Plant biomechanics and resilience to environmental changes are controlled by specific lignin chemistries in each vascular cell type and morphotype

The biopolymer lignin is deposited in the cell walls of vascular cells and is essential for long-distance water conduction and structural support in plants. Different vascular cell types contain distinct and conserved lignin chemistries, each with specific aromatic and aliphatic substitutions. Yet, the biological role of this conserved and specific lignin chemistry in each cell type remains unclear. Here, we investigated the roles of this lignin biochemical specificity for cellular functions by producing single cell analyses for three cell morphotypes of tracheary elements, which all allow sap conduction but differ in their morphology. We determined that specific lignin chemistries accumulate in each cell type. Moreover, lignin accumulated dynamically, increasing in quantity and changing in composition, to alter the cell wall biomechanics during cell maturation. For similar aromatic substitutions, residues with alcohol aliphatic functions increased stiffness whereas aldehydes increased flexibility of the cell wall. Modifying this lignin biochemical specificity and the sequence of its formation impaired the cell wall biomechanics of each morphotype and consequently hindered sap conduction and drought recovery. Together, our results demonstrate that each sap-conducting vascular cell type distinctly controls their lignin biochemistry to adjust their biomechanics and hydraulic properties to face developmental and environmental constraints.

During the development of each vascular cell, specific lignin chemistries control their biomechanics and water conduction properties to face environmental changes.

IN A NUTSHELL Background: Lignin comprises multiple cell wall–localized aromatic polymers that are essential for vascular plants to conduct water and strengthen their organs. It has long been thought that lignin was randomly and nonspecifically assembled to provide mechanical strengthening and waterproofing to cells by filling-up the empty spaces in the cell walls. However, the different cell types and morphotypes forming the different sap-conducting pipes and their cell wall layers (inner vs. outer layer) exhibit specific lignin chemistries that are conserved among plant species. We, therefore, investigated the function of these specific lignin chemistries at the cell and cell wall layer levels for the different sap-conducting pipes in plants. Question: What is the function of a specific lignin chemistry for the different plant sap-conducting pipe cells? Can changes in the lignin chemistry of sap-conducting cells affect their hydraulic capacity when facing environmental conditions such as drought? Findings: We answered these questions by changing lignin levels and composition, using drugs to block lignin formation, and/or genetic engineering to switch off genes, in three complementary systems: (1) isolated cells grown in test tubes that we can trigger to become sap conduits, (2) annual plants, and (3) hardwood trees. We show that lignin chemistry is specific to each cell morphotype and changes during cell maturation, modifying the amount of lignin, the chemical composition of lignin units, and the position of these units in the longer polymer. These specific lignin chemistries are required for the proper function of each cell morphotype to properly conduct the sap and strengthen plant organs. Modifying the amount, the composition, and the time when specific units with distinct chemistry are incorporated in lignin of each cell morphotype has dramatic effects, causing defects in sap conduit hydraulic and biomechanical properties. The ratio between the different chemical units of lignin needs to be fine-tuned to adjust plant sap conduction and mechanical strengthening. Thus, changes in the proportion of lignin units with distinct chemistries confer different hydraulic and mechanical properties enabling plants to better resist and/or recover from drought. We also revealed that increases in the proportion of lignin units with aldehyde modulate plant pipe hydraulic and mechanical properties. Next steps: We are now working to identify and understand the molecular mechanisms that control the formation of specific lignin chemistries in distinct sites and times during the development of the different cell wall layers in each cell type and morphotype.     

Epigenetic Silencing of CHOP Expression by the Histone Methyltransferase EHMT1 Regulates Apoptosis in Colorectal Cancer Cells

Colorectal cancer (CRC) has a high mortality rate among cancers worldwide. To reduce this mortality rate, chemotherapy (5-fluorouracil, oxaliplatin, and irinotecan) or targeted therapy (bevacizumab, cetuximab, and panitumumab) has been used to treat CRC. However, due to various side effects and poor responses to CRC treatment, novel therapeutic targets for drug development are needed. In this study, we identified the overexpression of EHMT1 in CRC using RNA sequencing (RNA-seq) data derived from TCGA, and we observed that knocking down EHMT1 expression suppressed cell growth by inducing cell apoptosis in CRC cell lines. In Gene Ontology (GO) term analysis using RNA-seq data, apoptosis-related terms were enriched after EHMT1 knockdown. Moreover, we identified the CHOP gene as a direct target of EHMT1 using a ChIP (chromatin immunoprecipitation) assay with an anti-histone 3 lysine 9 dimethylation (H3K9me2) antibody. Finally, after cotransfection with siEHMT1 and siCHOP, we again confirmed that CHOP-mediated cell apoptosis was induced by EHMT1 knockdown. Our findings reveal that EHMT1 plays a key role in regulating CRC cell apoptosis, suggesting that EHMT1 may be a therapeutic target for the development of cancer inhibitors.     

Greater subchondral vBMD at the tibia is observed between 1 and 5 years of anterior cruciate ligament injury

Objectives:This study aimed to determine if differences exist in tibial subchondral bone and muscle imbalances between individuals with and without an Anterior Cruciate Ligament (ACL) repair within the past 1 to 5 years (median 3 years).Methods:Fifteen individuals (ages 18-23 years) that had a unilateral ACL repair with no contralateral knee injuries and 15 age- and sex-matched controls (no prior knee injuries) were recruited to participate. Subchondral bone was measured using peripheral quantitative computed tomography (pQCT) distal to the tibial plateau. Muscle force, power, and force efficiency were measured using single leg jumps performed on a force platform.Results:Within subject analysis showed a greater subchondral vBMD in the injured versus uninjured legs of cases (278±11 mg/cm³ and 258±6 mg/cm³, respectively, mean±SD, p=0.01). Subchondral vBMD was greater on the injured leg of cases than controls (267±8 mg/cm³ and 237±8 mg/cm³, respectively, marginal mean±SE, p=0.01). No differences were observed between cases and controls for muscle force, power, or force efficiency.Conclusions:Greater subchondral bone mineral density was observed in participants between 1- and 5-years post-op. Given the results of this study and the known long-term effects of ACL injuries, future research must continue to focus on the prevention of these injuries.     

Multiplex TaqMan qPCR Assay for Detection,Identification, and Quantification of Three Sclerotinia Species

White mold (or Sclerotinia stem rot), caused by Sclerotinia species, is a major air, soil, or seed-transmitted disease affecting numerous crops and wild plants. Microscopic or culture-based methods currently available for their detection and identification are time-consuming, laborious, and often erroneous. Therefore, we developed a multiplex quantitative PCR (qPCR) assay for the discrimination, detection, and quantification of DNA collected from each of the three economically relevant Sclerotinia species, namely, S. sclerotiorum, S. minor, and S. nivalis. TaqMan primer/probe combinations specific for each Sclerotinia species were designed based on the gene sequences encoding aspartyl protease. High specificity and sensitivity of each probe were confirmed for sclerotium and soil samples, as well as pure cultures, using simplex and multiplex qPCRs. This multiplex assay could be helpful in detecting and quantifying specific species of Sclerotinia, and therefore, may be valuable for disease diagnosis, forecasting, and management.     

Induction of Apoptosis and Effect on the FAK/AKT/mTOR Signal Pathway by Evodiamine in Gastric Cancer Cells

Evodiamine isolated from Evodia rutaecarpa has been known to have anti-tumor activity against various cancer cell types. Although there have been reports showing the inhibitory effect of evodiamine on cell survival of gastric cancer cell, it is not clearly explained how evodiamine affects the expression and modification of proteins associated with apoptosis and upstream signal pathways. We confirmed the cytotoxic activity of evodiamine against AGS and MKN45 cells by a WST assay, cell morphological change, and clonogenic assay. The apoptotic cells were evaluated by Annexin V/PI analysis and Western blot and the expressions of apoptosis-related molecules were confirmed by Western blot. Evodiamine promoted apoptosis of AGS gastric cancer cells through both intrinsic and extrinsic signal pathways in a time- and dose-dependent manner. Evodiamine attenuated the expression of anti-apoptotic proteins, including Bcl-2, XIAP, and survivin, and elevated that of the pro-apoptotic protein Bax. Evodiamine also suppressed the FAK/AKT/mTOR signal pathway. Based on these results, we expect that the results from this study will further elucidate our understanding of evodiamine as an anti-cancer drug.     

Parkin drives pS65‐Ub turnover independently of canonical autophagy in Drosophila

Parkinson''s disease‐related proteins, PINK1 and Parkin, act in a common pathway to maintain mitochondrial quality control. While the PINK1‐Parkin pathway can promote autophagic mitochondrial turnover (mitophagy) following mitochondrial toxification in cell culture, alternative quality control pathways are suggested. To analyse the mechanisms by which the PINK1–Parkin pathway operates in vivo, we developed methods to detect Ser65‐phosphorylated ubiquitin (pS65‐Ub) in Drosophila. Exposure to the oxidant paraquat led to robust, Pink1‐dependent pS65‐Ub production, while pS65‐Ub accumulates in unstimulated parkin‐null flies, consistent with blocked degradation. Additionally, we show that pS65‐Ub specifically accumulates on disrupted mitochondria in vivo. Depletion of the core autophagy proteins Atg1, Atg5 and Atg8a did not cause pS65‐Ub accumulation to the same extent as loss of parkin, and overexpression of parkin promoted turnover of both basal and paraquat‐induced pS65‐Ub in an Atg5‐null background. Thus, we have established that pS65‐Ub immunodetection can be used to analyse Pink1‐Parkin function in vivo as an alternative to reporter constructs. Moreover, our findings suggest that the Pink1‐Parkin pathway can promote mitochondrial turnover independently of canonical autophagy in vivo.