Phytohormone-regulated UV-B photomorphogenesis and acclimation

Abstract

Ultraviolet-B radiation (UV-B, 280–315 nm), as an environmental signal and potential abiotic stressor, has a wide range of effects on plant growth and development. Plants sense UV-B through the UV-B photoreceptor UV RESISTANCE LOCUS 8, which regulates downstream gene expression. On the one hand, UV-B regulates a series of photomorphogenesis events, such as inhibition of hypocotyl and stem elongation, which are largely related to the endogenous levels of phytohormones. Plants down-regulate auxin, gibberellin, and brassinosteroid signals in response to UV-B photomorphogenesis. On the other hand, UV-B causes DNA damage, accumulation of reactive oxygen species and damage to the photosynthetic system. Plants prevent UV-B damage by accumulating a variety of 'sunscreens', in particular flavonoids, which are typical UV-absorbers. It is noteworthy that phytohormones may also be involved in UV-B acclimation. UV-B up-regulates the levels of endogenous phytohormones, including abscisic acid, melatonin, jasmonate, and salicylic acid. Here, we review the molecular pathways of UV-B photomorphogenesis and acclimation that have been reported in flowering plants. We also highlight the important role of phytohormones in response to UV-B to understand the mechanism of UV-B acclimation from different perspectives.