Modulation of Organogenesis and Somatic Embryogenesis by Ethylene: An Overview

Glutamine Metabolism, Sensing and Signaling in Plants

Glutamine (Gln) is the first amino acid synthesized in nitrogen (N) assimilation in plants. Gln synthetase (GS), converting glutamate (Glu) and NH4+ into Gln at the expense of ATP, is one of the oldest enzymes in all life domains. Plants have multiple GS isoenzymes that work individually or cooperatively to ensure that the Gln supply is sufficient for plant growth and development under various conditions. Gln is a building block for protein synthesis and an N-donor for the biosynthesis of amino acids, nucleic acids, amino sugars and vitamin B coenzymes. Most reactions using Gln as an N-donor are catalyzed by Gln amidotransferase (GAT) that hydrolyzes Gln to Glu and transfers the amido group of Gln to an acceptor substrate. Several GAT domain-containing proteins of unknown function in the reference plant Arabidopsis thaliana suggest that some metabolic fates of Gln have yet to be identified in plants. In addition to metabolism, Gln signaling has emerged in recent years. The N regulatory protein PII senses Gln to regulate arginine biosynthesis in plants. Gln promotes somatic embryogenesis and shoot organogenesis with unknown mechanisms. Exogenous Gln has been implicated in activating stress and defense responses in plants. Likely, Gln signaling is responsible for some of the new Gln functions in plants.

A Comparative Transcriptome Analysis Reveals the Molecular Mechanisms That Underlie Somatic Embryogenesis in Peaonia ostii ‘Fengdan’

Low propagation rate is the primary problem that limits industry development of tree peony. In this study, a highly efficient regeneration system for tree peony using somatic embryogenesis (SE) was established. The transcriptomes of zygotic embryo explants (S0), non-embryonic callus (S1), embryonic callus (S2), somatic embryos (S3), and regenerated shoots (S4) were analyzed to determine the regulatory mechanisms that underlie SE in tree peony. The differentially expressed genes (DEGs) were identified in the pairwise comparisons of S1-vs-S2 and S1-vs-S3, respectively. The enriched DEGs were primarily involved in hormone signal transduction, stress response and the nucleus (epigenetic modifications). The results indicated that cell division, particularly asymmetric cell division, was enhanced in S3. Moreover, the genes implicated in cell fate determination played central roles in S3. Hormone signal pathways work in concert with epigenetic modifications and stress responses to regulate SE. SERK, WOX9, BBM, FUS3, CUC, and WUS were characterized as the molecular markers for tree peony SE. To our knowledge, this is the first study of the SE of tree peony using transcriptome sequencing. These results will improve our understanding of the molecular mechanisms that underly SE in tree peony and will benefit the propagation and genetic engineering of this plant.

Can Ethylene Inhibitors Enhance the Success of Olive Somatic Embryogenesis?

An efficient in vitro morphogenesis, specifically through somatic embryogenesis, is considered to be a crucial step for the application of modern biotechnological tools for genetic improvement in olive (Olea europaea L.). The effects of different ethylene inhibitors, i.e., cobalt chloride (CoCl2), salicylic acid (SA), and silver nitrate (AgNO3), were reported in the cyclic somatic embryogenesis of olive. Embryogenic callus derived from the olive immature zygotic embryos of the cultivar Leccino, was transferred to the expression ECO medium, supplemented with the ethylene inhibitors at 20 and 40 µM concentrations. Among these, the maximum number of somatic embryos (18.6) was obtained in media containing silver nitrate (40 µM), followed by cobalt chloride (12.2 somatic embryos @ 40 µM) and salicylic acid (40 µM), which produced 8.5 somatic embryos. These compounds interfered on callus traits: white friable embryogenic calli were formed in a medium supplemented with 40 µM cobalt chloride and salicylic acid; in addition, a yellow-compact embryogenic callus appeared at 20 µM of all the tested ethylene inhibitors. The resulting stimulatory action of silver nitrate among all the tested ethylene inhibitors on somatic embryogenesis, clearly demonstrates that our approach can efficiently contribute to the improvement of the current SE protocols for olive.