The HY5-PIF Regulatory Module Coordinates Light and Temperature Control of Photosynthetic Gene Transcription

TLDR

Plants must interpret daily and seasonal light and temperature changes to regulate photosynthetic pigment production, a process mediated by phytochromes that suppress PIFs while HY5 antagonizes PIFs and, together with the circadian clock, fine‑tunes photopigment biosynthesis. The antagonistic HY5–PIF module directly redirects transcription of photosynthesis and photoprotection genes in response to environmental changes. We show that HY5 and PIFs bind the G‑box to form a dynamic activation‑suppression module that, upon sudden light or temperature shifts, alters their abundance to adjust target gene expression and optimize photosynthetic performance and growth.

Abstract

The ability to interpret daily and seasonal alterations in light and temperature signals is essential for plant survival. This is particularly important during seedling establishment when the phytochrome photoreceptors activate photosynthetic pigment production for photoautotrophic growth. Phytochromes accomplish this partly through the suppression of phytochrome interacting factors (PIFs), negative regulators of chlorophyll and carotenoid biosynthesis. While the bZIP transcription factor long hypocotyl 5 (HY5), a potent PIF antagonist, promotes photosynthetic pigment accumulation in response to light. Here we demonstrate that by directly targeting a common promoter cis-element (G-box), HY5 and PIFs form a dynamic activation-suppression transcriptional module responsive to light and temperature cues. This antagonistic regulatory module provides a simple, direct mechanism through which environmental change can redirect transcriptional control of genes required for photosynthesis and photoprotection. In the regulation of photopigment biosynthesis genes, HY5 and PIFs do not operate alone, but with the circadian clock. However, sudden changes in light or temperature conditions can trigger changes in HY5 and PIFs abundance that adjust the expression of common target genes to optimise photosynthetic performance and growth.