Abstract
Somatic embryogenesis (SE) is an in vitro biological process in which bipolar structures (somatic embryos) can be induced to form from somatic cells and regenerate into whole plants. Acquisition of the embryogenic potential in culture is initiated when some competent cells within the explants respond to inductive signals (mostly plant growth regulators, PRGs), and de-differentiate into embryogenic cells. Such cells, “canalized” into the embryogenic developmental pathway, are able to generate embryos comparable in structure and physiology to their in vivo counterparts. Genomic and transcriptomic studies have identified several pathways governing the initial stages of the embryogenic process. In this review, the authors emphasize the importance of the developmental signals required for the progression of embryo development, starting with the de-differentiation of somatic cells and culminating with tissue patterning during the formation of the embryo body. The action and interaction of PGRs are highlighted, along with the participation of master regulators, mostly transcription factors (TFs), and proteins involved in stress responses and the signal transduction required for the initiation of the embryogenic process.
Highlights
Plant embryogenesis starts with the fusion of the sperm cell with the egg, leading to the generation of the diploid zygote, which, through a coordinated cell division pattern, gives rise to a fully developed embryo [1]
It is apparent from the studies reported above that auxin has received most of the attention given its role in cellular de-differentiation, which is an obligatory step in any in vitro embryogenic processes
During Arabidopsis Somatic embryogenesis (SE), SOMATIC EMBRYOGENESIS RECEPTOR KINASE1 (SERK1) is highly present in all the embryogenic cells and developing embryos up to the heart stage of development, and its overexpression promotes the formation of somatic embryos [129]
Summary
Plant embryogenesis starts with the fusion of the sperm cell with the egg, leading to the generation of the diploid zygote, which, through a coordinated cell division pattern, gives rise to a fully developed embryo [1]. All the examples reported above highlight the fundamental concept of totipotency; that is, the inherent ability of plant cells to regenerate a whole plant through extensive reprogramming Such reprogramming requires changes in gene expression, modifications of signaling networks, and the activation of specific regulatory pathways. The requirement for auxins is transient and specific to the initial stages of embryogenesis, which are often characterized by the formation of the embryogenic tissue; the subsequent phases can occur in an auxin-free environment. This general notion is applicable to many species [9,13], including Arabidopsis, which is the model system in plant biology
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