HY5, a positive regulator of light signaling, negatively controls the unfolded protein response inArabidopsis

Abstract

Light influences essentially all aspects of plant growth and development. Integration of light signaling with different stress response results in improvement of plant survival rates in ever changing environmental conditions. Diverse environmental stresses affect the protein-folding capacity of the endoplasmic reticulum (ER), thus evoking ER stress in plants. Consequently, the unfolded protein response (UPR), in which a set of molecular chaperones is expressed, is initiated in the ER to alleviate this stress. Although its underlying molecular mechanism remains unknown, light is believed to be required for the ER stress response. In this study, we demonstrate that increasing light intensity elevates the ER stress sensitivity of plants. Moreover, mutation of the ELONGATED HYPOCOTYL 5 (HY5), a key component of light signaling, leads to tolerance to ER stress. This enhanced tolerance of hy5 plants can be attributed to higher expression of UPR genes. HY5 negatively regulates the UPR by competing with basic leucine zipper 28 (bZIP28) to bind to the G-box-like element present in the ER stress response element (ERSE). Furthermore, we found that HY5 undergoes 26S proteasome-mediated degradation under ER stress conditions. Conclusively, we propose a molecular mechanism of crosstalk between the UPR and light signaling, mediated by HY5, which positively mediates light signaling, but negatively regulates UPR gene expression.endoplasmic reticulum stress | light signaling | protein-folding capacity | crosstalk | unfolded protein response

ER-Anchored Transcription Factors bZIP17 and bZIP28 Regulate Root Elongation

“…integrates a range of external stimuli and hormone signals, which affect plant growth in 379 both positive and negative ways (Liu et al, 2007a,b;Che et al, 2010;Parra-Rojas et al, 380 2015;Zhou et al, 2015;Deng et al, 2106;Meng et al, 2017;Nawkar et al, 2017). 381 20 Therefore, it is likely that multiple signaling pathways conjunctly determine root 382 elongation through UPR regulation in plants via bZIP17 and bZIP28.…”

ER-Anchored Transcription Factors bZIP17 and bZIP60 Regulate Triterpene Saponin Biosynthesis inMedicago truncatula1[OPEN]

“…This inhibition is mediated by competition for binding to the G-box element (CACGTG) displayed within the ERSE motif(s) in the promoters of the UPR genes. Under ER stress conditions, HY5 undergoes proteasomal degradation, upon which bZIP28 can bind to the ERSE motif(s) and activate the UPR (Nawkar et al, 2017). Conversely, a similar scenario has been reported for JA-inducible genes by Van der Does et al (2013) (ORA 59).…”

“…Here, we also attempted to determine how the bZIP and TSAR TFs interact to modulate TS biosynthesis. It has been demonstrated in A. thaliana that under nonstressed conditions, the activity of bZIP28 in for instance the UPR, which causes ER stress, is inhibited by ELONGATED HYPOCOTYL 5 (HY5), another bZIP TF (Nawkar et al, 2017). This inhibition is mediated by competition for binding to the G-box element (CACGTG) displayed within the ERSE motif(s) in the promoters of the UPR genes.…”

Potentiation of concurrent expression of lipogenic genes by novel strong promoters in the oleaginous microalga Phaeodactylum tricornutum

“…Interestingly, we found that Pt667 harbors significant number of abiotic stress responsive components particularly the light responsive elements such as ACE, AE, G‐box, GAG‐motif, HSE, MBS, SpnI and TCT‐motif. Earlier studies in various plant systems have demonstrated that these elements involved in light responsiveness (Li et al, ; Nawkar et al, ; L. W. Wang, He, et al, ). It has been reported that light plays a crucial role in regulating carotenoid biosynthetic pathway and in silico analysis showed the presence of various light‐response motif in Pt667, thereby highlighted the role of these promoters on driving carotenogenic genes which warrant further investigation.…”

“…Interestingly, we found that Pt667 harbors significant number of abiotic stress responsive components particularly the light responsive elements such as ACE, AE, G-box, GAG-motif, HSE, MBS, SpnI and TCT-motif. Earlier studies in various plant systems have demonstrated that these elements involved in light responsiveness Nawkar et al, 2017;L. W. Wang, He, et al, 2017b).…”