UV-B regulation of microRNAs in maize

Differential expression of microRNAs was studied in maize leaves after an 8-h-exposure under UV-B light. As a control, plants were kept in the greenhouse in the absence of UV-B 4-week maize plants were grown in the greenhouse in the absence of UV-B. Then, they were divided in two groups. One group was treated with UV-B lights provided once for 8 h, starting 3 h after the beginning of the light period, using fixtures mounted 30 cm above the plants (Phillips, F40UVB 40 W and TL 20 W/12) at a UV-B intensity of 2 W m-2, UV-A: 0.65 W m-2. The bulbs were covered with cellulose acetate to exclude wavelengths <280 nm. For the second control group, plants were exposed for 8 h under the same lamps covered with polyester film (no UV-B treatment, UV-B: 0.04 W m-2, UV-A: 0.4 W m-2). Lamp output was recorded using a UV-B/UV-A radiometer (UV203 A+B radiometer, Macam Photometrics, Ltd, Livingston, UK) to insure that both the bulbs and filters provided the designated UV dosage in all treatments. Leaf samples were collected immediately after irradiation. RNA was extracted immediately after the treatments, and used for the microRNA microarray experiments.