Biology subjects

Duncan, O.

Publications and source records attributed to Duncan, O..

11 recordsLinked to original sources

bioRxiv2023

Characterization of DNA methylation reader proteins of Arabidopsis thaliana

In plants, cytosine DNA methylation (mC) is largely associated with transcriptional repression of transposable elements, but it can also be found in the body of expressed genes, referred to as gene body methylation (GbM). GbM is correlated with ubiquitously expressed genes, however its function, or absence thereof, is highly debated. The different output that mC can have raises questions as to how it is interpreted - or read - differently in these sequence and genomic contexts. To screen for potential mC binding proteins, we performed an unbiased DNA affinity pull-down assay combined with quantitative mass spectrometry using methylated DNA probes for each DNA sequence context. All mC readers known to date were found to preferentially bind to the methylated probes, along with a range of new mC binding protein candidates. Functional characterization of these mC readers, focused on the MBD and SUVH families, was undertaken by ChIP-seq mapping of genome-wide binding sites, their protein interactors, and the impact of high-order mutations on transcriptomic and epigenomic profiles. Together, this highlighted specific context preferences for these proteins, and in particular the ability of MBD2 to bind specifically to GbM. This comprehensive analysis of Arabidopsis mC readers emphasizes the complexity and interconnectivity between DNA methylation and chromatin remodelling processes in plants.

plant biology↗

bioRxiv2021

Enzymes degraded under high light maintain proteostasis by transcriptional regulation in Arabidopsis

Photo-inhibitory high light stress in Arabidopsis leads to increases in markers of protein degradation and transcriptional upregulation of proteases and proteolytic machinery, but proteostasis is largely maintained. We find significant increases in the in vivo degradation rate for specific molecular chaperones, nitrate reductase, glyceraldehyde-3 phosphate dehydrogenase, and phosphoglycerate kinase and other plastid, mitochondrial, peroxisomal, and cytosolic enzymes involved in redox shuttles. Coupled analysis of protein degradation rates, mRNA levels, and protein abundance reveal that 57% of the nuclear-encoded enzymes with higher degradation rates also had high light-induced transcriptional responses to maintain proteostasis. In contrast, plastid-encoded proteins with enhanced degradation rates showed decreased transcript abundances and must maintain protein abundance by other processes. This analysis reveals a light-induced transcriptional program for nuclear-encoded genes, beyond the regulation of PSII D1 subunit and the function of PSII, to replace key protein degradation targets in plants and ensure proteostasis under high light stress.

plant biology↗

bioRxiv2021

Protein turnover in the developing Triticum aestivum grain

Protein abundance in cereal grains is determined by the relative rates of protein synthesis and protein degradation during grain development. Through combining in vivo stable isotope labelling and in-depth quantitative proteomics, we have measured the turnover of 1400 different types of proteins during wheat grain development. We demonstrate that there is a spatiotemporal pattern to protein turnover rates which explain part of the variation in protein abundances that is not attributable to differences in wheat gene expression. We show that approximately 20% of total grain ATP production is used for grain proteome biogenesis and maintenance, and nearly half of this budget is invested exclusively in storage protein synthesis. We calculate that 25% of newly synthesized storage proteins are turned over during grain development rather than stored. This approach to measure protein turnover rates at proteome scale reveals how different functional categories of grain proteins accumulate, calculates the costs of protein turnover during wheat grain development and identifies the most and the least stable proteins in the developing wheat grain.

plant biology↗

bioRxiv2021

Autophagy promotes photomorphogenesis during seedling development in Arabidopsis in carbon limiting conditions

Autophagy is a conserved catabolic process that plays an essential role under nutrient starvation condition and influences different developmental processes. We observed that seedlings of autophagy mutants (atg2, atg5, atg7, and atg9) germinated in the dark showed delayed chloroplast development following illumination. The delayed chloroplast development was characterized by a decrease in photosynthetic and chlorophyll biosynthetic proteins, lower chlorophyll content, reduced chloroplast size, and increased levels of proteins involved in lipid biosynthesis. Confirming the biological impact of these differences, photosynthetic performance was impaired in autophagy mutants 12h post illumination. We investigated if the delayed chloroplast development could be explained by lower lipid import to the chloroplast or lower triglyceride (TAG) turnover. We observed that the limitations in the chloroplast lipid import imposed by trigalactosyldiacylglycerol1 are unlikely to explain the delay in photomorphogenesis. However, we found that lower TAG mobility in the triacylglycerol lipase mutant sugardependent1 significantly affected photomorphogenesis. Moreover, we showed that lower levels of carbon resources exacerbated the delay in photomorphogenesis whereas higher levels of carbon resources had an opposite effect. This work provides evidence that autophagic process operate during de-etiolation in a manner that contributes to photomorphogenesis through increasing lipid turnover to physically or energetically sustain photomorphogenesis.

plant biology↗

bioRxiv2021

Large scale measurement of protein synthesis rates over the diurnal cycle reveal pathway specific regulation of translation

Plants have a diurnal separation of metabolic fluxes and a need for differential maintenance of protein machinery in the day and night. To directly assess aggregate protein translation and degradation for specific proteins and to estimate the ATP investment involved, the individual rates of synthesis and degradation of hundreds of different proteins were measured in Arabidopsis thaliana rosettes. This quantification of translation control through incorporation of heavy hydrogen into newly synthesised protein confirmed that most protein synthesis occurs during the day hours (~3:1 day:night), but revealed it was highly divergent across functional categories. Proteins involved in photosynthesis, especially components of the light harvesting complexes, were synthesized much faster in the day (~10:1), while the protein components of carbon metabolism and vesicle trafficking were translated at similar rates day or night. Comparison of aggregate translation with a range of comparable studies using polysomal loading of transcripts or transcript abundance suggests that translational control is a major contributor to effective gene expression over the diurnal cycle. Diurnal protein degradation rate was observed to be tightly coordinated with protein synthesis rate as few leaf proteins changed in abundance despite reduced translation rates during the night. The direct, quantitative and aggregate analysis of protein synthesis provides an integration of transcriptional, post-transcriptional and translational control of leaf proteome homeostasis and an opportunity to assess the ATP investments involved. The data reveals how the pausing of photosystem synthesis and degradation at night allows the redirection of a decreased energy budget to a selective night-time maintenance schedule. One sentence summaryAdvances in collection and processing of stable isotope incorporation data has allowed characterisation of differential protein synthesis rates over the diurnal cycle which reveal both global and specific translational regulation programs of core biochemical pathways.

plant biology↗

bioRxiv2021

In vivo homopropargylglycine incorporation enables nascent protein tagging, isolation and characterisation from Arabidopsis thaliana

Determining which proteins are actively synthesised at a given point in time and extracting them for analysis is important to understand plant responses. Here we show that the methionine (Met) analogue homopropargylglycine (HPG) enables BONCAT (Bio-Orthogonal Non-Canonical Amino acid Tagging) of proteins being synthesised in Arabidopsis plants or cell cultures, facilitating their click-chemistry enrichment for analysis. The sites of HPG incorporation could be confirmed by peptide mass spectrometry at Met-sites throughout protein AA sequences and correlation with independent studies of protein labelling with 15N verified the data. We provide evidence that HPG-based BONCAT tags nascent plant proteins more efficiently than azidohomoalanine (AHA)-based BONCAT in Arabidopsis and show that AHAs induction of Met metabolism and greater inhibition of cell growth rate than HPG likely limits AHA incorporation at Met sites in Arabidopsis. We show HPG-based BONCAT provides a verifiable method for determining which plant proteins are being synthesised at a given time point and enriches new protein molecules from the bulk protein pool for identification, quantitation and subsequent biochemical analysis. Enriched nascent polypeptides were found to contain significantly fewer common post-translationally modified residues than the same proteins from whole plant extracts, providing evidence for age-related accumulation of PTMs in plants.

plant biology↗

bioRxiv2020

Increased wheat protein content via introgression of a HMW glutenin selectively reshapes the grain proteome

Introgression of a high molecular weight glutenin subunit (HMW-GS) gene, 1Ay21*, into commercial wheat cultivars increased overall grain protein content and bread-making quality by unknown mechanisms. As well as increased abundance of 1Ay HMW-GS, 115 differentially expressed proteins (DEPs) were discovered between three cultivars and corresponding introgressed near-isogenic lines (NILs). Functional category analysis showed that the DEPs were predominantly other storage proteins, and proteins involved in protein synthesis, protein folding, protein degradation, stress response and grain development. Nearly half the genes encoding the DEPs showed strong co-expression patterns during grain development. Promoters of these genes are enriched in elements associated with transcription initiation and light response, indicating a potential connection between these cis-elements and grain protein accumulation. A model of how this HMW-GS enhances the abundance of machinery for protein synthesis and maturation during grain filling is proposed. This analysis not only provides insights into how introgression of the 1Ay21* improves grain protein content, but also directs selection of protein candidates for future wheat quality breeding programmes. One sentence summaryIntrogression of the 1Ay21* HMW-GS increases wheat grain protein content and improves bread-making quality in association with a broad reshaping of the grain proteome network.

plant biology↗

bioRxiv2020

Bioinformatic and experimental evidence for suicidal and catalytic plant THI4s

Like fungi and some prokaryotes, plants use a thiazole synthase (THI4) to make the thiazole precursor of thiamin. Fungal THI4s are suicide enzymes that destroy an essential active-site Cys residue to obtain the sulfur atom needed for thiazole formation. In contrast, certain prokaryotic THI4s have no active-site Cys, use sulfide as sulfur donor, and are truly catalytic. The presence of a conserved active-site Cys in plant THI4s and other indirect evidence implies that they are suicidal. To confirm this, we complemented the Arabidopsis tz-1 mutant, which lacks THI4 activity, with a His-tagged Arabidopsis THI4 construct. LC-MS analysis of tryptic peptides of the THI4 extracted from leaves showed that the active-site Cys was predominantly in desulfurated form, consistent with THI4 having a suicide mech-anism in planta. Unexpectedly, transcriptome datamining and deep proteome profiling showed that barley, wheat, and oat have both a widely expressed canonical THI4 with an active-site Cys, and a THI4-like paralog (non-Cys THI4) that has no active-site Cys and is the major type of THI4 in devel-oping grains. Transcriptomic evidence also indicated that barley, wheat, and oat grains synthesize thiamin de novo, implying that their non-Cys THI4s synthesize thiazole. Structure modeling supported this inference, as did demonstration that non-Cys THI4s have significant capacity to complement thia-zole auxotrophy in Escherichia coli. There is thus a prima facie case that non-Cys cereal THI4s, like their prokaryotic counterparts, are catalytic thiazole synthases. Bioenergetic calculations show that, relative to suicide THI4s, such enzymes could save substantial energy during the grain filling period. AbbreviationsDHAla, dehydroalanine; EST, expressed sequence tag; FDR, false discovery rate; IPTG, {beta}-D-1-thiogalactopyranoside

plant biology↗

bioRxiv2020

Coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes is assisted by CLPP2 in Arabidopsis thaliana

Protein homeostasis in eukaryotic organelles and their progenitor prokaryotes is regulated by a series of proteases including the caseinolytic protease (CLPP). CLPP has essential roles in chloroplast biogenesis and maintenance, but the significance of the plant mitochondrial CLPP remains unknown and factors that aid coordination of nuclear and mitochondrial encoded subunits for complex assembly in mitochondria await discovery. We generated knock-out lines of the single gene for the mitochondrial CLP protease subunit, CLPP2, in Arabidopsis thaliana. Mutants had higher abundance of transcripts from mitochondrial genes encoding OXPHOS protein complexes, while transcripts for nuclear genes encoding other subunits of the same complexes showed no change in abundance. In contrast, the protein abundance of specific nuclear-encoded subunits in OXPHOS complexes I and V increased in CLPP2 knockouts, without accumulation of mitochondrial-encoded counterparts in the same complex. Protein complexes mainly or entirely encoded in the nucleus were unaffected. Analysis of protein import, assembly and function of Complex I revealed that while function was retained, protein homeostasis was disrupted through decreased assembly, leading to accumulation of soluble subcomplexes of nuclear-encoded subunits. Therefore, CLPP2 contributes to the mitochondrial protein degradation network through supporting coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes. One sentence summaryCLPP contributes to the mitochondrial protein degradation network through supporting coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes.

plant biology↗

bioRxiv2019

Refining the composition of the Arabidopsis thaliana 80S cytosolic ribosome

The cytosolic 80S ribosome is composed of protein and RNA molecules and its function in protein synthesis is modulated through interaction with other cytosolic components. Defining the role of each of the proteins associated with ribosomes in plants is a major challenge which is hampered by difficulties in attribution of different proteins to roles in ribosome biogenesis, the mature cytosolic ribosome (r-proteins) or to the broader translatome associated with functioning ribosomes. Here we refined the core r-protein composition in plants by determining the abundance of proteins in low, partially and highly purified ribosomal samples from Arabidopsis thaliana cell cultures. To characterise this list of proteins further we determined their degradation (KD) and synthesis (KS) rate by progressive labelling with 15N combined with peptide mass spectrometry analysis. The turnover rates of 55 r-proteins, including 26 r-proteins from the 40S subunit and 29 r-proteins from the 60S subunit could be determined. Overall, ribosome proteins showed very similar KD and KS rates suggesting that half of the ribosome population is replaced every 3-4 days. Three proteins showed significantly shorter half-lives; ribosomal protein P0D (RPP0D) with a half-life of 0.5 days and RACK1b and c with half-lives of 1-1.4 days. The ribosomal RPP0D protein is a homolog of the human Mrt4 protein, a trans-acting factor in the assembly of the pre-60S particle, while RACK1 has known regulatory roles in cell function beyond its role as a 40S subunit. Our experiments also identified 58 proteins that are not from r-protein families but co-purify with ribosomes and co-express with r-proteins in Arabidopsis. Of this set, 26 were enriched more than 10-fold during ribosome purification. A number have known roles in translation or ribosome-association while others are newly proposed ribosome-associated factors in plants. This analysis provides a more robust understanding of Arabidopsis ribosome content, shows that most r-proteins turnover in unison in vivo, identifies a novel set of potential plant translatome components, and reveals how protein turnover can identify r-proteins involved in ribosome biogenesis or regulation in plants. Data are available via ProteomeXchange with identifier PXD012839.

plant biology↗

bioRxiv2016

An improved assembly and annotation of the allohexaploid wheat genome identifies complete families of agronomic genes and provides genomic evidence for chromosomal translocations.

Advances in genome sequencing and assembly technologies are generating many high quality genome sequences, but assemblies of large, repeat-rich polyploid genomes, such as that of bread wheat, remain fragmented and incomplete. We have generated a new wheat whole-genome shotgun sequence assembly using a combination of optimised data types and an assembly algorithm designed to deal with large and complex genomes. The new assembly represents more than 78% of the genome with a scaffold N50 of 88.8kbp that has a high fidelity to the input data. Our new annotation combines strand-specific Illumina RNAseq and PacBio full-length cDNAs to identify 104,091 high confidence protein-coding genes and 10,156 non-coding RNA genes. We confirmed three known and identified one novel genome rearrangements. Our approach enables the rapid and scalable assembly of wheat genomes, the identification of structural variants, and the definition of complete gene models, all powerful resources for trait analysis and breeding of this key global crop. [Supplemental material is available for this article.]

genomics↗