Alex Ricardo Bermudez-Valle

2,4-Dichlorophenoxyacetic acid (2,4-D), originally developed as a synthetic auxinic herbicide, is the most widely used chemical inducer of somatic embryogenesis (SE) in plants. Despite extensive use of 2,4-D in plant regeneration, the systems-level regulatory mechanisms connecting hormonal signaling, metabolic reprogramming, translational control, and embryogenic competence remain poorly resolved. Here, we hypothesize that TOR signaling functions as an integrative molecular hub coordinating transcriptional, metabolic, and developmental reprogramming during somatic embryogenesis induction. To investigate the molecular regulatory landscape associated with 2,4-D-induced SE, we performed a systems-level analysis integrating publicly available transcriptomic data from Arabidopsis thaliana with high-confidence protein–protein interaction (PPI) network analyses using STRING v12.0 (confidence score ≥ 0.900). Using a previously published transcriptomic dataset, we identified 1927 upregulated genes associated with SE induction, which were organized into 34 functional modules related to transcriptional regulation, translation metabolism, hormone signaling and cellular homeostasis. Within this interactome, TARGET OF RAPAMYCIN (TOR) kinase emerged as an integrative regulatory hub associated with multiple pathways involved in embryogenic reprogramming. Network analyses revealed three major TOR-associated regulatory axes: (1) the TOR–FKBP12–RPS6A axis, associated with ribosome biogenesis and translational regulation; (2) the TOR–CBP20 axis, connected with transcriptional reprogramming; SE master regulators (LEC1, LEC2, and FUS3); and lipid, sterol, brassinosteroid (BR), and auxin-associated pathways; and (3) the TOR–TAP46 axis, linked with one-carbon metabolism, nucleotide biosynthesis, DNA replication and repair, and genome-stability pathways. Additionally, the network contained 411 embryo-lethal (EMBL) genes distributed across multiple regulatory modules, reinforcing the biological relevance of the identified interactome and highlighting the importance of coordinated developmental, metabolic, and transcriptional regulation during embryogenesis induction. These findings support a systems-level TOR-associated regulatory framework involved in the integration of transcriptional, translational, metabolic, hormonal, and genome-maintenance pathways during embryogenesis. This interactome model provides a foundation for functional studies aimed at dissecting the molecular mechanisms underlying SE and identifying candidate targets to improve regeneration and biotechnological application and crop genetic engineering. Collectively, this study proposes a mechanistic framework in which TOR signaling integrates developmental, metabolic, translational, and genome-stability pathways to orchestrate embryogenic competence, providing candidate molecular targets for improving plant regeneration and genome engineering platforms.

Grain amaranths are recalcitrant to conventional in vitro plant regeneration by organogenesis de novo or through somatic embryogenesis. Consequently, floral organogenesis by these methods, representing the culminating developmental point in angiosperms, is rarely achieved. In the present study, the manipulation of in vitro flowering was explored as part of a strategy designed to overcome grain amaranth’s regeneration recalcitrance. It led to an efficient and reproducible in vitro protocol in which half-longitudinally dissected zygotic embryos generated fully developed Amaranthus hypochondriacus (Ah) plants. The use of high-irradiance illumination with LED lamps with a 3:1 red–blue irradiance ratio was a critical factor, leading to a 70% rate of early flowering events under flowering-inhibiting long-day photoperiod conditions. Contrariwise, no flowering was induced under LED white lights. All in vitro flowering Ah plants yielded viable seeds. To understand the basic molecular mechanisms of the phenomenon observed, gene expression patterns and principal component analysis of key flowering-related genes were analyzed after cultivation in vitro for 4, 8, and 12 weeks under both lighting regimes. These coded for photoreceptors, photomorphogenetic regulators, embryogenic modulators, and flowering activators/repressors. The results highlighted the upregulation of key flowering-regulatory genes, including CONSTANS, FLOWERING LOCUS T, and LEAFY, together with the downregulation of the floral repressor TERMINAL FLOWER1. Ribosome biogenesis- and seed-development-related genes were also differentially expressed, supporting a key role in this process for protein synthesis and embryogenesis. A model is proposed to explain how this light-regulated molecular framework enables in vitro flowering and seed production in Ah plants kept under long-day photoperiods.