PAs Regulate Early Somatic Embryo Development by Changing the Gene Expression Level and the Hormonal Balance in Dimocarpus longan Lour

Physiological, Metabolic, and Transcriptomic Analyses Reveal Mechanisms of Proliferation and Somatic Embryogenesis of Litchi (Litchi chinensis Sonn.) Embryogenic Callus Promoted by D-Arginine Treatment

D-arginine (D-Arg) can promote embryogenic callus (EC) proliferation and increase the rate of somatic embryo induction of litchi (Litchi chinensis Sonn.), yet the mechanism underlying the processes is incompletely understood. To investigate the mechanism, physiological responses of polyamines (PAs) [putrescine (Put), spermidine (Spd), and spermine (Spm)] were investigated for D-Arg-treated litchi EC and enzyme activity related to polyamine metabolism, plant endogenous hormones, and polyamine- and embryogenic-related genes were explored. Results showed that the exogenous addition of D-Arg reduces the activity of diamine oxidase (DAO) and polyamine oxidase (PAO) in EC, reduces the production of H2O2, promotes EC proliferation, and increases the (Spd + Spm)/Put ratio to promote somatic embryo induction. Exogenous D-Arg application promoted somatic embryogenesis (SE) by increasing indole-3-acetyl glycine (IAA-Gly), kinetin-9-glucoside (K9G), and dihydrozeatin-7-glucoside (DHZ7G) levels and decreasing trans-zeatin riboside (tZR), N-[(-)-jasmonoyl]-(L)-valine (JA-Val), jasmonic acid (JA), and jasmonoyl-L-isoleucine (Ja-ILE) levels on 18 d, as well as promoting cell division and differentiation. The application of exogenous D-Arg regulated EC proliferation and somatic embryo induction by altering gene expression levels of the WRKY family, AP2/ERF family, C3H family, and C2H2 family. These results indicate that exogenous D-Arg could regulate the proliferation of EC and the SE induction of litchi by changing the biosynthesis of PAs through the alteration of gene expression pattern and endogenous hormone metabolism.

Proteome profiles during early stage of somatic embryogenesis of two Eucalyptus species

BACKGROUND

Somatic embryogenesis (SE) was recognized as an important tool for plants to propagate. However, our knowledge about the proteins involved in early SE including the callus dedifferentiation is still limited, especially in the economic woody tree - Eucalyptus.

RESULTS

We used the data-independent acquisition mass-spectrometry to study the different proteome profiles of early SE of two Eucalyptus species-E. camaldulensis (high regeneratively potential) and E. grandis x urophylla (low regenerative potential). Initially, 35,207 peptides and 7,077 proteins were identified in the stem and tissue-culture induced callus of the two Eucalyptus species. MSstat identified 2,078 and 2,807 differentially expressed proteins (DEPs) in early SE of E. camaldulensis and E. grandis x urophylla, respectively. They shared 760 upregulated and 420 downregulated proteins, including 4 transcription factors, 31 ribosomal proteins, 1 histone, 3 zinc finger proteins (ZFPs), 16 glutathione transferases, 10 glucosyltransferases, ARF19, WOX8 and PIN1. These proteins might be involved in the early SE of Eucalyptus. By combining the miRNA and RNA-Seq results, some miRNA ~ gene/protein regulatory networks were identified in early SE of Eucalyptus, such as miR160 ~ TPP2, miR164 ~ UXS2, miR169 ~ COX11 and miR535 ~ Eucgr.E01067. Further, we found SERK, WRKY, ZFP and ABC transporter might be related with high SE potential.

CONCLUSIONS

Overall, our study identified proteins involved in the early SE and related to the high regeneration potential of Eucalyptus. It greatly enhanced our understanding of the early SE and the SE capacity of Eucalyptus.