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Plant Cell. 2019 Jul 9. pii: tpc.00929.2018. doi: 10.1105/tpc.18.00929. [Epub ahead of print]

Differential UVR8 signal across the stem controls UV-B-induced inflorescence phototropism.

Author information

Ghent University CITY: Ghent STATE: East Flanders POSTAL_CODE: 9000 Belgium [BE].
Institute of Plant BIology, Biological Research Centre CITY: Szeged Hungary [HU].
University of Antwerp CITY: Antwerpen Belgium [BE].
IADIZA and CONICET CITY: Mendoza Argentina [AR].
Instituto de Investigaciones Forestales y Agropecuarias Bariloche, (CONICET-INTA) CITY: Modesta Victoria Argentina [AR].
Universidad de Buenos Aires CITY: 1417 Buenos Aires POSTAL_CODE: 1417 Argentina [AR].
Biological Research Centre of the Hungarian Academy of Sciences CITY: Szeged POSTAL_CODE: H-6726 Hungary [HU].
Ghent University CITY: Gent POSTAL_CODE: B-9000 Belgium [BE].
University Gent CITY: Gent POSTAL_CODE: 9000 Belgium [BE]


In the course of evolution, plants have developed mechanisms to orient their organs towards the incoming light. At the seedling stage, positive phototropism is mainly regulated by phototropin photoreceptors in blue and ultraviolet wavelengths. Contrasting with this, we report that UV RESISTANCE LOCUS 8 (UVR8) serves as predominant photoreceptor of UV-B-induced phototropic responses in inflorescence stems. We examined the molecular mechanisms behind this response and our findings support the Blaauw theory (1919), suggesting rapid differential growth through unilateral photomorphogenic growth inhibition. UVR8-dependent UV-B perception occurs mainly in the epidermis and cortex, but deeper tissues such as endodermis can also contribute. Within stems, a spatial difference of UVR8 signal causes transcript and protein increase of transcription factors ELONGATED HYPOCOTYL 5 (HY5) and its homologue HYH at the UV-B-exposed side. The irradiated side shows 1) strong activation of flavonoid synthesis genes and flavonoid accumulation, 2) Increased GA2oxidase expression, diminished gibberellin1 levels and accumulation of DELLA protein REPRESSOR OF GA1 (RGA) and, 3) increased expression of the auxin transport regulator, PINOID, contributing to diminished auxin signalling. Together the data provide a mechanism of phototropin-independent inflorescence phototropism through multiple, locally UVR8-regulated hormone pathways.


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