SARS-CoV-2 antibody prevalence by industry, workplace characteristics, and workplace infection prevention and control measures, North Carolina, 2021 to 2022

Background

The COVID-19 pandemic has disproportionately affected workers in certain industries and occupations, and the workplace can be a high risk setting for SARS-CoV-2 transmission. In this study, we measured SARS-CoV-2 antibody prevalence and identified work-related risk factors in a population primarily working at industrial livestock operations.

Methods

We used a multiplex salivary SARS-CoV-2 IgG antibody assay to determine infection-induced antibody prevalence among 236 adult (≥18 years) North Carolina residents between February 2021 and August 2022. We used the National Institute for Occupational Safety and Health Industry and Occupation Computerized Coding System (NIOCCS) to classify employed participants' industry and compared infection-induced IgG prevalence by participant industry and with the North Carolina general population. We also combined antibody results with reported SARS-CoV-2 molecular test positivity and vaccination history to identify evidence of prior infection. We used logistic regression to estimate odds ratios of prior infection by potential work-related risk factors, adjusting for industry and date.

Results

Most participants (55%) were infection-induced IgG positive, including 71% of animal slaughtering and processing industry workers, which is 1.5 to 4.3 times higher compared to the North Carolina general population, as well as higher than molecularly-confirmed cases and the only other serology study we identified of animal slaughtering and processing workers. Considering questionnaire results in addition to antibodies, the proportion of participants with evidence of prior infection increased slightly, to 61%, including 75% of animal slaughtering and processing workers. Participants with more than 1000 compared to 10 or fewer coworkers at their jobsite had higher odds of prior infection (adjusted odds ratio [aOR] 4.5, 95% confidence interval [CI] 1.0 to 21.0).

Conclusions

This study contributes evidence of the severe and disproportionate impacts of COVID-19 on animal processing and essential workers and workers in large congregate settings. We also demonstrate the utility of combining non-invasive biomarker and questionnaire data for the study of workplace exposures.

Industrial Hog Operation Workers' Perspectives on Occupational Exposure to Zoonotic Pathogens: A Qualitative Pilot Study in North Carolina, USA

Industrial hog operation (IHO) workers face a range of occupational hazards, including exposure to zoonotic pathogens such as livestock-associated antimicrobial-resistant Staphylococcus aureus and swine-origin influenza viruses with epidemic or pandemic potential. To better understand this population's occupational exposure to zoonotic pathogens, we conducted a community-driven qualitative research study in eastern North Carolina. We completed in-depth interviews with ten IHO workers and used thematic analysis to identify and analyze patterns of responses. Workers described direct and indirect occupational contact with hogs, with accompanying potential for dermal, ingestion, and inhalation exposures to zoonotic pathogens. Workers also described potential take-home pathways, wherein they could transfer livestock-associated pathogens and other contaminants from IHOs to their families and communities. Findings warrant future research, and suggest that more restrictive policies on antimicrobials, stronger health and safety regulations, and better policies and practices across all IHOs could afford greater protection against worker and take-home zoonotic pathogen exposures.

Characterizing metals in particulate pollution in communities at the fenceline of heavy industry: combining mobile monitoring and size-resolved filter measurements

Exposures to metals from industrial emissions can pose important health risks. The Chester-Trainer-Marcus Hook area of southeastern Pennsylvania is home to multiple petrochemical plants, a refinery, and a waste incinerator, most abutting socio-economically disadvantaged residential communities. Existing information on fenceline community exposures is based on monitoring data with low temporal and spatial resolution and EPA models that incorporate industry self-reporting. During a 3 week sampling campaign in September 2021, size-resolved particulate matter (PM) metals concentrations were obtained at a fixed site in Chester and on-line mobile aerosol measurements were conducted around Chester-Trainer-Marcus Hook. Fixed-site arsenic, lead, antimony, cobalt, and manganese concentrations in total PM were higher (p < 0.001) than EPA model estimates, and arsenic, lead, and cadmium were predominantly observed in fine PM (<2.5 μm), the PM fraction which can penetrate deeply into the lungs. Hazard index analysis suggests adverse effects are not expected from exposures at the observed levels; however, additional chemical exposures, PM size fraction, and non-chemical stressors should be considered in future studies for accurate assessment of risk. Fixed-site MOUDI and nearby mobile aerosol measurements were moderately correlated (r ≥ 0.5) for aluminum, potassium and selenium. Source apportionment analyses suggested the presence of four major emissions sources (sea salt, mineral dust, general combustion, and non-exhaust vehicle emissions) in the study area. Elevated levels of combustion-related elements of health concern (e.g., arsenic, cadmium, antimony, and vanadium) were observed near the waste incinerator and other industrial facilities by mobile monitoring, as well as in residential-zoned areas in Chester. These results suggest potential co-exposures to harmful atmospheric metal/metalloids in communities surrounding the Chester-Trainer-Marcus Hook industrial area at levels that may exceed previous estimates from EPA modeling.

SARS-CoV-2 Antibody Prevalence among Industrial Livestock Operation Workers and Nearby Community Residents, North Carolina, 2021 to 2022

Industrial livestock operations (ILOs), particularly processing facilities, emerged as centers of coronavirus disease 2019 (COVID-19) outbreaks in spring 2020. Confirmed cases of COVID-19 underestimate true prevalence. To investigate the prevalence of antibodies against SARS-CoV-2, we enrolled 279 participants in North Carolina from February 2021 to July 2022: 90 from households with at least one ILO worker (ILO), 97 from high-ILO intensity areas (ILO neighbors [ILON]), and 92 from metropolitan areas (metro). More metro (55.4%) compared to ILO (51.6%) and ILON participants (48.4%) completed the COVID-19 primary vaccination series; the median completion date was more than 4 months later for ILO compared to ILON and metro participants, although neither difference was statistically significant. Participants provided a saliva swab we analyzed for SARS-CoV-2 IgG using a multiplex immunoassay. The prevalence of infection-induced IgG (positive for nucleocapsid and receptor binding domain) was higher among ILO (63%) than ILON (42.9%) and metro (48.7%) participants (prevalence ratio [PR], 1.38; 95% confidence interval [CI], 1.06 to 1.80; reference category ILON and metro combined). The prevalence of infection-induced IgG was also higher among ILO participants than among an Atlanta health care worker cohort (PR, 2.45; 95% CI, 1.80 to 3.33) and a general population cohort in North Carolina (PRs, 6.37 to 10.67). The infection-induced IgG prevalence increased over the study period. Participants reporting not masking in public in the past 2 weeks had higher infection-induced IgG prevalence (78.6%) than participants reporting masking (49.3%) (PR, 1.59; 95% CI, 1.19 to 2.13). Lower education, more people per bedroom, Hispanic/Latino ethnicity, and more contact with people outside the home were also associated with higher infection-induced IgG prevalence. IMPORTANCE Few studies have measured COVID-19 seroprevalence in North Carolina, especially among rural, Black, and Hispanic/Latino communities that have been heavily affected. Antibody results show high rates of COVID-19 among industrial livestock operation workers and their household members. Antibody results add to evidence of health disparities related to COVID-19 by socioeconomic status and ethnicity. Associations between masking and physical distancing with antibody results also add to evidence of the effectiveness of these prevention strategies. Delays in the timing of receipt of COVID-19 vaccination reinforce the importance of dismantling vaccination barriers, especially for industrial livestock operation workers and their household members.

Application of systematic evidence mapping to assess the impact of new research when updating health reference values: A case example using acrolein

BACKGROUND

The environmental health community needs transparent, methodologically rigorous, and rapid approaches for updating human health risk assessments. These assessments often contain reference values for cancer and/or noncancer effects. Increasingly, the use of systematic review methods are preferred when developing these assessments. Systematic evidence maps are a type of analysis that has the potential to be very helpful in the update process, especially when combined with machine-learning software advances designed to expedite the process of conducting a review.

OBJECTIVES

To evaluate the applicability of evidence mapping to determine whether new evidence is likely to result in a change to an existing health reference value, using inhalation exposure to the air pollutant acrolein as a case example.

METHODS

New literature published since the 2008 California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA) Reference Exposure Level (REL) for acrolein was assessed. Systematic review methods were used to search the literature and screening included the use of machine-learning software. The Populations, Exposures, Comparators and Outcomes (PECO) criteria were kept broad to identify studies that characterized acute and chronic exposure and could be informative for hazard characterization. Studies that met the PECO criteria after full-text review were briefly summarized before their suitability for chronic point of departure (POD) derivation and calculation of a reference value was considered. Studies considered potentially suitable underwent a targeted evaluation to determine their suitability for use in dose-response analysis.

RESULTS

Over 15,000 studies were identified from scientific databases. Both machine-learning and manual screening processes were used to identify 60 studies considered PECO-relevant after full-text review. Most of these PECO-relevant studies were short-term exposure animal studies (acute or less than 1 month of exposure) and considered less suitable for deriving a chronic reference value when compared to the subchronic study in rats used in the 2008 OEHHA assessment. Thirteen epidemiological studies were identified but had limitations in the exposure assessment that made them less suitable for dose-response compared to the subchronic rat study. Among the 13 studies, there were four controlled trial studies that have the potential to be informative for future acute reference value derivation. Thus, the 2008 subchronic rat study used by OEHHA appears to still be the most appropriate study for chronic reference value derivation. In addition, advances in dosimetric modeling for gases, including new evidence pertinent to acrolein, could be considered when updating existing acrolein toxicity values.

CONCLUSIONS

Evidence mapping is a very useful tool to assess the need for updating an assessment based on understanding the potential impact of new studies on revising an existing health reference value. In this case example, the focus was to identify studies suitable for chronic exposure dose-response analysis, while also identifying studies that may be important to consider for acute exposure scenarios, hazard identification, or for future research. This allows the evidence map to be a useful resource for a range of decision-making contexts. Specialized systematic review software increased the efficiency of the process in terms of human resources and time to conduct the analysis.

Contrasting plant height can improve the control of rain-borne diseases in wheat cultivar mixture: modelling splash dispersal in 3-D canopies

Background and Aims

Growing cultivars differing by their disease resistance level together (cultivar mixtures) can reduce the propagation of diseases. Although architectural characteristics of cultivars are little considered in mixture design, they could have an effect on disease, in particular through spore dispersal by rain splash, which occurs over short distances. The objective of this work was to assess the impact of plant height of wheat cultivars in mixtures on splash dispersal of Zymoseptoria tritici, which causes septoria tritici leaf blotch.

Methods

We used a modelling approach involving an explicit description of canopy architecture and splash dispersal processes. The dispersal model computed raindrop interception by a virtual canopy as well as the production, transport and interception of splash droplets carrying inoculum. We designed 3-D virtual canopies composed of susceptible and resistant plants, according to field measurements at the flowering stage. In numerical experiments, we tested different heights of virtual cultivars making up binary mixtures to assess the influence of this architectural trait on dispersal patterns of spore-carrying droplets.

Key Results

Inoculum interception decreased exponentially with the height relative to the main inoculum source (lower diseased leaves of susceptible plants), and little inoculum was intercepted further than 40 cm above the inoculum source. Consequently, tall plants intercepted less inoculum than smaller ones. Plants with twice the standard height intercepted 33 % less inoculum than standard height plants. In cases when the height of suscpeptible plants was doubled, inoculum interception by resistant leaves was 40 % higher. This physical barrier to spore-carrying droplet trajectories reduced inoculum interception by tall susceptible plants and was modulated by plant height differences between cultivars of a binary mixture.

Conclusions

These results suggest that mixture effects on spore dispersal could be modulated by an adequate choice of architectural characteristics of cultivars. In particular, even small differences in plant height could reduce spore dispersal.

Using virtual 3-D plant architecture to assess fungal pathogen splash dispersal in heterogeneous canopies: a case study with cultivar mixtures and a non-specialized disease causal agent

BACKGROUND AND AIMS

Recent developments in plant disease management have led to a growing interest in alternative strategies, such as increasing host diversity and decreasing the use of pesticides. Use of cultivar mixtures is one option, allowing the spread of plant epidemics to be slowed down. As dispersal of fungal foliar pathogens over short distances by rain-splash droplets is a major contibutor to the spread of disease, this study focused on modelling the physical mechanisms involved in dispersal of a non-specialized pathogen within heterogeneous canopies of cultivar mixtures, with the aim of optimizing host diversification at the intra-field level.

METHODS

Virtual 3-D wheat-like plants (Triticum aestivum) were used to consider interactions between plant architecture and disease progression in heterogeneous canopies. A combined mechanistic and stochastic model, taking into account splash droplet dispersal and host quantitative resistance within a 3-D heterogeneous canopy, was developed. It consists of four sub-models that describe the spatial patterns of two cultivars within a complex canopy, the pathway of rain-splash droplets within this canopy, the proportion of leaf surface area impacted by dispersal via the droplets and the progression of disease severity after each dispersal event.

KEY RESULTS

Different spatial organization, proportions and resistance levels of the cultivars of two-component mixtures were investigated. For the eight spatial patterns tested, the protective effect against disease was found to vary by almost 2-fold, with the greatest effect being obtained with the smallest genotype unit area, i.e. the ground area occupied by an independent unit of the host population that is genetically homogeneous. Increasing both the difference between resistance levels and the proportion of the most resistant cultivar often resulted in a greater protective effect; however, this was not observed for situations in which the most resistant of the two cultivars in the mixture had a relatively low level of resistance.

CONCLUSIONS

The results show agreement with previous data obtained using experimental approaches. They demonstrate that in order to maximize the potential mixture efficiency against a splash-dispersed pathogen, optimal susceptible/resistant cultivar proportions (ranging from 1/9 to 5/5) have to be established based on host resistance levels. The results also show that taking into account dispersal processes in explicit 3-D plant canopies can be a key tool for investigating disease progression in heterogeneous canopies such as cultivar mixtures.

Tissue-dependent enhancement of transgene expression by introns of replacement histone H3 genes of Arabidopsis

Intron-bearing replacement histone H3 genes in Arabidopsis and other plants are highly and constitutively expressed. We demonstrate that the introns located within the 5'-untranslated regions (5'-UTR) of the two Arabidopsis replacement H3 genes will abolish the cell cycle dependence of an endogenous histone H4 promoter. We demonstrate that these introns, functionally combined with their endogenous promoters, could produce the high and constitutive expression of the replacement H3 genes observed in planta. They strongly increase gene expression whatever the promoter, from the strong 35S CaMV promoter to complete and resected promoters of cell cycle-dependent and replacement histone genes. Quantitative analysis of the extent of reporter gene enhancement in different parts of developing transgenic plantlets, ranging from 2-fold to 70-fold, supports the notion that trans-acting factors are responsible for this effect. Such factors appear most abundant in roots.

Distinct cyclin D genes show mitotic accumulation or constant levels of transcripts in tobacco bright yellow-2 cells

The commitment of eukaryotic cells to division normally occurs during the G1 phase of the cell cycle. In mammals D-type cyclins regulate the progression of cells through G1 and therefore are important for both proliferative and developmental controls. Plant CycDs (D-type cyclin homologs) have been identified, but their precise function during the plant cell cycle is unknown. We have isolated three tobacco (Nicotiana tabacum) CycD cyclin cDNAs: two belong to the CycD3 class (Nicta;CycD3;1 and Nicta;CycD3;2) and the third to the CycD2 class (Nicta;CycD2;1). To uncouple their cell-cycle regulation from developmental control, we have used the highly synchronizable tobacco cultivar Bright Yellow-2 in a cell-suspension culture to characterize changes in CycD transcript levels during the cell cycle. In cells re-entering the cell cycle from stationary phase, CycD3;2 was induced in G1 but subsequently remained at a constant level in synchronous cells. This expression pattern is consistent with a role for CycD3;2, similar to mammalian D-type cyclins. In contrast, CycD2;1 and CycD3;1 transcripts accumulated during mitosis in synchronous cells, a pattern of expression not normally associated with D-type cyclins. This could suggest a novel role for plant D-type cyclins during mitosis.

Molecular characterization of tobacco ribonucleotide reductase RNR1 and RNR2 cDNAs and cell cycle-regulated expression in synchronized plant cells

Eukaryotic ribonucleotide reductase (RNR), the enzyme involved in the synthesis of the deoxyribonucleotides, consists of two R1 and R2 subunits whose activities and gene expression are differentially regulated during the cell cycle and are preferentially induced at the G1/S transition. We have isolated three cDNA clones from a tobacco S phase library, two encoding the large R1 subunit, the first cloned in plants, and one encoding the small R2 subunit. From Southern blot hybridization we deduce that RNR2 is encoded by a single-copy gene whereas RNR1 is encoded by a small multigene family. The level of RNR mRNA is cell-cycle regulated showing a maximum in S phase. In mid-S phase, RNR2 transcripts show a higher maximum level than RNR1 transcripts. Analysis of the effects of various cell cycle inhibitors added to freshly subcultured stationary phase cells leads to the conclusion that RNR gene induction at the entry of the cells into the cell cycle takes place in late G1-early S phase. Addition of DNA synthesis-blocking agents to cycling cells synchronized in mid-S phase resulted in an enhancement of RNR transcript level, thus suggesting that RNR gene expression may be linked to the DNA synthesis rate by a feedback-like regulatory mechanism.

Multilevel regulation of histone gene expression during the cell cycle in tobacco cells

The respective involvement of transcriptional and post-transcriptional mechanisms in coupling H3 and H4 histone gene expression to the S phase of the cell cycle has been studied in synchronized tobacco cells. Induction of histone gene expression at the G1/S transition is shown to be essentially directed by an increase in the transcription rate in response to cellular signals occurring at the initiation step of DNA replication. Histone gene induction thus precedes the burst of DNA synthesis. However, when the elongation step of DNA replication is ineffective or artificially arrested, feedback mechanisms apparently act at the translation level to avoid overproduction of histone proteins from their mRNAs. At the end of S phase, post-transcriptional mechanisms ensure a rapid degradation of histone mRNAs. Transcription factors are bound to the cis -elements of histone promoters throughout the cell cycle, thus suggesting a post-translational modification of some of them to trigger promoter activation at the G1/S transition. Based on these results, a model is proposed for histone gene transcriptional induction in connection with the components of the cell cycle machinery.

Functional analysis of the promoter region of a maize (Zea mays L.) H3 histone gene in transgenic Arabidopsis thaliana

A 1023 bp fragment and truncated derivatives of the maize (Zea mays L.) histone H3C4 gene promoter were fused to the beta-glucuronidase (GUS) gene and introduced via Agrobacterium tumefaciens into the genome of Arabidopsis thaliana. GUS activity was found in various meristems of transgenic plants as for other plant histone promoters, but unexplained activity also occurred at branching points of both stems and roots. Deletion of the upstream 558 bp of the promoter reduced its activity to an almost basal expression. Internal deletion of a downstream fragment containing plant histone-specific sequence motifs reduced the promoter activity in all tissues and abolished the expression in meristems. Thus, both the proximal and distal regions of the promoter appear necessary to achieve the final expression pattern in dicotyledonous plant tissues. In mesophyll protoplasts isolated from the transformed Arabidopsis plants, the full-length promoter showed both S phase-dependent and -independent activity, like other plant histone gene promoters. Neither of the 5'-truncated nor the internal-deleted promoters were able to direct S phase-dependent activity, thus revealing necessary cooperation between the proximal and distal parts of the promoter to achieve cell cycle-regulated expression. The involvement of the different regions of the promoter in the different types of expression is discussed.

Protein complexes binding to cis elements of the plant histone gene promoters: multiplicity, phosphorylation and cell cycle alteration

The S phase-specific expression of histone genes provides an interesting model for studying activation of gene transcription during the cell cycle. In plants, however, trans-acting factors responsible for histone gene transcription are poorly documented. Using combined gel shift, UV cross-linking and competition analysis, we carried out a systematic study to identify and characterize proteins binding with the previously established cis elements of the plant histone gene promoters. Nuclear extracts prepared from the highly synchronizable tobacco BY2 cells were used. We confirmed the presence of proteins binding to the hexamer (ACGTCA) motif which has been previously identified as the binding site of wheat HBP-1 proteins. Interestingly, multiple proteins were found to bind specifically with the nonamer (CAATCCAAC) element and their DNA-binding activity was abolished upon in vitro protein phosphatase treatment. This later result imply phosphorylation/dephosphorylation as a potential post-translational control for DNA-binding activity of nonamer-binding proteins. In addition, the DNA-binding activity of these nonamer-binding proteins was found to be positively correlated with the S phase-specific expression of the histone genes in the synchronized cells, suggesting their function in the activation of transcription during the G1/S transition. Finally, several proteins were observed to bind specifically with an A/T-rich hexamer (TAATAT) motif. Their DNA-binding activity, however, was insensitive to phosphatase activity in vitro and relatively constitutive during the cell cycle. This A/T-rich hexamer as a new cis-acting element of plant histone genes is discussed.

Multiple A-type cyclins express sequentially during the cell cycle in Nicotiana tabacum BY2 cells

Four full-length and one partial cDNA clones encoding four different A-type cyclins were isolated from a tobacco S-phase-specific library. The corresponding mRNAs displayed sequential appearance and disappearance during the cell cycle of highly synchronized suspension-cultured tobacco cells. Sequence analysis showed that the plant A-type cyclins can be subdivided into three distinct structural groups that are likely to be represented in every plant species. Two of the isolated tobacco cyclins belonging to the same group were highly expressed throughout S and G2 phases but showed different kinetics of induction at the G1/S transition. Another one belonging to a second group was induced at mid-S phase and expressed until mid-M phase. A similar expression pattern was previously reported for a tobacco cyclin belonging to the third group. This sequential expression of multiple A-type cyclins in one type of plant cells makes a clear distinction from the situation in animal cells in which only one A-type cyclin exists in a given species. Furthermore, the expression of the different A-type cyclin genes responded differently upon a block at mid-S phase by DNA synthesis inhibitors. These results suggest that the multiple A-type cyclins act at different steps of the plant cell cycle and, therefore, exert distinct functions. In contrast, the expression of B-type cyclins was restricted to a narrow window corresponding to the M phase.

Histone H1 overexpressed to high level in tobacco affects certain developmental programs but has limited effect on basal cellular functions

Histone H1, a major structural component of chromatin fiber, is believed to act as a general repressor of transcription. To investigate in vivo the role of this protein in transcription regulation during development of a multicellular organism, we made transgenic tobacco plants that overexpress the gene for Arabidopsis histone H1. In all plants that overexpressed H1 the total H1-to-DNA ratio in chromatin increased 2.3-2.8 times compared with the physiological level. This was accompanied by 50-100% decrease of native tobacco H1. The phenotypic changes in H1-overexpressing plants ranged from mild to severe perturbations in morphological appearance and flowering. No correlation was observed between the extent of phenotypic change and the variation in the amount of overexpressed H1 or the presence or absence of the native tobacco H1. However, the severe phenotypic changes were correlated with early occurrence during plant growth of cells with abnormally heterochromatinized nuclei. Such cells occurred considerably later in plants with milder changes. Surprisingly, the ability of cells with highly heterochromatinized nuclei to fulfill basic physiological functions, including differentiation, was not markedly hampered. The results support the suggestion that chromatin structural changes dependent on H1 stoichiometry and on the profile of major H1 variants have limited regulatory effect on the activity of genes that control basal cellular functions. However, the H1-mediated chromatin changes can be of much greater importance for the regulation of genes involved in control of specific developmental programs.

Identification of cis-elements regulating the expression of an Arabidopsis histone H4 gene

Protein-DNA interactions in the proximal region of an Arabidopsis H4 histone gene promoter were analyzed by DMS in vivo footprinting combined with LMPCR amplification. Interactions were identified over six particular sequence motifs, five of which were previously shown to bind proteins in maize histone H3 and H4 promoters and are commonly found in the corresponding regions of other plant histone gene promoters. These motifs are located within a 126 bp fragment which was previously shown to confer preferential expression in meristems of transgenic plants. The contribution of each cis-element to the overall expression level and specificity was investigated by testing individual or combined mutations in transgenic Arabidopsis plants. All five motifs behaved as positive cis-elements of unequal strength. The GCCAAT-like sequence GCCACT behaved as a strong positive cis-element but had no influence on the specificity. In contrast, the nonamer AGATCGACG and to a lesser extent the closely linked hexamer CCGTCG proved to be essential for meristem-specific expression. Involvement of the highly conserved histone-specific octamer CGCGGATC in specific expression was revealed at some stages of meristem development. Importance of these three cis-elements, nonamer, hexamer, and octamer, was further confirmed by the fact that combining mutations of two of them either abolished the promoter activity or completely modified the promoter specificity. Mutation of the fifth cis-element, a degenerate copy of the octamer, little perturbed the promoter function. However disruption of both octamers had a dramatic negative effect, thus suggesting that the two copies cooperate to achieve maximal function in the wild-type promoter, possibly by mobilizing the proliferation-specific factors binding to the nonamer and CCGTCG cis-elements.

Functional expression of Saccharomyces cerevisiae CYP51A1 encoding lanosterol-14-demethylase in tobacco results in bypass of endogenous sterol biosynthetic pathway and resistance to an obtusifoliol-14-demethylase herbicide inhibitor

Nicotiana tabacum protoplasts have been transformed by Agrobacterium tumefaciens containing a T-DNA in which the gene CYP51A1 encoding lanosterol-14-demethylase (LAN14DM) from Saccharomyces cerevisiae is under the control of a cauliflower mosaic virus (CaMV) 35S promoter. Two transformants strongly expressed the LAN14DM as shown by Northern and Western experiments. These transgenic calli were killed by LAB 170250F (LAB) (a phytotoxic fungicide inhibiting both plant obtusifoliol-14-demethylase (OBT14DM) and LAN14DM) but were resistant to gamma-ketotriazole (gamma-kt), a herbicide which has been shown to inhibit OBT14DM but not LAN14DM at a concentration that was lethal to control calli. However, these transgenic calli were killed by mixtures of gamma-kt plus fungicide inhibitors of LAN14DM such as ketoconazole, itraconazole or flusilazole which alone were not effective. Further analysis of the transgenic calli grown in the presence of gamma-kt showed that their delta 5-sterol content was close to that of untreated control calli obtained from protoplasts transformed with control plasmid; this is in agreement with evidence that the LAN14DM expressed from the transgene could bypass the blocked OBT14DM by using the plant substate obtusifoliol. In contrast, control calli when treated with gamma-kt, displayed a sterol content strongly enriched in 14 alpha-methyl sterols and depressed in physiological delta 5-sterols. When the transgenic calli were cultured in mixtures of gamma-kt and LAN14DM inhibitors sterol compositions enriched in 14 alpha-methyl sterols were obtained, reflecting a strong inhibition of both 'endogenous' OBT14DM and 'exogenous' LAN14DM. Taken together these results show that in tobacco calli transformed with CYP51A1, resistance to a triazole herbicide arises from expression of a functional LAN14DM enzyme; its activity in transgenic tissues creates a bypass of the sterol biosynthetic pathway at the 14-demethylase level when this latter is blocked by an OBT14DM herbicide inhibitor.

Molecular characterization and cell cycle-regulated expression of a cDNA clone from Arabidopsis thaliana homologous to the small subunit of ribonucleotide reductase

A cDNA clone isolated from an Arabidopsis thaliana cell suspension library showed highly significant homology to the small subunit of ribonucleotide reductase (R2) from different species. The 340 amino acid-long deduced putative protein contains all the residues that are important for the enzyme activity and structure. In A. thaliana this enzyme is encoded by a single-copy gene. In synchronized tobacco BY2 cells the corresponding mRNAs specifically accumulate during the S phase of the cell cycle.

Molecular characterization of a beta-type proteasome subunit from Arabidopsis thaliana co-expressed at a high level with an alpha-type proteasome subunit early in the cell cycle

Proteasomes are the essential components of complexes involved in an extralysosomal energy- and ubiquitin-dependent proteolytic pathway. The first alpha-type proteasome subunit in plants has recently been described. In this work, the sequence of the first beta-type proteasome subunit in plants, isolated from Arabidopsis thaliana cDNA libraries is reported. The mRNA accumulation of both subunits was analysed and compared with those of the ubiquitin and histone mRNAs, in different tissues and during re-initiation of mitotic activity. It is demonstrated that in plants, as in animal cells, the transcripts of both the alpha-type and beta-type proteasome subunits accumulate to high levels during cell proliferation, in parallel with mRNAs coding for a ubiquitin fusion protein and several polyubiquitins, but earlier than those coding for histone H4 whose expression is known to be coupled to DNA synthesis. These results suggest that, as in animal cells, proteasomes may be involved in the progression of the cell cycle.

Nuclease sensitivity and functional analysis of a maize histone H3 gene promoter

A 1 kb region of a maize H3 histone gene promoter has been analysed at a structural and functional level. Micrococcal nuclease digestion of isolated nuclei showed that the promoter region is organized into nucleosomes but a zone extending over approximately one nucleosome (20 to 230 bp upstream of the TATA box) displays remarkable accessibility to digestion. Three DNase I-hypersensitive sites were found within this zone at the vicinity of consensus sequences, some of which are already known to act as cis elements. This promoter region is able to direct faithful expression of the GUS reporter gene in meristematic tissues of transgenic tobacco plants.

cDNA nucleotide sequence and expression of a maize cytoplasmic ribosomal protein S13 gene

The complete amino acid sequence of a cytoplasmic ribosomal protein S13 of maize was deduced from the cDNA isolated from a maize cDNA library. The encoded protein is 151 amino acids long and shows a homology of 73% with the corresponding protein S13 of rat. Southern blots analysis shows that the maize protein S13 is encoded by a small multigene family conserved in plant species closely related to maize. The S13 RNAs accumulate preferentially in proliferating tissues and cells and their transcription occurs in parallel to the DNA synthesis.

Histones and histone genes in higher plants: structure and genomic organization

The primary structure of the plant histone genes has been deduced from the comparison of the nucleotide sequences of 23 genes and 14 cDNAs from eight different species. These data confirmed the extreme conservation of histones H3 and H4 in plant and animal kingdoms. Histone H2B is more variable than H2A and the histone H1 is the less conserved histone. Some interesting observations concerning the non-conserved regions of H2A and H2B in their extended C- and N-terminal regions are reported. Only three plant histone genes were found to possess intervening sequences: one H1 gene and two H3.3 like genes. The most striking differences found between the two kingdoms are the absence from plant histone genes of the palindromic structure existing downstream of the animal genes and the fact that plant histone mRNAs are polyadenylated. This suggests that the post-transcriptional regulation of expression of histone genes is different in the two kingdoms. In plants the multiple copies of the histone genes are organized into multigenic families. In the complex genome of maize the multiple copies of the genes are highly dispersed on the genome.

Cloning and sequence analysis of a cDNA clone from Arabidopsis thaliana homologous to a proteasome alpha subunit from Drosophila

A cDNA clone isolated from an Arabidopsis thaliana cell suspension culture library showed considerable similarities to the proteasome 28 kDa alpha subunit of Drosophila [(1990) Gene 90, 235-241]. The 250 amino acid-long protein encoded by Arabidopsis TAS-g64 clone has important homologies in its primary structure and in the predicted secondary structure with the PROS-28.1 clone from Drosophila. The only divergence observed between the two sequences is for the 20 C-terminal amino acids. This subunit might share important functions in both kingdoms, as revealed by the important conservation between plants and animals. In plant cells it is encoded by a single-copy gene and probably regulated by stress and/of division.

Subfamilies of histone H3 and H4 genes are located on most, possibly all of the chromosomes in maize

It has been previously shown that in the genome of maize the multiple copies of the histone H3 and H4 multigenic families are organized into eight to ten subfamilies each containing a variable number of copies. Each subfamily is characterized by a specific proximal environment and thus can be revealed by blot-hybridization with its specific 5' probe. Restriction fragment length polymorphism (RFLP) combined with monosomic analysis was used to localize several H3 and H4 subfamilies on maize chromosomes. H3 and H4 genes were found to be located on most, possibly all of the chromosomes, revealing a remarkably dispersed organization of these multigenic families.

Genes encoding a histone H3.3-like variant in Arabidopsis contain intervening sequences

Two genes encoding a particular H3 histone variant were isolated from Arabidopsis thaliana. These genes differ from the H3 genes previously cloned from Arabidopsis and other plants by several interesting properties: (1) the two genes are located close to each other; (2) their coding regions are interrupted by two or three small introns, the two closest to the initiation codon being located at the same place in the two genes; (3) another, long intron is located in the 5'-untranslated region just before the initiation codon of gene I as deduced from the sequence of several corresponding cDNAs, and very likely also of gene II; (4) these genes do not show preferential expression in organs containing meristematic tissues contrary to the classical intronless replication-dependent histone genes, thus suggesting that their expression is not replication-dependent; (5) the protein encoded by both genes is the same and corresponds to a minor H3 variant highly conserved among all the plant species studied up to now. All these characteristics are common with the animal replication-independent H3.3 histone genes and it is assumed that the genes described here are the first example of the equivalent H3.3 gene family in plants. Interestingly, the promoter regions of the two genes have the same general structure as the Arabidopsis intronless genes. Possible implications on the regulation of H3 genes expression are discussed.

A plant histone gene promoter can direct both replication-dependent and -independent gene expression in transgenic plants

Chimeric genes containing the beta-glucuronidase (GUS) gene under the control of different Arabidopsis histone H3 and H4 promoters were found to be highly expressed in transient expression experiments using tobacco protoplasts. The activity of one of these promoters, H4A748, was further analyzed. The kinetics of H4A748-GUS activity are very similar to these of a CaMV 35S-GUS constitutive gene during protoplast culture. No increase in H4A748-GUS activity was found after 24 h of protoplast culture when DNA synthesis starts, nor was the GUS activity affected when an inhibitor of DNA synthesis was included in the culture medium. This failure to detect any replication-dependent activity is most likely to be due to the fact that transient transcription of the introduced construct is restricted to the first 24 h following transfection. Stable integration of the H4A748-GUS gene into tobacco plants showed that the histone promoter could confer increased expression in meristematic tissues but it is also expressed to significant levels in non-proliferating tissues. Protoplasts prepared from these transgenic tobacco plants were cultivated under different conditions that affect DNA synthesis. Analysis of H4A748-GUS activity revealed (i) the existence of a basal replication-independent activity and (ii) a replication-dependent activity induced in parallel with DNA synthesis. These results show that the histone H4 promoter is able to direct both replication-dependent and -independent gene expression.

An internal standard improves the reliability of transient expression studies in plant protoplasts

Transient expression of foreign genes introduced on a plasmid into isolated plant protoplasts is widely used to study the control of gene expression. Unfortunately, many experimental variables implicated in this technique are difficult or impossible to control, resulting in a disturbing degree of variability between otherwise identical experiments. We have studied the co-expression of two constitutively expressed genes located on the same plasmid. This has allowed us to identify the lot of plasmid DNA as an important source of variation, along with the protoplast lot. Plasmid DNA concentration was found to be of minor importance. Since the variation of expression level of the two genes was identical for the two genes in all experiments, we propose the use of an internal standard in all comparative transient expression studies, which allows the reduction of the variation between experiments by one order of magnitude.

Nucleotide sequence and expression of a maize H1 histone cDNA

The first complete amino acid sequence of a H1 histone of a monocotyledonous plant was deduced from a cDNA isolated from a maize library. The encoded H1 protein is 245 amino acid-long and shows the classical tripartite organization of this class of histones. The central globular region of 76 residues shows 60% sequence homology with H1 proteins from dicots but only 20% with the animal H1 proteins. However, several of the amino acids considered as being important in the structure of the nucleosome are conserved between this protein and its animal counterparts. The N-terminal region contains an equal number of acidic and basic residues which appears as a general feature of plant H1 proteins. The 124 residue long and highly basic C-terminal region contains a 7-fold repeated element KA/PKXA/PAKA/PK. Southern-blot hybridization showed that the H1 protein is encoded by a small multigene family. Highly homologous H1 gene families were also detected in the genomes of several more or less closely related plant species. The general expression pattern of these genes was not significantly different from that of these genes encoding the core-histones neither during germination nor in the different tissues of adult maize.

Polyadenylation of histone H3 and H4 mRNAs in dicotyledonous plants

The histone H3 and H4 genes are shown to be expressed in both Arabidopsis plantlets and transitory multicellular suspension. The 5'- and 3'-ends of the H4 mRNAs have been localized on two H4 genes previously sequenced, H4A748 and H4A777. S1-nuclease mapping and reverse-transcriptase-primer-elongation experiments revealed the existence of two start points for transcription, located 31 and 37 nucleotides downstream from the TATA-box. The 3'-end of the mRNA corresponding to H4A748 was localized at 177 nt after the stop codon. The other gene, H4A777, most probably is not expressed. In addition to a long 3'-untranslated region, the H4 mRNA was shown to be polyadenylated in both plantlets and cell-suspension. This observation was extended to the H3 mRNAs of Arabidopsis and of two other dicots, tobacco and sunflower. Previous results on maize H3 and H4 mRNAs suggest that polyadenylation is a common feature for histone mRNAs in higher plants.

The histone H3 and H4 mRNAs are polyadenylated in maize

Northern blot analysis revealed that the histone H3 and H4 mRNAs are of unusual large size in germinating maize embryos. S1-mapping experiments show that the 3'-untranslated regions of the mRNAs transcribed from 3 H3 and 2 H4 maize genes previously described are much longer than in the non-polyadenylated histone mRNAs which represent a major class in animals. Moreover, oligo d(T) cellulose fractionation of RNAs isolated at different developmental stages indicates that more than 99% of the maize H3 and H4 mRNAs are polyadenylated. A putative polyadenylation signal is present in all five genes 17 to 27 nucleotides before the 3'-ends of the mRNAs.

Genomic organization and nucleotide sequences of two histone H3 and two histone H4 genes of Arabidopsis thaliana

Two histone H3 and two histone H4 genes have been cloned from a λgtWESλ·B Arabidopsis thaliana gene library. From their nucleotide sequences and from studies on their genomic organization, the following conclusions can be drawn: : 1) The nucleotide sequences of the two H3 coding regions show only 85% homology, but encode the same proteins. The Arabidopsis H3 has the same amino acid sequence as its counterpart in corn, but differs from that of pea and wheat by replacement in position 90 of a serine by an alanine. The two H4 coding regions have 97% sequence homology and encode the same protein, identical to the sequence of their counterpart in pea, corn and one H4 variant in wheat. 2) The 5'-flanking regions of the 4 genes contain the classical histone-gene-specific consensus sequences, except H3A725 which lacks the GATCC-like pentamer. The conserved octanucleotide 5'-CGCGGATC-3' which was previously found in the 5'-flanking sequences of corn and wheat H3 and H4 genes is also present in all four genes described here approximately 200 to 250 nucleotides upstream from the initiation ATG. The 5'-flanking regions of the H4 genes display extensive sequence homology, whereas those of the H3 genes do not. 3) The 3'-flanking regions do not possess the classical histone-gene-specific T hyphenated dyad symmetry motif. 4) Each H3 and H4 gene exists as 5 to 7 copies per haploid genome.

Nucleotide sequences of two corn histone H3 genes. Genomic organization of the corn histone H3 and H4 genes

Two histone H3 genes have been cloned from a λgtWESλ.B corn genomic library. The nucleotide sequences show 96% homology and both encode the same protein, which differs from its counterpart in wheat and pea by one amino acid substitution. The 5'-flanking regions of the two corn H3 genes contain the classical histone-gene-specific consensus sequences and possess several regions of extensive nucleotide homology. A conserved octanucleotide 5'-CGCGGATC-3' occurs at approximately 200 nucleotides upstream from the initiation ATG codon. This octanucleotide was found to exist in all of the 7 plant histone genes sequenced so far. Codon usage is characterized by a very high frequency of C (67%) and G (28%) at the third position of the codons, those ending by A (1%) and T (4%) being practically excluded.Comparison of Southern blots of EcoRI, EcoRV and BamHI digested genomic DNA suggests that the corn H3 and H4 genes are not closely associated. The H3 genes exist as 60 to 80 copies and the H4 genes as 100 to 120 copies per diploid genome. re]19851002 rv]19851212 ac]19851216.

Genomic organization and nucleotide sequences of two corn histone H4 genes

The sea urchin histone H4 gene has been used as a probe to clone two corn histone H4 genes from a lambda gtWES X lambda B corn genomic library. The nucleotide (nt) sequences of both genes showed that the encoded amino acid sequences were identical to that of the H4 of pea and one variant of wheat. The nt sequences of the coding regions showed 92% homology. 5'- and 3'-flanking regions do not show extensive nt sequence analogies. Southern blotting of the EcoRI digested genomic DNA suggests the existence of multiple H4 genes dispersed throughout the genome.

HMG-like protein in barley and corn nuclei

Chromosomal proteins have been isolated from barley (Hordeum vulgare) and corn (Zea mays) nuclei by extraction with 5% perchloric acid. In each plant, one protein was shown to belong to the HMG proteins. Their molecular weights are very close to that of HMG 14 from chicken erythrocytes, as shown by electrophoretic mobility in SDS polyacrylamide gels. In acetic acid-urea-Triton polyacrylamide gels they migrate between HMG 1,2 and HMG 14, from chicken erythrocytes. Their amino acid compositions are typical of HMG proteins, with equivalent high values of acidic and basic residues.Extraction of HMG's from purified barley chromatin fractions with 0.35 M NaCl considerably reduces histone H2 contamination and increases the yield of HMG up to 0.7% of the total histones. In this technique a second protein was extracted which is soluble in 2% Trichloroacetic acid and shows electrophoretic mobility analogous to those of HMG 14 and 17 from chicken erythrocytes. Whether or not these proteins are counterparts of the animal HMG's 1-2 or HMG's 14-17 is discussed.

Fractionation and characterization of histones from barley (Hordeum vulgare) leaves : Existence of multiple H2A and H2B variants

Histones were extracted from purified nuclei isolated from four cereals,viz. barley (Hordeum vulgare), wheat(Triticum aestivum), Aegilops squarrosa and corn (Zea mais), and from tobacco (Nicotiana tabacum). Analysis of the histones on SDS gels showed complex electrophoretic patterns with one species of both H3 and H4, one to three species of H1 and two to five species of H2. Judged from the electrophoretic patterns, the histones from barley, wheat and Aegilops are identical but different from those of corn with respect to H2. Like tobacco, corn showed two H2 components, whereas barley, wheat and Aegilops showed five H2 components.SDS gel electrophoresis of histones extracted from buds and roots of germinating seeds at different steps of germination and from different parts of ten-day-old leaves revealed that the existence in barley of multiple histone 2 variants is not restricted to any particular stage of differentiation of barley.Histones from barley leaves were resolved into four fractions by Biogel P-100 gel filtration and histones 2 were further fractionated by their differential solubility in HCl-ethanol. Each of these five fractions (H1, H3, H4, H2A and H2B, respectively) were characterized by electrophoresis on SDS or Triton-acid-urea gels and by their amino acid compositions as compared with the homologous histones of calf thymus and chicken erythrocytes. This revealed the following: i) H3 and H4 are strictly analogous to their animal counterparts. However, H4 has an unexplained lower electrophoretic mobility in Triton-containing acid-urea gels. ii) H1 contains three components with lower electrophoretic mobilities than H1 from erythrocytes, contains more alanine than lysine and has a lower ratio of basic to acidic residues. iii) Both H2A and H2B contain at least four variants each, with higher molecular weights than in animals and higher lysine to arginine ratios. H2A variants comigrate in acid-urea-Triton gels with chicken erythrocytes H2A, whereas H2B migrate much slower. It was concluded that the presence of multiple major variants of H2A and H2B is a frequent but not universal feature in cereals. The existence of these variants is not restricted to the embryonic stage as previously suggested for wheat (31).

Visualization of a Spinach Plastid Transcriptionally Active DNA-Protein Complex in a Highly Condensed Structure

A transcriptionally active DNA-protein complex isolated from spinach Spinacia oleracea plastids is visualized by electron microscopy in different conditions. This structure, after glutaraldehyde fixation, is highly condensed. DNA is supertwisted with proteins bound to it producing a beaded substructure. When glutaraldehyde fixation is omitted this structure is less condensed and DNA fibrils come out from a proteinous central body. The DNA-protein complex can be separated into two populations by CsCl centrifugation: one with a buoyant density of 1.570 grams per cubic centimeter and the other of 1.610 grams per cubic centimeter. By visualization of these two populations, it is concluded that proteins are either firmly bound to DNA in the central body, or more loosely bound to the DNA fibrils. These latter proteins could play a role in enzymic functions and/or in the supercoiling of DNA.The DNA from the DNA-protein complex possesses all fragments that belong to pure circular chloroplast DNA hydrolyzed by two restriction enzymes: Bam HI and Eco RI. Some molecules observed in a supercondensed form with a beaded substructure probably contain entire chloroplast DNA molecules.A hydrolysis test with microccocal nuclease gives no indication of the presence of ;nucleosome-like' structures. Thirty-six polypeptides with molecular weights ranging from 12,000 to 180,000 are present in the complex, and seven of them are highly soluble in 0.4 n H(2)SO(4); their molecular weights range from 14,000 to 46,000 as shown by two-dimensional gel electrophoresis.No linolenic acid can be detected in the preparation, indicating the absence of chloroplast membranes.

Properties of condensed chromatin in barley nuclei

A method for isolation and purification of intact nuclei from barley leaves was developed and several properties of the chromatin were studied. The dense structure of the main part of the chromatin does not alter the accessibility of the DNA to nucleases. 60% of the nuclear DNA can be degraded by micrococcal endonuclease. Nevertheless the solubility of the chromatin fragments depends on the extent of nuclease digestion; solubilisation occurring only when the major part of the internucleosomal DNA was degraded (≃30% of digestion). Electron microscopic observations suggest that this was due to particularly dense organization of the chromatin "in situ". The possible physiological meaning of some of these properties are discussed.

DNA associated with nucleosomes in plants

50 to 55% of tobacco and barley nuclear DNA is accessible to micrococcal endonuclease digestion. The DNA fragments resulting from a mild endonuclease treatment are multiples of a basic unit of 194 +/- 6 base pairs in tobacco and 195 +/- 6 base pairs in barley. After extensive digestion, a DNA fragment of approximately 140 base pairs is predominant. Hence the "extra-core" or "linker"-DNA is 55 base pairs long. Other fragments having 158 and less than 140 base pairs are present as well. Treatment with DNase I results in multiples of 10 bases when analysed under denaturating conditions. These results show that the general organization of the DNA within the nucleosomes is about the same in higher plants as in other higher eukaryotes.

Some properties of tobacco protoplast chromatin

Chromatin was prepared from tobacco-leaf protoplasts. Its solubility in increasing molarities of NaCl was studied and the structure of the soluble fraction observed by electron microscopy. We demonstrate that in plants, the DNA and histones are associated in beaded structures similar to those called omicron-bodies or nucleosomes in animal chromatin. The nucleosomes were associated with DNA in either compact or extended forms. The compact arrangement was predominant in the fraction solubilized between 0.1 and 0.4 M NaCl. The extended form, present at 0.5 and 0.6 M NaCl. showed DNA filaments of various lengths interspacing the nucleosomes. At these ionic strengths ring structures were present, associated with the DNA. At 0.7 M NaCl and above, only DNA filaments were present, occasionally associated with big rings, and nucleosomes were compoetely dissociated. Free DNA molecules were present at all ionic strengths used. The possible origin and significance of the rings are discussed.