Based on Somatic Embryogenesis in Lilium pumilum DC. Fisch

Auxin transport mediates the asymmetric distribution of auxin that determines the fate of cell development. Agrobacterium-mediated genetic transformation is an important technical means to study gene function. Our previous study showed that the expression levels of LpABCB21 and LpPILS7 are significantly up-regulated in the somatic embryogenesis (SE) of Lilium pumilum DC. Fisch. (L. pumilum), but the functions of both genes remain unclear. Here, the genetic transformation technology previously developed by our team based on the L. pumilum system was improved, and the genetic transformation efficiency increased by 5.7-13.0%. Use of overexpression and CRISPR/Cas9 technology produced three overexpression and seven mutant lines of LpABCB21, and seven overexpression and six mutant lines of LpPILS7. Analysis of the differences in somatic embryo induction of transgenic lines confirmed that LpABCB21 regulates the early formation of the somatic embryo; however, excessive expression level of LpABCB21 inhibits somatic embryo induction efficiency. LpPILS7 mainly regulates somatic embryo induction efficiency. This study provides a more efficient method of genetic transformation of L. pumilum. LpABCB21 and LpPILS7 are confirmed to have important regulatory roles in L. pumilum SE thus laying the foundation for subsequent studies of the molecular mechanism of Lilium SE.

Agrobacterium rhizogenes-mediated transformation of grain (Amaranthus hypochondriacus) and leafy (A. hybridus) amaranths

Transgenic A. hypochondriacus and A. hybridus roots were generated. Further, a distinct plant regeneration program via somatic embryos produced from hairy roots was established. Work was implemented to develop an optimized protocol for root genetic transformation of the three grain amaranth species and A. hybridus, their presumed ancestor. Transformation efficiency was species-specific, being higher in A. hypochondriacus and followed by A. hybridus. Amaranthus cruentus and A. caudatus remained recalcitrant. A reliable and efficient Agrobacteruim rhizogenes-mediated transformation of these species was established using cotyledon explants infected with the previously untested BVG strain. Optimal OD₆₀₀ bacterial cell densities were 0.4 and 0.8 for A. hypochondriacus and A. hybridus, respectively. Hairy roots of both amaranth species were validated by the amplification of appropriate marker genes and, when pertinent, by monitoring green fluorescent protein emission or β-glucuronidase activity. Embryogenic calli were generated from A. hypochondriacus rhizoclones. Subsequent somatic embryo maturation and germination required the activation of cytokinin signaling, osmotic stress, red light, and calcium incorporation. A crucial step to ensure the differentiation of germinating somatic embryos into plantlets was their individualization and subcultivation in 5/5 media containing 5% sucrose, 5 g/L gelrite, and 0.2 mg/L 2-isopentenyladenine (2iP) previously acidified to pH 4.0 with phosphoric acid, followed by their transfer to 5/5 + 2iP media supplemented with 100 mg/L CaCl₂. These steps were strictly red light dependent. This process represents a viable protocol for plant regeneration via somatic embryo germination from grain amaranth transgenic hairy roots. Its capacity to overcome the recalcitrance to genetic transformation characteristic of grain amaranth has the potential to significantly advance the knowledge of several unresolved biological aspects of grain amaranths.

Research Tools for the Functional Genomics of Plant miRNAs During Zygotic and Somatic Embryogenesis

During early plant embryogenesis, some of the most fundamental decisions on fate and identity are taken making it a fascinating process to study. It is no surprise that higher plant embryogenesis was intensively analysed during the last century, while somatic embryogenesis is probably the most studied regeneration model. Encoded by the MIRNA, short, single-stranded, non-coding miRNAs, are commonly present in all Eukaryotic genomes and are involved in the regulation of the gene expression during the essential developmental processes such as plant morphogenesis, hormone signaling, and developmental phase transition. During the last few years dedicated to miRNAs, analytical methods and tools have been developed, which have afforded new opportunities in functional analyses of plant miRNAs, including (i) databases for in silico analysis; (ii) miRNAs detection and expression approaches; (iii) reporter and sensor lines for a spatio-temporal analysis of the miRNA-target interactions; (iv) in situ hybridisation protocols; (v) artificial miRNAs; (vi) MIM and STTM lines to inhibit miRNA activity, and (vii) the target genes resistant to miRNA. Here, we attempted to summarise the toolbox for functional analysis of miRNAs during plant embryogenesis. In addition to characterising the described tools/methods, examples of the applications have been presented.

Different Roles of Auxins in Somatic Embryogenesis Efficiency in Two Picea Species

The effects of auxins 2,4-D (2,4-dichlorophenoxyacetic acid), NAA (1-naphthaleneacetic acid) or picloram (4-amino-3,5,6-trichloropicolinic acid; 9 µM) and cytokinin BA (benzyloadenine; 4.5 µM) applied in the early stages of somatic embryogenesis (SE) on specific stages of SE in Picea abies and P. omorika were investigated. The highest SE initiation frequency was obtained after 2,4-D application in P. omorika (22.00%) and picloram application in P. abies (10.48%). NAA treatment significantly promoted embryogenic tissue (ET) proliferation in P. abies, while 2,4-D treatment reduced it. This reduction was related to the oxidative stress level, which was lower with the presence of NAA in the proliferation medium and higher with the presence of 2,4-D. The reduced oxidative stress level after NAA treatment suggests that hydrogen peroxide (H2O2) acts as a signalling molecule and promotes ET proliferation. NAA and picloram in the proliferation medium decreased the further production and maturation of P. omorika somatic embryos compared with that under 2,4-D. The quality of the germinated P. abies embryos and their development into plantlets depended on the auxin type and were the highest in NAA-originated embryos. These results show that different auxin types can generate different physiological responses in plant materials during SE in both spruce species.

Genome-wide identification and expression analyses of Sm genes reveal their involvement in early somatic embryogenesis in Dimocarpus longan Lour

The Sm proteins are a conserved protein family with Sm motifs. The family includes Sm and Sm-like proteins, which play important roles in pre-mRNA splicing. Most research on the Sm proteins have been conducted in herbaceous plants, and less in woody plants such as Dimocarpus longan (longan). And the embryo development status significantly affects the quality and yield of longan. In this study, we conducted a genome-wide analysis of longan Sm genes (DlSm) to clarify their roles during somatic embryogenesis (SE) and identified 29 Sm genes. Phylogenetic analysis deduced longan Sm proteins clustered into 17 phylogenetic groups with the homologous Sm proteins of Arabidopsis thaliana. We also analyzed the gene structures, motif compositions, and conserved domains of the longan Sm proteins. The promoter sequences of the DlSm genes contained many light, endosperm development, hormone, and temperature response elements, which suggested their possible functions. In the non-embryogenic callus(NEC) and during early SE in longan, the alternative splicing(AS) events of DlSm genes indicated that these genes may influence SE development by changing gene structures and sequences. The kinetin(KT) hormone, and blue and white light treatments affected the differentiation and growth of longan embryonic callus(EC) probably by affecting the AS events of DlSm genes. Expression profiles showed the possible functional divergence among Sm genes, and different hormones and light qualities affected their expression levels. The expression trends of the DlSm genes determined by RNA sequencing as fragments per kilobase of exon model per million mapped reads (FPKM) and by real-time quantitative PCR(qRT-PCR) during early SE in longan showed that the expression of the DlSm genes was affected by the growth and differentiation of longan SE, and decreased as the somatic embryo differentiation progressed. The results will contributed to understanding the longan Sm gene family and provide a basis for future functional validation studies.

Epigenetic Regulation of Auxin-Induced Somatic Embryogenesis in Plants

Somatic embryogenesis (SE) that is induced in plant explants in response to auxin treatment is closely associated with an extensive genetic reprogramming of the cell transcriptome. The significant modulation of the gene transcription profiles during SE induction results from the epigenetic factors that fine-tune the gene expression towards embryogenic development. Among these factors, microRNA molecules (miRNAs) contribute to the post-transcriptional regulation of gene expression. In the past few years, several miRNAs that regulate the SE-involved transcription factors (TFs) have been identified, and most of them were involved in the auxin-related processes, including auxin metabolism and signaling. In addition to miRNAs, chemical modifications of DNA and chromatin, in particular the methylation of DNA and histones and histone acetylation, have been shown to shape the SE transcriptomes. In response to auxin, these epigenetic modifications regulate the chromatin structure, and hence essentially contribute to the control of gene expression during SE induction. In this paper, we describe the current state of knowledge with regard to the SE epigenome. The complex interactions within and between the epigenetic factors, the key SE TFs that have been revealed, and the relationships between the SE epigenome and auxin-related processes such as auxin perception, metabolism, and signaling are highlighted.

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.

Molecular analysis of somatic embryogenesis through proteomic approach and optimization of protocol in recalcitrant Musa spp

Somatic embryogenesis (SE) is a complex stress related process regulated by numerous biological factors. SE is mainly applicable to mass propagation and genetic improvement of plants through gene transfer technology and induced mutations. In banana, SE is highly genome dependent as the efficiency varies with cultivars. To understand the molecular mechanism of SE, a proteomics approach was carried out to identify proteins expressed during embryogenic calli (EC) induction, regeneration and germination of somatic embryos in the banana cultivar cv. Rasthali (AAB). In total, 70 spots were differentially expressed in various developmental stages of SE, of which 16 were uniquely expressed and 17 were highly abundant in EC compared to non-embryogenic calli and explants. Also, four spots were uniquely expressed in germinating somatic embryos. The functional annotation of identified proteins revealed that calcium signaling along with stress and endogenous hormones related proteins played a vital role in EC induction and germination of somatic embryos. Thus, based on this outcome, the callus induction media was modified and tested in five cultivars. Among them, cultivars Grand Naine (AAA), Monthan (ABB) and Ney Poovan (AB) showed a better response in tryptophan added media, whereas Red Banana (AAA) and Karpuravalli (ABB) showed maximum EC induction in kinetin and CaCl₂ supplemented media respectively. Simultaneously, germination media were modified to induce proteins responsible for germination. In cv. Rasthali, media supplemented with 10 mM CaCl₂ showed a maximum increase in germination (51.79%) over control plants. Thus, the present study revealed that media modification based on proteomic analysis can induce SE in recalcitrant cultivars and also enhance germination in cultivars amenable for SE.

A step closer toward making many from the one

Somatic embryogenesis (SE) is a key technique used in plant biotechnology. The complex molecular changes associated with SE are uncharacterized in many crop species, and therefore, logically, formulating the culture conditions that induce these changes is difficult. In a study published in this issue of Physiologia Plantarum, Marimuthu et al. (2019) performed a proteomic study to characterize the molecular reprogramming during SE of an elite banana cultivar. Based on the results, they could customize culture conditions for optimal SE efficiency in several cultivars.

Genome-wide association study of callus induction variation to explore the callus formation mechanism of rice

Rice (Oryza sativa) is one of the most widely cultivated food crops, worldwide. Tissue culture is extensively used in rice breeding and functional genome research. The ability to induce callus determines whether a particular rice variety can be subjected to tissue culture and Agrobacterium-mediated transformation. Over the past two decades, many quantitative trait loci (QTLs) related to callus induction traits have been identified; however, individual genes associated with rice callus induction have not been reported. In this study, we characterized three callus-induction traits in a global collection of 510 rice accessions. A genome-wide association study of the rice population in its entirety as well as subpopulations revealed 21 significant loci located in rice callus induction QTLs. We identified three candidate callus induction genes, namely CRL1, OsBMM1, and OsSET1, which are orthologs of Arabidopsis LBD17/LBD29, BBM, and SWN, respectively, which are known to affect callus formation. Furthermore, we predicted that 14 candidate genes might be involved in rice callus induction and showed that RNA interference (RNAi)-mediated disruption of OsIAA10 inhibited callus formation on tissue culture medium. Embryo growth in the OsIAA10 RNAi line was not inhibited by synthetic auxin (2,4-D) treatment, suggesting that OsIAA10 may perceive auxin and activate the expression of downstream genes, such as CRL1, to induce callus formation. The significant loci and candidate genes identified here may provide insight into the mechanism underlying callus formation in rice.

Progress in Tissue Culture and Genetic Transformation of Oil Palm: An Overview

Oil palm (Elaeis guineensis, Jacq.) is a prominent vegetable-oil-yielding crop. Cultivating high-yielding oil palm with improved traits is a pre-requisite to meet the increasing demands of palm oil consumption. However, tissue culture and biotechnological approaches can resolve these concerns. Over the past three decades, significant research has been carried out to develop tissue culture and genetic transformation protocols for oil palm. Somatic embryogenesis is an efficient platform for the micropropagation of oil palm on a large scale. In addition, various genetic transformation techniques, including microprojectile bombardment, Agrobacterium tumefaciens mediated, Polyethylene glycol mediated mediated, and DNA microinjection, have been developed by optimizing various parameters for the efficient genetic transformation of oil palm. This review mainly emphasizes the methods established for in vitro propagation and genetic transformation of oil palm. Finally, we propose the application of the genome editing tool CRISPR/Cas9 to improve the various traits in this oil yielding crop.

Development of an Efficient Protocol to Obtain Transgenic Coffee, Coffea arabica L., Expressing the Cry10Aa Toxin of Bacillus thuringiensis

This report presents an efficient protocol of the stable genetic transformation of coffee plants expressing the Cry10Aa protein of Bacillus thuringiensis. Embryogenic cell lines with a high potential of propagation, somatic embryo maturation, and germination were used. Gene expression analysis of cytokinin signaling, homedomains, auxin responsive factor, and the master regulators of somatic embryogenesis genes involved in somatic embryo maturation were evaluated. Plasmid pMDC85 containing the cry10Aa gene was introduced into a Typica cultivar of C. arabica L. by biobalistic transformation. Transformation efficiency of 16.7% was achieved, according to the number of embryogenic aggregates and transgenic lines developed. Stable transformation was proven by hygromycin-resistant embryogenic lines, green fluorescent protein (GFP) expression, quantitative analyses of Cry10Aa by mass spectrometry, Western blot, ELISA, and Southern blot analyses. Cry10Aa showed variable expression levels in somatic embryos and the leaf tissue of transgenic plants, ranging from 76% to 90% of coverage of the protein by mass spectrometry and from 3.25 to 13.88 μg/g fresh tissue, with ELISA. qPCR-based 2^−ΔΔCt trials revealed high transcription levels of cry10Aa in somatic embryos and leaf tissue. This is the first report about the stable transformation and expression of the Cry10Aa protein in coffee plants with the potential for controlling the coffee berry borer.

Repetitive somatic embryogenesis induced cytological and proteomic changes in embryogenic lines of Pseudotsuga menziesii [Mirb.]

BACKGROUND

To explore poorly understood differences between primary and subsequent somatic embryogenic lines of plants, we induced secondary (2ry) and tertiary (3ry) lines from cotyledonary somatic embryos (SEs) of two Douglas-fir genotypes: SD4 and TD17. The 2ry lines exhibited significantly higher embryogenic potential (SE yields) than the 1ry lines initiated from zygotic embryos (SD4, 2155 vs 477; TD17, 240 vs 29 g- 1 f.w.). Moreover, we observed similar differences in yield between 2ry and 3ry lines of SD4 (2400 vs 3921 g- 1 f.w.). To elucidate reasons for differences in embryogenic potential induced by repetitive somatic embryogenesis we then compared 2ry vs 1ry and 2ry vs 3ry lines at histo-cytological (using LC-MS/MS) and proteomic levels.

RESULTS

Repetitive somatic embryogenesis dramatically improved the proliferating lines' cellular organization (genotype SD4's most strongly). Frequencies of singulated, bipolar SEs and compact polyembryogenic centers with elongated suspensors and apparently cleavable embryonal heads increased in 2ry and (even more) 3ry lines. Among 2300-2500 identified proteins, 162 and 228 were classified significantly differentially expressed between 2ry vs 1ry and 3ry vs 2ry lines, respectively, with special emphasis on "Proteolysis" and "Catabolic process" Gene Ontology categories. Strikingly, most of the significant proteins (> 70%) were down-regulated in 2ry relative to 1ry lines, but up-regulated in 3ry relative to 2ry lines, revealing a down-up pattern of expression. GO category enrichment analyses highlighted the opposite adjustments of global protein patterns, particularly for processes involved in chitin catabolism, lignin and L-phenylalanine metabolism, phenylpropanoid biosynthesis, oxidation-reduction, and response to karrikin. Sub-Network Enrichment Analyses highlighted interactions between significant proteins and both plant growth regulators and secondary metabolites after first (especially jasmonic acid, flavonoids) and second (especially salicylic acid, abscisic acid, lignin) embryogenesis cycles. Protein networks established after each induction affected the same "Plant development" and "Defense response" biological processes, but most strongly after the third cycle, which could explain the top embryogenic performance of 3ry lines.

CONCLUSIONS

This first report of cellular and molecular changes after repetitive somatic embryogenesis in conifers shows that each cycle enhanced the structure and singularization of EMs through modulation of growth regulator pathways, thereby improving the lines' embryogenic status.

Genetic Fine-Mapping of a Quantitative Trait Locus (QTL) Associated with Embryogenic Tissue Culture Response and Plant Regeneration Ability in Maize (Zea mays L.)

Embryogenic and regenerable tissue cultures are widely utilized in plant transformation, clonal propagation, and biological research applications. Germplasm utilized in those applications are limited, however, due to genotype-dependent culture response. The goal of this study was to identify genomic regions controlling embryogenic and regenerable tissue culture response in the globally important crop, maize ( L.), toward the long-term objective of developing approaches for genotype-independent plant genetic engineering and clonal propagation systems. An inbred maize line, WCIC2, nearly-isogenic to reference inbred B73, was developed by phenotypic selection and molecular marker analysis. WCIC2 has over 50x increase in tissue culture response relative to the recurrent parent, B73. This line was used to genetically fine-map a region on chromosome 3 controlling embryogenic and regenerable tissue culture response to a 23.9 Mb region. WCIC2 and derivatives will be useful materials to enable maize research in a genetic background similar to B73, and our genetic mapping results will advance research to identify causal genes controlling somatic embryo formation and plant regeneration in maize.

Multiple morphogenic culture systems cause loss of resistance to cassava mosaic disease

BACKGROUND

Morphogenic culture systems are central to crop improvement programs that utilize transgenic and genome editing technologies. We previously reported that CMD2-type cassava (Manihot esculenta) cultivars lose resistance to cassava mosaic disease (CMD) when passed through somatic embryogenesis. As a result, these plants cannot be developed as products for deployment where CMD is endemic such as sub-Saharan Africa or the Indian sub-continent.

RESULT

In order to increase understanding of this phenomenon, 21 African cassava cultivars were screened for resistance to CMD after regeneration through somatic embryogenesis. Fifteen cultivars were shown to retain resistance to CMD through somatic embryogenesis, confirming that the existing transformation and gene editing systems can be employed in these genetic backgrounds without compromising resistance to geminivirus infection. CMD2-type cultivars were also subjected to plant regeneration via caulogenesis and meristem tip culture, resulting in 25-36% and 5-10% of regenerated plant lines losing resistance to CMD respectively.

CONCLUSIONS

This study provides clear evidence that multiple morphogenic systems can result in loss of resistance to CMD, and that somatic embryogenesis per se is not the underlying cause of this phenomenon. The information described here is critical for interpreting genomic, transcriptomic and epigenomic datasets aimed at understanding CMD resistance mechanisms in cassava.

Somatic embryogenesis of muskmelon (Cucumis melo L.) and genetic stability assessment of regenerants using flow cytometry and ISSR markers

A new protocol for in vitro regeneration through direct somatic embryogenesis for two muskmelon cultivars (Cucumis melo L., "Mashhadi" and "Eivanaki") is reported. Somatic embryos were obtained culturing 4- and 8-day-old cotyledons, seeds, and hypocotyls on Murashige and Skoog medium supplemented with three different hormonal combinations never tested so far for melon (naphthoxyacetic acid (NOA) + thidiazuron (TDZ), NOA + 6-banzylaminopurine (BAP), and 2,4-dichlorophenoxyacetic acid (2,4-D) + N-(2-chloro-4-pyridyl)-N'-phenylurea (4-CPPU)). Results were compared with those obtained when explants were cultivated in the presence of 2,4-D + BAP, previously used on melon. Embryogenesis occurred more successfully in 4-day-old cotyledons and seeds than hypocotyls and 8-day-old cotyledons. The best result was achieved with NOA + BAP. Genotypes significantly affected embryogenesis. The number of embryos in "Eivanaki" was significantly higher than that in "Mashhadi." Embryo proliferation when explants were maintained in jars (9.3%) was found to be higher compared to that in petri dishes. For the first time, genetic stability of regenerated melon plants was evaluated using inter-simple sequence repeat markers. Polymerase chain reaction (PCR) products demonstrated a total of 102 well-resolved bands, and regenerants were 93% similar compared to the mother plant. Somaclonal changes during embryogenesis were evaluated by flow cytometry, showing 91% of the same patterns in regenerated plants. The results suggest that the new hormone components are effective when applied for in vitro embryogenesis of muskmelon as they show a high frequency in regeneration and genetic homogeneity.

Validating a probe from GhSERK1 gene for selection of cotton genotypes with somatic embryogenic capacity

Substantial progress is being reported in the techniques for plant transformation, but successful regeneration of some genotypes remains a challenging step in the attempts to transform some recalcitrant species. GhSERK1 gene is involved on embryo formation, and its overexpression enhances the embryogenic competence. In this study we validate a short GhSERK1 probe in order to identify embryogenic cotton genotypes using RT-qPCR and blotting assays. Cotton genotypes with contrasting somatic embryogenic capacity were tested using in vitro procedures. High expression of transcripts was found in embryogenic genotypes, and the results were confirmed by the RT-PCR-blotting using a non-radioactive probe. The regeneration ability was confirmed in embryogenic genotypes. We confirmed that GhSERK1 can be used as marker for estimating the somatic embryogenesis ability of cotton plants.

Histodifferentiation of oil palm somatic embryo development at low auxin concentration

Large-scale propagation of oil palm (Elaeis guineensis, Jacq.) is difficult due to its single apical meristem. Thus, obtaining plants is mainly through seed germination, and a long growing period is required before oil production is possible. An alternative to large-scale seedling production is indirect somatic embryogenesis. The aim of this study was to analyze the somatic embryogenesis process in oil palm (E. guineensis Jacq.) with amino acids and low concentrations of auxins. The Tenera hybrid was analyzed by cytochemical and ultrastructural methods and was used to regenerate oil palm plants. First, calli were induced in MS culture media supplemented with 2,4-D and picloram. Two types of calli were obtained, characterized by beige or translucent color. Beige calli had embryogenic characteristics, such as large nuclei with prominent nucleoli, and they were multiplied for 8 months in MM culture (half strength MS, 1 mg L^-1 2,4-D, 2 mg L^-1 2iP, 1 mg L^-1 IBA, 250 mg L^-1 citric acid, 10 mg L^-1 cysteine, 100 mg L^-1 inositol, 1 mg L^-1 thiamine, 1 mg L^-1 pyridoxine, 1 mg L^-1 nicotinic acid, 1 mg L^-1 glycine, 200 mg L^-1 malt extract, and 100 mg L^-1 casein hydrolysate). After multiplication, the MCB culture medium (half strength MS, supplemented with 0.25 mg L^-1 NAA, 2 mg L^-1 BAP, MM vitamins and 200 mg L^-1 malt extract, and 100 mg L^-1 casein hydrolysate) was the most efficient for embryo formation, showing meristematic centers with totipotent cells in histochemical analyses. The somatic embryos were developed and germinated in MG medium (half strength MS, 0.45 mg L^-1 IAA, 0.25 mg L^-1 BAP, and MM vitamins), transplanted into polyethylene tubes containing pine bark substrates, and acclimatized in a greenhouse, achieving a 97% survival rate. The use of picloram for callus induction and somatic embryogenesis is advantageous and multiplication in MM medium is an important step for increasing cell mass. The calli with light beige color and nodular structures have meristematic cells with dense cytoplasm and totipotential features that later give rise to protoderm, procambium, and ground meristem during the globular, cordiform, and torpedo embryogenesis phases. In MCB medium, the concentration of vitamins and amino acids are crucial for somatic embryogenesis.

Protocol for the Micropropagation of Coconut from Plumule Explants

Coconut is a crop that is economically important in several countries throughout the world. Unfortunately, production is decreasing because palms are affected by very serious phytoplasma diseases, such as lethal yellowing, and also most of coconuts are already very old. On the other hand, markets for coconut products have been rapidly growing in recent years. Hence, replanting of most cultivation surface worldwide, as well as establishing new surface, is urgently needed. This is an immense task, requiring at least a billion coconut palms that cannot be accomplished by traditional propagation through seed. Therefore the biotechnological alternative of micropropagation by somatic embryogenesis is needed. Research has been carried out on this subject in laboratories in several countries studying different approaches, testing different types of explants. The most responsive tissue has been plumule from zygotic embryos. A protocol for micropropagation of coconut based on plumule explants is described here. It involves the use of different media that are based on Y3 medium complemented with activated charcoal, gelling agent, sucrose, and growth regulators. These media allow the formation of embryogenic callus and somatic embryos, growth of shoots, and development of plantlets.

Somatic Embryogenesis of Quercus suber L. From Immature Zygotic Embryos

Quercus suber L., cork oak, is a forest tree of high social and economic value. The cork is traditionally used in the wine industry to produce bottle stoppers, but it is also a very good material for both thermal and acoustic insulation in construction. Since its harvest does not harm the tree, the use of cork in the industry has a positive impact on the environment.Somatic embryogenesis is considered a feasible system for in vitro regeneration procedures, with many advantages in woody species. Classical genetic breeding programs have important limitations in forest trees, like cork oak, due to their long life span and difficulties of seed conservation and vegetative reproduction. Therefore, somatic embryogenesis has a great potential for large-scale propagation and cryopreservation of elite genotypes, as well as for transformation strategies. In the case of Q. suber, several in vitro propagation systems through somatic embryogenesis have been reported, with different efficiency rates.In the present chapter, updated information is reported about an efficient protocol for induction of somatic embryogenesis of Q. suber from immature zygotic embryos, as well as methods for proliferation and maturation of somatic embryos, germination, plantlet regeneration, and acclimatization.

Transcription Factors: Their Role in the Regulation of Somatic Embryogenesis in Theobroma cacao L. and Other Species

Transcription factors are proteins that help with the control and regulation in the transcription of the DNA to mRNA by binding to special DNA sequences. With the aim to understand more about gene transcription regulation in Theobroma cacao L., this review outlines the principal transcription factors that were reported in other plants especially Arabidopsis thaliana and attempts at looking for the homologies with transcription factors in T. cacao. The information cited in this work is about the initiation, development, and maturation of the cacao somatic embryos and other crops. It is important to underline that there are very few publications in T. cacao discussing transcription factors that control the somatic embryogenesis process, but there is some information about transcription factors in other crops that we have used as a guide to try to understand this process.

Plant Regeneration from Somatic Embryogenic Suspension Cultures of Date Palm

Somatic embryogenesis is one of the most important technologies for plant regeneration of elite date palm cultivars. Recently, considerable progress has been made in the development and optimization of this technique from embryogenic cell suspension cultures. This chapter describes a procedure for the rapid development of a large number of somatic embryos from embryogenic cell suspension cultures. An efficient plant regeneration protocol via somatic embryogenesis from cell suspension cultures starting with shoot-tip explants to plantlet acclimatization also is fully described. Low concentrations of 6-benzylaminopurine (BAP) to 0.3 mg/L and high rate of subcultures each 7 days lead to improve the establishment and multiplication of somatic embryos in suspension cultures by limiting oxidative browning, associated with high total phenols and peroxidase activities. The detailed morphological observations have revealed the cells destined to become somatic embryos. Activated charcoal (AC) at 0.15 g/L has a positive effect on growth rate of somatic embryos by reducing tissue and medium browning, phenolics, and peroxidase activity.

Enhanced Indirect Somatic Embryogenesis of Date Palm Using Low Levels of Seawater

Date palm tolerates salinity, drought, and high temperatures. Arid and semiarid zones, especially the Middle East region, need a huge number of date palms for cultivation. To meet this demand, tissue culture techniques have great potential for mass production of plantlets, especially using the indirect embryogenesis technique; any improvement of these techniques is a worthy objective. Low levels of salinity can enhance growth and development of tolerant plants. A low level of seawater, a natural source of salinity, reduces the time required for micropropagation processes of date palm cv. Malkaby when added to MS medium. Medium containing seawater at 500 ppm total dissolved solid (TDS) (12.2 mL/L) improves callus proliferation, whereas 1500 ppm (36.59 mL/L) enhances plant regeneration including multiplication of secondary embryos, embryo germination, and rooting.

Histological Evidence of Indirect Somatic Embryogenesis from Immature Female Date Palm Inflorescences

Rapid production of somatic embryogenesis and date palm regeneration is achieved by culturing immature female inflorescence explants. Inflorescence explants are soft, creamy in color, average 6-7 cm in length, and cultured on Murashige and Skoog (MS) medium containing 1 mg/L thidiazuron (TDZ). Callus induction occurs after 4-5 weeks of culture on the callus induction medium. Subsequently, callus develops embryogenic calli on MS medium supplemented with 0.1 mg/L naphthalene acetic acid (NAA). Histological samples were collected successively at the culturing time and during morphogenetic changes throughout the developmental stages of somatic embryos. Initiation of callus and different successive developmental stages for somatic embryos including two-celled, four-celled, globular, bipolar, and fully developed cotyledonary somatic embryos were observed. Mature somatic embryos develop within 10-12 weeks after culture establishment.

Plant regeneration through somatic embryogenesis and genome size analysis of Coriandrum sativum L

In the present study, an improved plant regeneration protocol via primary and secondary somatic embryogenesis was established in two Co-1 and Rajendra Swathi (RS) varieties of Coriandrum sativum L. Callus was induced from root explants on 2, 4-D (0.5-2.0 mg/l) supplemented MS. The addition of BA (0.2 mg/l) improved callus induction and proliferation response significantly. The maximum callus induction frequency was on 1.0 mg/l 2, 4-D and 0.2 mg/l BA added MS medium (77.5 % in Co-1 and 72.3 % in RS). The callus transformed into embryogenic callus on 2, 4-D added MS with maximum embryogenic frequency was on 1.0 mg/l. The granular embryogenic callus differentiated into globular embryos on induction medium, which later progressed to heart-, torpedo- and cotyledonary embryos on medium amended with 0.5 mg/l NAA and 0.2 mg/l BA. On an average, 2-3 secondary somatic embryos (SEs) were developed on mature primary SEs, which increased the total embryo numbers in culture. Histology and scanning electron microscopy (SEM) studies are presented for the origin, development of primary and secondary embryos in coriander. Later, these induced embryos converted into plantlets on 1.0 mg/l BA and 0.2 mg/l NAA-amended medium. The regenerated plantlets were cultured on 0.5 mg/l IBA added ½ MS for promotion of roots. The well-rooted plantlets were acclimatized and transferred to soil. The genetic stability of embryo-regenerated plant was analyzed by flow cytometry with optimized Pongamia pinnata as standard. The 2C DNA content of RS coriander variety was estimated to 5.1 pg; the primary and secondary somatic embryo-derived plants had 5.26 and 5.44 pg 2C DNA content, respectively. The regenerated plants were genetically stable, genome size similar to seed-germinated coriander plants.

Proteomic analysis of stress-related proteins and metabolic pathways in Picea asperata somatic embryos during partial desiccation

Partial desiccation treatment (PDT) stimulates germination and enhances the conversion of conifer somatic embryos. To better understand the mechanisms underlying the responses of somatic embryos to PDT, we used proteomic and physiological analyses to investigate these responses during PDT in Picea asperata. Comparative proteomic analysis revealed that, during PDT, stress-related proteins were mainly involved in osmosis, endogenous hormones, antioxidative proteins, molecular chaperones and defence-related proteins. Compared with those in cotyledonary embryos before PDT, these stress-related proteins remained at high levels on days 7 (D7) and 14 (D14) of PDT. The proteins that differentially accumulated in the somatic embryos on D7 were mapped to stress and/or stimuli. They may also be involved in the glyoxylate cycle and the chitin metabolic process. The most significant difference in the differentially accumulated proteins occurred in the metabolic pathways of photosynthesis on D14. Furthermore, in accordance with the changes in stress-related proteins, analyses of changes in water content, abscisic acid, indoleacetic acid and H₂ O₂ levels in the embryos indicated that PDT is involved in water-deficit tolerance and affects endogenous hormones. Our results provide insight into the mechanisms responsible for the transition from morphologically mature to physiologically mature somatic embryos during the PDT process in P. asperata.