Overexpression of MdARD4 Accelerates Fruit Ripening and Increases Cold Hardiness in Tomato

Ethylene plays an important role in stress adaptation and fruit ripening. Acireductone dioxygenase (ARD) is pivotal for ethylene biosynthesis. However, the response of ARD to fruit ripening or cold stress is still unclear. In this study, we identified three members ofMalusARD family, and expression profile analysis revealed that the transcript level ofMdARD4was induced during apple fruit ripening and after apple plants were being treated with cold stress. To investigate its function in cold tolerance and fruit ripening,MdARD4was ectopically expressed inSolanum lycopersicumcultivar 'Micro-Tom', which has been considered as an excellent model plant for the study of fruit ripening. At the cellular level, the MdARD protein expressed throughoutNicotiana benthamianaepidermal cells. Overexpression ofMdARD4in tomato demonstrated thatMdARD4regulates the ethylene and carotenoid signaling pathway, increases ethylene and carotenoid concentrations, and accelerates fruit ripening. Furthermore,MdARD4increased the antioxidative ability and cold hardiness in tomato. To conclude,MdARD4may potentially be used in apple breeding to accelerate fruit ripening and increase cold hardiness.