Endogenous auxin directs development of embryonic stem cells into somatic proembryos in Arabidopsis

Abstract

Somatic embryogenesis (SE) is the process by which embryos develop from in vitro cultured vegetative tissue explants. The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is widely used for SE induction, but SE can also be induced by overexpression of specific transcription factors, such as AT-HOOK MOTIF NUCLEAR LOCALIZED 15 (AHL15). 2,4-D and AHL15 both trigger the biosynthesis of the natural auxin indole-3-acetic acid (IAA). However, the role of this endogenously produced auxin in SE is yet not well understood. In this study we show that the induction of embryonic stem cells from explants does not require IAA biosynthesis, whereas an increase in IAA levels is essential to maintain embryo identity and for embryo formation from these stem cells. Further analysis showed that YUCCA (YUC) genes involved in the IPyA auxin biosynthesis pathway are up-regulated in embryo-forming tissues. Chemical inhibition of the IPyA pathway significantly reduced or completely inhibited the formation of somatic embryos in both 2,4-D-and AHL15-dependent systems. In the latter system, SE could be restored by exogenous IAA application, confirming that the biosynthesis-mediated increase in IAA levels is important. Our analyses also show that PIN1 and AUX1 are the major auxin carriers that determine respectively auxin efflux and influx during SE. This auxin transport machinery is required for the proper transition of embryonic cells to proembryos and, later, for correct cell fate specification and differentiation. Taken together, our results indicate that auxin biosynthesis in conjunction with its polar transport are required during SE for multicellular somatic proembryo development and differentiation.

Prediction of the concentration of plant growth regulators for somatic embryogenesis and regeneration of Hyoscyamus niger using Box–Behnken design of response surface methodology

“…Plant growth regulators are considered one of the induction signals of dedifferentiation (Nic-Can and Loyola-Vargas 2016). Plant tissue culture researchers believe that auxin is required to induce somatic embryogenesis (Karami et al 2021). Studies show that during the early stages of somatic embryogenesis, the level of endogenous auxin increases, which is associated with the activation of stress signals and changes in chromatin status.…”

Insights into the Histone Acetylation-Mediated Regulation of the Transcription Factor Genes That Control the Embryogenic Transition in the Somatic Cells of Arabidopsis

“…However, less intensive, dispersed patches of Hac signals were also found in the IZE cotyledons that are directly involved in the development of the somatic embryos [ 79 ]. Moreover, auxin biosynthesis followed by an increase in IAA in SE-involved explant tissue has also been postulated [ 45 , 56 , 103 ]. In support of the postulated convergence between Hac and the IAA accumulation, the role of Hac in auxin biosynthesis, including the regulation of the YUCCA genes that control IAA biosynthesis in SE, has been indicated [ 45 , 104 , 105 ].…”

miR172 Regulates WUS during Somatic Embryogenesis in Arabidopsis via AP2

“…The hypothesis on the TOE1 function in SE induction is of particular interest given the interactions of TOE1 with KANADI1 (KAN1), which is the regulator of the development of the abaxial trichome of leaves [ 119 ]. Like leaves, the cotyledons have an adaxial–abaxial polarity [ 120 ] and the adaxial side of cotyledon exclusively contributes to somatic-embryo development in Arabidopsis [ 121 , 122 ]. In support of the role of the cotyledon polarity in the SE-induction mechanism, miR165/miR166 and PHB had adaxial-specific expression patterns in the SE-induced explants [ 30 , 123 ].…”