Biology subjects

Lazar, D.

Publications and source records attributed to Lazar, D..

7 recordsLinked to original sources

bioRxiv2025

Constitutive and regulatory responses of Arabidopsis thaliana to harmonically oscillating light

The rate of net CO2 uptake is proportional to dim light and saturates when the light exceeds the plant assimilation capacity. This simple relationship between constant light and photosynthesis becomes intriguingly complex when the light oscillates. The rates of photosynthesis may differ between the descending and ascending phases of light oscillation. This hysteresis changes with the frequency and amplitude of the light and reports on the dynamics of the photosynthetic reactions and their regulation. Here, we investigated the chlorophyll fluorescence response of Arabidopsis thaliana to light oscillating with three different amplitudes: 100-200, 100-400, and 100-800 mol photons{middle dot}m-2{middle dot}s-1, each with periods ranging from 1 s to 8 min. The light amplitudes and periods were chosen to represent light patterns often appearing in nature. Three genotypes were compared: wild-type Col-0 and npq1 and npq4 mutants that are incapacitated in the rapidly reversible energy-dependent non-photochemical quenching (qE). The experiments identified two major dynamic patterns. One was found in oscillation periods shorter than 30 s, characterized by constitutive non-linearity and hysteresis. The other was mainly formed by regulatory non-linearity and hysteresis, occurring when the oscillation periods were longer than 30 s. The mathematical model simulating the chlorophyll fluorescence dynamics qualitatively reproduced the constitutive and regulatory dynamic patterns observed in the experiments. The model simulations illustrated the dynamics of non-photochemical quencher activation, plastoquinone pool reduction, and lumen pH that form the constitutive and regulatory non-linearities. The model simulations provided mechanistic insight into molecular processes forming the plant response to oscillating light.

plant biology↗

bioRxiv2023

Hindbrain boundaries as niches of neural progenitor/stem cells regulated by the extracellular matrix proteoglycan chondroitin sulphate.

The interplay between neural progenitor/stem cells (NPSC) and their extracellular matrix (ECM), is a crucial regulatory mechanism that determines their behavior. Nonetheless, how the ECM dictates internal processes remains elusive. The hindbrain is valuable to examine this relationship, as cells in the hindbrain boundaries (HB), which arise between any two neighboring rhombomeres, express the NPSC-marker Sox2 while being surrounded with the ECM molecule chondroitin sulphate proteoglycan (CSPG), in chick and mouse embryos. CSPG expression was used to isolate HB/Sox2+ cells for RNA-sequencing, revealing their distinguished molecular properties as typical NPSCs, which express known and newly-identified genes relating to stem cells, cancer, matrisome and cell-cycle. In contrast, the CSPG-/non-HB cells, displayed clear neural-differentiation transcriptome. To address whether CSPG is significant for hindbrain development, its expression was manipulated in vivo and in vitro. CSPG-manipulations shifted the stem versus differentiation state of HB cells, evident by their behavior and altered gene expression. These results provide novel understanding on the uniqueness of hindbrain boundaries as repetitive pools of NPSCs in-between the rapidly-growing rhombomeres, which rely on their microenvironment to maintain undifferentiated during development. SUMMARY:Transcriptomic analysis of hindbrain boundaries revels them to harbor cells with neural progenitor\stem cell properties that rely on local extracellular matrix to maintain their undifferentiated state.

developmental biology↗

bioRxiv2022

On the regulation of photosynthesis in pea leaves exposed to oscillating light.

Plants grow in nature often in fluctuating irradiance. In the laboratory, the dynamics of photosynthesis is usually explored by instantaneously exposing dark-adapted plants to constant light and detecting the dark-to-light transient, which is only a poor approximation of natural phenomena. Aiming at a better approximation, we exposed pea leaves to oscillating light and measured, during oscillations, changes in function of photosystem I and II and of the proton-motive force at the thylakoid membrane. The dynamics depends on the oscillation period, leaving information about the regulatory networks. As demonstrated for selected period of the oscillation of 60 s, the regulations try to keep reactions centres of photosystems I and II open. A possible evaluation of obtained data is presented and involvement of particular processes in regulation of photosynthesis is discussed. The forced oscillations provide information-rich fingerprint of complex regulatory networks. Further progress in understanding the networks is expected from experiments involving chemical interventions, plant mutants, and by using mathematical modelling and the system identification and system control tools, as already applied in other parts of science. HighlightMeasurement of photosynthetic signals during illumination of plants by light, whose intensity oscillates as sinus function provides information about regulation of photosynthesis in fluctuating light.

plant biology↗

bioRxiv2022

The dynamics of non-photochemical quenching and cyclic electron transport in A.thaliana exposed to harmonically oscillating light

In natural environments, plants are exposed to rapidly changing light. Maintaining photosynthetic efficiency while avoiding photodamage requires equally rapid regulation of photoprotective mechanisms. We asked what the operation frequency range of regulation is in which plants can efficiently respond to varying light. Chlorophyll fluorescence, P700, plastocyanin, and ferredoxin responses of wild-type Arabidopsis thaliana were measured in oscillating light of various frequencies. We also investigated the npq1 mutant lacking violaxanthin de-epoxidase, the npq4 mutant lacking PsbS-protein, and the mutants crr2-2, and pgrl1ab impaired in different pathways of the cyclic electron transport. The fastest was the PsbS-regulation responding to oscillation periods longer than 10s. Processes involving violaxanthin de-epoxidase dampened changes of chlorophyll fluorescence in oscillation periods of 2min or longer. Knocking out the PGRL1-PGR5 pathway strongly reduced variations of all monitored parameters, probably due to congestion in the electron transport. Incapacitating the NDH-like pathway only slightly changed the photosynthetic dynamics. Our observations are consistent with the assumption that non-photochemical quenching in slow light oscillations involves violaxanthin de-epoxidase to produce, presumably, a stationary, non-oscillating level of zeaxanthin. We interpret the observed dynamics of Photosystem I components as being formed in slow light oscillations partially by thylakoid remodeling that modulates the redox rates.

plant biology↗

bioRxiv2021

Photosynthesis dynamics and regulation sensed in the frequency domain

Foundations of photosynthesis research have been established mainly by studying the response of plants to changing light, typically to sudden exposure to a constant light intensity after a dark acclimation or light flashes. This approach remains valid and powerful, but can be limited by requiring dark acclimation before time-domain measurements and often assumes that rate constants determining the photosynthetic response do not change between the dark- and light-acclimation. We present experimental data and mathematical models demonstrating that these limits can be overcome by measuring plant responses to sinusoidally modulated light of varying frequency. By its nature, such frequency-domain characterization is performed in light-acclimated plants with no need for prior dark acclimation. Amplitudes, phase shifts, and upper harmonic modulation extracted from the data for a wide range of frequencies can target different kinetic domains and regulatory feedbacks. The occurrence of upper harmonic modulation reflects non-linear phenomena, including photosynthetic regulation. To support these claims, we present a frequency- and time-domain response in chlorophyll fluorescence emission of the green alga Chlorella sorokiniana in the frequency range 1000 - 0.001 Hz. Based on these experimental data and numerical as well as analytical mathematical models, we propose that frequency-domain measurements can become a versatile new tool in plant sensing. One sentence summaryIt is proposed to characterize photosynthesis in the frequency domain without the need for dark adaptation and, thus, without assumptions about the dark-to-light transition.

plant biology↗

bioRxiv2020

AGE IS ASSOCIATED WITH INCREASED EXPRESSION OF PATTERN RECOGNITION RECEPTOR GENES AND ACE2, THE RECEPTOR FOR SARS-COV-2: IMPLICATIONS FOR THE EPIDEMIOLOGY OF COVID-19 DISEASE

Older aged adults and those with pre-existing conditions are at highest risk for severe COVID-19 associated outcomes. Using a large dataset of genome-wide RNA-seq profiles derived from human dermal fibroblasts (GSE113957) we investigated whether age affects the expression of pattern recognition receptor (PRR) genes and ACE2, the receptor for SARS-CoV-2. Older age was associated with increased expression of PRR genes, ACE2 and four genes that encode proteins that have been shown to interact with SAR2-CoV-2 proteins. Assessment of PRR expression might provide a strategy for stratifying the risk of severe COVID-19 disease at both the individual and population levels.

molecular biology↗

bioRxiv2019

An activity-guided map of electrophile-cysteine interactions in primary human immune cells

Electrophilic compounds originating from nature or chemical synthesis have profound effects on immune cells. These compounds are thought to act by cysteine modification to alter the functions of immune-relevant proteins; however, our understanding of electrophile-sensitive cysteines in the human immune proteome remains limited. Here, we present a global map of cysteines in primary human T cells that are susceptible to covalent modification by electrophilic small molecules. More than 3000 covalently liganded cysteines were found on functionally and structurally diverse proteins, including many that play fundamental roles in immunology. We further show that electrophilic compounds can impair T cell activation by distinct mechanisms involving direct functional perturbation and/or ligand-induced degradation of proteins. Our findings reveal a rich content of ligandable cysteines in human T cells, underscoring the potential of electrophilic small molecules as a fertile source for chemical probes and ultimately therapeutics that modulate immunological processes and their associated disorders.

immunology↗