Transcriptional cofactor AtSDR4L and its paralog DIG2 repress somatic embryogenesis during post-embryonic development in Arabidopsis

Somatic embryogenesis, a developmental process advantageous as an alternative means for plant propagation due to the lack of maternal tissues and the ease of in vivo to in vitro knowledge transfer of embryogenesis, has been applied in studies on the regulatory mechanisms governing the developmental plasticity in plants. Core and accessory components of the polycomb repressive complexes (PRCs), the epigenetic regulatory machinery, are known to repress the transcription of genes that positively regulate the somatic embryogenesis in seedlings. Recent studies revealed that Arabidopsis thaliana SEED DORMANCY 4-LIKE (AtSDR4L), an interactor of a PRC accessory, represses the embryo developmental program for a successful switch from seed to seedling. However, little is known about the regulation of cell differentiation by AtSDR4L in seedlings. Here, we show that AtSDR4L, its paralog Dynamic Influencer of Gene expression 2 (DIG2), and PRC components share similar transcriptional regulatory dynamics, particularly on somatic embryogenesis-related genes. We further demonstrate that mutations in AtSDR4L and DIG2 lead to the formation of somatic embryo-like structures and a delay in cellular differentiation. Thus, transcriptional changes reflected by morphological defects associated with somatic embryogenesis in Atsdr4l dig2 mutants suggest that AtSDR4L and DIG2 prevent the dedifferentiation of cells for proper seedling growth through the transcriptional control of cell identity.