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.

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 ( Mt WUS, MtWOX5, MtSTM ), two ( Mt WUS and Mt WOX5 ) can serve as markers of cell dedifferentiation in leaf explants of both lines. Moreover, Mt STM 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 Mt WUS, MtWOX5 and Mt STM in the process.