title: Re-interpreting plant morphological responses to UV-B radiation.
abstract: There is a need to reappraise the effects of UV-B radiation on plant morphology in light of improved mechanistic understanding of UV-B effects, particularly elucidation of the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor. We review responses at cell and organismal levels, and explore their underlying regulatory mechanisms, function in UV protection and consequences for plant fitness. UV-induced morphological changes include thicker leaves, shorter petioles, shorter stems, increased axillary branching and altered root:shoot ratios. At the cellular level, UV-B morphogenesis comprises changes in cell division, elongation and/or differentiation. However, notwithstanding substantial new knowledge of molecular, cellular and organismal UV-B responses, there remains a clear gap in our understanding of the interactions between these organizational levels, and how they control plant architecture. Furthermore, despite a broad consensus that UV-B induces relatively compact architecture, we note substantial diversity in reported phenotypes. This may relate to UV-induced morphological changes being underpinned by different mechanisms at high and low UV-B doses. It remains unproven whether UV-induced morphological changes have a protective function involving shading and decreased leaf penetration of UV-B, counterbalancing trade-offs such as decreased photosynthetic light capture and plant-competitive abilities. Future research will need to disentangle seemingly contradictory interactions occurring at the threshold UV dose where regulation and stress-induced morphogenesis overlap.
authors.affiliation: Department of Biosciences, University of Helsinki, Helsinki, 00014, Finland.
authors.forename: T Matthew
authors.initials: TM
authors.lastname: Robson
authors.forename: Karel
authors.initials: K
authors.lastname: Klem
authors.forename: Otmar
authors.initials: O
authors.lastname: Urban
authors.forename: Marcel A K
authors.initials: MA
authors.lastname: Jansen
mesh_terms: D005419:Flavonoids / Q000378:metabolism; D009024:Morphogenesis / Q000528:radiation effects; D010641:Phenotype; D010944:Plants / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D005419:Flavonoids
keywords: UVR8 photoreceptor; auxin homeostasis; canopy structure and light interception; chronic/acute stress; flavonoid accumulation; plant-plant interactions; stress-induced morphogenic responses (SIMR); ultraviolet radiation; whole-plant phenotype