High-efficiency somatic embryogenesis and plant regeneration in California poppy, Eschscholzia californica Cham

Efficient plant regeneration from embryogenic cell suspension cultures of Euonymus alatus

To establish an efficient plant regeneration system from cell suspension cultures of Euonymus alatus, embryogenic callus formation from immature embryos was investigated. The highest frequency of embryogenic callus formation reached 50% when the immature zygotic embryos were incubated on Murashige and Skoog (MS) medium supplemented with 1 mg/L 2,4-dichlorophenoxy acetic acid (2,4-D). At higher concentrations of 2,4-D (over 2 mg/L), the frequency of embryogenic callus formation declined significantly. The total number of somatic embryos development was highest with the 3% (w/v) sucrose treatment, which was found to be the optimal concentration for somatic embryo formation. Activated charcoal (AC) and 6-benzyladenine (BA) significantly increased the frequency of plantlet conversion from somatic embryos, but gibberellic acid (GA₃) had a negative effect on plantlet conversion and subsequent development from somatic embryos. Even though the cell suspension cultures were maintained for more than 1 year, cell aggregates from embryogenic cell suspension cultures were successfully converted into normal somatic embryos with two cotyledons. To our knowledge, this is the first successful report of a plant regeneration system of E. alatus via somatic embryogenesis. Thus, the embryogenic cell line and plant regeneration system established in this study can be applied to mass proliferation and production of pharmaceutical metabolite in E. alatus.

Somatic Embryogenesis: Still a Relevant Technique in Citrus Improvement

The genus Citrus contains numerous fresh and processed fruit cultivars that are economically important worldwide. New cultivars are needed to battle industry threatening diseases and to create new marketing opportunities. Citrus improvement by conventional methods alone has many limitations that can be overcome by applications of emerging biotechnologies, generally requiring cell to plant regeneration. Many citrus genotypes are amenable to somatic embryogenesis, which became a key regeneration pathway in many experimental approaches to cultivar improvement. This chapter provides a brief history of plant somatic embryogenesis with focus on citrus, followed by a discussion of proven applications in biotechnology-facilitated citrus improvement techniques, such as somatic hybridization, somatic cybridization, genetic transformation, and the exploitation of somaclonal variation. Finally, two important new protocols that feature plant regeneration via somatic embryogenesis are provided: protoplast transformation and Agrobacterium-mediated transformation of embryogenic cell suspension cultures.

Genetic transformation via somatic embryogenesis to establish herbicide-resistant opium poppy

A reliable genetic transformation protocol via somatic embryogenesis has been developed for the production of fertile, herbicide-resistant opium poppy plants. Transformation was mediated by Agrobacterium tumefaciens using the pCAMBIA3301 vector, which harbors the phosphinothricin acetyltransferase (pat) gene driven by a tandem repeat of the cauliflower mosaic virus (CaMV) 35S promoter and the beta-glucuronidase (gus) structural gene driven by a single copy of the CaMV 35S promoter between left- and right-border sequences. Co-cultivation of explants and A. tumefaciens was performed in the presence of 50 microM ATP and 50 microM MgCl(2). Root explants pre-cultured on callus induction medium were used for transformation. Herbicide-resistant, proliferating callus was obtained from explants on a medium containing both 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BA). Globular embryogenic callus, induced by removal of the BA from the medium, was placed on a hormone-free medium to form somatic embryos, which were converted to plantlets under specific culture conditions. Plantlets with roots were transferred to soil, allowed to mature and set seed. Both pat and gus gene transcripts, and PAT and GUS enzyme activities were detected in the transgenic lines tested. Histochemical localization of GUS activity in T(1) opium poppy plants revealed transgene expression in most tissues of all plant organs. The protocol required 8-12 months to establish transgenic T(1) seed stocks and was developed using a commercial opium poppy cultivar that produces high levels of pharmaceutical alkaloids.

Antisense RNA-mediated suppression of benzophenanthridine alkaloid biosynthesis in transgenic cell cultures of California poppy

California poppy (Eschscholzia californica Cham.) cell cultures produce several benzophenanthridine alkaloids, such as sanguinarine, chelirubine, and macarpine, with potent pharmacological activity. Antisense constructs of genes encoding two enzymes involved in benzophenanthridine alkaloid biosynthesis, the berberine bridge enzyme (BBE) and N-methylcoclaurine 3'-hydroxylase (CYP80B1), were introduced separately into California poppy cell cultures. Transformed cell lines expressing antisense BBE or antisense CYP80B1 constructs and displaying low levels of BBE or CYP80B1 mRNAs, respectively, showed reduced accumulation of benzophenanthridine alkaloids compared with control cultures transformed with a beta-glucuronidase gene. Pathway intermediates were not detected in any of the transformed cell lines. The suppression of benzophenanthridine alkaloid biosynthesis using BBE or CYP80B1 antisense RNA constructs also reduced the growth rate of the cultures. Two-dimensional (1)H-nuclear magnetic resonance and in vivo (15)N-nuclear magnetic resonance spectroscopy showed no difference in the abundance of carbohydrate metabolites in the various transgenic cell lines. However, transformed cells with reduced benzophenanthridine alkaloid levels contained larger cellular pools of several amino acids including alanine, leucine, phenylalanine, threonine, and valine compared with controls. The relative abundance of tyrosine, from which benzophenanthridine alkaloids are derived, was less than 2-fold higher in antisense-suppressed cells relative to controls. These results show that alterations in the metabolic flux through benzophenanthridine alkaloid biosynthesis can affect the regulation of amino acid pools. These data provide new insight into the metabolic engineering of benzophenanthridine alkaloid pathways.

Cytokinin-induced somatic embryogenesis and plant regeneration in Corydalis yanhusuo (Fumariaceae) - a medicinal plant

An efficient method has been developed for regeneration of complete plants via somatic embryogenesis in Corydalis yanhusuo (Fumariaceae), an important medicinal plant, using tuber-derived callus. Primary callus was induced by culturing mature tuber pieces on Murashige and Skoog's (MS) medium supplemented with 2.0 mg l(-1) N(6)-benzyladenine (BA) and 0.5 mg l(-1) alpha-naphthaleneacetic acid (NAA) in darkness. Somatic embryos were induced by subculturing the primary callus on MS medium supplemented with 0.5-4.0 mg l(-1) BA, kinetin, or zeatin, within 2 weeks of culture in light. Embryos with well-developed cotyledonary leaves were transferred in half-strength liquid MS medium supplemented with 1.0 mg l(-1) zeatin riboside for the development of roots. Converted somatic embryos were cultured on half-strength MS medium supplemented with 6% sucrose, and with 0.5-10.0 mg l(-1) abscisic acid (ABA), paclobutrazol, or ancymidol, 0.5-5.0 mg l(-1) GA(3) and 15-100 mg l(-1) polyethylene glycol (PEG) 4000 for further development of plantlets and in vitro tuber formation. The development of somatic embryos over the surface of tuber and/or cotyledonary leaf base region of the converted primary somatic embryo was observed. Before ex vitro establishment of somatic embryo-derived plants, plants with well-developed tubers were cultured on half-strength MS medium with 2% sucrose and 0.1 mg l(-1) GA(3) for 3 weeks.