Abstract
Somatic embryogenesis is commonly used for clonal propagation of a wide variety of plant species. Induction of protocorm-like-bodies (PLBs), which are capable of developing into individual plants, is a routine tissue culture-based practice for micropropagation of orchid plants. Even though PLBs are often regarded as somatic embryos, our recent study provides molecular evidence to argue that PLBs are not derived from somatic embryogenesis. Here, we report and characterize the somatic embryonic tissues induced by Phalaenopsis aphrodite LEAFY COTYLEDON1 (PaLEC1) in Phalaenopsis equestris. We found that PaLEC1-induced somatic tissues are morphologically different from PLBs, supporting our molecular study that PLBs are not of somatic embryonic origin. The embryonic identity of PaLEC1-induced embryonic tissues was confirmed by expression of the embryonic-specific transcription factors FUSCA3 (FUS3) and ABSCISIC ACID INSENSITIVE3 (ABI3), and seed storage proteins 7S GLOBULIN and OLEOSIN. Moreover, PaLEC1-GFP protein was found to be associated with the Pa7S-1 and PaFUS3 promoters containing the CCAAT element, supporting that PaLEC1 directly regulates embryo-specific processes to activate the somatic embryonic program in P. equestris. Despite diverse embryonic structures, PaLEC1-GFP-induced embryonic structures are pluripotent and capable of generating new shoots. Our study resolves the long-term debate on the developmental identity of PLB and suggests that somatic embryogenesis may be a useful approach to clonally propagate orchid seedlings.
Highlights
Plant totipotency provides a means of clonally propagating a wide variety of plant species (Ikeuchi et al, 2013; Kareem et al, 2016; Radhakrishnan et al, 2017)
To explore the possibility of inducing a somatic embryonic program in Phalaenopsis orchids and to investigate whether somatic embryonic potential can be utilized for micropropagation, transgenic P. equestris plants overexpressing the embryonic maker Phalaenopsis aphrodite LEAFY COTYLEDON1 (PaLEC1) that has been shown to induce somatic embryogenesis in Arabidopsis (Fang et al, 2016) were generated
Similar to Protocorm-like body (PLB) induction, active cell division is a prerequisite for PaLEC1induced somatic embryonic structures (Figures 4B, C)
Summary
Plant totipotency provides a means of clonally propagating a wide variety of plant species (Ikeuchi et al, 2013; Kareem et al, 2016; Radhakrishnan et al, 2017). One of the most common in vitro regeneration methods is somatic embryogenesis (Zimmerman, 1993; Pulianmackal et al, 2014). Somatic embryogenesis is crucial for establishing genetic transformation platforms for. PaLEC1-Induced Orchid Somatic Embryos many non-model plant species and for clonal propagation of numerous high-value plants. The regeneration capacity of somatic embryos has made somatic embryogenesis a common method through which to clonally propagate economically important trees or herbal plants (Joshee et al, 2007; Nordine et al, 2014; Guan et al, 2016; Kim et al, 2019)
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