The role of small RNAs in plant somatic embryogenesis

Abstract

In plants, differentiated somatic cells can revert their identity to pluripotent, reprogrammed cells in order to optimize growth and development depending on external conditions and in aid of overcoming their limitations as sessile organisms. Different modes of regeneration include tissue repair, de novo organogenesis and somatic embryogenesis (SE). The latter usually comprise the formation of proliferating pluripotent cell masses called callus. Identification and characterization of genes involved in the SE process allows the exploitation of distinctive features that make a tissue susceptible to change its normal cell fate and produce new plants massively. Small RNAs (sRNAs) are non-coding RNA (ncRNA), 20-24 nucleotides long molecules involved in plant development, reproduction and genome reprogramming. Likely, the enormous variety of operating sRNA pathways contributes to the plant phenotypic plasticity. Two main sRNAs classes are defined by their modes of biogenesis: a class in which the precursor is a single-stranded, hairpin loop forming RNA (hpRNA), mainly represented by microRNAs (miRNAs) and a class in which the precursor is a dsRNA molecule (dsRNA) comprising several small interfering RNAs (siRNAs). sRNAs, especially miRNAs, are common regulators of transcription factors (TFs) essential for plant meristem maintenance, growth and proliferation control, and with recently uncovered role in somatic to embryonic cell reprogramming. Although the siRNA function in plant development and SE has been much less explored, recent findings shape out their relevance in organ patterning and stress responses, both involved in cell plasticity. This review focuses on compiling and integrating the described function of miRNAs and siRNAs as a molecular basis in establishing cell dedifferentiation and further plant regeneration in economically relevant crops.