Identification of Polycomb Repressive Complex1, Trithorax group genes and their simultaneous expression with WUSCHEL, WUSCHEL-related Homeobox5 and SHOOT MERISTEMLESS during the induction phase of somatic embryogenesis in Medicago truncatula Gaertn.

Anna Orłowska,Ewa Kępczyńska

doi:10.1007/s11240-018-1425-6

Anna Orłowska, Ewa Kępczyńska

Open Access

https://doi.org/10.1007/s11240-018-1425-6

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Abstract

The Polycomb Repressive Complex1 (LHP1, RING1, BMI1, EMF1, VRN1) and Trithorax group (ATX2, ATX3.1, ATX3.2, ATX5-like) genes, were for the first time identified in the genome of Medicago truncatula. Their expression, along with that of the earlier-identified MtWUS, MtWOX5 and MtSTM, was investigated during the induction phase (IP). During the 21-day-long IP, all the genes mentioned, except for MtSTM, were expressed in non-embryogenic (M9) and embryogenic (M9–10a) genotype of M. truncatula. The lower expression level of all the PRC1 genes in primary explants of the M9–10a line compared to their expression in the M9 line probably triggers processes leading to the formation of embryogenic cells. In addition, the higher—from the second day of the induction phase—expression of the ATX2, ATX3.1 and ATX3.2 genes from the TrxG in cells of the embryogenic line, compared to the expression in the non-embryogenic one, suggests their involvement in acquisition of cell competence for embryogenesis. Among the three tested genes known for their involvement in organization of the meristematic centers in zygotic embryos (MtWUS, MtWOX5, MtSTM), two (MtWUS and MtWOX5) can serve as markers of cell dedifferentiation in leaf explants of both lines. Moreover, MtSTM may mark embryogenic cells, since its expression was registered only in the embryogenic line. The study provides new data regarding involvement of the PRC1 and TrxG genes during prime events of the SE and sheds new light on the involvement of MtWUS, MtWOX5 and MtSTM in the process.

Highlights

Somatic embryogenesis (SE) is a complex biological process in which somatic plant cells acquire the capacity to transform into embryos, following which a complete plant can be regenerated
The amino acid sequences of A. thaliana Polycomb Repressive Complex1 (PRC1) and Trithorax group (TrxG) Before the gene expression experiments the sequence aligngenes were obtained from the TAIR database
Amino acid analysis of LIKE HETEROCHROMATIN PROTEIN1 (LHP1) showed all of the Fabaceae (M. truncatula, Cicer arietinum, Glycine max and Phaseolus vulgaris) LHP1 belonged to the same clade (Fig. 2a)

Summary

Introduction

Somatic embryogenesis (SE) is a complex biological process in which somatic plant cells acquire the capacity to transform into embryos, following which a complete plant can be regenerated. Under specific in vitro conditions, the embryogenic pathway may be directly (direct somatic embryogenesis, DSE) or indirectly (indirect somatic embryogenesis, ISE) initiated in differentiated explant’s cells through the callus/PEM (proembryogenic mass) origination. Plant Cell, Tissue and Organ Culture (PCTOC) (2018) 134:345–356 formation, i.e., the emergence of cell masses showing varying degree of dedifferentiation of explants, mainly in the presence of an auxinic herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), and cytokinins, is associated with significant changes within the cells. Such reorganization in cell identities and growth patterns is accompanied by changes in the expression of numerous genes on transcriptional and epigenetic levels. Several marker genes have been reported that are able to distinguish between embryogenic and non-embryogenic cells such as SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK; Schmidt et al 1997; Nolan et al 2009), LEAFY COTYLEDON1 (LEC1; Lotan et al 1998; Ledwoń and Gaj 2011; Orłowska et al 2017), LEAFY COTYLEDON1-LIKE (L1L; Orłowska et al 2017), FUSCA3 (FUS3; Luerssen et al 1998; Ledwoń and Gaj 2011) and BABY BOOM (BBM; Igielski and Kępczyńska 2017)

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