Mutual upregulation of HY5 and TZP in mediating phytochrome A signaling

Abstract

Phytochrome A (phyA) is the far-red (FR) light photoreceptor in plants that is essential for seedling de-etiolation under FR-rich environments, such as canopy shade. TANDEM ZINC-FINGER/PLUS3 (TZP) was recently identified as a key component of phyA signal transduction in Arabidopsis thaliana; however, how TZP is integrated into the phyA signaling networks remains largely obscure. Here, we demonstrate that ELONGATED HYPOCOTYL5 (HY5), a well-characterized transcription factor promoting photomorphogenesis, mediates FR light induction of TZP expression by directly binding to a G-box motif in the TZP promoter. Furthermore, TZP physically interacts with CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), an E3 ubiquitin ligase targeting HY5 for 26S proteasome-mediated degradation, and this interaction inhibits COP1 interaction with HY5. Consistent with those results, TZP post-translationally promotes HY5 protein stability in FR light, and in turn, TZP protein itself is destabilized by COP1 in both dark and FR light conditions. Moreover, tzp hy5 double mutants display an additive phenotype relative to their respective single mutants under high FR light intensities, indicating that TZP and HY5 also function in largely independent pathways. Together, our data demonstrate that HY5 and TZP mutually upregulate each other in transmitting the FR light signal, thus providing insights into the complicated but delicate control of phyA signaling networks.

Light Intensity- and Spectrum-Dependent Redox Regulation of Plant Metabolism

“…HY5 mediates FRL induction of TANDEM ZINC-FINGER/PLUS3 (TZP) expression by directly binding to a G-box motif in the TZP promoter. Furthermore, TZP physically interacts with COP1, which inhibits COP1 interaction with HY5, ensuring its feedback regulation [ 32 ].…”

TANDEM ZINC-FINGER/PLUS3 regulates phytochrome B abundance and signaling to fine-tune hypocotyl growth

“…Since the initial identification of TZP by QTL mapping ( Loudet et al, 2008 ), several studies have reported a function for TZP in blue light and far-red light-mediated photomorphogenesis and photoperiod regulation of flowering ( Kaiserli et al, 2015 ; Perrella et al, 2018 ; Zhang et al, 2018 ; Li et al, 2021 ). The direct interaction between TZP and phyB in response to red light, as well as its association with clock and thermoregulatory components such as ELF3 ( Kaiserli et al, 2015 ) and PCH1 ( Huang et al, 2016b ), indicates that TZP integrates multiple light, temperature, and photoperiod pathways.…”

“…By contrast, in response to far-red light, TZP acts as a positive regulator in phyA signaling by directly associating with and controlling phyA abundance and phosphorylation ( Zhang et al, 2018 ). In addition, a recent study revealed a mutual upregulation of TZP and ELONGATED HYPOCOTYL5 (HY5), a key positive regulator of photomorphogenesis, in transducing far-red light signaling ( Li et al, 2022 ). However, it is still unclear how TZP is involved in regulating red light signaling and whether it affects the function, stability, or nuclear localization of phyB and other red light signaling components.…”

HY5: A Pivotal Regulator of Light-Dependent Development in Higher Plants

“…HY5 directly binds to the G-box cis -element present in TANDEM ZINC-FINGER/PLUS3 ( TZP ) promoter to activate its expression in the far-red light. In turn, TZP competes with COP1 for binding of HY5, thus leading to the accumulation of HY5 that promotes phyA signaling ( Li C. et al, 2021 ). Blue light-activated CRY1 competes with AGB1 for binding of HY5, thus leading to the enhanced biochemical activity of HY5 in promoting photomorphogenesis ( Lian et al, 2018 ).…”