UV-B induced phototropism in Arabidopsis

VANHAELEWYN, L; SERRANO, A; BALLARE, C; VAN DER STRAETEN, D; ARANA, MV; VANDENBUSSCHE, F

Barcelona

Congreso; XV Spanish Portuguese Congress of Plant Physiology; 2017

To efficiently capture light for photosynthesis or to regulate floral display, plants orient their organs towards the light in a process called phototropism. Phototropism has been mainly associated with blue light, perceived by specific photoreceptors called phototropins. Recently we found that in Arabidopsis, monochromatic unilateral ultraviolet (UV)-B (280-315nm) induces phototropism in etiolated phot1phot2 seedlings devoid of phototropins. This response is mediated by the specific UV-B receptor UV RESISTANCE LOCUS 8 (UVR8) and its downstream component ELONGATED HYPOCOTYL 5 (HY5).However, wild type seedlings respond faster and are more sensitive to UV-B than phot1phot2 seedlings, indicating participation of phototropins to UV-B perception. Moreover, since uvr8 mutant seedlings behave as wild type in unilateral UV-B, phototropins appear important UV-B receptors and mask any UVR8 effect. The photosignaling mechanism of phototropins in UV-B is similar to that in blue light, and has differentialauxin signaling downstream. In addition, we found that in Arabidopsis inflorescence stems, UV-B appears more effective than blue light to stimulate phototropism. Contrasting to the situation in etiolated seedlings, the main photoreceptor for UV-B phototropism in inflorescence stems is UVR8, with only a minor role for phototropins. In these conditions, based on reportergenes, a light signal gradient can be observed. Downstream, based on pharmacological assays, mutant analysis and reporter lines, again an auxin signal gradient is associated with the differential growth in the inflorescence stem. Thus, UV-B phototropism in etiolated seedlings and inflorescence stems relies on similar components, yet balanced in a different way.