MdATG10 Is Targeted by MdbHLH155 and Delays Leaf Senescence in Apple Plants by Activating Autophagy

Leaf senescence is a type of programmed cell death characterised by irreversible physiological and biochemical changes. Autophagy, a cellular degradation pathway, plays a crucial role in regulating plant development, senescence, and resistance to environmental stresses. However, how this pathway affects leaf senescence remains incompletely understood. We showed that MdATG10 plays a negative role in leaf senescence. Following the induction of leaf senescence via dark treatment, the expression of MdATG10 was upregulated, and overexpression of MdATG10 mitigated the yellowing of leaves during the dark-induced senescence process. The opposite patterns were observed in MdATG10-silenced apple plants. Additional studies revealed that a bHLH transcription factor, MdbHLH155, can bind to the promoter of MdATG10 and activate its expression, and MdbHLH155 further accelerated the expression of MdATG10 under dark treatment. MdbHLH155 was also induced by dark-induced leaf senescence before the expression of MdATG10. Silencing of MdbHLH155 in apple plants accelerated dark-induced leaf senescence and suppressed the expression of MdATG10 and autophagy activity. In sum, our findings suggest that MdATG10 delayed leaf senescence by elevating autophagy activity, and this was positively controlled by the upstream regulator MdbHLH155, which negatively regulates dark-induced leaf senescence in apple plants.