Research on the Physiological Response Mechanism and Expression of Key Leaf Color Genes in ‘Duojiao’ Crabapple Under Partial Shading

The first yellow-leafed crabapple variety developed in China is Malus ‘Duojiao’. The light level affects its leaf color. (1) Background: Plants are frequently shaded by photovoltaic panels and green buildings. It is unknown how genetic regulation and partial shadowing regulate leaf color. (2) Methods: Four 28-day shading treatments were used for ‘Duojiao’ crabapple and its maternal ‘Xifu’ crabapple. Virus-induced gene silencing (VIGS), overexpression transgenic validation experiments, and physiological index analysis were employed to identify the expression levels of significant candidate genes. (3) Results: Improvements in chlorophyll synthesis, mineral metabolism, and antioxidant status were observed. The net photosynthetic rate was 39.29% higher under double-layer shade than in the control. (4) Conclusions: Partial double-layer shading exhibited the optimal effect. MsCPOX was the key gene controlling leaf color. Our results provide a theoretical basis for analyzing light responses and determining genes regulating leaf color in crabapple.