Differentiation Of Somatic Embryos Research Articles

Metabolome profiling of cacao (Theobroma cacao L.) callus under drought stress conditions induced by polyethylene glycol (PEG) as osmoticant.

The cacao tree (Theobroma cacao), a perennial crop that serves as a source of cacao beans, can suffer from drastic climate changes such as irregular rainfall and shorter rainy seasons. The search for hybrids which are capable of producing specific metabolites favoring adaptation in new climatic conditions is a challenge in cacao farming. We aimed to (1) analyze the metabolic changes in calli of three cacao genotypes during water deficit induced by incubation with polyethylene glycol and (2) assess their response to water deficit stress with regard to somatic embryo differentiation. Metabolic profiling was carried out using 1H-NMR spectroscopy and multivariate data analysis was applied to crude extracts of calli grown in non-stress or water deficit stress conditions. Water deficit stress influences the capacity of calli to produce embryos. The SCA12 genotype exhibited the best conversion capacity under severe conditions and was considered as tolerant to drought, followed by the SCA6 genotype (mid-tolerant) and the MA12 genotype (sensitive). Fifty-four metabolites were identified in the three cacao genotypes and discriminant metabolites were identified. Metabolites involved in water stress tolerance such as fructose, trans-aconitic acid, leucine, and hydroxybenzene derivatives were observed in SCA12, the tolerant genotype. These results demonstrate the utility of 1H-NMR metabolomics as an essential tool for the analysis of the drought tolerance characteristics of T. cacao.

Cell wall remodeling and callose deposition during the embryogenic transition in the tree fern Cyathea delgadii Sternb.

With the discovery in 2015 of the ability to induce somatic embryos in Cyathea delgadii, learning more about the relationship between the structure of apoplast and cell differentiation has become possible among ferns. In this study, the distribution of arabinogalactan proteins, pectins, extensins, and callose with specific epitopes recognized by monoclonal antibodies was investigated during direct somatic embryogenesis (SE) of C. delgadii. Eight antigens against the arabinogalactan proteins (JIM8, JIM13, LM2), pectins (JIM5, JIM7), extensins (JIM11, JIM12), and callose (anti-1 → 3-β-glucan) were selected. Two types of explants were analyzed, i.e. stipe fragments and internodes, which give rise to embryos of unicellular and multicellular origin, respectively. The study showed that embryogenic transition in C. delgadii is preceded by cell wall remodeling of initial explants. Dynamic changes in JIM13, JIM12, and anti-1 → 3-β-glucan localization were observed. The differences in the distribution of studied epitopes were observed between the cell walls of the epidermis and those located in the other layers of the explant. Moreover, within the somatic embryos, a stronger fluorescence of the examined antibodies was observed, mainly those reacting with arabinogalactan proteins, extensins, and callose. These results also implicated that, with the exception of the earlier appearance of callose in the stipe explants, the uni- and multicellular pathways of somatic embryo differentiation do not differ in the quality of cell wall components. The presented studies document the first time that SE in ferns can be regulated by changes in apoplast structure and they provide a basis for more detailed research.

Genetic and epigenetic modes of the regulation of somatic embryogenesis: a review.

Somatic embryogenesis (SE) is a mode of stimulated plant cell totipotency wherein embryos form without fertilization either through somatic or vegetative origins. SE has two main phases: induction and a developmental phase. The induction phase comprises cell proliferation and dedifferentiation, whereas the developmental phase involves the differentiation of somatic embryos under appropriate stimuli. As such, SE is categorized into two main types: direct (without an intervening callus) and indirect (includes a callus phase). This review presents the influence of various major factors such as explants, abiotic stresses, and the concentrations and variations of plant growth regulators on SE. In addition, genetic components such as miRNA, transcription factors, and epigenetic events (DNA methylation and chromatin remodeling) that are potentially implicated in SE are described briefly. Furthermore, SE applications and SE-related abnormalities are also discussed in detail.

Morphological and endogenous phytohormone changes during long-term embryogenic cultures in Korean pine

In SE of Korean pine, decreasing embryogenic potential was observed in embryogenic callus (EC) with successive subcultures, especially when the cultures were maintained for more than 5–6 months. Thus, aiming to investigate the changes in morphology and the endogenous phytohormone associated with the decreasing somatic embryo differentiation capacity of Korean pine, here, we compared Korean pine calli with different embryogenic potential. It was found that both the external morphological characteristics and internal cell structure were significantly different among the different types of calli. Specifically, similar to zygotic counterparts of conifer trees, the calli with high embryogenic potential were characterized by a higher number of designated proembryogenic masses (PEMs) structure. In addition, surface of this types of callus was covered with a large amount of mucilaginous extracellular matrix (ECM), which could further differentiate into globular embryos containing the embryonal masses (EM) and embryonic tube (ET) structure.In contrast, in those low embryogenic potential calli, we observed disintegrated PEMs structure, a large amount of irregularly shaped cells, and degraded cells, which failed to form somatic embryos. The endogenous hormone results showed that high levels of abscisic acid (ABA) were beneficial for promoting early somatic embryo differentiation in Korean pine, but maintaining high embryogenic potential required moderate levels of indole-3-acetic acid (IAA), and low levels of zeatin-riboside (ZR). Additionally, a high ratio of IAA/ABA, methyl jasmonate (MeJA)/ABA, and gibberellins (GA3)/ABA were conducive to maintaining high embryogenic potential, whereas a low ratio of IAA/ABA and MeJA/ABA were effective for early somatic embryos morphological differentiation. The results can provide morphological and physiological indicators for identifying high embryogenic potential calli suitable for SE and help determine the best protocol on addition of exogenous hormones in the construction of a maintainable system of EC in Korean pine.

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.

Integrative proteomics and phosphoproteomics reveals phosphorylation networks involved in the maintenance and expression of embryogenic competence in sugarcane callus

Plant embryogenic cell culture allows mass propagation and genetic manipulation, but the mechanisms that determine the fate of these totipotent cells in somatic embryos have not yet been elucidated. Here, we performed label-free quantitative proteomics and phosphoproteomics analyses to determine signaling events related to sugarcane somatic embryo differentiation, especially those related to protein phosphorylation. Embryogenic calli were compared at multiplication (EC0, dedifferentiated cells) and after 14 days of maturation (EC14, onset of embryo differentiation). Metabolic pathway analysis showed enriched lysine degradation and starch/sucrose metabolism proteins during multiplication, whereas the differentiation of somatic embryos was found to involve the enrichment of energy metabolism, including the TCA cycle and oxidative phosphorylation. Multiplication-related phosphoproteins were associated with transcriptional regulation, including SNF1 kinase homolog 10 (KIN10), SEUSS (SEU), and LEUNIG_HOMOLOG (LUH). The regulation of multiple light harvesting complex photosystem II proteins and phytochrome interacting factor 3-LIKE 5 were predicted to promote bioenergetic metabolism and carbon fixation during the maturation stage. A motif analysis revealed 15 phosphorylation motifs. The [D-pS/T-x-D] motif was overrepresented during somatic embryo differentiation. A protein-protein network analysis predicted interactions among SNF1-related protein kinase 2 (SnRK2), abscisic acid-responsive element-binding factor 2 (ABF2), and KIN10, which indicated the role of these proteins in embryogenic competence. The predicted interactions between TOPLESS (TPL) and histone deacetylase 19 (HD19) may be involved in posttranslational protein regulation during somatic embryo differentiation. These results reveal the protein regulation dynamics of somatic embryogenesis and new players in somatic embryo differentiation, including their predicted phosphorylation motifs and phosphosites.

EFFECT OF 2,4-D AND NAA ON SOMATIC EMBRYOGENESIS FROM APICAL PORTION OF GROUNDNUT (ARACHIS HYPOGAEA L.)

Somatic embryogenesis was carried out epicotyl portion of the mature embryo/apical portion. The somatic embryo induction medium containing 2,4-D or NAA (10.0 to 50.0 mg/l). Of the two concentrations tested 2,4-D (30.0mg/l) recorded the highest percentage of response followed by NAA (30.0mg/l). But the highest number of somatic embryo were recorded in 30.0mg/l of 2,4-D followed by NAA. The apical portion of the mature embryo formed direct embryos without any intervention of callus. The maximum percentage of embryogenic cultures were noticed in 30.0mg/l of 2,4-D followed by NAA at 30.0mg/l. for the differentiation of somatic embryos, the embryogenic masses were transferred to medium without any growth regulator. The maximum number of somatic embryos per culture was recorded in 30 mg/l of 2,4-D followed by 30.0 mg/l of NAA. Keywords: Arachis hypogaea L.,Somatic Embryogenesis, 2,4-D and NAA

Alterations in endogenous hormone levels and energy metabolism promoted the induction, differentiation and maturation of Begonia somatic embryos under clinorotation

The present study provides a visual insight into the effects of simulated microgravity (MG) on somatic embryogenesis (SE) in Begonia through the analysis of phytohormone fluctuations and energy metabolism. To investigate this relationship, thin cell layer culture model was first used. The results showed that MG changed the phytohormone content and stimulated starch biosynthesis to convert into sugar to release energy needed for regeneration and proliferation. Moreover, from the results it is likely that MG accelerated the initiation and subsequently maturation and aging of SE via decrease of AUX and increase of ABA. High content of GA, CKs, starch, sugar and low ABA as well as high CKs/ABA ratio were responsible for the increase in the number of embryos under clinorotation which was 1.57-fold higher than control after 90 days. The increase in fresh and dry weight of somatic embryos and chlorophyll content under MG were confirmed as their adaptive responses to gravitational stress. However, long-term exposure to MG (120 days) stimulated biosynthesis of ABA levels 1.85-fold higher than controls, which resulted in a decrease in chlorophyll content, increase in number of mature embryos and stomata length. These results revealed that MG regulated the induction, differentiation and senescence of somatic embryos via a biochemical interaction pathway.

Pretreatment free of 2,4-dichlorophenoxyacetic acid improves the differentiation of sugarcane somatic embryos by affecting the hormonal balance and the accumulation of reserves

Pretreatment free of 2,4-dichlorophenoxyacetic acid improves the differentiation of sugarcane somatic embryos by affecting the hormonal balance and the accumulation of reserves

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.

Capacity for somatic embryogenesis of adult oil palm genitors (Elaeis guineensis, var. Pisifera) from immature leaf tissues

Admittedly, Pisifera genotypes are less responsive to somatic embryogenesis than other genotypes, such as inter- or intra-specific oil palm hybrids. However, clonal propagation of Pisifera plants can be useful for increasing the number of male parents to cross with the Dura variety for mass producing the Tenera commercial varieties. The capacity for somatic embryogenesis (SE) of Brazilian Pisifera genitors was therefore investigated using achlorophyllous leaf explants from four field growing genotypes (A251424, A251427, A251512, A251513). A Murashige & Skoog (MS) medium supplemented with 0.5 gL−1 glutamine, 0.5 gL−1 casein, 2.5 gL−1 activated charcoal, 450 µM Picloram and 2.5 gL−1 Phytagel was used for the induction. A251424 showed the higher capacity for SE induction with 45.8% of callus formation compared to 11.3% for A251427, 7.7% for A251513 and 0.6% for A251512. The materials remained in these conditions for up to 360 days, being subcultured every 150 days before transfer for 90 days onto the multiplication medium (MM), containing 40 μM Picloram and 10 μM 2-isopentenyladenine (2iP). Callus fresh biomass increased approximately fivefold in these MM conditions. The calli were then placed onto the somatic embryo differentiation medium (DM), composed of 12.3 μM 2iP and 0.54 μM naphthalene acetic acid (NAA) until the formation of the first somatic embryo clusters. These were transferred to the somatic embryo regeneration medium (RM) totally lacking growth regulators but with 2.5 gL−1 activated charcoal. Histocytological observations indicated that cells showing the greater concentration of starch granules could be considered as embryogenic with the higher capacity for SE. To our knowledge, this is the first report on the successful use of immature leaf explants for producing SE from Pisifera genitors of Elaeis guineensis.

Induction of somatic embryogenesis in leaf and root explants of Digitalis lanata Ehrh.: Direct and indirect method

Somatic embryogenesis was reported via direct and indirect method in cardio-tonic plant Digitalis lanata Ehrh. MS basal medium supplemented with cytokinins BAP, Kinetin (Kin) and TDZ, either alone or in combinations with auxins IAA, 2,4-D and IBA,- at different concentrations (00–3.0 mg/l) were studied. The best direct induction of somatic embryogenesis was observed in leaf (100% response with 11.3 SEs/explant) and root (85.7% response with 7.2 SEs/explant) explants on MS medium fortified with combination of Kin and IBA (2.0 mg/l each). Among the combinations tried, 2,4-D with Kin both at 1.0 mg/l was superior for the production of embryogenic calli and indirect induction of somatic embryos (95.2% with 9.8 SEs/explant). Incorporation of PEG (10 mg/l) in MS medium was beneficial for differentiation (13.0 ± 1.5 globular, 16.4 ± 1.4 heart and 19.8 ± 0.7 cotyledonary) and maturation of somatic embryos. SEM study confirmed the origin of somatic embryos directly from explants, and different developmental stages. The somatic embryo derived plantlets were hardened and successfully established in the field. As the direct and indirect somatic embryogenesis protocols are played significant role in genetic transformation, thereof thus the protocol reported here having importance in genetic improvement of a cardio-tonic herb D. lanata using recombinant DNA technology.

LED lamps enhance somatic embryo maturation in association with the differential accumulation of proteins in the Carica papaya L. ‘Golden’ embryogenic callus

The use of light-emitting diode (LED) lamps has been shown to be a promising approach for improving somatic embryo maturation during somatic embryogenesis. The aim of this work was to study the influence of the light source on somatic embryo differentiation and its relationship with the differential abundance of proteins in the Carica papaya L. ‘Golden’ embryogenic callus at 14 days of maturation. The white plus medium-blue (WmB) LED and fluorescent lamp treatments produced an average of 82.4 and 47.6 cotyledonary somatic embryos per callus, respectively. A shotgun proteomics analysis revealed 28 upaccumulated and 7 downaccumulated proteins. The proteins upaccumulated in the embryogenic callus matured under the WmB LED lamp compared with that matured under the fluorescent lamp included indole-3-acetic acid-amido synthetase (GH3) and actin-depolymerizing factor 2 (ADF2), which are involved in the regulation of auxin levels by auxin conjugation and transport. Additionally, proteins related to energy production (aconitate, ADH1, GAPCp, PKp and TPI), cell wall remodeling (PG and GLPs), and intracellular trafficking (NUP50A, IST1, small GTPases and H+-PPase) showed significantly higher abundance in the embryogenic callus incubated under the WmB LED lamp than in that incubated under the fluorescent lamp. The results showed that the WmB LED lamp improved somatic embryo maturation in association with the differential accumulation of proteins in the C. papaya ‘Golden’ embryogenic callus.

Efficient plant regeneration and Agrobacterium-mediated transformation via somatic embryogenesis in purslane (Portulaca oleracea L.): an important medicinal plant

Portulaca oleracea is an important medicinal plant, which is a source of pharmacologically active molecules such as β-Carotene, ascorbic acid, and Omega-3 fatty acids. The present research focuses on the development of an efficient protocol for micropropagation and Agrobacterium-mediated genetic transformation of P. oleracea. Callus induction, somatic embryogenesis, and plant regeneration from stem and leaf explants were investigated at various concentrations of kinetin (Kin) and 6-Benzylaminopurine (BAP) alone or in combination with indole-3-acetic acid, 1-Naphthaleneacetic acid and 2,4-Dichlorophenoxyacetic acid (2,4-D). Direct differentiation of somatic embryos from leaf explants occurred on the MS medium supplemented with 1.5 mg/L BAP under dark conditions. The embryos were transferred to the same medium without growth regulators under 16 h light/8 h dark cycles. In this medium, germinated somatic embryos rapidly developed into healthy plantlets with shoots and roots. Several parameters such as pre-culture of explants, co-cultivation period, wounding of explants, type of explants and bacterial strains were studied to optimize transformation efficiency. Different kanamycin concentrations were assessed for the selection of transgenic plants. Agrobacterium tumefaciens strains LBA4404 and GV3101, harbouring the GUS gene on pBI121 binary vector, were used for plant transformation and strain LBA4404 was found to be more efficient. The results indicated that use of leaf as explant, pre-culture of explants for 7 days, co-cultivation period for 4 days at 25 ± 2 °C and wounding of leaf explants produced the best transformation results. Expression, integration and inheritance of GUS reporter gene were confirmed by histochemical and molecular analyses.

Explant type and stress treatment determine the uni- and multicellular origin of somatic embryos in the tree fern Cyathea delgadii Sternb.

Cyathea delgadii is the first fern species for which somatic embryogenesis (SE) has recently been described. With this discovery, a new experimental model for exploration of SE was found. In this study, the effect of explant type (stipe and internode), length and diameter of the explant-donor frond, and stress treatment (by sucrose and air desiccation) on somatic embryo origin and SE efficiency was studied. In control culture, somatic embryos originated from single cells of stipe explants, whereas those induced on internodes were of multicellular origin. Although the activation of cell divisions was more abundant and the formation of somatic embryos occurred earlier in a culture of internodes than of stipe explants, the morphogenic capacity of internodes was much smaller. On their surface, the groups of competent cells formed protuberances that give rise to only three somatic embryos per internode. In contrast, almost 92% of stipe explants that were excised from the first frond, measuring 10 mm in length and less than 300 µm in diameter, produced an average of 21 somatic embryos. Stipes treated with sucrose were not able to SE. More than fourfold increase in SE efficiency was obtained on internodes by their treatment with 0.4 M sucrose for 45 min. It was achieved by changing the pathway of somatic embryo differentiation from multicellular to unicellular. These results provide an excellent basis for further research on the mechanism of SE induction associated with a single- and multi-cell proliferation, especially that both types of the embryogenic pathway can occur on the same hormone-free medium.

Direct somatic embryogenesis of potato [Solanum tuberosum (L.)] cultivar ‘Kufri Chipsona 2’

Direct somatic embryo induction was achieved from leaf and internodal explants of Solanum tuberosum (L.) cultivar ‘Kufri Chipsona 2’ on Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium containing 10.0 µM silver nitrate (MS1 medium) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D; 2.5 µM) and 6-benzyladenine (BA; 1.0 µΜ). It was observed that in absence of AgNO3, friable callus was induced from cut ends of the explants, which does not develop into any kind of organised structure; thus highlighting the requirement of AgNO3 for somatic embryogenesis in potato. Furthermore, the effect of medium strength, sucrose concentration and heat shock treatment on somatic embryogenic potential of explants was also investigated. When the strength of basal medium was reduced to half, the frequency of internodal segments differentiating somatic embryos was almost double in comparison to full strength MS medium. Sucrose concentration and heat shock treatment were found to have interactive effect on somatic embryo induction. Explants subcultured on medium containing 174 mM sucrose and subjected to heat shock (1 h; 50 °C) showed maximum somatic embryo differentiation. Although, the percent explants differentiating somatic embryos decreased sharply with increase in sucrose concentration (> 174 mM), yet the number of somatic embryos differentiated per explant were found to increase with further increase in sucrose concentration. Histological observations revealed that somatic embryos directly developed from epidermis of leaf explant and cut ends of internodal segments progressed from globular to cotyledonary stage after passing through intermediate embryogenic stages (heart shaped and torpedo shaped). Conversion of somatic embryos into plantlets (92%) was achieved on MS1 medium supplemented with BA (10.0 µM) and gibberellic acid (15.0 µM) and all regenerated plants were found to be phenotypically alike.

Morphological analyses and variation in carbohydrate content during the maturation of somatic embryos of Carica papaya.

Efficient protocols for somatic embryogenesis of papaya (Carica papaya L.) have great potential for selecting elite hybrid genotypes. Addition of polyethylene glycol (PEG), a nonplasmolyzing osmotic agent, to a maturation medium increases the production of somatic embryos in C. papaya. To study the effects of PEG on somatic embryogenesis of C. papaya, we analyzed somatic embryo development and carbohydrate profile changes during maturation treatments with PEG (6%) or without PEG(control). PEG treatment (6%) increased the number of normal mature somatic embryos followed by somatic plantlet production. In both control and PEG treatments, pro-embryogenic differentiation to the cotyledonary stage was observed and was significantly higher with PEG treatment. Histomorphological analysis of embryonic cultures with PEG revealed meristematic centers containing small isodiametric cells with dense cytoplasm and evident nuclei. Concomitant with the increase in the differentiation of somatic embryos in PEG cultures, there was an increase in the endogenous content of sucrose and starch, which appears to be related to a rising demand for energy, a key point in the conversion of C. papaya somaticembryos. The endogenous carbohydrate profile may be a valuable parameter for developing optimized protocols for the maturation of somatic embryos in papaya.

Direct somatic embryogenesis and encapsulation of somatic embryos for in vitro conservation of Bacopa monnieri (L.) Wettst

Direct somatic embryogenesis and shoot organogenesis were achieved from leaf explants excised from microshoots of Bacopa monnieri cultured on Murashige and Skoog medium containing N6-benzyladenine (BA) and 2,4-dichlorophenoxyacetic acid (2,4-D). The maximum frequency of explants differentiated somatic embryos and shoot buds on MS medium supplemented with 12.5 µM BA and 1 µM 2,4-D. The frequency of explants differentiating somatic embryos decreased with increasing concentration of 2,4-D. Light and scanning electron microscopy revealed direct differentiation of somatic embryos and shoot buds from explants, and various developmental stages of the somatic embryos were observed. Somatic embryos and apical shoot tips were encapsulated in sodium alginate gel to produce synthetic seeds. The storage of synthetic seeds produced by encapsulation was studied at 4 and 25 °C (room temperature) for a period of 140 days. Encapsulated somatic embryos were found to retain viability after 140 days of storage at both temperatures, whereas encapsulated apical shoot buds failed to germinate even after 40 days when stored at 4 °C. The viability of synthetic seeds was higher when stored at 25 °C. All amplified markers scored by random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) were monomorphic for all the plants produced from synthetic seeds following different periods of storage, thus establishing the clonal fidelity of propagated plantlets.

Decoding regulatory landscape of somatic embryogenesis reveals differential regulatory networks between japonica and indica rice subspecies.

Somatic embryogenesis is a unique process in plants and has considerable interest for biotechnological application. Compare to japonica, indica rice has been less responsive to in vitro culture. We used Illumina Hiseq 2000 sequencing platform for comparative transcriptome analysis between two rice subspecies at six different developmental stages combined with a tag-based digital gene expression profiling. Global gene expression among different samples showed greater complexity in japonica rice compared to indica which may be due to polyphyletic origin of two rice subspecies. Expression pattern in initial stage indicate major differences in proembryogenic callus induction phase that may serve as key regulator to observe differences between both subspecies. Our data suggests that phytohormone signaling pathways consist of elaborate networks with frequent crosstalk, thereby allowing plants to regulate somatic embryogenesis pathway. However, this crosstalk varies between the two rice subspecies. Down regulation of positive regulators of meristem development (i.e. KNOX, OsARF5) and up regulation of its counterparts (OsRRs, MYB, GA20ox1/GA3ox2) in japonica may be responsible for its better regeneration and differentiation of somatic embryos. Comprehensive gene expression information in the present experiment may also facilitate to understand the monocot specific meristem regulation for dedifferentiation of somatic cell to embryogenic cells.

Somatic Versus Zygotic Embryogenesis: Learning from Seeds.

Plant embryogenesis is a fascinating developmental program that is very successfully established in nature in seeds. In case of in vitro somatic embryogenesis this process is subjected to several limitations such as asynchronous differentiation and further development of somatic embryos, malformations and disturbed polarity, precocious germination, lack of maturity, early loss of embryogenic potential, and strong genotypic differences in the regeneration efficiency. Several studies have shown the similarity of somatic and zygotic embryos in terms of morphological, histological, biochemical, and physiological aspects. However, pronounced differences have also been reported and refer to much higher stress levels, less accumulation of storage compounds and a missing distinction of differentiation and germination by a quiescent phase in somatic embryos. Here, an overview on recent literature describing both embryogenesis pathways, comparing somatic and zygotic embryos and analyzing the role of the endosperm is presented. By taking zygotic embryos as the reference and learning from the situation in seeds, somatic embryogenesis can be improved and optimized in order to make use of the enormous potential this regeneration pathway offers for plant propagation and breeding.