Ultraviolet-B radiation induces cell death in root tips and reprograms metabolism in Arabidopsis

Abstract

Ultraviolet-B (UV-B) radiation inhibits root system growth, however, the influence of UV-B radiation on the regulation of root development remains unclear. Here, we investigated the effects of UV-B radiation on root growth and metabolism in Arabidopsis using physiological, pharmacological, and transcriptome approaches. Our previous study has demonstrated that UV-B radiation depresses auxin accumulation in roots by reducing auxin biosynthesis, transport, and response. In this study, we found that UV-B radiation inhibited primary root (PR) growth by inducing root tip cell death and thereby disrupting cell division and elongation in root tips. The destructed root structure and distorted auxin flow caused by UV-B-induced root tip cell death also led to a reduced auxin accumulation in roots. Supplementation with an auxin α-naphthylacetic acid alleviated UV-B-repressed PR growth and further supported a notion that auxin is involved in UV-Brepressed PR growth. The UV-B radiation downregulated the expression of genes encoding the enzymes or regulators of the biosyntheses and degradations of the structural constituents of cell wall and genes involved in wax, cutin, and suberin biosyntheses, thereby repressing root system growth and development. The UV-B radiation also markedly repressed photosynthesis-related gene expression in roots, a non-photosynthetic organ. Taken together, this study suggests that UV-B radiation affects root growth by inducing cell death in root tips and reprogramming metabolism in roots. Additional key words: endogenous auxin flow, gene expression, α-naphthylacetic acid application, primary root growth. Submitted 2 April 2020, last revision 27 July 2020, accepted 19 August 2020. Abbreviations: ANAC032 NAC domain containing protein 32; bZIP60 basic region/leucine zipper motif 60; Col-0 Columbia-0; CYCs cell cycle regulators cyclins; DAPI 4,6-diamidino-2-phenylindole; DEGs differentially expressed genes; DIN2 dark inducible 2; GO gene ontology; IBS1 BABA-induced sterility 1; MYB2 myeloblastosis domain protein 2; NAA α-naphthylacetic acid; PCD programmed cell death; PI propidium iodide; PR primary root; ROS reactive oxygen species; SRA Short Read Archive; UV-B ultraviolet-B; WOX WUSCHEL-related homeobox. Acknowledgements: The authors gratefully acknowledge the Central Laboratory of the Xishuangbanna Tropical Botanical Garden for providing research facilities. This work was supported by the National Key Research and Development Program of China (2016YFC0501901), the China National Natural Sciences Foundation (31772383), the Basic Research Program of Qinghai Province (2019-ZJ-7033), and the Qinghai innovation platform construction project: Qinghai Provincial Key Laboratory of Restoration Ecology of Cold Area (2017-ZJ-Y20). * Corresponding authors; e-mails: zhangping2@xtbg.ac.cn; wangyb02@126.com This is an open access article distributed under the terms of the Creative Commons BY-NC-ND Licence