Identification of microRNAs associated with the exogenous spermidine-mediated improvement of high-temperature tolerance in cucumber seedlings (Cucumis sativus L.)

High-temperature stress inhibited the growth of cucumber seedlings. Foliar spraying of 1.0 mmol·L− 1 exogenous spermidine (Spd) to the sensitive cucumber cultivar ‘Jinchun No. 2’ grown at high-temperature (42 °C/32 ° C) in an artificial climate box improved the high-temperature tolerance. Although there have been many reports on the response of microRNAs (miRNAs) to high-temperature stress, the mechanism by which exogenous Spd may mitigate the damage of high-temperature stress through miRNA-mediated regulation has not been studied.