Abstract

Light is a major environmental factor regulating plant growth and development. Photosynthesis in plants provides the materials and energy necessary for their long-term survival. Autophagy plays a crucial role in the degradation of substances in eukaryotic cells and is essential for plant growth, development, and stress regulation. However, the molecular link between the light response and autophagy pathways in plants remains poorly understood. Here, we found that autophagy-related cysteine protease ATG4 (MdATG4a) responds to low-light stress and positively regulates the light utilization efficiency of apple plants. Overexpression of MdATG4a in apple plants enhanced tolerance to low-light stress, while silencing MdATG4a resulted in the opposite phenotype. Chlorophyll content, photosynthetic parameters, and chlorophyll fluorescence parameters were greater under low-light conditions in transgenic apple plants overexpressing MdATG4a than in wild-type plants, which contributed to their enhanced light utilization efficiency. Moreover, MdATG4a enhanced autophagy activity in apple plants under low-light treatment. The BPC transcription factor basic pentacysteine 2 (MdBPC2) bound to the promoter of MdATG4a and inhibited its expression. Under low-light stress, MdBPC2 further weakened the expression of MdATG4a and negatively modulated the response of apple plants to low-light stress. The light-signaling transcription factor phytochrome-interacting factor 3 (MdPIF3) interacted with MdBPC2, which further inhibited the expression of MdATG4a under low light. Our results clarify the transcriptional regulation of MdATG4a in response to low-light stress in apple (Malus domestica) plants.