Abstract
Embryogenesis is the primary developmental program in plants. The mechanisms that underlie the regulation of embryogenesis are an essential research subject given its potential contribution to mass in vitro propagation of profitable plant species. Somatic embryogenesis (SE) refers to the use of in vitro techniques to mimic the sexual reproduction program known as zygotic embryogenesis (ZE). In this review, we synthesize the current state of research on proteomic and metabolomic studies of SE and ZE in angiosperms (monocots and dicots) and gymnosperms. The most striking finding was the small number of studies addressing ZE. Meanwhile, the research effort focused on SE has been substantial but disjointed. Together, these research gaps may explain why the embryogenic induction stage and the maturation of the somatic embryo continue to be bottlenecks for efficient and large-scale regeneration of plants. Comprehensive and integrative studies of both SE and ZE are needed to provide the molecular foundation of plant embryogenesis, information which is needed to rationally guide experimental strategies to solve SE drawbacks in each species.
Highlights
Accepted: 27 October 2021Embryogenesis is a critical stage in plant development, in which the single-celled zygote undergoes a polarization process and a succession of cell divisions based on cell-tocell communication to generate a complex patterning
A comparative proteomics study of zygotic and somatic embryos at the torpedo stage [58] showed that glycolytic enzymes were overaccumulated in Somatic embryogenesis (SE) while proteins related to TCA cycle, glyoxylate cycle, pyruvate metabolism, and ascorbate metabolism were overrepresented in zygotic embryogenesis (ZE)
Transcriptomics, proteomics, and targeted metabolomics studies of embryo development in the presence of gellan gum showed that overproduction of ABA during development was associated with the activation of ABA signal pathways, the ubiquitin/proteasome pathway, flavonoid pathways, reactive oxygen species (ROS)-scavenger proteins, proteins involved in cell division, embryogenesis, and starch synthesis [65]
Summary
Embryogenesis is a critical stage in plant development, in which the single-celled zygote undergoes a polarization process and a succession of cell divisions based on cell-tocell communication to generate a complex patterning. Included in the review relevant information from monocots and gymnosperm species when available In all of these groups, zygotic embryo development can be divided into three stages: (1) histodifferentiation, during which the proembryo is formed (ontogeny);. The partitioning that occurs following proembryo formation follows a uniform pattern of division in both angiosperms and gymnosperms, though embryogenesis after the octant stage differs between dicots and monocots. We show the major molecular events needed to achieve the somatic-to-embryogenic cell transition which represent the most frequently faced problems during the induction and proliferation phase, while during maturation it is the programming of the somatic embryo conversion potential to plantlet. Proteomics and metabolomics approaches have significantly improved due to innovations in molecule separation, mass spectrometry (MS), and bioinformatic analysis All of this is aided by the continuous generation of genomics information. Additional information related to protein extraction protocols, separation method, mass spectrometry (MS) identification, number of proteins or metabolites identified, as well as the specification of the explant and media formulation for SE studies are presented in Tables S1 and S2
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