Apple DELLA Is Degraded Under Warm Temperature Conditions in Nicotiana benthamiana Leaves Through a COP1‐Dependent Mechanism

In apple (Malus domestica), flowering is repressed by the phytohormone gibberellin (GA) and high temperatures (> 27°C), but the molecular mechanisms underlying this repression remain unknown. In Arabidopsis thaliana (Arabidopsis), GA and temperature signaling converge on DELLA protein regulation, with both factors promoting DELLA degradation through independent 26S proteasome-mediated pathways. Here, we tested whether high-temperature-induced DELLA degradation is conserved in apple. Using the heterologous systems Arabidopsis and Nicotiana benthamiana, we characterized the function of the apple DELLA protein DELLA REPRESSOR OF ga1-3 (MdRGL1a) and found that high temperatures promote its degradation via a 26S proteasome-dependent mechanism. Additionally, MdRGL1a interacts with apple orthologs of Arabidopsis CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) and SUPPRESSOR OF phyA-105 2 (SPA2), components of an E3 ubiquitin ligase complex that mediates protein ubiquitination and degradation. These findings suggest a conserved mechanism of temperature-induced DELLA degradation between apple and Arabidopsis. The degradation of MdRGL1a may underlie flowering suppression in apple under high temperatures, providing molecular insights that could aid in developing strategies to stabilize apple and other crop production in the face of climate change.