Project description:Light is a major determinant of plant growth and survival. NONEXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1) acts as a receptor for salicylic acid (SA) and serves as the key regulator of SA-mediated immune responses. However, the mechanisms by which plants integrate light and SA signals in response to environmental changes, as well as the role of NPR1 in regulating plant photomorphogenesis, remain poorly understood. This study shows that SA promotes plant photomorphogenesis by regulating PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Specifically, NPR1 promotes photomorphogenesis under blue light by facilitating the degradation of PIF4 through light-induced polyubiquitination. NPR1 acts as a substrate adaptor for the CULLIN3-based E3 ligase, which ubiquitinates PIF4 at Lys129, Lys252, and Lys428, and leading to PIF4 degradation via the 26S proteasome pathway. Genetically, PIF4 is epistatic to NPR1 in the regulation of blue light-–induced photomorphogenesis, suggesting it acts downstream of NPR1. Furthermore, cryptochromes mediate the polyubiquitination of PIF4 by NPR1 in response to blue light by promoting the interaction and ubiquitination between NPR1 and PIF4. Transcriptome analysis revealed that, under blue light, NPR1 and PIF4 coordinately regulate numerous downstream genes related to light and auxin signaling pathways. Overall, these findings unveil a role for NPR1 in photomorphogenesis, highlighting a mechanism for post-translational regulation of PIF4 in response to blue light. This mechanism plays a pivotal role in the fine-tuning of plant development, enabling plants to adapt to complex environmental changes.
Project description:Phytochromes are evolutionarily conserved photoreceptors in bacteria, fungi, and plants. The prototypical phytochrome comprises an N-terminal photosensory module and a C-terminal histidine kinase signaling-output module. However, the plant phytochrome has been postulated to transduce light signals by interacting with a group of nodal Phytochrome-Interacting transcription Factors (PIFs) and triggering their degradation via the N-terminal photosensory module, while its C-terminal output module, including a Histidine Kinase-Related Domain (HKRD), is thought not to participate directly in signaling. Here, we show that the C-terminal module of Arabidopsis phytochrome B (PHYB) is unexpectedly sufficient to mediate the degradation of PIF3 and to induce a distinct set of PIF-regulated photosynthetic genes. These signaling functions require the HKRD and particularly its dimerization. A D1040V mutation, which disrupts the dimerization of HKRD and the interaction between the C-terminal module and PIF3, abrogates the early light signaling functions of PHYB in nuclear accumulation, photobody biogenesis, and PIF3 degradation. In contrast, disruption of the interaction between PIF3 and PHYB’s N-terminal photosensory module has little effect on PIF3 degradation. Together, this study provides novel insight into the central mechanism of early phytochrome signaling that the C-terminal signaling-output module of PHYB interacts with PIF3 in the nucleus to mediate PIF3 degradation by light.
Project description:Nonsteroidal anti-inflammatory drugs (NSAIDs), including salicylic acid (SA), target mammalian cyclooxygenases. In plants, SA is a defense hormone that regulates NON-EXPRESSOR OF PATHOGENESIS RELATED GENES 1 (NPR1), the master transcriptional regulator of immunity-related genes. We identify that the oxicam-type NSAIDs tenoxicam (TNX), meloxicam, and piroxicam, but not other types of NSAIDs, exhibit an inhibitory effect on immunity to bacteria and SA-dependent plant immune response. TNX treatment decreases NPR1 levels, independently from the proposed SA receptors NPR3 and NPR4. Instead, TNX induces oxidation of cytosolic redox status, which is also affected by SA and regulates NPR1 homeostasis. A cysteine labeling assay reveals that cysteine residues in NPR1 can be oxidized in vitro, leading to disulfide-bridged oligomerization of NPR1, but not in vivo regardless of SA or TNX treatment. Therefore, this study indicates that oxicam inhibits NPR1-mediated SA signaling without affecting the redox status of NPR1.
Project description:phytochrome B (phyB) acts as the red light photoreceptor and negatively regulates the growth-promoting factor PHYTOCHROME INTERACTING 4 (PIF4) through a direct physical interaction, which in turn changes the expression of a large number of genes. phyB-PIF4 module regulates a variety of biological and developmental processes in plants. In this study, we demonstrate that B-BOX PROTEIN 11 (BBX11) physically interacts with both phyB and PIF4. BBX11 negatively regulates PIF4 accumulation as well as its biochemical activity, consequently leading to the repression of PIF4-controlled genes' expression and promotion of photomorphogenesis in the prolonged red light. This study reveals a regulatory mechanism that mediates red light signal transduction and sheds a light on phyB-PIF4 module in promoting red light-dependent photomorphognenesis.
Project description:The plant immune hormone salicylic acid (SA) modulates transcriptional reprogramming via controlling the master transcriptional coactivator, NPR1. Here we examined the role of HECT-type ubiquitin ligases, UPL1 and UPL5, in SA/NPR1-dependent transcriptional control. We showed that UPL1 and UPL5 are essential regulators of SA-responsive genes, and regulate SA-induced transcriptional reprogramming in a NPR1-dependent manner. Four-week old Arabidopsis thaliana plants of wild-type Col-0, mutant upl1, mutant upl5, and mutant npr1-1 genotypes were germinated on soil in 100% relative humidity. Plants were continuously grown in an environmental chamber with 16/8 hour day/night light regime (120 mol m-2 s-1 light intensity), 21/18 degrees celcius day/night cycle and 65% relative humidity. 4-week-old plants were sprayed with water or 0.5 mM SA until all leaves were thoroughly covered with fine droplets, samples were collected after 24 hours treatment. In total two independent biological repeats were collected.
Project description:Salicylic acid (SA) and ethylene (ET) are two important plant hormones that regulate numerous plant growth, development, and stress response processes. Previous studies have suggested functional interplay of SA and ET in defense response, but precisely how these two hormones co-regulate plant growth and development processes remains unclear. The present findings reveal an antagonism between SA and ET in apical hook formation, a process that ensures successful soil emergence of dicotyledonous etiolated seedlings. Exogenous SA inhibited the ET-induced expression of HOOKLESS1 (HLS1) in a manner dependent on ETHYLENE INSENSITIVE3 (EIN3)/EIN3-LIKE1 (EIL1), the core transcription factors in the ET signaling pathway. We found that SA-activated NONEXPRESSER OF PR GENES1 (NPR1) physically interacted with EIN3 and interfered with the direct binding of EIN3 to target gene promoters, including the HLS1 promoter. Transcriptomic analysis further revealed that NPR1 and EIN3/EIL1 coordinately regulated subsets of genes that mediate plant growth and stress responses, suggesting that the interaction between NPR1 and EIN3/EIL1 might be an important mechanism for integrating the SA and ET signaling pathways in multiple physiological processes. Taken together, our findings shed light on the molecular mechanism underlying SA regulation of apical hook formation as well as the antagonism between SA and ET in early seedling establishment and possibly other physiological processes.
Project description:Global gene-expression profiles of WT Arabidopsis (Col-0), npr1-1, and hac1/5 were generated by RNA seq to study functional relationship between NPR1 and HACs in plant defense
Project description:Light and microRNAs (miRNAs) are key external and internal signals for plant development respectively. However the relationship between light signaling and miRNA biogenesis pathways remains unknown. Here we found that miRNA processer DCL1/HYL1 interacts with a basic helix–loop–helix (bHLH) transcription factor, phytochrome-interacting factor 4 (PIF4), which mediates the destabilization of DCL1 during dark-red light transition. PIF4 acts as a transcription factor for some miRNA genes and is necessary for the proper accumulation of miRNAs. DCL1/HYL1 and mature miRNAs play roles in the regulation of plant hypocotyl growth. These results uncovered a previously unknown crosstalk between miRNA biogenesis and red light signaling through the PIF4-dependent regulation of miRNA transcription and processing to affect red light-directed plant photomorhogenesis.
Project description:Activation of plant immunity is associated with dramatic transcriptome reprogramming to prioritise immune responses over normal cellular functions. Changes in gene expression are coordinated by the immune hormone salicylic acid (SA). Here we investigated the involvement of the E4 ubiquitin ligase UBE4/MUSE3 in SA-induced transcriptional reprogramming. We show that loss of UBE4 function results in amplified expression of SA-induced, NPR1-dependent gene expression. Twelve-day old Arabidopsis thaliana seedlings of wild-type Col-0, mutant ube4 (SAIL_713_A12) and mutant npr1-1 genotypes were grown on MS media supplemented with 1X Gamborg vitamins in an environmental chamber with 16/8 hour day/night light regime (120 mol m-2 s-1 light intensity) and 22 degrees Celcius. Seedlings were then transferred to 6-well plates and immersed in 10 ml of 0.5 mM SA or water. After 12 hours seedlings were harvested and for each treatment ~50 seedlings were pooled together into a single biological repeat. In total two independent biological repeats were collected. After harvesting seedlings were briefly dried on tissue and immediately frozen in liquid nitrogen until further analysis.