2.1 Plant materials and growth conditions
Experiments were conducted in a controlled environment of the greenhouse in Qufu Normal University, China. Seeds of an elite cultivar G. hirsutum cv. Acala Maxxa, kindly provided by Wendel laboratory in Iowa State University, were sown in plastic pots (10 × 10 cm) containing a mixture of nutrient soil and vermiculite in a ratio of 3:1. From sowing to three-leaf stage, plants were grown in a growth chamber with a photoperiod of 16 h of light and 8 h of darkness at temperature of 23±1℃.
An earlier study confirmed that cotton could produce a stress response when exposed to high UV-B level (16 kJ m–2 d–1) (Kakani et al., 2003). Here, to examine the response of cotton seedlings to UV-B stress, each three plants were placed under normal control condition (CK) or 6 h of UV-B radiation (16 kJ m-2 d-1). A UV-B lamp (Beijing Zhongyi Boteng Technology Co., LTD) was used to generate UV-B radiation. After treatment, the second and third true leaves of control and treated plants were collected for physiological index determination, RNA extraction, transcriptome sequencing, and gene expression quantitative comparison. All the treatments were conducted in triplicates.