Pretreatment with Silver Thiosulfate Increases the Auxin-Inductive Effect for Rooting Mature Chestnut Shoots

Chestnut is a highly valuable species at both the ecological and economic levels, but vegetative propagation protocols have not been optimized for mature material due to its recalcitrant behaviour, thus limiting potential biotechnological applications. In this study, we focused on the formation of adventitious roots in mature chestnut microshoots, which show low rooting responses. Silver thiosulfate, an ethylene-signalling inhibitor, was applied as a pretreatment before auxin induction to study the role of ethylene in this developmental process. Rooting rate was significantly improved in response to the pretreatment, suggesting that ethylene negatively influences the induction of adventitious roots in mature shoots. Transcriptomics and real-time PCR analyses suggest that the improvement in the rooting response was mainly due to the activity of different auxin transport genes, whose expression seems to be repressed by ethylene. However, other hormones might also be negatively influencing rooting in mature shoots, although their specific role remains to be characterized.