2.1 Rice material and culture conditions

The experiment was conducted in two growth chambers (CMP6050, Conviron, Winnipeg, Manitoba, Canada) at the Yangzhou University in Yangzhou, Jiangsu Province, China. Japanese rice variety Nipponbare (Oryza sativa , ssp. japonica ) was used in the experiments. Nipponbare is widely used in rice production, breeding, and molecular genetics studies. It is the first rice variety being deeply genome sequenced as a monocots model plant (Sasaki et al, 2005; Matsumoto et al, 2016).
Rice seeds were acquired from Yangzhou Agricultural Research Center, and surface sterilized with disinfectant prochloraz (Jinbao, Yangzhou Suling Agricultural Chemicals, Jiangdu, China) following the supplier recommendation. Seeds were immersed in tap water for 48 hrs before subjected to germination promotion at 32°C with a humidity of 85% in an incubator for 15 hrs, and at 28°C till shoot and root appearance to 0.5~1 cm. The germinated seeds were screened for uniformity and planted to soil in plastic trays at a spacing of 3.5 cm x 3.2 cm, with each tray containing 96 plants. The plastic tray contained premixed soil, 12 cm in depth (Zhang et al, 2019), prepared in a similar way as in field nursery for seedling.
During the growth period, soil was checked three times a day to keep its moisture at saturated point but without persistent water layer. The temperature of the growth chamber was preset to 30/22°C (actual records at ± 0.67°C range) in the 12/12hrs day/night regime, respectively. The illumination was programmed to 800 μmol photons m−2s−1 (actual records at ± 58 μmol photons m−2 s−1) during the day and 0 at night. The relative humidity was set at 70% (actual records range 65-80%).