DNA extraction
Fresh seedling (0.1 g) samples were cut, wrapped in tinfoil, and quick-frozen in liquid nitrogen barrels. The quick-frozen samples were then placed into a mortar and pestle and ground quickly and thoroughly. Next, 650 µL of preheated cetyltrimethylammonium bromide buffer was added and mixed with the ground samples; the same amount of chloroform was then added, and the contents were mixed slowly. After centrifugation at 12,000 rpm for 15 min, the supernatant of the liquid was transferred to a 1.5 mL Eppendorf (EP) tube, the same amount of pre-cooled isopropyl alcohol on ice was added, and the mixture was mixed by slowly inverting the EP tube. The supernatant was removed after centrifugation at 12,000 rpm and 4ºC for 10 min. One mL of 70 % ethanol was added to the EP tube to remove the liquid supernatant, and DNA was recovered by immersing the EP tube in ethanol solution. Centrifugation was performed at 12,000 rpm and 4ºC for 10 min, the supernatant was discarded, and this procedure was repeated (i.e., a total of two rounds of centrifugation). The EP tube was left open, and the ethanol was dried at room temperature until it had completely volatilized; 50 µL of sterile water was then added to dissolve the DNA. After dissolution, the DNA was stored at –20ºC.