UV RESISTANCE LOCUS 8 (UVR8) is a UV-B photoreceptor that regulates various aspects of plant photomorphogenesis. Physiological functions of UVR8 have been extensively investigated in Arabidopsis. However, functions of Tomato UVR8 (SIUVR8) are largely unknown. To analyze physiological functions of SIUVR8, we generated sluvr8 knock-out mutant lines with CRISPR-CAS9 gene editing approach. At seedling stage, SIUVR8 regulates hypocotyl elongation and anthocyanin accumulation under UV-B. Moreover, SIUVR8 regulates acclimation to low dose UV-B and promotes tolerance to elevated UV-B stress. These results revealed pivotal roles of SIUVR8 in the regulation of Tomato seedling development and UV-B stress tolerance. The manipulation of photoreceptor SIUVR8 may represent a powerful tool to improve Tomato plant performance in nature where high dose UV-B is present. (C) 2019 Elsevier Inc. All rights reserved.