A. Bastías, R. Almada, P. Rojas, J.M. Donoso, P. Hinrichsen, and B. Sagredo. 2016. Aging gene pathway of microRNAs 156/157 and 172 is altered in juvenile and adult plants from in vitro propagated Prunus sp. Cien. Inv. Agr. 43(3):429-441. In vitro culture is a very popular technique to mass propagate valuable plant genotypes, including Prunus sp. cultivars. Plants that undergo tissue culture processes often change their morphology and behavior due to the "rejuvenation" caused by the plant growth regulators included in the medium. To evaluate the effects of rejuvenation by tissue culture in Prunus sp., the expression patterns of the aging gene pathway described in plant models, which include the highly conserved microRNA (miRNA or miR) 156/157 and 172 families and several of their respective target genes, were analyzed in distinct Prunus sp. genotypes at different phases of maturity, including true seedling and tissue culture micropropagated plants. In genotypes from true seedling plants, the expression of miR156 and miR157 was higher in the leaves of juvenile plants (one year old) than in those of adult plants (six year old). The opposite pattern was observed with miRNA172 expression. Our results suggest that the aging gene pathway is relatively conserved in Prunus and likely plays a key role in vegetative phase change. However, Prunus sp. plants that were rejuvenated and propagated by in vitro methods showed more erratic behavior for miR156 and miR157 and their target genes, suggesting that tissue culture alters the normal control of the aging pathway.