Rejuvenation of Mature Ilex paraguariensis Plants Through Serial Rooted Cuttings: Exploring the Roles of miRNAs in Reversing Adult Phase, Promoting Root Formation, and Determining Root Structure

In plants, the transition from the juvenile to adult stage involves physiological and anatomical changes initiated and partially controlled by evolutionarily conserved microRNAs. This process is of particular significance for the successful propagation of woody plant species that have transitioned to vegetative maturity and are recalcitrant to propagation. Conserved miRNAs differentially expressed between rejuvenated and mature <i>Ilex paraguariensis</i> plants were identified using high-throughput sequencing of small RNA libraries. The expression of miR156/miR157/miR528 was high in the leaves of juvenile plants and gradually decreased as the plant transitioned from juvenile to adult stages. In contrast, miR172 was predominantly expressed in adult plants. This variation confirmed that adults transitioned back to a juvenile phase after serial-rooted cuttings, allowing the plants to regain juvenile characteristics. Rejuvenation promotes the formation of adventitious roots and improves root structure, which supports the overall growth of the plant and results in greater vigour. The results will offer insights for further investigation into the molecular mechanisms regulating vegetative phase change in <i>I. paraguariensis</i> and other recalcitrant woody plant species. This knowledge could facilitate the earlier identification of rejuvenated material by analysing a wider range of genotypes and maturation stages, enhancing the efficiency of <i>Ilex paraguariensis</i> mass propagation.