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"Ellis, Brian"
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Xylem tissue specification, patterning, and differentiation mechanisms
Vascular plants (Tracheophytes) have adapted to a variety of environments ranging from arid deserts to tropical rainforests, and now comprise >250 000 species. While they differ widely in appearance and growth habit, all of them share a similar specialized tissue system (vascular tissue) for transporting water and nutrients throughout the organism. Plant vascular systems connect all plant organs from the shoot to the root, and are comprised of two main tissue types, xylem and phloem. In this review we examine the current state of knowledge concerning the process of vascular tissue formation, and highlight important mechanisms underlying key steps in vascular cell type specification, xylem and phloem tissue patterning, and, finally, the differentiation and maturation of specific xylem cell types.
Journal Article
Arabidopsis Ovate Family Proteins, a Novel Transcriptional Repressor Family, Control Multiple Aspects of Plant Growth and Development
The Arabidopsis genome contains 18 genes that are predicted to encode Ovate Family Proteins (AtOFPs), a protein family characterized by a conserved OVATE domain, an approximately 70-amino acid domain that was originally found in tomato OVATE protein. Among AtOFP family members, AtOFP1 has been shown to suppress cell elongation, in part, by suppressing the expression of AtGA20ox1, AtOFP4 has been shown to regulate secondary cell wall formation by interact with KNOTTED1-LIKE HOMEODOMAIN PROTEIN 7 (KNAT7), and AtOFP5 has been shown to regulate the activity of a BEL1-LIKEHOMEODOMAIN 1(BLH1)-KNAT3 complex during early embryo sac development, but little is known about the function of other AtOFPs.
We demonstrated here that AtOFP proteins could function as effective transcriptional repressors in the Arabidopsis protoplast transient expression system. The analysis of loss-of-function alleles of AtOFPs suggested AtOFP genes may have overlapping function in regulating plant growth and development, because none of the single mutants identified, including T-DNA insertion mutants in AtOFP1, AtOFP4, AtOFP8, AtOFP10, AtOFP15 and AtOFP16, displayed any apparent morphological defects. Further, Atofp1 Atofp4 and Atofp15 Atofp16 double mutants still did not differ significantly from wild-type. On the other hand, plants overexpressing AtOFP genes displayed a number of abnormal phenotypes, which could be categorized into three distinct classes, suggesting that AtOFP genes may also have diverse functions in regulating plant growth and development. Further analysis suggested that AtOFP1 regulates cotyledon development in a postembryonic manner, and global transcript profiling revealed that it suppress the expression of many other genes.
Our results showed that AtOFPs function as transcriptional repressors and they regulate multiple aspects of plant growth and development. These results provided the first overview of a previously unknown transcriptional repressor family, and revealed their possible roles in plant growth and development.
Journal Article
The influence of dog ownership on objective measures of free-living physical activity and sedentary behaviour in community-dwelling older adults: a longitudinal case-controlled study
Background
There is some evidence to suggest that dog ownership may improve physical activity (PA) among older adults, but to date, studies examining this, have either depended on self-report or incomplete datasets due to the type of activity monitor used to record physical activity. Additionally, the effect of dog ownership on sedentary behaviour (SB) has not been explored. The aim of the current study was to address these issues by using activPAL monitors to evaluate the influence of dog ownership on health enhancing PA and SB in a longitudinal study of independently-mobile, community-dwelling older adults.
Methods
Study participants (43 pairs of dog owners and non-dog owners, matched on a range of demographic variables) wore an activPAL monitor continuously for three, one-week data collection periods over the course of a year. Participants also reported information about their own and their dog demographics, caring responsibilities, and completed a diary of wake times. Diary data was used to isolate waking times, and outcome measures of time spent walking, time spent walking at a moderate cadence (>100 steps/min), time spent standing, time spent sitting, number of sitting events (continuous periods of sitting), and the number of and of time spent sitting in prolonged events (>30 min). For each measure, a linear mixed effects model with dog ownership as a fixed effect, and a random effects structure of measurement point nested in participant nested in pair was used to assess the effect of dog ownership.
Results
Owning a dog indicated a large, potentially health improving, average effect of 22 min additional time spent walking, 95%CI (12, 34), and 2760 additional steps per day, 95%CI (1667, 3991), with this additional walking undertaken at a moderate intensity cadence. Dog owners had significantly fewer sitting events. However, there were no significant differences between the groups for either the total time spent sitting, or the number or duration of prolonged sedentary events.
Conclusions
The scale of the influence of dog ownership on PA found in this study, indicates that future research regarding PA in older adults should assess and report dog ownership and/or dog walking status.
Journal Article
Mitogen-activated protein kinase signaling in plant-interacting fungi: distinct messages from conserved messengers
Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved proteins that function as key signal transduction components in fungi, plants, and mammals. During interaction between phytopathogenic fungi and plants, fungal MAPKs help to promote mechanical and/or enzymatic penetration of host tissues, while plant MAPKs are required for activation of plant immunity. However, new insights suggest that MAPK cascades in both organisms do not operate independently but that they mutually contribute to a highly interconnected molecular dialogue between the plant and the fungus. As a result, some pathogenesis-related processes controlled by fungal MAPKs lead to the activation of plant signaling, including the recruitment of plant MAPK cascades. Conversely, plant MAPKs promote defense mechanisms that threaten the survival of fungal cells, leading to a stress response mediated in part by fungal MAPK cascades. In this review, we make use of the genomic data available following completion of whole-genome sequencing projects to analyze the structure of MAPK protein families in 24 fungal taxa, including both plant pathogens and mycorrhizal symbionts. Based on conserved patterns of sequence diversification, we also propose the adoption of a unified fungal MAPK nomenclature derived from that established for the model species Saccharomyces cerevisiae. Finally, we summarize current knowledge of the functions of MAPK cascades in phytopathogenic fungi and highlight the central role played by MAPK signaling during the molecular dialogue between plants and invading fungal pathogens.
Journal Article
Microwave-based CO2 desorption for enhanced direct air capture: experimental validation and techno-economic perspectives
This study explores the feasibility and potential techno-economic advantages of employing microwaves for direct air capture (DAC) applications. The experimental setup resembles an industrial-scale microwave system, utilizing a single-mode applicator and zeolite 13x beads arranged in a panel configuration. This configuration essentially represents a miniaturized version of a potential DAC plant based on microwaves. The results demonstrate that microwave irradiation rapidly and efficiently desorbs the CO2 from sorbents with approximately 90% desorption achieved in 10 min—substantially shorter than conventional conduction-based methods. The desorption process occurred at a low temperature of about 50 °C, in contrast to nearly 120 °C in conventional bulk heating, due to selective heating near CO2 binding sites. Our results support that desorption duration and temperature could be further reduced by applying more uniform heating while intensifying the selective process. Based on our research and recent literature, we propose three key techno-economic advantages of designing a DAC system with microwaves that are unattainable by the conventional approach. A reduced regeneration time could allow for a more compact system design while maintaining throughput. The selectivity of microwave absorption could drastically reduce energy demand, bringing it close to the sorbent’s thermodynamic energy limits. Furthermore, the low-temperature process could inhibit the thermal degradation of amines on the sorbents, which is unavoidable in conventional processes. Potential resonant CO2 desorption by forming nonthermal plasma (NTP) is discussed. Our research highlights the feasibility and significance of employing advanced regeneration methods in the development of next-generation DAC systems.
Journal Article
Extensive Comparison of the Effect of Anthelmintic Classes on Diverse Nematodes
Soil-transmitted helminths are parasitic nematodes that inhabit the human intestine. These parasites, which include two hookworm species, Ancylostoma duodenale and Necator americanus , the whipworm Trichuris trichiura , and the large roundworm Ascaris lumbricoides , infect upwards of two billion people and are a major cause of disease burden in children and pregnant women. The challenge with treating these diseases is that poverty, safety, and inefficient public health policy have marginalized drug development and distribution to control infection in humans. Anthelmintics (anti-worm drugs) have historically been developed and tested for treatment of non-human parasitic nematodes that infect livestock and companion animals. Here we systematically compare the in vitro efficacy of all major anthelmintic classes currently used in human therapy (benzimidazoles, nicotinic acetylcholine receptor agonists, macrocyclic lactones, nitazoxanide) against species closely related to human parasitic nematodes- Ancylostoma ceylanicum , Trichuris muris , and Ascaris suum --- as well as a rodent parasitic nematode used in veterinary drug discovery, Heligmosomoides bakeri , and the free-living nematode Caenorhabditis elegans . Extensive in vitro data is complemented with single-dose in vivo data in three rodent models of parasitic diseases. We find that the effects of the drugs in vitro and in vivo can vary greatly among these nematode species, e.g., the efficacy of albendazole is strong on A. ceylanicum but weak on H . bakeri . Nonetheless, certain commonalities of the in vitro effects of the drugs can be seen, e.g., nitazoxanide consistently shows an all-or-nothing response. Our in vitro data suggest that further optimization of the clinical efficacy of some of these anthelmintics could be achieved by altering the treatment routine and/or dosing. Most importantly, our in vitro and in vivo data indicate that the hookworm A. ceylanicum is a particularly sensitive and useful model for anthelmintic studies and should be incorporated early on in drug screens for broad-spectrum human soil-transmitted helminth therapies.
Journal Article
MAP kinases MPK9 and MPK12 are preferentially expressed in guard cells and positively regulate ROS-mediated ABA signaling
Reactive oxygen species (ROS) mediate abscisic acid (ABA) signaling in guard cells. To dissect guard cell ABA-ROS signaling genetically, a cell type-specific functional genomics approach was used to identify 2 MAPK genes, MPK9 and MPK12, which are preferentially and highly expressed in guard cells. To provide genetic evidence for their function, Arabidopsis single and double TILLING mutants that carry deleterious point mutations in these genes were isolated. RNAi-based gene-silencing plant lines, in which both genes are silenced simultaneously, were generated also. Mutants carrying a mutation in only 1 of these genes did not show any altered phenotype, indicating functional redundancy in these genes. ABA-induced stomatal closure was strongly impaired in 2 independent RNAi lines in which both MPK9 and MPK12 transcripts were significantly silenced. Consistent with this result, mpk9-1/12-1 double mutants showed an enhanced transpirational water loss and ABA- and H₂O₂-insensitive stomatal response. Furthermore, ABA and calcium failed to activate anion channels in guard cells of mpk9-1/12-1, indicating that these 2 MPKs act upstream of anion channels in guard cell ABA signaling. An MPK12-YFP fusion construct rescued the ABA-insensitive stomatal response phenotype of mpk9-1/12-1, demonstrating that the phenotype was caused by the mutations. The MPK12 protein is localized in the cytosol and the nucleus, and ABA and H₂O₂ treatments enhance the protein kinase activity of MPK12. Together, these results provide genetic evidence that MPK9 and MPK12 function downstream of ROS to regulate guard cell ABA signaling positively.
Journal Article
Mitigating CO2 emissions of concrete manufacturing through CO2-enabled binder reduction
Past studies on CO2 utilization in the concrete industry have primarily focused on maximizing sequestered CO2, while focusing less on CO2 avoidance possible by reducing binder use through the addition of CO2 to concrete formulations. In this paper, we study the net CO2 reduction and cost benefits achievable by reducing binder loading while adding CO2 via three approaches: carbonation during curing, carbonation during mixing, or carbonation with recycled concrete aggregate. These techniques are evaluated for a cohort of concrete formulations representing the diverse mixture designs found in the US ready-mixed and precast industries. Each formulation is optimized for reduced binder loading where the use of CO2 directly in the formulation recovers the lost compressive strength from reduced binder. We show that over an order of magnitude more CO2 can be avoided when binder reduction is jointly implemented with CO2 utilization compared to utilizing CO2 alone. As a result, nearly 40% of the annual CO2 emissions from the US concrete industry could, in principle, be eliminated without relying on novel supplemental materials, alternative binder, or carbon capture and sequestration. The recently amended 45Q tax credit will not incentivize this strategy, as it only considers carbon sequestration. However, we find that the saved material cost from reduced binder use on its own may provide a significant economic incentive to promote the joint strategy in practice. We conclude that the real value of CO2 utilization in concrete hinges on exploiting CO2-induced property changes to yield additional emission reduction, not by maximizing absorbed CO2.
Journal Article
MYB75 Functions in Regulation of Secondary Cell Wall Formation in the Arabidopsis Inflorescence Stem
Deposition of lignified secondary cell walls in plants involves a major commitment of carbon skeletons in both the form of polysaccharides and phenylpropanoid constituents. This process is spatially and temporally regulated by transcription factors, including a number of MYB family transcription factors. MYB75, also called PRODUCTION OF ANTHOCYANIN PIGMENT1, is a known regulator of the anthocyanin branch of the phenylpropanoid pathway in Arabidopsis (Arabidopsis thaliana), but how this regulation might impact other aspects of carbon metabolism is unclear. We established that a loss-of-function mutation in MYB75 (myb75-1) results in increased cell wall thickness in xylary and interfascicular fibers within the inflorescence stem. The total lignin content and S/G ratio of the lignin monomers were also affected. Transcript profiles from the myb75-1 inflorescence stem revealed marked up-regulation in the expression of a suite of genes associated with lignin biosynthesis and cellulose deposition, as well as cell wall modifying proteins and genes involved in photosynthesis and carbon assimilation. These patterns suggest that MYB75 acts as a repressor of the lignin branch of the phenylpropanoid pathway. Since MYB75 physically interacts with another secondary cell wall regulator, the KNOX transcription factor KNAT7, these regulatory proteins may form functional complexes that contribute to the regulation of secondary cell wall deposition in the Arabidopsis inflorescence stem and that integrate the metabolic flux through the lignin, flavonoid, and polysaccharide pathways.
Journal Article