Biology subjects

Smeekens, S.

Publications and source records attributed to Smeekens, S..

4 recordsLinked to original sources

bioRxiv2023

Sucrose-mediated translational stalling involves a conserved ribosomal pocket

Within eukaryotes, 20-50% of the mRNAs contain short open reading frames (uORFs) located upstream of the main ORF. A significant fraction of these uORFs encode conserved peptides (CPuORFs) that regulate translation in response to specific metabolites. A well-studied example includes uORF2 of the plant growth inhibiting transcription factor bZIP11. Elevated intracellular sucrose levels lead to ribosome stalling at the stop codon of uORF2, thus reducing bZIP11 protein synthesis. Similar examples can be found in bacteria and animals, e.g. on the bacterial TnaC and human CDH1-NPN* ORFs that both induce stalling at the stop codon when in the presence of tryptophan and the drug-like molecule PF846, respectively. In this study, we affinity-purified in vitro translated sucrose-stalled wheat ribosomes translating bZIP11-uORF2 and determined the ribosomes structures using cryo-electron microscopy. This revealed density inside a pocket in the ribosomal exit tunnel of the plant Triticum aestivum, that colocalizes with the binding locations of tryptophan and PF846 in E. coli and humans, respectively. We suggest this density corresponds to sucrose. Tryptophan and PF846 mode-of-action was previously proposed to inhibit release factor binding or function. Mutation of the uORF2 stop codon shows that its presence is crucial for sucrose-induced stalling, suggesting that the stalling only manifests during termination and not elongation. Moreover, the structural similarities with tryptophan-induced stalled ribosomes near the peptidyl transferase center indicates that an analogous mechanism of inhibition of release factor function is likely. Our findings suggest a conserved mechanistic framework across different organisms, wherein specific molecules interact with the nascent peptide and ribosome to modulate protein synthesis.

molecular biology↗

bioRxiv2022

Developmental shift in testosterone influence on prefrontal emotion control

A paradox of testosterone effects is seen in adolescents vs. adults in social emotional approach-avoidance behavior. During adolescence, high testosterone levels are associated with increased anterior prefrontal (aPFC) involvement in emotion control, whereas during adulthood this neuro-endocrine relation is reversed. Rodent work shows that, during puberty, testosterone transitions from a neuro-developmental to a social-sexual activating hormone. In this study, we explored whether this functional transition is also present in human adolescents and young adults. Using a prospective longitudinal design, we investigated the role of testosterone on neural control of social emotional behavior during the transitions from middle to late adolescence and into young adulthood. Seventy-one individuals (tested at ages 14, 17, and 20 years) performed an fMRI-adapted approach-avoidance (AA) task involving automatic and controlled actions in response to social emotional stimuli. In line with predictions from animal models, the effect of testosterone on aPFC engagement decreased between middle and late adolescence, and shifted into an activational role by young adulthood - impeding neural control of emotions. This change in testosterone function was accompanied by increased testosterone-modulated amygdala reactivity. These findings qualify the testosterone-dependent maturation of the prefrontal-amygdala circuit supporting emotion control during the transition from middle adolescence into young adulthood.

neuroscience↗

bioRxiv2022

Arabidopsis thaliana rosette growth habit is a photomorphogenic trait controlled by the TALE homeodomain protein ATH1 and involves TOR kinase

Here, we demonstrate that Arabidopsis rosette habit is a bona fide photomorphogenic trait controlled by the homeodomain protein ATH1. In light, ATH1 expression at the SAM is induced by broad wavelengths, mediated through multiple photoreceptors, and requires inactivation of COP1 and PIF photomorphogenesis inhibitors. Such induced ATH1 prevents elongation of rosette internodes by maintaining the rib zone area of the SAM in an inactive state. In the absence of light, Arabidopsis plants cannot complete seedling establishment after germination due to inactivity of the shoot apical meristem (SAM). Light requirement for SAM activation can be overcome by availability to the meristem of metabolizable sugars, such as sucrose. However, under these conditions plants fail to establish a typical compact rosette and display a caulescent growth habit. We show that this is due to insufficient expression of ATH1 at the SAM. ATH1 induction restores rosette habit in dark-grown plants through inhibition of PIF gene expression. Together, this suggests that a SAM-specific, double-negative ATH1-PIF feedback loop is at the basis of Arabidopsis rosette habit. Induction of ATH1 expression and restoration of rosette habit in darkness also occurs at increased levels of sucrose. Both sugar and light signals that induce ATH1 are mediated by TOR kinase. Overall, these results support a fundamental role for ATH1 in Arabidopsis rosette habit and further strengthen a role for TOR kinase as a central hub for integration of energy and light signals controlling organogenesis at the SAM.

plant biology↗

bioRxiv2020

Arabidopsis bZIP11 is a susceptibility factor during Pseudomonas syringae infection

AO_SCPLOWBSTRACTC_SCPLOWThe induction of plant nutrient secretion systems is critical for successful pathogen infection. Some bacterial pathogens, e.g. Xanthomonas species, use TAL (transcription activator-like) effectors to induce transcription of SWEET sucrose efflux transporters. Pseudomonas syringae pathovar (pv.) tomato strain DC3000 lacks TAL effectors, yet is able to induce multiple SWEETs in Arabidopsis thaliana by unknown mechanisms. Since bacteria require other nutrients besides sugars for efficient reproduction, we hypothesized that Pseudomonas may depend on host transcription factors involved in secretory programs to increase access to essential nutrients. Bioinformatic analyses identified the Arabidopsis basic-leucine zipper transcription factor bZIP11 as a potential regulator of nutrient transporters, including SWEETs and UmamiT amino acid transporters. Inducible downregulation of bZIP11 expression in Arabidopsis resulted in reduced growth of P. syringae pv. tomato strain DC3000, whereas inducible overexpression of bZIP11 resulted in increased bacterial growth, supporting the hypothesis that bZIP11 regulated transcription programs are essential for maximal pathogen titer in leaves. Our data are consistent with a model in which a pathogen alters host transcription factor expression upstream of secretory transcription networks to promote nutrient efflux from host cells.

plant biology↗