Use of auxin and cytokinin for somatic embryogenesis in plant: a story from competence towards completion

Plant growth regulators (PGRs)enhance plants regeneration ability to form various organs and tissues by determining embryonic fate in vivo and boosting regeneration efficiency in vitro. Recent advances in molecular biology have identified that auxin and cytokinin biosynthesis, transportation, and signaling affect cell fate both transcriptionally and non-transcriptionally. Growth regulators have a key role in cell reprogramming. The ratio between auxin and cytokinin application in the plant tissue culture can control the state of cell di- or dedifferentiation. In this study, the different regenerative pathways of these PGRs are systematically overviewed for the first time, with the objective of better understanding somatic embryogenesis. Secondly, the different biosynthetic and signaling pathways of auxin and cytokinin interactions are thoroughly discussed. Finally, future research directions are identified for somatic embryogenesis. This review article provides a unique reference for a wide range of plant science communities to narrate the recent developments of auxin and cytokinin-related signaling and developmental pathways for a better understanding of the regeneration phenomena of somatic embryogenesis.