Ultraviolet – B -mediated control of PHYTOCHROME INTERACTING FACTOR (PIF) transcription in Arabidopsis thaliana

Abstract

Plants, as sessile autotrophic organisms, rely on light cues not only as a source of energy, but also to regulate developmental responses to cope with their everchanging environment. Physiological changes triggered by light vary according to the light quality that is perceived by specific specialized photoreceptors, including phytochromes, cryptochromes and UV RESISTANCE LOCUS 8 (UVR8). These photoreceptors transduce the light cues to regulate PHYTOCHROME-INTERACTING FACTORS (PIFs). PIFs are a small subset of transcription factors of the basic helix-loop-helix (bHLH) subfamily, which act as a cellular signalling hub that integrates multiple signals, including light and temperature, to regulate plant morphogenesis. The mechanisms underlying transcriptional regulation of PIFs are poorly understood in comparison to their posttranscriptional regulation. This thesis examines the transcriptional regulation of PIFs in response to low dose ULTRAVIOLET-B (UV-B) light. UV-B is shown to suppress the transcript abundance of PIF3, PIF4 and PIF5 by inhibition of promoter activity, in a UVR8- dependent manner. Evidence supporting a role for COP1 in the suppression of PIF4 and PIF5transcript abundance in UV-B is also presented. Three different mechanisms controlling UV-B - mediated suppression of PIF transcript abundance are investigated. The first involves the plant hormones, brassinosteroids (BR). This thesis shows that BR signals are not involved in the UV-B - mediated suppression of PIF4 transcript at high temperatures, but support a role for BR signalling in the UV-B-mediated suppression of thermomorphogenesis. The second involves a potential autoregulatory loop involving UV-B-mediated degradation of PIF protein. Data suggest that UV-B - mediated PIF4 degradation may occur via an alternative pathway to PIF5. The third investigates the role of MYB30 in regulating PIF transcript abundance. Data show that MYB30 is suppressed by UV-B in a UVR8-dependent manner and promotes PIF7 transcription in white light. In addition, MYB30 regulates shade-avoidances responses to green shade.

Date of Award	5 Dec 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Andy M Bailey (Supervisor) & Keara A Franklin (Supervisor)