Biology subjects

Hicks, L. M.

Publications and source records attributed to Hicks, L. M..

6 recordsLinked to original sources

bioRxiv2024

Fluorescence Shadow Imaging of Hypsibius exemplaris Reveals Morphological Differences Between Sucrose- and CaCl2-Induced Osmobiotes

Tardigrades are renowned for their ability to survive a wide array of environmental stressors. In particular, tardigrades can curl in on themselves while losing a significant proportion of their internal water content to form a structure referred to as a tun. In surviving varying conditions, tardigrades undergo distinct morphological transformations that could indicate different underlying mechanisms of stress sensing and tolerance specific to the stress condition. Presently, methods to effectively distinguish between morphological transformations, including between tuns induced by different stress conditions, are lacking. Herein, a new approach for discriminating between tardigrade morphological states is developed and utilized to compare sucrose- and CaCl2-induced tuns. A novel method of shadow imaging with confocal laser scanning microscopy enabled production of three-dimensional renderings of tardigrades in various physiological states resulting in tardigrade volume measurements. Combining these measurements with qualitative morphological analysis using scanning electron microscopy revealed that sucrose- and CaCl2-induced tuns have distinct morphologies, including differences in the amount of water expelled during tun formation. Further, varying the concentration of the applied stressor did not affect the amount of water lost, pointing towards water expulsion being a controlled process that is adapted to the specific stressors. Summary StatementA novel method for volume measurements of biological specimens was developed and paired with scanning electron microscopy to allow for morphological comparisons between tardigrade osmobiotes.

physiology↗

bioRxiv2024

Phototropin connects blue light perception to starch metabolism in green algae

In photosynthetic organisms light acts as an environmental signal to control their development and physiology, and as energy source to drive the conversion of CO2 into carbohydrates used for growth or storage. The main storage carbohydrate in green algae is starch, which accumulates during the day and is broken down at night to meet cellular energy demands. The signalling role of light quality in the regulation of starch accumulation remains unexplored. Here, we identify PHOTOTROPIN-MEDIATED SIGNALLING KINASE 1 (PMSK1) as a key regulator of starch metabolism in Chlamydomonas reinhardtii. In its phosphorylated form (PMSK1-P), it activates GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE (GAP1), promoting starch biosynthesis. We show that blue light, perceived by PHOTOTROPIN, induces PMSK1 dephosphorylation that in turn represses GAP1 mRNA levels and reduces starch accumulation. These findings reveal a novel blue light-mediated signaling pathway that advances our understanding of photoreceptor-controlled carbon metabolism in microalgae. One-Sentence SummaryBlue light perception by PHOTOTROPIN triggers kinase-mediated signaling to inhibit starch accumulation in the green alga Chlamydomonas.

plant biology↗

bioRxiv2023

Chemobiosis reveals tardigrade tun formation is dependent on reversible cysteine oxidation

Tardigrades, commonly known as waterbears, are eight-legged microscopic invertebrates renowned for their ability to withstand extreme stressors, including high osmotic pressure, freezing temperatures, and complete desiccation. Limb retraction and expelling their internal water stores results in the tun state, greatly increasing their ability to survive. Emergence from the tun state and/or activity regain follows stress removal, where resumption of life cycle occurs as if stasis never occurred. However, the mechanism(s) through which tardigrades initiate tun formation is yet to be uncovered. Herein, we use chemobiosis to demonstrate that tardigrade tun formation is mediated by reactive oxygen species (ROS). We further reveal that tuns are dependent on reversible cysteine oxidation, and that this reversible cysteine oxidation is facilitated by the release of intracellular reactive oxygen species (ROS). We provide the first empirical evidence of chemobiosis and map the initiation and survival of tardigrades via osmobiosis, chemobiosis, and cryobiosis. In vivo electron paramagnetic spectrometry suggests an intracellular release of reactive oxygen species following stress induction; when this release is quenched through the application of exogenous antioxidants, the tardigrades can no longer survive osmotic stress. Together, this work suggests a conserved dependence of reversible cysteine oxidation across distinct tardigrade cryptobioses.

biochemistry↗

bioRxiv2022

High throughput peptidomics elucidates immunoregulatory functions of plant thimet oligopeptidase-directed proteostasis

Targeted proteolysis activities activated during the plant immune response catalyze the synthesis of stable endogenous peptides. Little is known about their biogenesis and biological roles. Herein, we characterize an Arabidopsis thaliana mutant top1top2 in which targeted proteolysis of immune-active peptides is drastically impaired during effector-triggered immunity (ETI). For effective ETI, the redox-sensitive thimet oligopeptidases TOP1 and TOP2 are required. Quantitative mass spectrometry-based peptidomics allowed differential peptidome profiling of wild type (WT) and top1top2 mutant at the early ETI stages. Biological processes of energy-producing and redox homeostasis were enriched, and TOPs were necessary to maintain the dynamics of ATP and NADP(H) accumulation in the plant during ETI. Subsequently, a set of novel TOPs substrates validated in vitro enabled the definition of the TOP-specific cleavage motif and informed an in-silico model of TOP proteolysis to generate bioactive peptide candidates. Several candidates, including those derived from proteins associated with redox metabolism, were confirmed in planta. The top1top2 background rescued WTs ETI deficiency caused by treatment with peptides derived from targeted proteolysis of the negative immune regulator FBR12, the reductive enzyme APX1, the isoprenoid pathway enzyme DXR, and ATP-subunit {beta}. These results demonstrate TOPs role in orchestrating the production and degradation of phytocytokines.

plant biology↗

bioRxiv2019

Receptor-Like Kinase Phosphorylation of Arabidopsis Heterotrimeric G-Protein Gα - Subunit AtGPA1

As molecular on-off switches, heterotrimeric G protein complexes, comprised of a G subunit and an obligate G{beta}{gamma} dimer, transmit extracellular signals received by G protein- coupled receptors (GPCRs) to cytoplasmic targets that respond to biotic and abiotic stimuli. Signal transduction is modulated by phosphorylation of GPCRs and G protein complexes. In Arabidopsis thaliana, the G subunit AtGPA1 is phosphorylated by the receptor-like kinase (RLK) BRI1-ASSOCIATED Kinase 1 (BAK1), but the extent that other RLKs phosphorylates AtGPA1 is unknown. We mapped 22 trans-phosphorylation sites on AtGPA1 by 12 RLKs hypothesized to act in the Arabidopsis G protein signaling pathway. Cis-phosphorylation sites on these RLKs were also identified. BRI1, BAK1, and SERK1 have been reported as Ser/Thr and Tyr dual specificity kinases. We identified 4 more dual specificity kinases: IOS1, PSY1R, PEPR1, and AT2G37050. Multiple sites are present in the core AtGPA1 functional units, including pSer52 and pThr53 of the conserved P-loop that directly binds nucleotide/phosphate, pThr164 and pSer175 from E helix in the intramolecular domain interface for nucleotide exchange and GTP hydrolysis, and pThr193 or pThr194 in Switch I (SwI) that coordinates nucleotide exchange and protein partner binding. Several AtGPA1 S/T phosphorylation sites are nucleotide-dependent phosphorylation patterns, such as S52/T53 in the P-loop and T193 and/or T194 in SwI.

plant biology↗

bioRxiv2018

Investigating the effect of Target of Rapamycin kinase inhibition on the Chlamydomonas reinhardtii phosphoproteome: from known homologs to new targets

O_LITarget of Rapamycin (TOR) kinase is a conserved regulator of cell growth whose activity is modulated in response to nutrients, energy and stress. Key proteins involved in the pathway are conserved in the model photosynthetic microalga Chlamydomonas reinhardtii, but the substrates of TOR kinase and downstream signaling network have not been elucidated. Our study provides a new resource for investigating the phosphorylation networks governed by the TOR kinase pathway in Chlamydomonas.\nC_LIO_LIWe used quantitative phosphoproteomics to investigate the effects of inhibiting Chlamydomonas TOR kinase on dynamic protein phosphorylation. Wild-type and AZD-insensitive Chlamydomonas strains were treated with TOR-specific chemical inhibitors (rapamycin, AZD8055 and Torin1), after which differentially affected phosphosites were identified.\nC_LIO_LIOur quantitative phosphoproteomic dataset comprised 2,547 unique phosphosites from 1,432 different proteins. Inhibition of TOR kinase caused significant quantitative changes in phosphorylation at 258 phosphosites, from 219 unique phosphopeptides.\nC_LIO_LIOur results include Chlamydomonas homologs of TOR signaling-related proteins, including a site on RPS6 with a decrease in phosphorylation. Additionally, phosphosites on proteins involved in translation and carotenoid biosynthesis were identified. Follow-up experiments guided by these phosphoproteomic findings in lycopene beta/epsilon cyclase showed that carotenoid levels are affected by TORC1 inhibition and carotenoid production is under TOR control in algae.\nC_LI

plant biology↗