Transduction of Signals during Somatic Embryogenesis

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.

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.

In Vitro Regeneration of Tea (Camellia sinensis (L). O. Kuntze) By Somatic Embryogenesis from Immature Cotyledon Tissues

Tea (Camellia sinensis) is the world's most popular beverage plant, as well as an important plantation crop with high commercial value. It has been maintained for centuries through conventional vegetative propagation. Tea clonal propagation in vitro has the advantage of producing a large number of elite plants. If an efficient in vitro regeneration technology is available, this technique could be exploited for selection of tea plants for desired trait. The selected plants could be later on multiplied through in vitro or ex vitro techniques. The study aimed to induced somatic embryogenesis from immature embryo explants to genetic variaton. Different concentrations of phenylboronic acid with benzyladenine and phenylboronic acid with kinetin were tested in MS medium with 30 g/L sucrose and 8 g/L agar. MS medium without any plant growth regulators was used as control group. Considering the embryo survival rate, 1.5 mg/ L-1 phenylboronic acid + 1 mg/ L-1 kinetin produced highest result as 87.3% while lowest was in control group as 36.7%. The highest plant regeneration rate was found in 1,5 mg/ L-1 phenylboronic acid + 1 mg/ L-1 kinetin and 1.5 mg/ L-1 phenylboronic acid + 1 mg/ L-1 benzyladenine medium respectively as 58.3% and 55.6%. Kinetin treatment with increasing phenylboronic acid concentrations gave the best results in terms of somatic embryo survival rate. Also, kinetin treatment produced better results when compared to benzyladenine concentrations.

Identification and expression analysis of histone modification gene (HM) family during somatic embryogenesis of oil palm

Background Oil palm (Elaeis guineensis, Jacq.) is an important vegetable oil-yielding plant. Somatic embryogenesis is a promising method to produce large-scale elite clones to meet the demand for palm oil. The epigenetic mechanisms such as histone modifications have emerged as critical factors during somatic embryogenesis. These histone modifications are associated with the regulation of various genes controlling somatic embryogenesis. To date, none of the information is available on the histone modification gene (HM) family in oil palm. Results We reported the identification of 109 HM gene family members including 48 HMTs, 27 HDMs, 13 HATs, and 21 HDACs in the oil palm genome. Gene structural and motif analysis of EgHMs showed varied exon–intron organization and with conserved motifs among them. The identified 109 EgHMs were distributed unevenly across 16 chromosomes and displayed tandem duplication in oil palm genome. Furthermore, relative expression analysis showed the differential expressional pattern of 99 candidate EgHM genes at different stages (non-embryogenic, embryogenic, somatic embryo) of somatic embryogenesis process in oil palm, suggesting the EgHMs play vital roles in somatic embryogenesis. Our study laid a foundation to understand the regulatory roles of several EgHM genes during somatic embryogenesis. Conclusions A total of 109 histone modification gene family members were identified in the oil palm genome via genome-wide analysis. The present study provides insightful information regarding HM gene’s structure, their distribution, duplication in oil palm genome, and also their evolutionary relationship with other HM gene family members in Arabidopsis and rice. Finally, our study provided an essential role of oil palm HM genes during somatic embryogenesis process.