Figures (1)  Tables (1)

    • Figure 1. 

      Conifer embryo development represented by Picea abies. (a) Schematic representation of the developmental stages of somatic embryo development. (b)−(f) Somatic embryo development process: (b) proembryogenic mass (PEM); (c) cultures after one week on maturation medium, insert presents an early somatic embryo (EE); (d) culture contains late embryos (LEs); (e) culture contains maturing and (f) matured somatic embryo (ME). (g), (h) Dissected seeds to show (g) the early zygotic embryo, indicated by the black arrow, and (h) the maturing zygotic embryo. Bar = 500 μm.

    • Gene familyGeneDescriptionReferences
      LRR-RLKsSOMATIC EMBRYOGENESIS RECEPTOR-
      LIKE KINASE 1-5 (SERKs)      		Transmembrane proteins; involved in signal transduction and have been strongly associated with somatic embryogenesis and apomixis in a number of plant species.[23]
      AP2/ERFBABYBOOM (BBM)Tanscription factor; activates LEC1-ABI3-FUS3-LEC2 network to induce somatic embryogenesis.[24]
      EMBRYOMAKER (EMK/AIL5 )Tanscription factors; promote the formation of somatic embryo on cotyledons.[25]
      WOUND INDUCED DEDIFFERENTIATION1 (WIND1)Tanscription factor; controls cell dedifferentiation in Arabidopsis and functions as a key molecular switch for plant cell dedifferentiation.[26,27]
      B3-AFLLEAFY COTYLEDON 1 (LEC1)Tanscription factor; promote somatic embryo development in vegetative organs.[28]
      LEC1-LIKE (L1L)Tanscription factor; promote somatic embryo development in vegetative organs.[29]
      LEAFY COTYLEDON 2 (LEC2)Tanscription factor; activates the expression of embryonic traits in vegetative tissues.[28]
      ABSCISIC ACID INSENSITIVE 3 (ABI3)/VIVI PAROUS (VP1)Transcript factor; regulates embryo-specific ABA-induced genes.[30]
      FUSCA3 (FUS3)Transcription factor; promotes embryogenesis by regulating synthesis of storage proteins and lipids.[31]
      VP1/ABI3-LIKE (VAL)Transcription factor; repress plant embryo development.[32]
      WOXWUSCHEL (WUS)Transcription factor; a central player in stem cell maintenance in the SAM.[33]
      WUSCHEL-related homeobox (WOX) 2Transcription factor; promotes apical embryonic cell division.[34]
      WOX 5Transcription factor; a central player in stem cell maintenance in the SAM.[35]
      WOX 8 and WOX9WOX8 and WOX9 functionally overlap in promoting basal embryonic cell division.[34]
      NACCUP SHAPED COTYLEDONS 1-3 (CUCs)CUP SHAPED COTYLEDONS 1-3 act redundantly to specify the cotyledon boundary.[36−38]
      HD-GL2Arabidopsis thaliana meristem L1 layer (ATML1)An early molecular marker for the establishment of both apical-basal and radial patterns during plant embryogenesis.[39]
      ANTHOCYANINLESS2 (ANL2)anl2 mutant shows aberrant cellular organization.[40]
      Class I KNOX geneSHOOTMERISTEMLESS (STM)Tanscription factors regulate the architecture of the SAM by maintaining a balance between cell division and differentiation.[41]
      GRASSCARECROW (SCR)Regulates the radial organization of the root.[42]
      AGO proteinsARGONAUTE (AGO)Participate in post-transcriptional gene silencing and influence stem cell fate specification in both plants and animals.[43]
      PcG proteinsPOLYCOMB REPRESSIVE COMPLEX
      subunit genes      		Epigenetic effector proteins; stem cell self-renewal, pluripotency, gene silencing; repressive effect on dedifferentiation ability of cells.[15,16]

      Table 1. 

      List of some of the major regulatory genes in somatic embryogenesis.