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

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.解析光与温度信号的昼夜及季节变化，是植物存活的必要条件。这一过程在幼苗建成阶段尤为关键：此时光敏色素光受体（phytochrome photoreceptors）会激活光合色素合成，以支撑植物的光合自养生长。光敏色素部分通过抑制光敏色素互作因子（PIFs）来实现该功能——这类因子是叶绿素与类胡萝卜素生物合成的负调控因子。碱性亮氨酸拉链（bZIP）转录因子长下胚轴5（HY5）作为强效的PIF拮抗因子，可响应光照信号促进光合色素积累。本研究证实，HY5与PIFs可通过直接靶向同一启动子区域的顺式作用元件（G-box），形成一个可响应光与温度信号的动态激活-抑制转录调控模块。这一拮抗调控模块提供了一套简洁直接的机制，使环境变化能够重定向调控光合与光保护相关基因的转录。在光合色素生物合成基因的调控过程中，HY5与PIFs并非独立发挥作用，而是与生物钟（circadian clock）协同调控。然而，光照或温度的突发变化可触发HY5与PIFs的丰度改变，进而调整其共同靶基因的表达水平，以优化光合性能与植株生长。