Suppression of MdPRP6 enhances adaptation of apple plants to long-term drought.

Abstract

Apples are one of the world's four most economically significant fruits, and drought stress is an important factor limiting the development of the global apple industry. Here, we demonstrate that a proline-rich protein (PRP), MdPRP6, is an important factor regulating the long-term drought adaptation of apple plants. Suppression of MdPRP6 in apple plants (MdPRP6-Ri) enhances their adaptation to long-term moderate drought conditions, as indicated by their significantly higher biomass and relative water content (RWC) compared with wild-type (WT) plants. Under drought stress, the net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), stomatal conductance (Gs), and transpiration rate (Tr) were higher, and photosystem II (PSII) damage was lower in MdPRP6-Ri plants than in WT plants. Suppression of MdPRP6 increased the activity of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), which reduced oxidative damage to apple leaves under drought stress. The stomatal openings of MdPRP6-Ri plants were larger than those of WT plants; the WUE_I and WUE_L were thus higher in MdPRP6-Ri plants than in WT plants under long-term moderate drought stress. We also found that suppression of MdPRP6 increased the wax content of the leaf epidermis, which limits water evaporation caused by non-stomatal factors under drought stress. In sum, our findings suggest that MdPRP6 negatively affects the long-term drought adaptation of apple plants, possibly by modulating both stomatal and non-stomatal water loss.