Biology subjects

Assmann, S. M.

Publications and source records attributed to Assmann, S. M..

8 recordsLinked to original sources

bioRxiv2026

Phosphovariants of the canonical heterotrimeric Gα protein, GPA1, differentially affect G protein activity and Arabidopsis development

Heterotrimeric G protein signaling downstream of receptor-like kinases (RLKs) is an emerging and important signal transduction mechanism in plants. However, little is known about the effects of phosphorylation events on the function of the canonical G subunit, GPA1. That several known phosphosites reside within important nucleotide co-factor binding sites suggests a role of phosphorylation in modulating the GTP/GDP binding and hydrolysis cycle of GPA1. To mimic and assess the effects of GPA1 phosphorylation, we created ten different phosphovariants of GPA1 and then comprehensively measured in vitro biochemical activity, in vivo protein-protein interactions, and developmental phenotypes of phosphomutant-complemented Arabidopsis gpa1 null mutants. Our assays confirmed both that phosphovariants of S49 and S52 in the G1 nucleotide binding motif impair GTP and GDP binding, and that the gpa1 morphological phenotypes of reduced etiolated hypocotyl elongation, rounded leaves, and short round flowers are not dependent on the nucleotide status of GPA1. Phosphomimetic mutations at S49, S52, T53, and T164 each exhibited a distinct pattern in complementing gpa1 phenotypes, indicating that GPA1 employs multiple signaling states based on phosphorylation status. The multi-state hypothesis provides a key insight into the mechanism by which a limited repertoire of plant heterotrimeric G protein subunits can transduce a wide variety of signals with exquisite specificity.

plant biology↗

bioRxiv2024

Manipulating rice canonical Gα and extra-large G protein subunits for improved agronomic traits

Rice productivity is fundamentally linked to its architecture, governed by signaling networks including those based on heterotrimeric G proteins. In this study, we investigated the individual gene impacts and genetic interactions of the canonical G gene (RGA1), and the non-canonical extra-large G genes (OsXLG1, OsXLG3a, OsXLG3b, OsXLG4) in controlling plant architecture. We generated OsXLG mutants using CRISPR/Cpf1 gene editing in Nipponbare (WT) and d1, a Nipponbare null mutant of RGA1. We then phenotyped 25 different genotypes in the greenhouse for 19 different agronomic traits. In wild type (WT), mutations in RGA1, OsXLG3a, OsXLG3b, or OsXLG4, as well as any combination of G genes, resulted in a shorter stature, a desirable trait. Mutations in OsXLG1 and OsXLG4 increased the number of spikelets and grains per panicle, showcasing advantageous traits that led to higher yield. Mutations in OsXLG3a, OsXLG3b, any combination of OsXLGs, or any OsXLG combined with the d1 mutation, reduced seed production and yield. Flag leaf width was the only trait influenced solely by RGA1. RGA1 transcript abundance in the osxlg mutants was positively correlated with height, culm length, panicle exsertion, and harvest index, implicating OsXLG regulation of RGA1 expression as an underlying mechanism. Overall, increased RGA1 expression is correlated with more favorable reproductive traits but less favorable vegetative traits. Our study reveals the complex interaction of RGA1 and OsXLGs within the signaling networks that shape rice architecture, from vegetative to post-harvest stages. Our results suggest modulation of RGA1, OsXLG1, OsXLG3a, or OsXLG4 expression as strategies to enhance yield.

plant biology↗

bioRxiv2023

Oryza CLIMtools: An Online Portal for InvestigatingGenome-Environment Associations in Rice

Modern crop varieties display a degree of mismatch between their current distributions and the suitability of the local climate for their productivity. To this end, we present Oryza CLIMtools (https://gramene.org/CLIMtools/oryza_v1.0/), the first resource for pan-genome prediction of climate-associated genetic variants in a crop species. Oryza CLIMtools consists of interactive web-based databases that allow the user to: i) explore the local environments of traditional rice varieties (landraces) in South-Eastern Asia, and; ii) investigate the environment by genome associations for 658 Indica and 283 Japonica rice landrace accessions collected from georeferenced local environments and included in the 3K Rice Genomes Project. We exemplify the value of these resources, identifying an interplay between flowering time and temperature in the local environment that is facilitated by adaptive natural variation in OsHD2 and disrupted by a natural variant in OsSOC1. Prior QTL analysis has suggested the importance of heterotrimeric G proteins in the control of agronomic traits. Accordingly, we analyzed the climate associations of natural variants in the different heterotrimeric G protein subunits. We identified a coordinated role of G proteins in adaptation to the prevailing Potential Evapotranspiration gradient and their regulation of key agronomic traits including plant height and seed and panicle length. We conclude by highlighting the prospect of targeting heterotrimeric G proteins to produce crops that are climate resilient.

plant biology↗

bioRxiv2023

Influence of expression protocols on Gα biochemical activity: kinetics of plant and mammalian G protein cycles

Heterotrimeric G proteins are a class of signal transduction complexes with broad roles in human health and agriculturally important plant traits. In the classic paradigm, guanine nucleotide binding to the G subunit regulates the activation status of the complex. Using the Arabidopsis thaliana G subunit, GPA1, we developed a rapid StrepII-tag mediated purification method that facilitates isolation of protein with increased enzymatic activities as compared to conventional methods, and is demonstrably also applicable to mammalian G subunits. We subsequently utilized domain swaps of GPA1 and human GNAO1 to demonstrate the instability of recombinant GPA1 is a function of the interaction between the Ras and helical domains, and can be partially uncoupled from the rapid nucleotide binding kinetics displayed by GPA1.

biochemistry↗

bioRxiv2021

Adaptive growth homeostasis in response to drought in Iberian Arabidopsis accessions

Natural genetic variation influences plant responses to environmental stressors. However, the extent to which such variation underlies plastic versus homeostatic response phenotypes deserves more attention. We quantified the extent of drought-induced changes in leaf area in a set of Iberian Arabidopsis accessions and then performed association studies correlating plasticity and homeostasis in this phenotype with genomic and transcriptomic variation. Drought-induced plastic reductions in relative leaf area typified accessions originating from productive environments. In contrast, homeostasis in relative leaf area typified accessions originating from unproductive environments. Genome-Wide Association Studies (GWAS), Transcriptome Wide Association Studies (TWAS), and expression GWAS (eGWAS) highlighted the importance of auxin-related processes in conferring leaf area plasticity. Homeostatic responses in relative leaf area were associated with a diverse gene set and positively associated with a higher intrinsic water use efficiency (WUEi), as confirmed in a TWAS metanalysis of previously published {delta}13C measurements. Thus, we have identified not only candidate "plasticity genes" but also candidate "homeostasis genes" controlling leaf area. Our results exemplify the value of a combined GWAS, TWAS, and eGWAS approach to identify mechanisms underlying phenotypic responses to stress. HighlightInformation on phenotype, genotype, and transcript abundance is integrated to identify candidate plasticity and homeostasis genes and processes associated with local adaptation to drought stress in Arabidopsis accessions of the Iberian Peninsula.

evolutionary biology↗

bioRxiv2020

A G protein-coupled receptor-like module regulates Cellulose Synthase secretion from the endomembrane system in Arabidopsis

Cellulose synthesis is essential for plant morphology, water transport and defense, and provides raw material for biomaterials and fuels. Cellulose is produced at the plasma membrane by Cellulose Synthase (CESA) protein complexes (CSCs). CSCs are assembled in the endomembrane system and then trafficked from the Golgi apparatus and trans-Golgi Network (TGN) to the plasma membrane. Since CESA enzymes are only active in the plasma membrane, control of CSC secretion is a critical step in the regulation of cellulose synthesis. However, the regulatory framework for CSC secretion is not clarified. In this study, we identify members of a family of seven transmembrane domain-containing proteins (7TMs) as important for cellulose production during cell wall integrity stress. 7TM proteins are often associated with guanine nucleotide-binding protein (G) protein signalling and mutants in several of the canonical G protein complex components phenocopied the 7tm mutant plants. Unexpectedly, the 7TM proteins localized to the Golgi apparatus/TGN where they interacted with the G protein complex. Here, the 7TMs and G proteins regulated CESA trafficking, but did not affect general protein secretion. Furthermore, during cell wall stress, 7TMs localization was biased towards small CESA-containing vesicles, specifically associated with CSC trafficking. Our results thus outline how a G protein-coupled module regulates CESA trafficking and reveal that defects in this process lead to exacerbated responses upon exposure to cell wall integrity stress.

plant biology↗

bioRxiv2020

Structure-seq2 probing of RNA structure upon amino acid starvation reveals both known and novel RNA switches in Bacillus subtilis

RNA structure influences numerous processes in all organisms. In bacteria, these processes include transcription termination and attenuation, small RNA and protein binding, translation initiation, and mRNA stability, and can be regulated via metabolite availability and other stresses. Here we use Structure-seq2 to probe the in vivo RNA structurome of Bacillus subtilis grown in the presence and absence of amino acids. Our results reveal that amino acid starvation results in lower overall dimethyl sulfate (DMS) reactivity of the transcriptome, indicating enhanced protection owing to protein binding or RNA structure. Starvation-induced changes in DMS reactivity correlated inversely with transcript abundance changes. This correlation was particularly pronounced in genes associated with the stringent response and CodY regulons, which are involved in adaptation to nutritional stress, suggesting that RNA structure contributes to transcript abundance change in regulons involved in amino acid metabolism. Structure-seq2 accurately reported on four known amino acid-responsive riboswitches: T-box, SAM, glycine, and lysine riboswitches. Additionally, we discovered a transcription attenuation mechanism that reduces yfmG expression when amino acids are added to the growth medium. We also found that translation of a leader peptide (YfmH) encoded just upstream of yfmG regulates yfmG expression. Our results are consistent with a model in which a slow rate of yfmH translation caused by limitation of the amino acids encoded in YfmH prevents transcription termination in the yfmG leader region by favoring formation of an overlapping antiterminator structure. This novel RNA switch offers a way to simultaneously monitor the levels of multiple amino acids.

microbiology↗

bioRxiv2019

Molecular changes in Mesembryanthemum crystallinum guard cells underlying the C3 to CAM transition

Crassulacean acid metabolism (CAM) is a specialized type of photosynthesis: stomata close during the day, enhancing water conservation, and open at night, allowing CO2 uptake. Mesembryanthemum crystallinum (common ice plant) is a facultative CAM species that can shift from C3 photosynthesis to CAM under salt or drought stresses. However, the molecular mechanisms underlying the stress induced transition from C3 to CAM remain unknown. Here we determined the transition time from C3 to CAM in M. crystallinum under salt stress. In parallel, single-cell-type transcriptomic profiling by 3-mRNA sequencing was conducted in guard cells to determine the molecular changes in this key cell type during the transition. In total, 495 transcripts showed differential expression between control and salt-treated samples during the transition, including 285 known guard cell genes, seven CAM-related genes, 18 transcription factors, and 185 other genes previously not found to be expressed in guard cells. PEPC1 and PPCK1, which encode key enzymes of CAM photosynthesis, were up-regulated in guard cells after seven days of salt treatment, indicating that guard cells themselves can transition from C3 to CAM. This study provides important information towards introducing CAM stomatal behavior into C3 crops to enhance water use efficiency.\n\nSummary statementWe determined the timing of salt induced transition of common ice plant from C3 to CAM and identified transcriptomic changes during the transition. The data support the notion that guard cells themselves can transition from C3 to CAM.

plant biology↗