Molecular aspects of somatic-to-embryogenic transition in plants

Abstract

Somatic embryogenesis (SE) is a model system for understanding the physiological, biochemical, and molecular biological events occurring during plant embryo development. Plant somatic cells have the ability to undergo sustained divisions and give rise to an entire organism. This remarkable feature is called plant cell totipotency. SE is a notable illustration of plant totipotency and involves reprogramming of development in somatic cells toward the embryogenic pathway. Plant growth regularities, especially auxins, are key components as their exogenous application recapitulates the embryogenic potential of the mitotically quiescent somatic cells. It has been observed that there are genetic and also physiological factors that trigger in vitro embryogenesis in various types of plant somatic cells. Analysis of the proteome and transcriptome has led to the identification and characterization of certain genes involved in SE. Most of these genes, however, are upregulated only in the late developmental stages, suggesting that they do not play a direct role in the vegetative-to-embryogenic transition. However, the molecular bases of those triggering factors and the genetic and biochemical mechanisms leading to in vitro embryogenesis are still unknown. Here, we describe the plant factors that participate in the vegetative-to-embryogenic transition and discuss their possible roles in this process.

Fig. 1

Interacting partners in brassinosteroid (BR) signaling. Upon binding of brassinolide (BL) to BRI1, SERK3 dissociates from the receptor and transphosphorylation take place with SERK1/SERK3. Subsequently phosphorylation of BZR1 by BIN2 is inhibited. This leads to accumulation of dephosphorylated BZR1 and BES1 in the nucleus, which induces gene transcription. Furthermore, phosphorylated BZR1 translocated to the cytoplasm is retained there by 14-3-3 proteins, and only dephosphorylated BZR1 translocates back to the nucleus

Fig. 2

A model for ERF1 play role in ethylene signal transduction. Ethylene is perceived by a family of two-component receptors containing a consensus or degenerate HK domain (H). Three of the receptors also contain a C-terminal receiver domain (R). The receptors negatively regulate ethylene response together with CTR1 in a complex on the endoplasmic reticulum membrane. Perception results in reduced receptor and CTR1 activities and activation of a MAP kinase kinase, which transmits the signal through the EIN2 membrane protein, ultimately resulting in the activation of a transcriptional cascade in the nucleus

Fig. 3

The Ubiquitin-mediated proteolysis of Aux/IAA proteins regulates auxin response. In the absence of an auxin stimulus, Aux/ IAA proteins inhibit ARF transcriptional activity by forming heterodimers. Auxin perception (by an unknown receptor) targets the Aux/IAA proteins to the SCFTIR1 complex, resulting in their ubiquitination and degradation, thereby derepressing the ARF transcription factors. Among the ARF targets are the Aux/IAA genes themselves, which produce nascent Aux/IAA proteins that restore repression upon the pathway in a negative feedback loop

Fig. 4

A model of the acquiring the embryogenic competence by DNA methylation at present of 2,4-d. DNA methylation afterward chromatin remolding take place in somatic cell. At last, somatic cell was undergoing genomic reprogramming and acquiring the embryogenic competence