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

First author: Lucas Vanhaelewyn; Affiliations: Ghent University (根特大学): Ghent, Belgium

Corresponding author: Filip J. Vandenbussche

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.

在演化过程中，很多植物演化出了令其器官朝向光源的机制。在苗期，植物向光性主要由蓝光和紫外光的向光素光感受器所调控。与此相反，作者在本文中报道了UVR8蛋白在花序轴中作为UV-B诱导的向光性反应的主要受体发挥功能。作者研究了该响应潜在的分子机制，研究结果支持Blaauw理论，即植物通过单侧光形态生长抑制来达到两侧快速的差异生长。UVR8依赖型UV-B感知主要发生在植物的表皮和皮层组织，但更深处的组织如内皮层也有参与。在茎杆中，UVR8信号的空间分布差异导致了转录因子HY5及其同源蛋白HYH在UV-B照射一侧的转录本和蛋白积累增加。被UV-B辐一侧会表现出一下特征：1. 类黄酮生物合成基因的激活以及类黄酮的积累；2. GA2氧化酶表达量的增加，GA1水平降低，同时DELLA蛋白RGA的积累下降；生长素转运调控基因PINOID的表达增加，使得生长素信号转导减弱。综上，本文的研究揭示了植物中一个不依赖于向光素、而是通过多个区域化UVR8调控的激素通路介导的花序向光性分子机制。

通讯：Filip J. Vandenbussche (http://www.fpb.ugent.be/index.php?page=LabMembers&person=FilipVandenbussche)

研究方向：植物中的光生物学和激素信号转导。

doi: https://doi.org/10.1105/tpc.18.00929

Journal: Plant Cell

Accept date: April 01, 2019