Transcriptomic and physiological analyses reveal the acquisition of somatic embryogenesis potential in Agapanthus praecox

Somatic embryogenesis (SE)is an ideal cell model for plant cell totipotency study. The poor frequency of embryogenic callus (EC)induction limits the application of SE in many plants, such as Agapanthus praecox. Herein, we performed transcriptomic and physiological analyses with different callus (Ca)differentiation directions (SE and organogenesis)and stages (initial SE and repetitive SE)to better understand the physiological and molecular characteristics of the acquisition of embryogenic potential in A. praecox. A number of differentially expressed genes (DEGs)were significantly related to plant hormonal signaling transduction, starch and sucrose metabolism, and reactive oxygen species (ROS)responses. Compared to Ca, DEGs including heat shock protein, isoamylase, histone H4, alpha-1,2-mannosyltransferase, and sucrose synthase substantially changed expression levels in EC formation. Corresponding to DEGs, physiological indicators including indole-3-acetic acid, cytokinins, brassinosteroids, ethylene, abscisic acid, ROS, hydrogen peroxide, superoxide dismutase, catalase, starch and sucrose may be responsible for the acquisition of embryogenic potential in A. praecox. Moreover, plant growth regulators, carbon source combination, osmotic regulating substance, and DNA methylation inhibitors in the culture medium significantly affected the acquisition of SE potential. Altogether, our results suggested that plant hormone signal regulation, starch and sucrose metabolism, ROS scavenging, chromatin accessibility and DNA methylation jointly contributed to the activation of embryogenic ability in A. praecox.