The tRNA thiolation-mediated translational control is essential for plant immunity.

Plants have evolved sophisticated mechanisms to regulate gene expression to activate immune responses against pathogen infections. However, how the translation system contributes to plant immunity is largely unknown. The evolutionarily conserved thiolation modification of transfer RNA (tRNA) ensures efficient decoding during translation. Here, we show that tRNA thiolation is required for plant immunity in Arabidopsis. We identify a cgb mutant that is hyper-susceptible to the pathogen Pseudomonas syringae. CGB encodes ROL5, a homolog of yeast NCS6 required for tRNA thiolation. ROL5 physically interacts with CTU2, a homolog of yeast NCS2. Mutations in either ROL5 or CTU2 result in loss of tRNA thiolation. Further analyses reveal that both transcriptome and proteome reprogramming during immune responses are compromised in cgb. Notably, the translation of salicylic acid receptor NPR1 is reduced in cgb, resulting in compromised salicylic acid signaling. Our study not only reveals a regulatory mechanism for plant immunity but also uncovers an additional biological function of tRNA thiolation.

The ATR-WEE1 kinase module promotes SUPPRESSOR OF GAMMA RESPONSE 1 translation to activate replication stress responses.

DNA replication stress threatens genome stability and is a hallmark of cancer in humans. The evolutionarily conserved kinases ATR (ATM and RAD3-related) and WEE1 are essential for the activation of replication stress responses. Translational control is an important mechanism that regulates gene expression, but its role in replication stress responses is largely unknown. Here we show that ATR-WEE1 control the translation of SUPPRESSOR OF GAMMA RESPONSE 1 (SOG1), a master transcription factor required for replication stress responses in Arabidopsis thaliana. Through genetic screening, we found that the loss of GENERAL CONTROL NONDEREPRESSIBLE 20 (GCN20) or GCN1, which function together to inhibit protein translation, suppressed the hypersensitivity of the atr or wee1 mutant to replication stress. Biochemically, WEE1 inhibits GCN20 by phosphorylating it; phosphorylated GCN20 is subsequently polyubiquitinated and degraded. Ribosome profiling experiments revealed that that loss of GCN20 enhanced the translation efficiency of SOG1, while overexpressing GCN20 had the opposite effect. The loss of SOG1 reduced the resistance of wee1 gcn20 to replication stress, whereas overexpressing SOG1 enhanced the resistance to atr or wee1 to replication stress. These results suggest that ATR-WEE1 inhibits GCN20-GCN1 activity to promote the translation of SOG1 during replication stress. These findings link translational control to replication stress responses in Arabidopsis.

RAD51 supports DMC1 by inhibiting the SMC5/6 complex during meiosis.

Meiosis is a fundamental process for sexual reproduction in most eukaryotes and the evolutionarily conserved recombinases RADiation sensitive51 (RAD51) and Disrupted Meiotic cDNA1 (DMC1) are essential for meiosis and thus fertility. The mitotic function of RAD51 is clear, but the meiotic function of RAD51 remains largely unknown. Here we show that RAD51 functions as an interacting protein to restrain the Structural Maintenance of Chromosomes5/6 (SMC5/6) complex from inhibiting DMC1. We unexpectedly found that loss of the SMC5/6 partially suppresses the rad51 knockout mutant in terms of sterility, pollen inviability, and meiotic chromosome fragmentation in a DMC1-dependent manner in Arabidopsis thaliana. Biochemical and cytological studies revealed that the DMC1 localization in meiotic chromosomes is inhibited by the SMC5/6 complex, which is attenuated by RAD51 through physical interactions. This study not only identified the long-sought-after function of RAD51 in meiosis but also discovered the inhibition of SMC5/6 on DMC1 as a control mechanism during meiotic recombination.

A novel WEE1 pathway for replication stress responses.

DNA replication stress poses a severe threat to genome stability and is a hallmark of cancer as well as a target for cancer therapy. It is well known that the evolutionarily conserved protein kinase WEE1 regulates replication stress responses by directly phosphorylating and inhibiting the major cell cycle driver CDKs in many organisms. Here, we report a novel WEE1 pathway. We found that Arabidopsis WEE1 directly interacts with and phosphorylates the E3 ubiquitin ligase FBL17 that promotes the degradation of CDK inhibitors. The phosphorylated FBL17 is further polyubiquitinated and degraded, thereby leading to the accumulation of CDK inhibitors and the inhibition of CDKs. In strong support for this model, either loss of function of FBL17 or overexpression of CDK inhibitors suppresses the hypersensitivity of the wee1 mutant to replication stress. Intriguingly, human WEE1 also phosphorylates and destabilizes the FBL17 equivalent protein SKP2, indicating that this is a conserved mechanism. This study reveals that the WEE1-FBL17/SKP2-CKIs-CDKs axis is a molecular framework for replication stress responses, which may have clinical implications because the WEE1 inhibitor AZD1775 is currently in phase II clinical trial as an anticancer drug.

High-efficiency As(III) oxidation and electrocoagulation removal using hematite with a charge-discharge technique.

Arsenite (As(III)) is generally removed by adsorption or coprecipitation after being oxidized to arsenate (As(V)). Electrocoagulation is regarded as an effective and environment-friendly method for arsenic (As) removal from wastewater. However, some disadvantages including the passivation of electrode and high energy consumption limit its wide application. Herein, a multi-cycle galvanostatic charge-discharge technique was employed to remove aqueous As(III) using hematite prepared through a microwave-assisted hydrothermal reaction. When charge-discharge experiments were conducted at the potential window of -0.8-0 V (vs. SCE) in As(III) solution with NaCl as the background electrolyte, ClO- intermediates and the counter electrode at high potential contributed much to As(III) oxidation. As(V) was adsorbed on ferrihydrite generated from the re-oxidation of released Fe2+, forming FeAsO4 precipitate. A higher removal ratio of As(T) was achieved at initial pH 7.0 compared with that at initial pH 5.0 and 9.0. When the hematite mass was 4, 10 and 15 mg, the removal ratio of As(T) reached 55.2%, 79.6% and 98.6% after 600 cycles of charge-discharge. The periodic redox reactions of hematite electrodes occurred in each charge-discharge process, effectively avoiding the passivation of electrode. Additionally, the electrochemical system can be used as a supercapacitor for power output. The present work provides a novel strategy for high-efficiency As(III) immobilization and removal from aqueous solution.

Platelet-neutrophil interaction aggravates vascular inflammation and promotes the progression of atherosclerosis by activating the TLR4/NF-κB pathway.

Platelet-neutrophil interaction is well known for its role in inflammatory diseases; however, its biological role in atherosclerosis (AS) progression remains unclear. Human peripheral blood neutrophils were obtained to compare toll-like receptor 4 (TLR4), tumor necrosis factor α (TNF-α), interleukin (IL)-1ß and myeloid-related proteins 8/14 (Mrp8/14) levels in 22 AS patients with those in 18 healthy controls using quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). Meanwhile, mouse marrow neutrophils subjected to different treatment were collected for the ELISA assay, cell apoptosis, and Western blot analysis. Normal diet or high-fat diet ApoE-/- mice with or without administration of Mrp8/14 antagonist paquinimod were used for plasma collection to measure total cholesterol, triglycerides, low-density lipoprotein cholesterol and high-density lipoprotein cholesterol, TNF-α, IL-1ß, Mrp8/14, TLR4, and nuclear factor (NF)-κB p65 levels. The results showed that Mrp8/14 and TLR4-mediated inflammatory pathway was activated in neutrophils of AS patients. In vitro experiments demonstrated that platelet-neutrophil interaction promoted the Mrp8/14 release and inhibited neutrophil apoptosis via P-selectin. Furthermore, platelet-neutrophil interaction upregulated TLR4/myeloid differentiation factor 88/NF-κB pathway. Conversely, Mrp8/14/TLR4/NF-κB interference alleviated AS progression. In conclusion, Mrp8/14/TLR4/NF-κB activated by platelet-neutrophil interaction is an important inflammatory signaling pathway for AS pathogenesis.

Negative regulator of E2F transcription factors links cell cycle checkpoint and DNA damage repair.

DNA damage poses a serious threat to genome integrity and greatly affects growth and development. To maintain genome stability, all organisms have evolved elaborate DNA damage response mechanisms including activation of cell cycle checkpoints and DNA repair. Here, we show that the DNA repair protein SNI1, a subunit of the evolutionally conserved SMC5/6 complex, directly links these two processes in Arabidopsis SNI1 binds to the activation domains of E2F transcription factors, the key regulators of cell cycle progression, and represses their transcriptional activities. In turn, E2Fs activate the expression of SNI1, suggesting that E2Fs and SNI1 form a negative feedback loop. Genetically, overexpression of SNI1 suppresses the phenotypes of E2F-overexpressing plants, and loss of E2F function fully suppresses the sni1 mutant, indicating that SNI1 is necessary and sufficient to inhibit E2Fs. Altogether, our study revealed that SNI1 is a negative regulator of E2Fs and plays dual roles in DNA damage responses by linking cell cycle checkpoint and DNA repair.